Production and microwave thermal processing considerations for a prototype reformed roast made from the beef forequarter


Material Information

Production and microwave thermal processing considerations for a prototype reformed roast made from the beef forequarter
Physical Description:
ix, 195 leaves : ill. ; 28 cm.
Yates, Joseph A., 1955-
Publication Date:


Subjects / Keywords:
Cookery (Beef)   ( lcsh )
Microwave cookery   ( lcsh )
Animal Science thesis Ph. D
Dissertations, Academic -- Animal Science -- UF
bibliography   ( marcgt )
non-fiction   ( marcgt )


Thesis (Ph. D.)--University of Florida, 1988.
Includes bibliographical references (leaves 176-193).
Statement of Responsibility:
Joseph A. Yates
General Note:
General Note:

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University of Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001472434
oclc - 20809243
notis - AGY4191
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Full Text







This dissertation is dedicated
to my wife, Diana, and my son, Brandon,
whose never-ending love,
patience, and unselfish support
help make my dreams reality.

To my parents, Josephine and Joseph Yates,
my brothers, Christopher and Phillip,
and my mother-in-law, Betty Gene Mosel,
for their support and prayers,
throughout my college endeavors.


There were many people who assisted in the completion of

this project. The author expresses his appreciation to Dr.

Roger L. West, chair of the supervisory committee, and to Dr.

Rachel B. Shireman, cochair, for their guidance, supervision,

and contributions in preparation of this manuscript.

The contributions of Dr. S.C. Denham, Dr. D.D. Johnson,

Dr. J.W. Lamkey, Dr. F.W. Leak, Jr., Dr. M. Marshall, and Dr.

A. Teixeira are appreciated for the valued support,

encouragement, and assistance they provided during his

graduate program.

Appreciation is extended to Ms. Karen Christensen for

her support and willingness to help in getting this project

completed. Special thanks are also extended to Ms. Jannet

Eastridge, Ms. Debbie Neubauer, and Ms. Ana Zometa for their

technical help. I am very grateful to Mr. Larry Eubanks,

manager of the meat laboratory. Despite my impatience, his

friendship and expertise during this project have proven to

be invaluable. For his light-hearted attitude, while being

serious about his work, he will always be remembered.


The author's appreciation is also extended to his fellow

graduate students for their friendship and assistance during

his graduate program.

The author wishes to extend his thanks to the Jet Net

Corporation and Viskase Corporation for their generosity in

providing equipment and supplies necessary for completion of

this research.

The author is grateful to the Beef Industry Council for

providing the monitary support required to conduct this


Finally, his deepest thanks of appreciation and love are

extended to his wife Diana and son Brandon, for it has been

their never-ending encouragement that turned this dream into




ACKNOWLEDGEMENTS........................................ iii

ABSTRACT ..................................... .... vii


1 INTRODUCTION................................. 1

2 LITERATURE REVIEW............................... 8

Restructured Products........................... 8
Manufacturing Considerations for Re-
structured Beef Products............... 10
Muscle Selection Criterion................ 20
Muscle Protein Functionality.............. 26
Mechanisms of Protein-Water Interactions.. 28
Influence on Protein-Water Interactions... 34
pH influence......................... 34
Sodium chloride influence............ 35
Influence of phosphates.............. 39
Water Distribution............................. 44
Heat-Induced Changes in Meat.................. 51
Microwave Heating........................... 70

MICROWAVE POWER LEVELS........................ 90

Introduction.......................... 90
Materials and Methods......................... 92
Preparation of Sample.................... 92
Microwave Cooking....................... 94
Proximate Analysis........................ 96
Statistical Analysis..................... 96
Results and Discussion......................... 98
Summary. .......... ............... ..... .. 116


Introduction................................... 118
Materials and Methods.......................... 121
Raw Material............................ 122
Cooking Methods........................... 123
Proximate Analysis and Sarcomere Length... 126
Shear Force................................ 127
Bind Strength............................. 127
Sensory analysis..................... 128
Statistical analysis................. 129
Results and Discussion......................... 130
Study I................................... 130
Cooking times........................ 132
Cooking losses....................... 138
Changes in sarcomere length.......... 140
Proximate analysis................... 142
Texture measurements................. 144
Binding strength.................... 146
Sensory evaluation................... 148
Study II................ ....... ........... 163
Overall Summary................................ 170


REFERENCES............................................ 176

BIOGRAPHICAL SKETCH................................. 194

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



Joseph A. Yates

December 1988

Chair: R.L. West
Cochair: R.B. Shireman
Major Department: Animal Science

Latissimus dorsi (LD) and Serratis ventralis (SV)

muscles were removed from 48 USDA Choice, yield grade 3 beef

forequarters, processed into reformed roasts and used to

compare palatability, chemical and physical characteristics

resulting from conventional and microwave cooking. Equations

were developed for predicting the extent to which post-

cooking temperature rise occurred within the roasts during

microwave cooking to control final internal end-point

temperature and allow comparison of methods.

Study I used a factorial arrangement to quantify changes

in meat components as related to heating rate (slow in

conventional vs fast in microwave cooking): three

replications by two roast types (LD and SV) by four cooking

methods (conventional, low, medium, and high power microwave

levels) by three end-point temperatures (60oC, 700C, and

750C). Study II used LD roasts in a factorial arrangement to

study changes in extracellular water space (ESC) as related


to the method of heat production (conventional vs. microwave)

when heating rate was equivalent. Heating rates were made

equivalent by slowing the cooking rate in the microwave.

Results of Study I indicated microwave cooking required

less time than conventional cooking for all treatment

combinations tested. Total cooking loss was higher with high

power microwave cooking and lower (P < 0.05) for conventional

and low power microwave cooking. End-point temperature of

60oC produced lower cooking losses than 70 or 75oC which were

not different (P < 0.05). Changes in chemical composition

indicated greater water losses for medium and high power

microwave cooking (P < 0.05) compared to other cooking

methods. The percentage change in sarcomere length from raw

to cooked samples increased as end-point temperature

increased. Kramer shear force values were lower for SV than

LD roasts, while cooking method and end-point temperature had

no effect. Instron assessment of the binding junction

indicated to difference in peak force, work, tensile

strength, strain, or modulus of rigidity due to cooking

method (P > 0.05). Sensory panelists rated SV roasts

superior in juiciness, connective tissue content, and overall

tenderness compared to LD roasts, but no differences were

detected among methods.

In Study II, ECS assessment was conducted using inulin

[14C] carboxylic acid. Thermal processing reduced ECS;
however, method of heat generation did not affect ECS.


In summary, when final internal end-point temperature

is controlled differences in chemical and physical

characteristics due to cooking methods are minimized.


The 1985/86 Annual Report of the National Live Stock and

Meat Board indicates that the beef industry must become more

consumer-oriented to maintain its market share. In the

present decade, one out of four American households consists

of a single individual, compared with one out of ten in 1955

(Anonymous, 1983). The annual report also indicated that

only seven percent of families in America consisted of one

breadwinner, indicating more and more households with two

incomes. Therefore, consumers have more active lifestyles

and an increasing need for convenience. A recent consumer

marketing survey conducted for the National Live Stock and

Meat Board and the American Meat Institute concluded that the

consumer's decision to serve red meat was determined

primarily by convenience, taste and economics (Anonymous,


As a result of changing lifestyles, consumers of the

eighties do not tend to have the same needs, wants, or

concerns as did consumers twenty years ago. The results of a

1984 Food Marketing Institute study indicated that 71% of

supermarket customers surveyed were concerned with diet and

health issues (Anonymous, 1984). This same study indicated


that 48% of the supermarket customers surveyed selected

recipes based on their nutritional content and 44% avoided

buying products that had no nutritional information.

A national consumer-retail beef study (Savell et al.,

1986) suggested that beef products must be lean (free of

trimmable fat), high in quality and convenient to prepare in

order to attract today's consumer. To accomplish these

goals, many retailers have reduced trimmable fat levels on

retail cuts to 6.25 mm and others have removed all of the

outside fat. However, the 1987 Consumer Climate for Meat

Marketing Study indicated that, while per capital consumption

has responded slightly, future progress will be dependent on

continued development of products that meet the consumers'

criteria. In response to these consumer demands, many meat

processors are providing entrees in a ready-to-eat or

precooked form, requiring a reheating period which frequently

involves the use of a microwave oven.

The advent of the microwave oven has opened up a new

dimension in food preparation and management, both in the

home and in the food service industry. The greatest

advantage of microwave cooking is the time and energy saving

considerations. In 1984, 9.1 million microwave ovens

comprised the largest annual purchase of any home appliance

in history (Markov, 1985a).

A major challenge confronting progress toward

consumer-driven marketing approaches is the high price

charged for precooked items. This price level is

necessitated by the use of high valued muscles, cooking

losses and equipment for thermal processing and aseptic

packaging. However, consumers appear to resist this higher

price when buying a precooked beef roast, even though they

pay comparable prices for sliced roast beef at the

delicatessen. Perhaps a ready-to-cook roast product designed

for rapid microwave cooking would be more appealing.

In addition to price considerations, the occurrence of

off-flavors in precooked beef entrees is another source of

concern for meat processors. To help overcome the presence

of any off-flavors in a precooked entree, a package of gravy

or seasoned sauce is frequently included with most products.

Perhaps an alternative to precooked meat entrees is

producing a reformed meat product using muscles from the

chuck and plate that could be cooked rapidly in a microwave

oven. Muscles from the chuck and plate are traditionally

lower in economic value compared to muscles from the rib,

loin, and round. The lower economic value associated with

the chuck is due in part to compositional differences between

many of the muscles that make up the chuck. Numerous

researchers have documented significant differences in

connective tissue, contractile status, and intermuscular fat

between the many muscles of the chuck (Ramsbottom et al.,

1945; Ramsbottom and Stradine, 1947; Prost et al., 1975; Zinn

et al., 1970; McKeith et al., 1985; Paterson and Parrish,


1986; Recio et al., 1987). Therefore, raw materials from

these regions would provide a means of lowering production

costs and aid in producing a competitively priced product.

In addition, these muscles would provide a source of lean

meat since all surface fat and surface connective tissue

could be removed. This would provide the meat processor with

the ability to produce a boneless roast beef product in which

size, shape, and fat content could be controlled. A roast

beef product of this type could help the beef industry

provide entrees that address the diet-health issues and

fulfill the convenience needs of the consumer.

In contrast to traditional restructured products the

texture of this reformed product should be comparable to that

of a whole muscle entree. The convenience attribute could be

achieved by producing a portion size needed by a two or three

member family for one meal (340 to 450 g) that could be

cooked quickly in a microwave or conventional oven.

Several major obstacles currently hinder production of such a

product. First, little research has been conducted on

feasible procedures for producing reformed whole beef muscle

products that utilize lower valued muscles. Research is

needed to develop production procedures that consider:

1) Economically feasible methods for removal of heavy

surface layer connective tissue (epimysium).


2) Protein extraction methods that do not result in

loss of muscle integrity and yet produce acceptable

binding characteristics upon thermal processing.

3) Stuffing procedures that generate a uniformly shaped


Also, previous attempts to cook meat entrees in a microwave

oven have failed to produce a product of acceptable quality.

Although the microwave oven has been shown to decrease

cooking time, labor and energy costs, it has not been readily

accepted by food service institutions or homemakers for

cooking beef entrees. The skepticism surrounding the use of

the microwave oven for preparation of beef entrees is thought

to be due in part to uneven cooking, greater cooking losses,

and less palatable meat (Headley and Jacobson, 1960; Kylem et

al., 1964; Law, 1967; Ream et al., 1974; Drew et al., 1980;

Moore et al., 1980; Griffin et al., 1981). However, many of

these studies have been "trial and error" rather than a

deliberate approach to understanding the microwave heating

process and its effect on muscle tissue. Major questions

still remain unanswered regarding microwave oven cookery of

beef entrees and the perceived relationship with toughness

and lack of product juiciness. Research is needed to

understand the effects on muscle tissue of rapid heating

rates, greater moisture losses and excessive post-cooking

temperature increases. Research emphasis should be directed

so as to study:


1) The rate at which heat is conducted into the

product as a result of different heating methods (microwave

or conventional). Knowledge of this information would be

useful in developing a computer aided model to predict

thermal processing conditions required to achieve a certain

degree of doneness.

2) The influence of different heating rates (rapid or

slow) when associated with different cooking methods,

(microwave or conventional) and their effects on the

chemical, textural, and sensory attributes of a meat product.

3) The effects of incorporating different amounts of

water into the meat product during production processes,

subsequent effects on water loss during thermal processing,

and the perceived juiciness and overall palatability of the


The proposed research involves production of a reformed

whole muscle roast beef product and the systematic study of

microwave and conventional cookery effects on beef and

addresses the research needs listed previously.

The objectives of this study are

1) To develop feasible processing procedures for

reforming whole beef muscles, the serratus ventralis and

latissimus dorsi. These two muscles were chosen for several

reasons: a) currently they are not being used to their

highest potential; b) they are unipennate muscles with fibers

oriented in one direction; c) they contain mainly surface


connective tissue with no large septums of internal

connective tissue; d) they are two of the larger muscles

found in the forequarter; and e) they differ compositionally

in fat content (>10% and <5% fat for the serratus and

latissimus, respectively).

2) To quantify the changes in meat components that occur

during thermal processing with microwave and conventional

cooking at different cooking rates (low, medium, and high

power) and relate these to changes in physical and sensory

measures of tenderness and palatability.

3) To study changes in tissue fluid distribution, as

influenced by thermal processing (microwave versus

conventional) when beef roasts are cooked to the same

internal end point temperature at the same rate.


Restructured Products

Breidenstein (1982) refers to restructuring as a

processing method by which raw meat materials are converted

into ready-to-cook products. This method of meat processing

has been extensively reviewed by Mandigo (1975), Huffman

(1979), Mandigo (1982a,b), and Breidenstein (1982). The

primary objective for utilizing restructuring technology is

to add economic value to under-utilized raw materials that

are currently considered to be of limited economic value. As

a result, restructuring methodology is considered to be a

means of enhancing the economic value of the raw materials,

and the enhanced value will be received as being greater

than the cost of its achievement (Breidenstein, 1982).

Restructured products created to date have been produced

from a variety of different meat species and formulated to

contain different types and levels of non-meat ingredients.

The phrase "intermediate value beef products" was used by

Breidenstein (1982) to refer to a group of restructured beef

products. This group of products is considered to have an

economic value received by the consumer to lie between that

of ground beef and that of intact muscle steaks and roasts.


Breidenstein (1982) warned that caution must be exercised

when selecting raw materials that contain heavy

concentrations of connective tissue embedded in the muscle

mass. Therefore, selection criteria of raw materials and

production methods used for producing restructured beef

products are very important to their acceptability. The

restructuring process typically requires the raw meat

materials to undergo a process of particle size reduction,

blending and reshaping. Several mechanical methods have been

developed to reduce particle size. They include grinding,

flaking, chunking, slicing, and emulsifying. Reducing the

particle size produces numerous meat pieces that must be

bound back together at the various meat interfaces. To

accomplish this, the intracellular protein, myosin, is

commonly used as a binding agent. Extraction of myosin to

the meat surface is accomplished by mechanical mixing,

massaging, or tumbling of the meat particles in the presence

of sodium chloride and phosphates. Maintaining a cohesive

bind in the uncooked product is accomplished by freezing,

while the bind in the cooked product is dependent upon a heat

induced bonding (Breidenstein, 1982).

As a result of the numerous mechanical methods used to

reduce particle size, a wide variety of products have

resulted. In an effort to categorize the various products

produced, Field (1982) identified four groups of restructured

products for retail and food service: 1) frozen, flaked and


formed restructured meats; 2) chunked and formed or sectioned

and formed restructured meats; 3) emulsified, ground or

chopped restructured meats; and 4) sliced restructured meats.

Mandigo (1982a) suggested that cured and smoked products also

represented a distinctive group of meat products produced by

restructuring technology.

Formulation considerations and manufacturing procedures

are vital components in the production of a restructured or

reformed roast beef product. The term "reformed," as used

throughout this dissertation, refers to a type of

restructuring process whereby no reduction in particle size

is imposed. Therefore, production methods used to

manufacture a reformed beef product are very important to its

acceptability. The focus of this review will discuss product

manufacturing, muscle selection, protein functionality,

distribution of cellular water and thermal processing of the

final product.

Manufacturing Considerations for Restructured
Beef Products

Through extensive research efforts, many variables have

been identified that influence manufacturing procedures and

organoleptic characteristics of a restructured meat product.

To date, restructured meat products have typically involved

reducing the particle size of the starting material. As

previously stated, particle reduction can be acheived by a

number of methods; flaking is one of the more recently


developed methods. This method is capable of using meat in

the fresh or frozen state; however, particle uniformity is

enhanced if the meat is crust frozen or frozen solid (Huffman

and Cordray, 1982). The meat is cut in a shaving-like manner

into flakes of varying particle sizes and texture (Fenters

and Ziemba, 1971; Mandigo et al., 1972; Pietraszek, 1972).

Advantages for products made from flaked meat include

improved texture, reduced drip loss, enhanced binding and

cohesive properties, decreased cooking losses and improved

sensory characteristics (color, flavor, juiciness, and

tenderness) over those products produced from sectioned meat

(Anonymous, 1973).

Reducing the particle size of meat by sectioning

involves cutting large muscles into chunks, which may or may

not be uniform in size. The primary advantage of this method

is that the resulting product should have the palatability

attributes that more nearly resemble that of intact muscle,

compared to products produced from flake cut particles

(Acton, 1972). The main disadvantage of this process is that

fat particles are easily detected. This effectively reduces

the amount of fat that could be incorporated into the


Although most restructured products contain 12 to 25%

fat, increasing the fat content from 20 to 30% was reported

to improve the products sensory properties (Seideman, 1982).

Typically, formulating a product to contain a desired fat


content requires using at least two meat sources, one higher

and one lower in fat content.

Booren et al. (1981a) produced sectioned and formed beef

steaks to contain 12% fat in the final product. This

involved utilizing beef chucks trimmed of excess fat and

connective tissue, to provide a source of lean meat that

contained 8 to 10% fat and another source that contained 48

to 52% fat. However, the authors indicated that because of

the heterogenous nature of meat, the fat levels achieved in

the final product were deemed to be the most variable

component. The authors concluded that this was due to the

diverse amounts of inter- and intramuscular fat present in

Choice, Yield Grade 3 chucks. Previously vacuum packaged

beef chucks were allocated to vacuum or non-vacuum mixing

treatments for periods of 6 or 12 minutes. Under the

experimental conditions described by these authors, the added

fat source separated and accumulated on the sides of the

mixer or appeared as large fat pockets within the steak

product. Vacuum mixing was reported to produce a less

desirable surface color in the finished steak product, as

determined by spectrophotometric analysis. It was theorized

that low oxygen tension present during storage of the vacuum

packaged beef chuck and during vacuum mixing caused the

globin molecule to become denatured, which resulted in a less

desirable color. The occurence of this problem had been

previously reported by Lawrie (1974). Two-thiobarbituric

acid (TBA) values did not change following 60 d of freezer

storage, regardless of mixing treatment. Vacuum mixing

treatments had no effect on cooked yields, Kramer shear area

or Kramer shear force values. Sensory analysis indicated a

significant increase in bind between meat pieces for vacuum

mixed steaks. The authors reasoned that vacuumization may

function to remove tiny air bubbles from the extracted

protein exudate, resulting in a denser mass of the extracted

myofibrillar proteins at the bind area. Juiciness,

tenderness, flavor and connective tissue residue were not

different due to mixing treatments.

To help create acceptable product tenderness in a

sectioned and formed product, Huffman (1978) proposed a

restructuring process that combined both chunks and wafer

thin slices of meat. The process resulted in a product that

closely resembled whole muscle cuts of meat. A patent was

issued for this restructuring process. Huffman (1979)

concluded that raw meat materials to be used in sectioned and

formed products should be subjected to mechanical

tenderization prior to use. Mechanical tenderization would

help ensure maximum cell disruption and enhance the binding

characteristics of the product. However, this processing

step requires additional equipment, which, in turn, increases

the cost of production.

Independent of the methods utilized to obtain a

reduction in particle size is the importance of the actual


particle size. Acton (1972), in an effort to study the

effects of various particle sizes in the production of

poultry loaves, used muscles cut into strips, cubes, coarse

ground, finely ground and finely ground five times. He

reported that decreasing the particle size resulted in

increasing the amount of salt soluble proteins extracted, and

hence, the binding strength of the final product. This was

concluded to be a result of increased surface area associated

with decreasing the particle size. In addition, the author

reported a decrease in cooking loss as particle size


In contrast, Chesney and co-workers (1978), in a study

of fabricated pork products, reported that particle size did

not significantly influence the water holding capacity, shear

force values or proximate chemical analysis values. However,

in accordance with Acton (1972), a significant decrease in

cooking loss percentage was also reported as particle size

decreased. Studies by Chesney and co-workers (1978) and

Acton (1972) also agreed on taste characteristics. These

studies indicated that products prepared from large particles

were inferior in cohesion, juiciness, tenderness and overall

acceptability when compared to products prepared from medium

or smaller particle sizes.

Variations in product bite, mouth feel and other sensory

properties can be achieved by altering the ratio of various

particle sizes, fat and moisture content, mixing time and


size and shape of the final product (Huffman, 1979).

Popenhagen et al. (1973) reported that combining meat flakes

of different sizes and varying temperatures yielded steaks

that were more desirable in texture and overall eating

quality than steaks made from a single size of flake and

temperature. Similarly, Mandigo (1974) reported that a meat

temperature of -50C at the time of flaking significantly

influenced the texture and appearance of the final product.

Mixing is a processing step required to achieve uniform

distribution of the lean, fat and nonmeat components. Mixing

also facilitates extraction of the intracellular myofibrillar

proteins to the surface of the meat. Extraction of the salt

soluble proteins actinn, myosin, and actomyosin) provides the

binding material necessary to bond the various meat

components together. Two of the most popular processing

methods used to extract the proteins needed to facilitate

binding are massaging and tumbling. Both of these methods

are physical processes designed to mix ingredients, enhance

quality attributes (tenderness) and accelerate meat product

manufacturing (Addis and Schanus, 1979).

Tumbling involves generating "impact energy" as a result

of meat striking the sides and bottom of a rotating drum or

being struck with paddles or baffles (Addis and Schanus,

1979). This action results in a transfer of kinetic energy

to the muscle mass and a resultant rise in temperature. The

tumbling process typically occurs within the confines of a


sealed vessel capable of operating while under vacuum.

Vacuumization of the tumbler is reported to help overcome

potential problems such as tissue softening and the

incorporation of air into the extracted protein matrix (Addis

and Schanus, 1979).

Massaging is considered to be a less vigorous process

when compared to the action of tumbling. It involves

generating frictional energy as a result of rubbing meat

surfaces together. Vacuumization of the massager is also

possible and is done to help overcome potential problems

previously stated. The primary purpose of massaging or

tumbling is to facilitate the extraction of the salt soluble

myofibrillar proteins, myosin, actin and actomyosin. The

physical actions associated with massaging or tumbling,

provide a tenderizing effect and help to incorporate added

fluids into the raw meat materials (Addis and Schanus, 1979).

Weiss (1974), in a report on ham tumbling and massaging,

indicated that Europeans categorize muscle tissue as either

firm or soft when selecting the appropriate method for

protein extraction. Beef, mutton and turkey are considered

firm muscles and are subjected to impact tumbling, while soft

muscles, pork and chicken, are subjected to massaging. The

basis for this segregation is due to differences in the

physiological and biochemical composition of the muscle

tissue, and the response of the tissue to various physical

and chemical processing techniques.


MacFarlane and coworkers (1977) measured the binding

strength between adjacent meat pieces using myosin,

actomyosin and sarcoplasmic proteins as binding agents.

These authors concluded that myosin exhibited the greatest

binding capability with or without the addition of salt. The

role of the myofibrillar proteins in binding chunk-type

products together has been demonstrated by a number of

researchers (Anonymous, 1971; Rahelic et al., 1974; Ford et

al., 1978; Siegel et al., 1978a,b; Booren et al., 1982).

Booren and coworkers (1981a) studied the effects of

blade tenderization, vacuum mixing, salt addition and mixing

time on the binding of meat pieces from A maturity (young),

Standard grade beef rounds when processed into sectioned and

formed steaks. All rounds were defatted and cut into 2-3 cm

pieces; one group of rounds was blade tenderized twice. Each

group was divided into 18 kg meat blocks and assigned to

treatments of vacuum and non-vacuum mixing. The groups were

further divided into 9 kg blocks and allocated to 0 and 0.5%

added salt. Salt was incorporated into the product by

sprinkling it over the meat during the first 30 sec of

mixing. Each block was sampled after 0, 8, 16, and 24 min

blending. Samples were stuffed into plastic bags, crust

frozen at -300C and pressed into logs in the shape of a strip

loin. Steaks 2.5 cm thick were cut, vacuum packaged and

frozen for further analysis. All steaks for sensory

evaluation were oven broiled in a rotary hearth oven. The


oven was set to maintain an internal temperature of 1500C,

and steaks were cooked to an internal temperature of 700C.

Analysis of beef steaks indicated that the percentage of ash

and salt was significantly higher in the 0.5% salt

treatments. Moisture, protein, fat percentage and pH were

not different for blade tenderization, vacuum mixing or salt

addition treatments. Mean fat content of the final product

was 1.65%. The percentage of fat measured during the various

mixing times was highest at 0 min and lowest at 8 min. The

authors indicated that fat accumulated on the sides of the

blender as mixing time progressed. Twenty-four minutes of

mixing time was reported to yield the lowest cooking loss

23.8% compared to 27.5% for 0 min of mixing time. The TBA

values increased due to salt addition over a 90-day frozen

storage period, but did not change due to mixing time. A

significant interaction between blade tenderization and salt

addition for TBA values was reported. Products that were not

subjected to blade tenderization and no added salt had the

lowest TBA value of 0.77 compared to a value of 1.03 when

salt was added. Blade tenderization, regardless of added

salt content, resulted in higher TBA values compared to

non-tenderized products. The authors indicated that blade

tenderization increased the surface area of the meat,

allowing oxygen to be more accessible to the cut surfaces. A

significant interaction between vacuum and salt level was

also reported to exist, whereby removal of oxygen by vacuum


mixing resulted in a lower TBA value (0.83), compared to no

vacuum mixing (0.90) in steaks processed with 0.0% added

salt. The effect of mixing time on binding strength

indicated a 60% increase in particle adhesion as mixing time

increased from 8 to 16 min. Tenderness, as measured by the

Kramer shear cell, increased with increasing mixing times.

The authors indicated that the increase in tenderness

associated with increased mixing time may be an advantage

when restructuring with lower quality meats. Sensory

evaluations for initial tenderness were more desirable

following 8 min of mixing. However, tenderness desirability

decreased with 16 and 24 min of mixing. The authors

theorized that increased protein exudate content, extracted

as a result of increased mixing time, may have produced a

case hardening effect on the product surface.

In a similar study, Booren et al. (1981b) investigated

the influence of muscle type on characteristics of sectioned

and formed beef steaks. The processing procedures for

product preparation were equivalent to the one described for

their previous experiment (Booren et al., 1981a), with some

exceptions. In this study (Booren et al., 1981b), a coarsely

ground lean meat source was obtained from beef rounds of "A"

maturity, Standard grade carcasses. A fat meat source was

obtained from the plate region of the corresponding beef

carcass. Beef plates were sliced thin to permit formulating

a steak product to contain 12% fat. They reported similar


results as described by their previous study (Booren et al.,

1981a). Cooking yields increased with increased mixing

times, from a low of 70.55% at 0 minutes to a high of 77.35%

after 18 minutes of mixing. Flavor and juiciness sensory

scores also increased with increased mixing time. Longer

mixing times accelerated the rate at which the fresh

(uncooked) meat color deteriorated. The product made from

beef top rounds and beef plates was found to be more tender

and to contain less connective tissue residue as measured by

sensory panelists, when compared to their previous experiment

(Booren et al., 1981a).

Muscle Selection Criterion

One of the primary objectives of producing a

restructured meat product is to enhance the economic value of

lower valued meat cuts and trimmings. Traditionally, the

beef chuck has been a wholesale cut of lower economic value

when compared to the round, loin or rib. The wholesale beef

chuck represents approximately 27% of the beef carcass and is

typically merchandised at the retail level in the form of low

priced roasts and steaks, or as ground chuck (Paterson and

Parrish, 1986). The lower economic value associated with the

chuck is due in part to compositional and palatability

differences that occur within and between many of the muscles

that make up the chuck. Numerous researchers have documented

significant differences in connective tissue content,


contractile status, and intermuscular fat between the many

muscles comprising the chuck (Ramsbottom et al., 1945;

Ramsbottom et al., 1947; Prost et al., 1975; Zinn et al.,

1970; Marsh, 1977; McKeith et al., 1985; Paterson and

Parrish, 1986).

Marsh (1977) cited the contractile status of the muscle

fiber and the collagen content (connective tissue) of the

muscle as two primary structural components responsible for

variation in muscle tenderness. The muscle fiber component

is termed myofibrillar toughness, and it is thought to

respond to the handling procedures from the time of slaughter

(Rowe, 1977). It is this muscle fiber component that is

considered to be responsible for changes in meat tenderness

resulting from cold shortening, aging, TenderstretchingTM and

electrical stimulation. The contractile status of a muscle

refers to the sarcomere length of an individual muscle fiber.

A decreased sarcomere length caused by cold shortening is

associated with an increase in muscle toughness. Increasing

the sarcomere length of a muscle beyond its normal resting

length would be associated with stretched muscle fibers and

an increase in muscle tenderness.

The influence of connective tissue content, relative to

meat texture has been extensively reviewed by Tahir (1979).

Meat is classified as tender or less tender principally on

the basis of connective tissue content (McCrae and Paul,

1974). Connective tissue toughness is usually referred to as


background toughness and is regarded as not being

significantly influenced by treatments applied to the meat

from the point of slaughter up to the point of cooking (Rowe,


Collagen is the major protein in connective tissue and

was considered to be the single major factor influencing meat

tenderness (Tahir, 1979). However, Doty and Pierce (1961)

concluded that collagen content was not significantly related

to tenderness. In addition, Carpenter et al. (1963) found no

significant relationship between tenderness measurements and

the total amount of connective tissue.

Certain physical properties of collagen change with age.

The total quantity of collagen in muscle does not increase

with the age of the animal (Goll et al., 1963). However, the

number of crosslinkages between the collagen molecules within

the connective tissue increase with age. As the degree of

crosslinking increases, the structural stability of the

tissue increases. This increase in structural stability

decreases the ability of collagen to become solubilized

during thermal processing thereby influencing the tenderness

of the meat (Goll et al., 1963). Two types of crosslinking

structures are known to occur. Intramolecular bonds occur

within the collagen molecule, and intermolecular bonds link

one triple helix to another (Sims and Bailey, 1982). The

function of the intramolecular crosslink is as yet unknown;


however, intermolecular crosslinks provide the mechanical

stability of the collagen fiber.

Collagen contains a unique amino acid profile that is

high in glycine and hydroxyproline. Together, they comprise

about half of the total amino acids found in collagen (Sims

and Bailey, 1982). The presence of the amino acid

hydroxyproline in collagen (about 14%) is thought to be

confined almost exclusively to the stromal proteins of

collagen and elastin (Gross and Piez, 1960). Because of the

unique distribution of hydroxyproline in collagen, its

presence has been used as a means of determining the amount

of collagen present in tissue (Sims and Bailey, 1982).

Sensory and chemical analysis for moisture and fat

percentage, sarcomere length and total collagen content of

thirteen major beef muscles from the round, loin, rib and

chuck were reported by McKeith and co-workers (1985). The

infraspinatus, triceps, supraspinatus and deep pectoral were

evalulated from the chuck. Sensory panel tenderness scores

and Warner Bratzler shear force values (WBS) indicated that

the infraspinatus was the most tender and that the deep

pectoral was the least tender. From the 13 muscles

evalulated, only the psoas major (tenderloin) was ranked

higher than the infraspinatus in overall tenderness. Mean

collagen content of muscles from the chuck, round, loin and

rib were 11.44, 8.94, 5.33, and 4.66 (mg/g wet tissue basis),

respectively. Muscles from the round and chuck had lower


sensory scores than muscles from the loin and rib. However,

fat percentage, sarcomere length and collagen content from

each muscle were not significantly correlated to palatability

traits (McKeith et al., 1985). Although not determined in

the previous study, the authors concluded that soluble

collagen content may be a more important factor relating to

meat tenderness than total collagen content. In addition,

these authors concluded that some muscles would have a

potentially greater economic value if they were separated

from the wholesale primal and used independently.

Smith and coworkers (1978) reported on the tenderness of

20 different muscles from the chuck and other wholesale cuts.

They also indicated that the infraspinatus muscle when

prepared as a steak or roast had lower (more tender)

Warner-Bratzler Shear (WBS) values than the longissimus dorsi

from the chuck or rib. Results from these two studies

(McKeith et al., 1985 and Smith et al., 1978) indicate that

boning line production techniques should be developed and

implemented so as to facilitate removal of the more desirable

muscles from the chuck. Current industrial practices of

whole-muscle boning and merchandising boxed beef make single

muscle groups available to consumers and processors.

Therefore, knowledge of the palatability characteristics of

these muscles combined with current restructuring or

reforming technology could improve consumer acceptance of the

final product.


The serratus ventralis (SV) muscle is located

immediately ventral to the rib bones of both the wholesale

rib and chuck. The SV is a large, fanshaped muscle that

contains both surface and internal septums of connective

tissue. The SV contains about 10% fat and is one of the

larger muscles comprising approximately 5% of the wholesale

chuck (Huffman and Cecchi, 1986). The SV is intermediate in

palatability characteristics of the major chuck muscles

(Paterson and Parrish, 1986). However, no reports regarding

the characteristics of the latissimus dorsi (LD) have been

found. This large, thin muscle lies on the outside of the

plate and extends into the chuck. The LD is approximately

half the size and weight of the SV and contains about 5%

intramuscular fat.

Both the SV and LD muscles provide an excellent source

of raw material from which a reformed whole-muscle beef

product could be produced. Currently these two muscles are

not being used to their greatest economic potential. In

addition, both muscles are unipennate, with fibers oriented

in one direction, and contain mainly surface connective

tissue. Also, these muscles comprise a major portion of the

forequarter and differ compositionally in internal fat

composition (>10% and <5% for SV and LD, respectively) (Recio

et al., 1988).

Muscle Protein Functionality

Muscle protein functionality denotes any physiochemical

property that affects the processing and behavior of protein

in food systems as judged by the quality attributes of the

final product (Hand, 1986). Three major protein

functionality interactions have been reported to occur in

processed meat products: 1) protein-water; 2) protein-lipid;

and 3) protein-protein (Acton et al., 1983; Acton and Dick,

1984; 1985).

It is generally accepted that the myofibrillar proteins,

actin and myosin, are the primary proteins that provide the

structural stability to processed meat products. Although

many other myofibrillar proteins are present in meat tissue,

their quantity and contribution to structural stability in a

processed meat product is insignificant. The ability to bind

meat pieces back together in a restructured meat product is a

heat induced phenomenon involving protein-protein

interactions (Asghar et al., 1985). Several researchers have

attempted to explain the mechanism by which meat binding


Hamm (1966) studied the changes that occur in meat

proteins during cooking and concluded that thermal processing

caused the helical portions of the protein molecules to

denature into random chains. These unraveled proteins were

postulated to produce random crosslinkages that may be

responsible for binding.


Vadehra and Baker (1970) and Kotter and Fischer (1975)

theorized that the mechanism of binding involves structural

rearrangement of the soluble proteins. This resulted in a

loosely ordered protein structure that allowed the proteins

to become more reactive during thermal processing.

The extraction of myofibrillar proteins is required to

facilitate binding of meat pieces. The binding properties of

purified muscle proteins were studied by MacFarlane et al.

(1977). They determined the binding strength of myosin to be

superior to that of actomyosin at salt concentrations up to 1

M. However, increasing the myosin concentration did not

result in increased binding strength (MacFarlane et al.,

1977; Siegel and Schmidt, 1979a). Siegel and Schmidt (1979a)

concluded that the decreased binding associated with

increased myosin concentrations implied ionic interactions in

binding. MacFarlane et al. (1977) further reported that, in

the absence of salt, the binding strength of myosin was

enhanced by incorporating sarcoplasmic proteins. The

contribution of sarcoplasmic proteins to the binding strength

was reported to be similar to that for salt. However, it was

reported that as salt concentrations increased, the

sarcoplasmic proteins exerted a deleterious effect on the

binding strength of myosin. This was attributed to the

adsorption of denatured sarcoplasmic proteins onto the

myofibrillar protein molecules, which resulted in decreasing

the availability of the binding sites.


Theno et al. (1978a) studied the binding junctions of

thermally processed sectioned and formed ham products. Their

research detected the presence of aligned elements occurring

within the binding junctions of the meat pieces. Siegel and

Schmidt (1979b), in an effort to determine the mechanism of

binding between meat pieces, described the ultrastructure of

a crude myosin gel as affected by salt, phosphate, pH and

temperature. They concluded that the mechanism of binding

meat pieces involved the following events. Intact

myosin-heavy chains are extracted to the muscle surface where

they combine with heavy myofilaments located on or near the

surface of the muscle cells. This results in producing super

thick synthetic filaments that bind the meat pieces together.

Formation of super thick filaments at higher temperatures was

stated to be possible because heavy chains are freed from the

parent molecule at lower heating temperatures due to salt

solubilization (Siegel and Schmidt, 1979b).

From this discussion it becomes evident that the

mechanisms involved in binding meat pieces together are

multifaceted. The heat-induced protein-protein interactions

are influenced by salt, ionic strength, protein type and

protein quantity.

Mechanisms of Protein-Water Interactions

Myofibrillar proteins are primarily responsible for the

binding of water in muscle and that different types of water


and water binding occur in muscle tissue (Hamm, 1975a).

Fennema (1985) presented a classification system for water

occurring in food systems. Type I water, also referred to as

bound water, is the mono- and possibly the bimolecular layer

of water surrounding proteins and other substances having an

electrostatic charge affinity. Type I water is present in

small quantities (4.5% of total water), unfreezable, and

displays little mobility. Type II or restricted water exists

as multiple layers surrounding the bound Type I water. Type

II water is subject to freezing and can be removed by drying.

Type III water or free water represents the major portion of

water located in animal and plant tissues and is subject to

easy removal. Type IV water refers to water in the pure

state and does not naturally occur in biological matter.

Because Type I water is bound and Type IV water does not

naturally exist in muscle tissue, the types of water that are

of interest from a food processing standpoint are Types II

and III. Therefore, a primary objective of meat processing

is to reduce the amount of water in the free state (Type III)

and increase the amount in restricted (Type II) state.

Variations in water content can result from gains that

occur during processing (in the form of added water), or

losses from improper chilling, drip, evaporation or cooking.

Such gains or losses are important for two reasons: first,

economics (since meat is sold by weight); and second,

consumer satisfaction, (the juiciness and tenderness of meat


and meat products depends to a great extent on their water

content). Additionally, subsequent water losses that occur

during cooking act to reduce the edible portion size (Offer

and Trinick, 1983).

Hamm (1960) defined water-holding capacity as the

ability of meat to hold its own or added water during

application of any force (pressing, heating, grinding). Hamm

(1975b) defined swelling or water binding ability as the

spontaneous uptake of water by meat from any surrounding

fluid, resulting in an increase in muscle weight. Although

the forces that restrict the mobility of loose water are not

well understood, the factors that influence changes in the

water-holding capacity of meat have been described (Hamm,

1960; 1966; 1975a,b). Hamm (1975b) described the swelling of

muscle fibers in terms of colloidal chemistry. The amount of

water immobilized within the tissue is influenced by the

spatial molecular arrangements of the myofibrillar proteins,

or filaments, of actin and myosin (Hamm, 1975b). Decreasing

the cohesion between adjacent molecules or myofibrillar

filaments by increasing the electrostatic repulsion between

similarly charged groups or by weakening of hydrogen bonds,

causes the network to enlarge or swell. Increasing the

degree of swelling increases the amount of water that can be

immobilized within the filamentous network, thus

water-holding capacity increases. However, a continued

decreasing of intermolecular cohesion will result in network


collapse, and the gel becomes a colloid solution of

myofibrillar proteins. Increasing the electrostatic

attraction of oppositely charged groups between adjacent

molecules can produce new interlinking bonds. This results

in less space being available for the retention of

immobilized water. Therefore, when the myofibrillar network

tightens as a result of applied pressure, heat, or grinding,

shrinkage occurs. This causes part of the immobilized (Type

II) water to become free (Type III) water and flow out of the

product (Hamm, 1975a).

Wierbicki and Deatherage (1958) offered the following

hypothesis regarding the forces that immobilize and bind

water. The highly polar water molecules are attracted to the

muscle proteins by ionizable basic and acidic amino acids and

by polar nonionic amino acids.

Offer and Trinick (1983) redefined water-holding

capacity (WHC) as the ability of meat to retain its natural

water content. Their studies reported on the mechanism of

water holding in meat and the swelling and shrinking of

isolated myofibrils, which provided evidence that myofibrils

were able to swell to at least twice their original volume

using salt concentrations that are commonly used in the

processed meats industry. These authors suggested that

myofibrils were the site of water retention. In their study,

Offer and Trinick (1983) made the same basic assumptions as

Hamm (1960), i.e., that as chloride concentration increased,


chloride ions became bound to network filaments. This

interaction increased the repulsive force between filaments

and tended to cause expansion of the network lattice.

However, Offer and Trinick (1983), in their discussion of the

mechanism of water holding in meat, stated that Hamm's model

was not complete for two reasons. It did not consider that

only a part of the myofibril (the A-band) was solubilized, or

the high degree of structural order of the myofibrils (Hand,

1986). Their reasoning was based on the fact that myofibrils

occupy about 70% of the volume of lean meat, and the degree

of observed swelling was related to the amount of water

retained as a result of meat processing. An additional

factor supporting their claim was that the binding of water

to the surface of protein molecules was too small to account

for the observed changes in water content (Hamm, 1960). This

was also based on a protein content of 20% and the belief

that proteins only bind water to an extent of 0.5g of

hydration water per gram of protein (Kunz and Kauzmann,

1974). Therefore, water that is actually bound to protein

molecules represents a small fraction of the total water


Offer and Trinick (1983) concluded that the transverse

linkages, more specifically the cross-bridges, act to

restrain myofibrillar expansion. They indicated that the

influence of attached cross-bridges could be removed in one

of two ways: 1) disruption of the thick filament myosinn)



backbone, would result in disrupting mechanical continuity

and 2) detachment of the cross-bridges from the filaments.

The concentration of sodium chloride (0.4 M) required to

yield maximum swelling was less when pyrophosphate (0.8 M)

was used compared to its absence. However, pyrophosphate did

not alter the maximum extent of swelling. Increasing the

concentrations of sodium chloride and/or pyrophosphate were

shown to 1) displace the equilibrium existing between the

myosin filament and the myosin molecules, in favor of the

myosin molecules and 2) decrease the binding strength of

myosin heads to actin molecules. These actions function to

remove effectively the influence of the protein-protein

cross-bridges and act to increase water-holding capacity.

The authors also reported that maximum myofibrillar swelling

occurred when a substantial part of the A-band had been

extracted, providing further evidence that a large degree of

myofibrillar swelling could occur under conditions where more

than half of the protein was lost.

In summary, the mechanisms of protein-water interactions

are complex. They involve chemical bonding, charge repulsion

and attraction forces, as well as molecular and structural

arrangement. As a result, all of these factors interact to

influence the water-holding capacity of the meat product.


Influences on Protein-Water Interactions

In a review of the factors influencing water-holding

capacity of proteins, Acton and co-workers (1983) indicated

that most factors function in one or more of these three

ways: 1) the ionization and charge density of the protein

(tissue pH); 2) the extent of physical tissue disruption

(particle size); and 3) the distance the water is located

from the protein surface.

DH influence

The relationship of muscle pH to water-holding capacity

is well understood (Briskey, 1964; Dutson, 1983; Honkel et

al., 1981a,b). The relationship of WHC to pH is a function

of the myofibrillar proteins losing their affinity for water

as the pH approaches the isoelectric point for the given

protein (Szent-Gyorgyi, 1960). The decrease in pH that

accompanies postmortem glycolysis of muscle tissue has an

important bearing on meat quality. The final pH attained is

called the "ultimate pH" and for many mammalian species this

is close to a pH of 5.5 (Hultin, 1985). When the ultimate pH

of meat (5.3 to 5.5) approaches the isoelectric point (5.2)

of actomyosin, the WHC of the muscle is decreased (Dutson,

1983). However, when the ultimate pH of beef remains

elevated approximately 1.0 pH unit above the normal

postmortem pH (5.3 to 5.5), more water is retained or bound.

Meat of this type appears darker in color and is referred to


as "dark cutting beef." The ultimate pH attained by beef

muscle has been reported to influence the quality and

textural properties of the meat (Dutson, 1983). He concluded

the ultimate pH of meat affected color development, marbling

perception, WHC, cooler shrinkage, texture, cooking loss,

tenderness and processing characteristics of comminuted and

restructured meats.

Bouton and co-workers (1975) reported a threefold

increase in tenderness scores for mutton at pH 7.0 when

comparing an ultimate pH of 5.9 to 7.0. These authors noted

that the amount of juice centrifugally expressed from a

cooked meat sample had a high positive correlation with

sensory organoleptic juiciness scores and increased linearly

with pH.

Sodium chloride influence

There exists a broad variety of salts found in nature,

but because of taste and toxicological considerations, the

two most commonly used in meat products are sodium chloride

and the sodium salts of polyphosphoric acids (Trout and

Schmidt, 1983). The addition of salt to meat has a

multi-functional affect. Salt was initially used as a

preservative to retard bacterial spoilage. Today, the

primary role of salts in a meat system is to influence the

ionic strength and alter the pH of the system (Trout and

Schmidt, 1983).


Closely related to water-holding capacity is the ability

of meat to absorb additional water at elevated salt

concentrations; this was termed water-binding capacity by

Hamm (1982). Salt concentrations of 0.8 to 1 M (4.6 to 5.8%)

sodium chloride (NaC1) have been reported to yield maximum

water uptake (Offer and Trinick, 1983). However, a somewhat

lower NaCl level (2%) is more often used in the manufacturing

of processed meat products. Hamm (1960) concluded that the

chloride ion (ClV) from NaCl was the ion responsible for

myofibrillar swelling, as the ions from sodium acetate failed

to induce swelling. It was theorized by Hamm (1960) and

again by Offer and Trinick (1983) that if a substantial

number of Cl~ were bound to the filaments at high NaCl

concentrations, the negative charge on the filaments would

increase, resulting in an increased electrostatic repulsive

force that would induce filamental swelling. Offer and

Trinick (1983) further concluded that as the salt

concentration increases, the attachment of the cross-bridges

(actomyosin) weakened. At the same time, increased ClV

binding causes increased electrostatic repulsive forces.

These authors concluded that as long as the cross-bridges

remain attached, the myofibrillar lattice network cannot

swell to the same degree, and that if the lattice does swell,

then the cross-bridges cannot remain attached. When the

lattice swells, the thick filament will depolymerize allowing

water uptake to occur.


The use of Nacl and phosphates in a restructured meat

product facilitates extraction of the salt soluble proteins

(Theno et al., 1978a). Salt and phosphate contribute to the

disruption of muscle fibers during mixing, solubilization of

the myofibrillar proteins and the production of an exudate

rich in solubilized proteins. Restructured products made

without added salt and phosphate did not possess the desired

textural properties and were rated as unacceptable by a

sensory panel. Theno and co-workers (1978a) demonstrated

that massaging raw meat for 24 hours without the addition of

salt and phosphate would not permit an acceptable binding

between meat pieces. The addition of salt or phosphate alone

was not sufficient to attain an acceptable binding, but when

both were used in the proper combination, there was a

positive synergistic effect on binding. However, Ford et al.

(1978), in an effort to reduce the added salt content of

restructured products, determined that additions of crude

myosin extracts with sarcoplasmic proteins had the ability to

bind meat pieces into a cohesive restructured product.

Further support of this work was reported by Siegel and

Schmidt (1979a) using isolated crude myosin extractions as a

binding agent between meat peices as stated previously.

Bard (1965) studied the influence of temperature, mixing

time, pre-rigor and post-rigor meat addition and level of

added salt on the extractability of salt soluble proteins

from muscle tissue. Temperatures in the range of -5o to 20C


provided maximum protein extraction and increasing mixing

times up to 16 hours increased protein extraction. Protein

was more readily extractable from pre-rigor meat than

post-rigor meat, and a sodium chloride content of 10%

extracted the greatest amount of protein. In contrast to

these findings, Gillett et al. (1977) reported the optimum

temperature for protein extraction to be 7.20C, with

extractability decreasing at OOC. However, this difference

is probably a result of the different experimental conditions

that existed between studies. Gillett et al. (1977) used a

shorter extraction time (6 min vs 30 min), a higher salt

concentration (6% vs. 3.9%) and a higher solvent to meat

ratio (3:1 vs. 2:1) than Bard (1965).

The addition of salt to processed meat products has also

been reported to increase the flavor, texture and/or

juiciness ratings of restructured steaks (Cross and

Stanfield, 1976; Huffman, 1979; Mandigo, 1974; Mandigo et

al., 1972; Neev and Mandigo, 1974; Schwartz, 1975). Salt has

been, and to many people still is, considered to be an

essential part of our everyday lives. However, research has

established a relationship between sodium intake and

hypertension (Altschut and Grommet,1980; Pearson and Wolzak,

1982). As a result, many health conscious consumers are

avoiding foods that contain elevated sodium levels, and in

particular, processed meat products. In response, meat

processors are reducing the sodium content of their products


by decreasing the amount of salt used during processing.

Reducing NaCi levels, however, has decreased the functional

properties and characteristics (water binding ability and

texture) of the product (Sofos, 1983; Trout and Schmidt,

1986). In an effort to regain some of the functional

properties without greatly increasing the sodium content of

the product, meat processors are utilizing food grade

phosphates (Trout and Schmidt, 1983).

Influence of phosphates

Mahon (1961) indicated that the type and amount of

alkaline polyphosphates added to meat would increase the pH

by 0.1 to 0.4 units. Trout and Schmidt (1983) theorized that

the alkaline nature of the polyphosphates was the primary

factor in producing the altered pH effect. However, when

NaCl was added, the pH of the meat system decreased by 0.1 to

0.2 units. These same researchers theorize that the effect

of NaCl on pH is due to the displacement of hydrogen ions by

sodium ions on the meat surface and that the liberated

hydrogen ions produce the change in pH.

The ability of phosphate compounds to enhance the uptake

of water by meat has been known for some time (Bendall,

1954; Hamm, 1960; Sherman, 1961; Ranken, 1976; Offer and

Trinick, 1983). Phosphates can be used to buffer, sequester

metal ions, and increase the ionic strength of solutions.

Phosphate compounds have also been reported to promote the


extraction of myofibrillar proteins from meat pieces (Kotter

and Fisher, 1975; MacFarlane et al., 1977; Siegel et al.,

1978a,b; Theno et al., 1978a,b,c; Offer and Trinick, 1983;

Trout and Schmidt, 1986).

Phosphates are salts of phosphoric acid. The two

general classes of phosphates are orthophosphates and

polyphosphates (Shimp, 1983). Orthophosphates contain a

single phosphorus atom while the polyphosphates contain two

or more phosphorus atoms. Orthophosphates are made by

partial or complete neutralization of phosphoric acid with an

alkali source. This reaction replaces one or more of the

three available hydrogen atoms on phosphoric acid with alkali

metal ions (Shimp, 1983). Monobasic orthophosphates have one

hydrogen atom replaced with an alkali metal. Dibasic

orthophosphates have two hydrogen atoms replaced, and

tribasic orthophosphates have all three hydrogens replaced

with an alkali metal.

Polyphosphates are produced by heating mixtures of

orthophosphates to high temperatures causing them to condense

into phosphate chains. Pyrophosphate is the simplest

polyphosphate containing two phosphorus atoms, while sodium

hexametaphosphate is one of the largest containing 10 to 15

phosphorus atoms. Pyro- and tripolyphosphate are white

crystalline solids containing one or three phosphorus atoms,

respectively. When phosphorus atoms exceed three chain


lengths the atoms are no longer crystalline, but amorphous

structures, commonly called glassy phosphates.

Buffers have the ability to maintain a constant pH when

components of a different pH are added to the system.

According to Shimp (1983), orthophosphates provide the best

buffering capacity, while ability to buffer decreases as

chain length increases.

Sequestering metal ions refers to a chemical process of

tying up metal ions in solution so that the ions cannot

participate in chemical reactions. Long chain polyphosphates

are the best sequestering agents for metal ions such as

calcium and magnesium (Shimp, 1983).

The three basic chemical functions of phosphates-pH

buffering, sequestering metal ions, and polyvalent anionic

properties-provide many beneficial effects in food systems

(Shimp, 1983). These effects include color stabilization,

water binding, prevention of coagulation, texture

improvement, emulsification, dry acid leveling, fast curing,

nutritional enhancement, and easier processing (Shimp, 1983).

Pyrophosphate and tripolyphosphate are two common

phosphate compounds added to processed meat products. They

are used to reduce water loss during cooking and to improve

the texture of the product (Ellinger, 1972). Trout and

Schmidt (1986) stated that phosphates increase the functional

properties of meat products in one or more of the following

ways: (a) by increasing the pH and ionic strength of the

product; (b) by dissociating actomyosin into actin and

myosin; (c) by binding to the meat proteins. A

generalization or ranking of the ability of different food

grade phosphates to increase the functional properties of

meat occur in the following order: 1) pyrophosphate; 2)

tripolyphosphate; 3) tetrapolyphosphate; 4) hexametaphosphate

and orthophosphate (Bendall, 1954; Shults et al., 1972; Trout

and Schmidt, 1984; Trout and Schmidt, 1986).

Trout and Schmidt (1986) studied the effects of various

types of phosphates, at different pH and ionic strengths and

their ability to influence the functional properties of

restructured beef rolls. Semimembranosus muscles were

removed 48 hr postmortem and trimmed of all visual fat and

connective tissue. Initial pH of all muscles was between 5.4

and 5.8. Muscles were ground through a 2.5 cm plate and

mixed by hand. The additives used were deionized water (5%

of the product weight), sodium chloride and disodium

phosphate (as analytical reagent grade), and the following

food grade phosphates: tetrasodium pyrophosphate (PP), sodium

tripolyphosphate (TPP), sodium tetrapolyphosphate (TTPP) and

sodium hexametaphosphate (HMP). The treatments utilized the

six phosphate types, three ionic strength levels ((0.15,

0.29, and 0.43), and three pH levels (5.50, 5.95, and 6.35).

The phosphates were used at a constant ionic strength of

0.055 and the different ionic strengths were obtained by

varying the NaCl content. Product pH was controlled by


adding 1 M NaOH or HC1 during product mixing. Beef rolls

were thermally processed to an internal temperature of 700C

in an air agitated, thermostatically controlled retort.

Increasing the ionic strength (from 0.15 to 0.43) and pH

(from 5.50 to 6.35) produced increases in the cooking yields

and tensile strength. Both of these properties increased

linearly with increasing ionic strength and increasing pH

until reaching maximum values and then plateauing. These

maximum values occurred when the pH and ionic strength was

between 5.95 and 6.35 and 0.29 and 0.43, respectively (i.e.,

at NaCi concentrations between 1.7 to 2.5% and 1.4 to 2.4% in

the absence and presence of phosphates, respectively). The

majority of the increase in cooking yield (53%) was due to

the increase in ionic strength, while the increase in tensile

strength (26%) was attributed to the increase in pH. All

phosphate sources produced synergistic increases in cooking

yields and tensile strengths when ionic strengths were

greater than 0.15. The ability of phosphates to produce the

synergistic effects decreased as their chain length

increased. In addition, the ability of phosphates to

increase tensile strength at high ionic strengths could not

be reproduced simply by increasing the pH or by increasing

the ionic strength with only NaCl.


Water Distribution

Fresh meat at slaughter contains approximately 75%

water. The main structural component of meat is the

myofibril which occupies approximately 70% of the volume of

lean tissue (Offer and Trinick, 1983). The majority of the

water in meat is associated with the myofibrils, occupying

the spaces between the thick and thin filaments.

The tissue water of an animal can be divided into two

compartments: 55% intracellular (ICF) and 45% extracellular

(ECF). The extracellular space (ECS) is the fluid

compartment situated externally to the cells of the body

(Law, 1982). Law (1982) reviewed the techniques and

applications of determining ECS in mammalian tissues. The

ECS consists of the plasma component of the vascular space

and the interstitial fluid (Law, 1982). The volume of the

ECS within a tissue is calculated by adding the plasma

component to the interstitial fluid component.

Experimentally, this is determined by introducing a marker

molecule into the space and determining its concentration at

equilibrium. Law (1982) indicated a marker should have the

following characteristics: 1) ready and uniform distribution

throughout the entire anatomical ECS; 2) exclusion from the

cells; 3) no influence on the size of the ECS; 4) non-

metabolizable; 5) uniform molecular size and diffusion; 6)

easy and accurate estimation at low concentrations (i.e.,

involves use of radioisotopic labling); and 7) minimal loss

of the marker by urinary elimination or lymphatic draining.

Several different saccharides and ion molecules have

been tested in trying to satisfy the requirements stated

above. Of these, the compound inulin (which is readily

available as the 3H-methoxy- or 14C-carboxylic acid compound)

has been the most widely used. Other radio labeled

saccharides that have been used include sorbitol, mannitol,

sucrose and raffinose.

The earliest reported attempts to measure ECS were those

of Fenn (1936) using tissue chloride levels. Although the

values obtained using this method were not grossly misleading

for whole body content or in tissues with low intracellular

chloride (e.g., skeletal muscle), they were unacceptable for

tissues with high concentrations of intracellular chloride

(e.g., intestinal, cardiac and vascular tissue) (Law, 1982).

Ions such as sulphate, bromide and iodide and compounds such

as thiosulphate and thiocyanate have been evaluated and found

to occupy spaces greater than those available for markers of

higher molecular weight (Law, 1982). Law (1982) indicated

that under a given set of physiological conditions, a unique

anatomical space will exist and the measured ECS will

decrease as the molecular weight of the marker increases.

This was explained on the basis that markers of high

molecular weight fail to penetrate fully the ECS or that

lower molecular weight markers penetrate the cell. Thus,


several factors are capable of contributing to the over- or

under-estimation of the ECS.

Law (1982) concluded that no conclusive evidence

currently exists that recognizes an ECS marker as being

rigidly excluded from cells. Also, in isolated tissue slices

in which markers do not have to cross a capillary wall, the

marker is not able to penetrate instantaneously the ECS.

This is viewed as a problem in classical equilibration

experiments. The measured ECS may also be over-estimated due

to the entry of marker into damaged peripheral cells. The

use of tritiated markers (3H) has presented some problems

because of their known ability to exchange H-atoms in

functional groups, resulting in an overestimation of the ECS.

Williams and Woodbury (1971) indicated that inulin may also

become bound by connective tissue causing an over-estimation

of the ECS. A lack of, or a reduction in, the normal

proportion of oxygen in skeletal muscle during ECS

measurements has been reported to cause measurable increases

in the interfiber space (Law, 1967). Law (1967) used an

oxygenated saline solution containing rat muscle to study the

distribution of 14C-labeled sucrose. Histological

examination of these muscles indicated distorted muscle fiber

patterns which were interpreted as indicating severe

physiological deterioration of the muscle. It was concluded

that even though previously oxygenated Ringer's solution was

utilized, tissue hypoxia was responsible for this occurrence,


and doubted the validity of such a method as a means of

extracellular space examination.

Law (1982) indicated several factors that could

contribute to an under-estimation of the ECS. Under-

estimation normally occurs when the marker is not adequately

able to penetrate the ECS, or it does so at a very slow rate.

Ogston and Phelps (1961) reported that hyaluronic acid-rich

mucopolysaccharides present in connective tissue create a

partial resistance to inulin and possibly other large

markers, effectively reducing the ECS estimate. The use of

highly charged markers to estimate ECS, e.g., sulphate, may

be impeded or exaggerated by the presence of fixed charges

within the tissues (Law, 1982).

A variety of techniques, independent of or complimentary

to the use of marker molecules, have been reported for

estimation of the ECS. However, these alternative methods do

not seek to express ECS in precise quantitative terms. The

value of these methods lies in their ability to a) detect

rapid changes and b) to visualize small but significant

changes in specialized areas of the ECS (Law, 1982). These

methods include 1) autoradiography to follow uptake of

inulin (Stirling, 1972), 2) light or electron microscopy to

determine total tissue ECS outlined by chemical markers

(Prosser et al., 1960), and 3) electrical resistivity or

potential differences that rapidly occur in the dimensions of

lateral cellular interspaces (Schultz et al., 1974).


To date, the majority of mammalian skeletal tissue

studies designed to study ECS have relied on one of the

following methods: tissue perfusion, in situ or in isolation,

or determination of washout kinetics following marker

equilibration in nephrectomized animal models. The

equilibration procedures involves soaking or incubating small

muscles or strips of muscles in a Ringer-lactate solution

containing 0.3% inulin according to the procedure of Heffron

and Hagarty (1974), modified by the use of low oxygen tension

or incubating muscle strips in 14C-inulin as described by

Vaccari and Maura (1978).

Heffron and Hagarty (1974) studied the rate at which

fiber diameter changed during the development of rigor mortis

in the biceps brachii of the mouse. They reported a 14 to

16% decrease in fiber diameter when the muscle entered rigor,

followed by an increase in ECS. In addition, total muscle

volume (fibers + ECS) did not change during rigor

contraction. Measurements of the ECS determined at 1, 2, 3,

4 and 24 hr postmortem indicated increases of 49.7, 76.7,

83.5, 135.7 and 432.9 % respectively in ECS. The authors

concluded that the decrease in fiber diameter when the muscle

entered rigor mortis was associated with a depletion in ATP.

The authors describe two hypotheses to explain their results.

The first hypothesis was that ATP may act as a plasticizerr"

for the sarcolemma in the same manner it does for the

myofibrils, and that fiber shrinkage or contraction results


when ATP supplies are completely exhausted. The second is

that the interfiber fluid becomes hyperosmotic soon after

death, causing movement of the intrafiber water to the ECS

and resulting in a decrease in muscle fiber diameter.

A study designed to relate changes in the mechanical

properties and ECS of beef semitendinosus and biceps femoris

muscles during the onset of rigor mortis was presented by

Curri and Wolfe (1980). It was suggested that intrafiber

water was a significant factor contributing to the tensile

and adhesive properties of muscle; it should be considered as

equally important as the state of contraction and the

collagen angle of the connective tissue network when

assessing muscle tenderness. They presented the following

hypothesis to convey the importance of intrafiber water to

muscle tenderness: during early post-mortem, muscle pH is

high, water-binding capacity of the contractile proteins is

high and ATP levels are high. This results in low tensile

and extensibility properties. As the pH drops, the

water-binding capacity of the proteins decreases. In

addition, the ECS was shown to increase as rigor progressed

until pH 5.9, which agreed with observations of Heffron and

Hegarty (1974). Associated with this increase in ECS was an

increase in the tension and extensibility. Curri and Wolfe

(1980) indicated that the initial increase in ECS was

expected, but the occurrence of a brief unexpected decrease

in ECS near pH 5.95 followed by another increase in the ECS


back to its previous volume was not expected. In an

explanation of this occurrence, the authors hypothesized that

the release of Ca2+ from the sarcoplasmic reticulum or other

Ca2+ containing organelles within the fiber created a

hyperosmotic intracellular region, causing water to move from

the ECS back into the fiber. The secondary increase in ECS

was attributed to the continuing decline in pH. As the pH

continued to decline, the isoelectric point of the

sarcoplasmic and contractile proteins was approached, causing

some proteins to undergo denaturation and lose their ability

to bind water. The increase in "loose" water intracellularly

could cause a dilution effect of the Ca2+ ion and the

extracellular region becoming hyperosmotic again. This would

promote water movement out of the fiber and into the ECS. The

information obtained from these experiments helped to explain

the observed changes in tensile and adhesive measurements

that occur during the onset of rigor mortis.

The reagent grade inulin used in their previous work

(Currie and Wolfe, 1980) was not pure enough to provide

reasonable value estimations for the ECS and over estimated

the volume. To overcome this drawback, Currie and Wolfe

(1983) utilized the ECS procedure of Vaccari and Maura

(1978). Highly purified inulin [14C] carboxylic acid was

used as the extracellular marker to determine the location of

water in the post-mortem muscle. Incubating muscle strips in

inulin [14C] carboxylic acid provided a means in which to


assess the functionality of the muscle membranes. The

authors expressed hope that this research would provide an

avenue through which the variations in water-holding capacity

and the interfilamental spacing of meat and thus meat quality

could be further advanced.

Heat-Induced Changes in Meat

It has been established that the heating of muscle

tissue during processing or cooking changes the chemical and

physical composition of muscle proteins and that these

changes influence the palatability characteristics of the

final product. When meat is heated to a certain temperature

range, the proteins in the muscle cells undergo

denaturation/coagulation with a subsequent loss in solubility

(Hamm and Deatherage, 1960; Hamm, 1977; Cheng and Parrish,

1976; Leander et al., 1980; Moller, 1981; Martens et al.,

1982). "Denaturation" is a change in the specific steric

conformation of a protein, i.e., a change in the secondary

and tertiary structure without a chemical modification of the

amino acids (Hamm, 1977). Fennema (1985) described

denaturation as a process in which hydrogen bonds,

hydrophobic interactions, and salt linkages are broken and

the protein unfolds. A protein molecule in its natural state

consists of a backbone chain of amino acids intertwined in a

"native" structure. The native molecules may exist in

solution (i.e., sarcoplasmic proteins in meat) or as natural


aggregates (i.e., myofibrillar proteins and collagen fibers).

Intramolecular forces function to hold the native protein

structure together. However, these forces can become

strained or broken as the ambient temperature of the protein

increases, leading to thermal denaturation. Heat induced

protein denaturation does not occur as an "all or none"

process, but rather as a continuous process with various

regions of the protein molecule changing at different rates

depending on the rate and duration of heating (Paul and

Palmer, 1972). The application of heat to a native protein

structure is said to cause chain unfolding. Unfolding the

chain exposes the interior of the previously protected

internal chain which results in changing affinity for other

molecules (Martens et al., 1982). Thus, denaturation is

considered to be a physical process and not a chemical one.

When protein affinity increases, the degree of aggregation

between protein molecules will increase. Depending on the

physical properties of the native protein, the precipitating

or coagulating particles will form strong, continuous,

water-binding gels, as in egg white (Hegg et al., 1979).

However, if the affinity decreases, a solubilization of the

native components may result. Martens et al. (1982)

concluded that increases or decreases in affinity were

dependent upon which affinity was mechanically stronger.

In a meat protein system, the denaturation of protein

structures may result in changes in the physical properties


of meat such as water holding capacity (WHC), thermal

diffusivity, heat conductivity, porosity, etc. The influence

of heat on the structural components of meat has been the

subject of a number of studies (Hamm and Deatherage, 1960;

Trautman, 1966; Hamm, 1966; Hamm, 1977; Cheng and Parrish,

1976; Bouton et al., 1981; Bouton and Harris, 1981; Moller,

1981; Martens et al., 1982; Ziegler and Acton, 1984a,b).

Hamm (1966) reported on various physical and chemical changes

that muscle tissue undergo as it is heated from 200C to above

800C. Heating of beef muscle produces a stepwise series of

physical and chemical changes as it undergoes thermal

denaturation. From 200 to 300C, no changes occurred in the

physical or chemical properties of muscle proteins. Heating

from 300-500C resulted in an increase in tissue pH and

rigidity, followed by a decrease in water-holding capacity.

During heating, peptide chains initially undergo an unfolding

process, yielding new unstable cross-links which results in a

tighter protein structure. Between 500-550C rearrangement of

myofibrillar proteins continues, and newly formed cross

linkages become stable. At 650C most of the myofibrillar and

globular muscle proteins are coagulated. Collagen shrinks at

temperatures around 630C and may be practically transformed

into gelatin. Between 700C and 900C disulfide bonds are

formed due to the oxidization of sulfhydryl groups

originating from actomyosin. Disulfide bond formation

continues to occur with increasing temperatures between 700

and 900C. Above 900C, hydrogen sulfide (H2S) is split off

from the sulfhydryl groups of actomyosin and collagen is

transformed to gelatin, resulting in an increase of


Hamm (1977) reviewed the changes muscle proteins undergo

during heating of meat. Heating actomyosin to temperatures

above 400C removed the Ca2+ sensitivity of actomyosin, which

resulted in an increase in ATPase activity. The heating

effect on actomyosin ATPase was theorized to be responsible

for producing conformational changes in the actomyosin

complex. The temperature of maximum ATPase activity was

reported to occur between 430 and 470C, however increasing

the temperature above this range resulted in inactivation and

irreversible denaturation. Heating actomyosin to 600 to 700C

produced an increase in sulfhydryl (SH) groups. The increase

in SH group content was thought to occur as a result of an

unfolding of the protein molecules during heating. The

temperature at which actomyosin begins to release SH groups

was reported to coincide with the temperature at which

maximum ATPase activity and maximum change in conformational

changes occurred (450C). Increasing the temperature to 700C

did not produce additional SH groups, but between 700 and

1200C the total number of SH groups was reported to decrease

as a result of oxidation of SH to disulfide (SS) groups.

Heat coagulation of myofibrillar proteins was not considered

to occur as a result of SH oxidation, but rather as a result

of intermolecular association of other side-groups on the

molecules. In summary, between 300 and 500C, the

myofibrillar proteins undergo an unfolding of the protein

molecule, followed by protein coagulation and a loss of

enzyme activity.

Because isolated myofibrillar proteins might not respond

the same as those in the intact fiber, Hamm (1977) reviewed

the changes incurred during the heating of muscle fibers or

tissue. At temperatures between 400 and 600C, myosin

proteins reportedly broke down into smaller compounds, while

actin molecules underwent changes in its helical structure.

Myofibrillar proteins reportedly underwent their greatest

decrease in solubility at temperatures between 400 and 600C

and became essentially insoluble at temperatures above 600C.

This decrease in protein solubility coincided with a decrease

in Ca2+-activated ATPase and Mg2+-activated ATPase in

myofibrils. However continuous heating for 7 hr at 550C did

not result in complete solubilization. It was concluded that

the temperature range yielding the maximum change in

solubility seemed to be about the same in the intact muscle

fiber or the isolated state. However, ATPase activity did

not follow this trend. ATPase activity decreased faster in

solution than in the muscle fiber when stored at 350C.

Heating of muscle from 300 to 700C increased the number of SH

groups, indicating an unfolding of the protein molecules as

previously observed for isolated myosin and actomyosin. The

relative changes in SH and SS groups occurring in meat was

considered to be important because 97% of the SH and SS

content of muscle tissue is bound to myofibrillar proteins.

At temperatures above 800C, SH and SS content decreased due

to oxidation to cysteic acid or by the splitting off of H2S.

The amount of H2S released increases exponentially with

increasing temperatures. In addition, the amount of H2S

produced increased significantly as the fat content of the

meat increased. Problems arise when the the production of

H2S occurs during the heating of processed canned meat

products. H2S can corrode the interior of a tin can,

discolor the contents and produce an unfavorable or offensive

smell when the can is opened.

When muscle tissue was heated to temperatures between

400 and 600C, the pH of the system increased in a manner

similar to that reported for myofibrillar proteins.

Associated with the shift in pH is a simultaneous shift in

the isoelectric point of the myofibrillar proteins (when

measured as the pH at which water-holding capacity is at a

minimum). The increase in pH and isoelectric point was

reportedly due to an increase in available basic protein

groups. It was theorized that some imidazolinium groups of

histidine are initially masked in the native myofibrils, and

become uncovered as actomyosin unfolds due to heating (Hamm,



The decrease in myofibrillar solubility between 300 and

600C was attributed to the unfolding of the protein chain

followed by protein coagulation. Protein coagulation was not

attributed to the formation of SS bonds resulting from SH

group oxidation because coagulation occurred at temperatures

below the temperature at which the formation of SS begins.

The influence of pH on the water-holding capacity of raw meat

and meat heated to between 300 and 500C revealed the presence

of unstable cross-linkages. These occurred between unfolded

protein chains that tightened as the isoelectric point of the

proteins was approached (Hamm, 1977).

Hamm (1977) in the same review also reported on the

changes that connective tissue proteins undergo when

subjected to heat. Collagen fibers shrink from a quarter to

a third of their initial length at 600C while at higher

temperatures collagen is transformed into water-soluble

gelatin. Although meat contains several types of connective

tissue proteins, collagen is considered to be the most

important thermolabile protein of this type because of its

ability to influence the eating quality of the final product.

Paul (1963), Hamm (1966) and Draudt (1972) theorized

that heat-related changes which influence meat tenderness

result from two opposite effects. First, the changes that

connective tissue undergoes apparently has a tenderizing

effect and second, hardening of myofibrillar proteins imparts

a toughening effect. Dutson and co-workers (1976) utilized


two muscles that had been stretched to various sarcomere

lengths (1.35-2.60 um and 1.70-3.25 um) and differed in

collagen content (13.13 and 2.47 mg collagen/g of muscle).

Differences in tenderness of these muscles were related to

differences in connective tissue content at all sarcomere

lengths measured. This finding was thought to be due to a

shortening of both connective and muscle tissue fibers, which

resulted in decreased muscle tenderness, whereas in the low

connective tissue muscle, only the shortening of muscle

fibers influenced tenderness. Martens et al. (1982)

concluded that the resultant strength of connective tissue in

meat was dependent upon several factors: the amount of

collagen in the sample (as influenced by animal type and

muscle type), the case of collagen gelatinization during

heating (varied with the age of the animal) and the method of

cooking in terms of time and temperature. Lawrie (1985)

reported myofibrillar tenderness to be dependent on several

factors: the extensibility of fibrils

(stretching/shortening) as influenced by the state of rigor

mortis contraction, pH of post-rigor muscle and time and

temperature used to cook meat.

Deng et al. (1976) hypothesized that protein

denaturation produced an intramolecular swelling and

structural loosening of the protein as opposed to an

unfolding of the protein structure. The shrinkage of tissue

and the release of juice during heating of muscle tissue is


due to changes in myofibrillar proteins. Hamm and Deathrage

(1960) and Hamm (1960, 1966) studied WHC of muscle protein as

a function of temperature. The WHC started to decrease

slightly at 300C, decreased significantly between 400 and

500C, remained constant from 500 to 550C, decreased again in

the range of 550 to 700C, and was considered to be at its

lowest level at 800C. However, later reports indicate that

weight loss from meat started to be significant at 600C or

higher (Bengtsson et al., 1976; Nykvist and Decareau, 1976;

Godslave et al., 1977a,b). This implies a weak relationship

between weight loss and WHC.

Bengtsson et al. (1976) measured temperature and water

distribution in bovine semimembranosus muscle as functions of

cooking time. Muscles were oven roasted at 1750 or 2250C

from initial temperatures of -200 and +50C. Temperature

profiles as related to heating time were reported, as were

corresponding moisture and fat content profiles. Moisture

and temperature profiles were inversely related to each

other, with temperature minimum and moisture maximums

occurring near the sample center. Fat content had no

significant influence on any parameters measured. Heating

time was shorter and yield was lower at 2250C than at the

1750C cooking temperatures. Cooking time increased 50% when

cooking from the frozen state. Weight loss was reported to

occur almost entirely by evaporation from the product surface

up to 650C. Above 650C, weight loss became significant due

to liquid drip. Time/temperature profiles of weight loss for

thin slices of meat indicated that cooking temperature was

more important than the time required to produce the first

drip loss. The importance of this issue to meat tenderness

warrants additional detailed discussion.

Godslave et al. (1977a) studied water emission rates and

the mechanism of water loss (drip) from the surface of frozen

bovine semitendinosus muscle samples during oven roasting

(dry heating) temperatures between 1210C and 2040C and an air

flow rate of 13.7 m3/h. Muscle fiber direction was oriented

parallel to the direction of air flow within the cooking

environment. The moisture (drip) emission rate data

contained two constant rate periods followed by a falling

rate period. In general, moisture emission rate curves for

the samples exhibited peaks rather than plateaus, and in both

studies, temperature and time were found to be related to the

amount of weight lost (Godslave et al., 1977a). The

magnitude and duration of both the first and second constant

rate periods were reported to be dependent on the oven

temperature. Oven temperatures of 1770C or 2040C produced

greater water emission rates that were shorter in duration

when compared to oven temperatures of 1210C or 1490C. The

first constant rate period occurred when the surface

temperature of the product was 1000C. This was said to

produce moisture loss resulting from water vaporizing from a

boiling front that moved slowly inward. The second constant


rate period began when the protein at the interior of the

sample started to heat denature in the temperature range of

570C to 670C. The water released by denaturation flowed to

the surface of the sample. This action was said to wash out

the effect of the inwardly traveling boiling front and more

surface evaporation. The second constant rate period was

reported to end and the first period begin again when the

weight ratio of water to protein decreased to two. During

this time period water was still evaporating near or at the

product surface but the fraction of wetted surface was

continuously decreasing. The second falling rate period

started when the weight to water ratio was approximately one

(Godslave et al., 1977a). The rate at which the falling rate

period occurred was temperature dependent, with the higher

temperatures approaching zero more rapidly (Godslave et al.,


A basis for understanding water emission behavior from

muscle tissue during cooking has been provided by Godslave et

al. (1977a). Muscle was viewed as a wet porous medium with

protein forming the porous matrix and water the wetting

fluid. Water emission from cooking muscle (as a heated

porous medium) occurs when protein transformation gives rise

to an increase in water mobility and matrix shrinkage. In

porous material, water flows by capillary action such that

inside a porous body there exists a complicated network of

interconnected pores and passages with some opening to the


surface of the solid. When the solid is wet, the pores are

filled with water. During drying, water evaporates from the

surface at the mouths of pores. This process produces a

meniscus at the product surface that draws water from the

internal network to the exterior of the solid by surface

tension forces. Hence, a smaller pore with a large meniscus

curvature will have a greater interfacial tension capable of

drawing water from the larger pores. Thus, during drying the

larger pores will drain first, provided they do not collapse

on themselves and the empty pores will fill with air.

Because the amount of moisture in a solid is finite, there

comes a point in time when the larger pores run out of water

and the water layer on the surface starts to recede into the

sample in the vicinity of the larger pores. Therefore as the

drying process procedes, air occupies more of the pore space

and eventually the water no longer covers the walls of the

pores with a continuous film. As a result, pool structures

occur within isolated areas of the pore network (Godslave et

al., 1977a). Knowledge of the processes that influence the

rate at which heat penetration occurs within a meat product

is important to minimize the energy required for thermal

processing and yield losses.

Hung (1980) using a modified version of the oven

previously utilized by Godslave et al. (1977a,b), studied the

relationship of water loss to muscle shortening and protein

denaturation during oven roasting of frozen bovine

semitendinosus muscle. Muscles were cut into cylindrically

shaped samples with fibers oriented parallel to the axis of

the cylinder. Two sample sizes were used, 100 g and 600 g.

The respective dimensions (length x diameter) of these

samples were 10.8 cm x 3.49 cm for the 100 g sample and 19.1

cm x 6.35 cm for the 600 g sample. In agreement with the

previous work of Godslave et al. (1977a,b), Hung (1980)

concluded that increasing the oven temperature increased the

amount and rate at which water was lost. However, the amount

of weight loss was not dependent on the orientation of the

sample fibers. Because of this finding, it was hypothesized

that the majority of weight loss was not due to the effect of

gravity. Hung (1980) also reported observing two distinct

drip periods which agreed with previous reports by Godslave

et al. (1977a,b). During the first drip period, the drip

amount for vertical or 450 oriented samples was greater than

for horizontal samples. It was suggested that, it is more

difficult for water to migrate across the fibers than along

the fibers and that gravity played a role in determining the

amount of drip in this period. When previously frozen

samples were allowed to partially thaw, only one drip period

occurred. The amount of drip was small, red in color and

appeared viscous and turbid. Hung (1980) concluded that the

first drip period occurred when the interfiber ice crystals

near the surface or cut ends thawed. Part of this liquid was

absorbed by the muscle fibers, and the rest migrated parallel


in the direction of the fibers or reached the bottom and/or

ends of the sample where it either formed a drip or

evaporated. If the rate of thawing is slow compared to the

rate of absorption, it is possible that absorption could be

sufficiently effective to pick up most of the thawed liquid.

According to Ramsbottom and Koonz (1939) and Wang et al.

(1954), if meat samples are rapidly frozen (e.g., -1500C),

both interfiber and intrafiber ice crystals occur. If the

meat samples are slowly frozen (e.g., -170C), only interfiber

freezing takes place and the muscle fibers are partially

dehydrated. Slow freezing also results in larger ice crystal

formations, which can act as tiny knives to cut or rupture

myofiber cell membranes and contribute to muscle dehydration.

During the second drip period, the drip was clear and

evaporated explosively when contacting the pan. Thus it was

considered to be composed mostly of water. Meat surfaces

appeared dry, or at least partically dry corresponding to the

first peak of the drying curve. However, as the cooking

process continued, liquid drops appeared on the previously

dry surface and continued to grow until they dripped from the

sample. Hung (1980) implied that the liquid drops were

squeezed out of the meat samples due to shrinkage and

gravity. As muscle protein is heat denatured, the rate of

mass transfer increases greatly, possibly due to 1) cracking

across muscle fibers and 2) damage to muscle cell membranes

(Paul, 1963; Davey and Gilbert, 1976).


Changes in tenderness of meat that occur during cooking

are considered to be influenced by heat-induced changes in

the myofibrillar and stromal structural protein components of

muscle tissue. In mammalian skeletal tissue, the myofibrillar

proteins, i.e., actin and myosin, constitute 50 to 55% of the

total protein. Myosin is the predominant protein in prerigor

meat, whereas actomyosin is the predominant protein complex

in postrigor meat. The fibrous actin and myosin in

myofibrils can be histologically identified in raw and cooked

(time and temperature dependent) muscle samples. Hung (1980)

employed transmission electron microscopy (TEM) to evaluate

structural changes that occurred during cooking of bovine

semitendinosus muscle and found a normal distribution of

sarcomere lengths for raw samples (mean = 2.5 microns).

However, a two peak distribution for cooked samples appeared

at 2.05 microns and 1.55 microns. These peak values

suggested that two chemical reactions were involved in

sarcomere shortening. The first reaction caused a decrease

of sarcomere length from 2.5 um to 2.05 um. The second

reaction caused a shortening from 2.05 um to 1.55 um and was

thought to be responsible for water loss during cooking.

Cooked muscle samples that contained long sarcomers had

fibrous looking I-bands actinn filaments), while short

sarcomeres contained nonfibrous looking I-bands. The two

sarcomere distribution peaks that were previously described

(2.05 and 1.55 microns) were reported to represent the two

types of I-band structures (fibrous and nonfibrous).

Disruption of myofibrils upon heating has been reported

(Giles, 1969; Jones et al., 1977; Hung, 1980; Leander et al.,

1980). Myofibrillar breaking points were reported either at

Z-I junctions (Giles, 1969; Hung, 1980; Leander et al., 1980)

or at A-I junctions (Giles, 1969; Jones et al., 1977).

Therefore, breaks in myofibrils occurring during heating are

thought to involve the I-band region of a sarcomere (perhaps

at the weak link point).

Draudt (1972) suggested that heat acted to solubilize

connective tissue providing a tenderizing effect, while

toughening myofibrillar proteins. These changes were

temperature dependent, such that myofibrillar protein

coagulation offsets the tenderization effect of any

additional collagen solubilization at temperatures above 600C

and results in a decrease in tenderness of beef cooked beyond

the rare to medium-rare state.

Numerous researchers (Machlik and Draudt, 1963; Bouton

and Harris, 1972a,b; Davy and Gilbert, 1974; Hamm, 1977;

Bouton and Harris, 1981) have reported that meat tenderness

was greater at final internal temperature of 600C than at

500C. Draudt (1972), in a review, stated that the decrease

in shear force value that occurred as internal temperature

increased from 500C to 600C was due to the shrinkage of

collagen. However, Bouton and Harris (1972b) concluded that

the effect was dependent on the age of the animal and related

it to changes in connective tissue strength. Davey and

Neiderer (1977) suggested that heating muscle tissue to 650C

increased proteolytic enzyme activity and improved meat

tenderness by reducing myofibrillar tensile strength.

Futhurmore, heating to temperatures above 650C improved

tenderness through a reduction in the structural contribution

of the connective tissue. From this discussion, it is

obvious that some disagreement exists between the earlier

work of Machlik and Draudt (1963), Bouton and Harris (1972b)

and Davey and Gilbert (1974). It has also been reported by

Bouton and Harris (1981) that Warner-Bratzler (WB) shear

force values decreased for veal muscles as cooking

temperatures were increased from 500C to 600C. Increased

proteolytic enzyme activity at these temperatures, which may

produce an accelerated aging condition, did not appear to

explain the effect since there was a substantial decrease in

shear force when cooking temperatures were increased from

500C to 600C, even when the meat had been aged (7 wk at

50-60C) or when cooked for 24 hr. Bouton and Harris (1981)

concluded that even at these relatively low temperatures,

changes in connective tissue were involved since: 1) the

magnitude and direction of the changes in shear force with

increasing temperature was dependent on animal age and

cooking time, and 2) the effects of increasing cooking

temperature and/or time on the adhesion strength between the



meat fibers was significantly greater for samples from

younger animals.

The most dramatic changes that occur in meat as a result

of heating are the shrinkage and hardening of tissue, release

of juice and discoloration caused by changes in the muscle

proteins (Hamm, 1977).

Cheng and Parrish (1979) used SDS-polyacrylamide gel

electrophoresis to study the heat induced changes in the

solubility of myofibrillar proteins from bovine longissimus

muscle. Muscle samples were diced (particles size of 1 cm3),

placed into glass test tubes and heated in a water bath to

450, 500, 550, 600, 700, and 800C and held at the designated

temperature for 30 min. In addition, a control (raw) muscle

sample was also included for comparison. The heated and

control muscle tissues were homogenized and the myofibrillar

proteins extracted with 25 ml of 0.6M KC1, 0.1M K phosphate,

pH 7.4 for 1 hr and centrifuged at 15,000 x G for 15 min.

Because the control (raw) sample and samples heated to 450,

500, and 550C contained residue of unheated protein, 1 mM

MgCl2 and 1 mM sodium pyrophosphate were added to aid in
suspension and separation of the protein supernatant. The

SDS-polyacrylamide gels indicated that the extractability of

actin, myosin and Z-disk myofibrillar proteins react

differently to heat. The heavy and light chains of myosin

were reported to be the first major proteins to become

insoluble at 550C. This was in agreement with the earlier


work of Locker (1956) who heated purified myosin and reported

that 82 to 92% of the protein became coagulated at 530C.

However the thin filament proteins, including actin,

tropomysin and troponin T and I, became more extractable with

heating and were reported to be more heat resistant than

myosin. Troponin T and tropomyosin bands were more intensive

between 450 and 600C than in unheated samples or samples

heated at 700 or 800C, indicating their ability to resist

denaturation. The appearance of a 30,000 dalton component

within the gels was used as an indication that troponin T had

been degraded. The presence of this 30,000 dalton component

was reported to occur in samples heated at 550 and 600C. The

observation that this 30,000 dalton component was more

prominent after heating led the authors to conclude that

calcium-activated factor (CAF) activity was stimulated during

heating. Actin was reported to become insoluble between 700

and 800C and tropomyosin and troponin became insoluble above

800C. In response to these findings the authors theorized

the following possible explanations: a) the loss of

alpha-actinin solubility at 500C results in weakening the

I-Z-I protein bonds and allows release of thin-filament

proteins; b) because actin was still soluble and myosin

insoluble at 550C, a weakening or dissociation of the thin

filament proteins occurred allowing their release into

solution; and c) the action of CAF activity on Z-disks

permits an increase in the extractability of thin filament


proteins. It was concluded that the state of the Z-disk and

thin filament proteins were a major factor to be considered

when determining the level of tenderness in bovine

longissimus muscle. Knowledge of these changes and the study

of protein denaturation are important when trying to

understand the mechanisms by which heat and mass transfer

occur in meat during heating.

Microwave Heating

Copson (1975) and Decareau (1985) provides an excellent

source of basic references for heating with microwaves and

microwave power engineering. Together these two books

provide invaluable background information regarding microwave

heating properties as related to food.

Decareau (1985) described microwaves as a form of low

frequency non-ionizing electromagnetic energy, like radio and

television waves. In terms of frequency, microwaves lie

between television waves and infrared waves. The two ISM

(Industrial, Scientific and Medical) frequencies assigned by

the FCC (Federal Communications Commission) for microwave

heating in the U.S. are 915 and 2450 MHz. Microwaves are

capable of penetrating materials such as wood, water and

food. In addition, they are capable of passing through air,

vacuum, glass, paper and some plastics such as teflon.

However, they are reflected by metals or perforated metals

with holes much smaller than the wavelengths of the


microwaves. A 3.2 mm hole (1/8 inch) in metal is small

enough to reflect 2450 MHz microwaves.

Hung (1980) described the three basic components

contained within a microwave heating apparatus: the

generator, the waveguide assembly and the cavity. The

generator is considered to be the major part of the microwave

oven. Two types of microwave generating tubes are presently

used: the klystron and the magnetron. The klystron tube

possess higher or stronger power than a magnetron.

The waveguide is a rectangular piece of metal tubing

that transmits the power from one end to the other. A

waveguide assembly can be either a single component or a

combination of several components. Each component can be a

waveguide equipped with particular microwave hardware

capable of controlling or monitoring microwave transmission.

The design of the cavity is related to the uniformity of

the microwave field in it. The cavity is the chamber that

accepts the microwave energy and holds the product that is to

be heated. Another device associated with the cavity is

called a mode stirrer and functions to improve distribution

and uniformity of the microwave field. It consists of a

rotating metal fan that acts to reflect and distribute the

microwaves that contact it.

Electromagnetic waves produced by microwave ovens are

rapidly absorbed by water molecules present in food. This

form of energy is transformed into a random thermal motion of


water molecules. A water molecule will rotate in the

presence of the electric field of a microwave oven due to the

electric charge within the molecule. Walker (1987) offered

the following explanation on the physics of microwaves and

the water molecule. The electrons associated with hydrogen

atoms are shifted toward the eight protons in the oxygen

atom. The shift leaves the oxygen end of the molecule

negative and the hydrogen ends positive, resulting in a

charge distribution called an electric dipole. Normally the

dipole moments in water are randomly oriented. If an

electrical field is imposed, however, it creates a torque on

each molecule. The torque causes the molecule to rotate in

an effort to align its dipole moment with the imposed

electrical field. Therefore, a microwave oven operating at a

frequency of 2450 MHz attempts to rotate a water molecule at

2.45 X 109 rotations per second, and as a result the

temperature increases. Bakanowski and Zoller (1984)

described how this heating process occurs within foods. Some

molecules within food are electrically polarized and will

respond to the applied electromagnetic field by oscillating

in synchronization with it. These molecules are electrically

coupled to the rest of the food, and through this coupling,

the energy of oscillation is passed on as an increased

thermal motion. If the source of the electromagnetic field

is removed, the polar molecules stop oscillating in

synchronization with the field and no additional heating


occurs. However, a redistribution of the heat already

deposited will occur as a result of temperature gradients

established during the microwave heating. The redistribution

of heat results from thermal conduction and is not due to

microwaves "left behind" after the magnetron is turned off.

In a microwave oven when the magnetron is turned off, the

production of microwave energy ceases to exist in both the

oven and the food.

Microwave ovens have only been on the market for a

little more than two decades, yet they appear to have

revolutionized the way Americans prepare food. Microwave

ovens have opened up a new dimension in food preparation and

management both in the home and in food service processing.

In 1984, the largest annual shipment of any home appliance in

history was claimed for microwave ovens at 9.1 million units

(Markov, 1985a). In a survey of 2000 American households

nationwide, nearly 60% had microwave ovens, while about 50%

had dish washers (MRCA, 1987).

The greatest advantages of microwave cooking are its

time and energy savings. Meat can be cooked four or five

times faster and require approximately 75% less energy in

comparison with conventional methods (Moore et al., 1980;

Hoffman and Zabik, 1985). Markov (1985b), in an overview,

reported of the microwave oven market concluded that

excellent meals could be prepared with microwave technology.

However, the majority of consumers reported that they use


their ovens primarily for reheating and defrosting of foods.

The microwave has not been well accepted by homemakers and

food services for reheating or cooking of muscle tissue due

to uneven cooking, greater cooking losses, and less palatable

meat (Markov, 1985b). It is important to realize that the

microwave heating characteristics of a food product may vary

considerably with the processing frequency, temperature,

chemical composition, and physical state of the product

(Mudgett, 1982).

In developing products for microwave processing,

Schiffmann (1986) stressed that microwaves are a form of

energy, not a form of heat. The energy is only manifested as

heat upon interaction with a material as a result of one or

more energy transfer mechanisms. The heating of materials by

microwave energy is influenced by the oven equipment and the

material being heated (Schiffmann, 1986). Designing a

microwave cooking process involves understanding the thermal

properties of the food in question, and a number of

interrelated electrical properties. These properties vary

extensively with the processing frequency and product

time-temperature profiles which can affect transmission of

microwave energy at the products surface and energy

absorption by the product (Mudgett, 1986).

In a review, Schiffmann (1986) indicated the following

factors that must be considered when developing a

product/processing system: processing frequency, power

level, moisture content, product density, product geometery,

conductivity properties and specific heat of the product.

The depth to which microwave energy is capable of

penetrating into a food product is dependent upon the

frequency used to produce the electromagnetic microwave

energy. The primary difference between heating at 915 MHz

and 2450 MHz is in the differing penetration depths. The 915

MHz frequency has a longer wavelength which produces a

greater effective penetration depth of 33 cm compared to 12.2

cm for the shorter 2450 MHz frequency. Microwave energy at

915 MHz has an initial advantage in penetration depth but

loses penetration depth as the temperature of the product

increases. Nykvist and Decareau (1976) stated that 44 times

more energy reached the center of a 12 cm thick beef slab at

915 MHz compared to 2450 MHz. The frequency selected is

important, because it relates to the size of the object being

heated. In general, a large 220 kg block of frozen material

would be processed better at 915 MHz, while cooking an

individual sausage patty should be done at 2450 MHz.

The speed of microwave heating (power output) is usually

controlled by varying the power level setting. The speed or

rate at which microwaves heat is often the most attractive

feature of microwave heating. However, it is possible to

heat too rapidly, such that heat can be generated faster

than the product can keep up with it. When this occurs, the

outer regions of the product become over heated, which


results in excessive loss of product moisture and decreased

palatability. Another problem associated with excessive

heating rates is non uniform temperature distribution. This

occurs because the heating rate may be so fast as to prevent

effective thermal conductivity of the heat to the cooler

interior regions. The author suggested "heating fast; but as

slow as possible" (Schiffmann, 1986).

Nykvist and Decareau (1976) studied the effect of roast

diameter (6 to 14 cm) on the resulting temperature profiles

when applying 275 W of effective heating power generated at

915 MHz or 2450 MHz. These researches concluded that greater

energy dissipation occurred near the roast surface for the

2450 MHz frequency, resulting in higher surface temperatures,

in less power penetration and less energy being "focused"

and in relatively low center temperatures. However, for 915

MHz as the surface heated up the penetration depth decreased,

thus decreasing the amount of energy reaching the roast

center. From these results it would appear that to attain

optimum microwaving conditions for meat entrees the product

should initially be heated at 915 MHz to attain interior

heating followed by 2450 MHz for surface heating. The

authors stated that methods that promoted radial (uniform)

microwave penetration, such as a perfect cylindrical shape

roast would provide a more uniform temperature profile.

Schiffmann (1986) also agreed that the physical geometry

(size and shape) of a product influences the heating


properties of the product in several ways. He indicated that

the size of an individual product should be considered when

selecting a microwave frequency for heating. For example,

915 MHz would be more effective at thawing a 200 kg block of

meat because of greater penetrating characteristics than to

2450 MHz which produces greater surface heating. In

addition, sharp edges and corners should be avoided because

of their tendency to overheat. Schiffmann (1986) stated that

cylindrical shaped products tend to avoid this problem and

should therefore be considered when designing a microwavable


The moisture content of a product is considered to be

one of the most important factors influencing how well the

product will absorb microwave energy. Usually, the more

water present in a product, the higher the dielectric loss

factor will be for the product. This should result in

superior heating of the product. At very low moisture

levels, the water is considered bound and not available to be

affected by the rapidly alternating microwave field. Product

density affects the dielectric constant properties and hence,

the heating of the product. As the density of the material

increases, so does its dielectric constant.

The transmission properties of electromagnetic energy

relate to the depth of penetration from the product surface

inward. Penetration depths are reported to increase as the

moisture content of the product and processing frequency are



decreased. Very porous materials, such as bread, because of

the air inclusions, are considered good insulators. As a

result heat transfer into these products is difficult and


The conductivity of a product describes the ability of a

material to conduct electric currents by displacing electrons

and ions. In a microwave system, dipolar rotation is the

most frequently discussed means of generating heat. The

presence of sodium chloride ions in the water matrix of a

product acts to increase the heating rate. When sodium

chloride dissociates in water, the positive and negative ends

of a water molecule are electrically attracted to the charged

ions. The electric field of a microwave drives the hydrated

ions through the water, pushing the sodium ions in the

direction of the field and the chloride ions in the opposite

direction. Whenever hydrated ions bump into water molecules,

energy is transferred, and the water is subjected to

additional heating.

The specific heating properties of a product can cause a

material which has a relatively low dielectric loss value

(low water content) to heat well in a microwave field. An

example of this effect is the ability of oils to heat faster

than water because of their lower specific heat.

The dielectric properties collectively reflect the

ability of a material to store and dissipate electrical

energy and, consequently, determine the product's ability to


act as an insulator. However, most foods are poor

insulators. As a result, they typically absorb a large

portion of the energy produced in a microwave field. Energy

absorption by the product is said to be instantaneous and

causes internal heating of the product. As a result the

dielectric properties and subsequent cooking properties of

food products in the liquid or semisolid state depend

primarily on their moisture, salt, and solid contents (Kent

and Jason, 1975; Mudgett et al., 1980; Mudgett, 1982).

Microwave cookery has been shown to decrease cooking

time, labor and energy costs, but has not been well accepted

by food services or homemakers for cooking beef roasts due to

uneven cooking, greater cooking losses, and less palatable

meat when compared to conventional heating methods (Headley

and Jacobson, 1960; Marshall, 1960; Kylem et al., 1964; Law

et al., 1967; Ream et al., 1974; Drew et al., 1980; Moore et

al., 1980; Griffin et al., 1981). In further support of

this, Taki (1986) reported that homemakers still approach

meat cookery in a microwave oven by a trial and error


The scientific literature on microwave cooking of beef

or other muscle tissues has not been overly complimentary.

Comparisons between microwave and conventionally cooked meat

has indicated differences in sensory attributes, cooked

yields, microbial quality, and physical or chemical

characteristics of the final product, depending upon the


cooking method (Pollack and Foin, 1960; Marshall, 1960;

Korschgen et al., 1976; Drew et al., 1980; Moore et al.,

1980; Bodrero et al., 1980; Zimmermann, 1983; Sawyer et al.,

1984; Sawyer, 1985).

Marshall (1960) reported on the use of an "electronic

oven" in meat cookery. In her study, paired five pound

pieces of choice grade top round of beef were roasted in an

"electronic oven" or in a conventional oven. The author

indicated that in previous studies utilizing the "electronic

oven" the internal temperature of the product would rise

approximately 110C after removal from the oven. Therefore,

roasts cooked in the "electronic ovens" were cooked fat side

down for one-half to two-thirds of the time and then turned

fat side up until an internal temperature of 800C was reached

and then removed. The other half of the paired roasts were

cooked in a 1480C electric oven fat side up until an internal

temperature of 800C was reached. The average cooking time

for roasts prepared in the "electronic oven" was 23.5 minutes

per kilogram compared to 100.0 minutes for the conventional

oven. The author also indicated that the shape of each roast

was such that one end was smaller than the other. As a

result of this uneven shape, the small end on roasts prepared

in the "electronic oven" became excessively brittle and

porous and it was deemed unpalatable. In addition, the fiber

hardening effect was reported to occur along all of the edges

and corners of the these roasts. Cooking losses included


losses due to drip, evaporation, and trimming of cooked

surface fat. "Electronic oven" prepared roasts averaged

60.6% cooking loss compared to 34.7% for conventional

cookery. Appearance and palatability of the roasts as judged

by a six-member taste panel indicated that roasts prepared in

the "electronic oven" were rated lower in appearance,

tenderness, juiciness, and flavor when compared to those

cooked conventionally. The author concluded that a method of

cooking whereby a more satisfactory product is obtained is

needed before the "electronic oven" will be practical for

roasting top round of beef to a well-done degree of doneness.

Korschgen and coworkers (1976) compared quality factors

in beef, pork, and lamb cooked by microwave and conventional

means. Regardless of meat species cooked, microwave cooked

roasts were prepared in less than half the time required to

prepare conventionally cooked roasts. The cooking loss

percentage for all three species indicated that the greatest

losses occurred via evaporation. Microwave cooked beef had

a smaller cooking loss compared to conventional cooking,

while there was no difference between pork and lamb roasts.

Shear force values indicated no difference due to cooking

method for beef and lamb, however, microwave cooked pork

roasts had lower shear force values than conventionally

prepared roasts. Sensory analysis indicated that no one

cooking method was superior for all three species. Beef and

lamb samples were significantly less tender when cooked by


microwaves compared to conventional cookery. No meaningful

trends were apparent in sensory scores for juiciness across

meat species. However, the interior portion of

conventionally cooked beef roasts was scored significantly

juicier than were those from microwave cookery. The authors

concluded that aside from the time-saving advantage for

microwave cooking, there were no major advantages for

microwave cooking over conventional cooking.

Drew and coworkers (1980) compared the effects of

cooking top round beef roasts from the frozen and thawed

states at different microwave power levels and conventional

methods on energy consumption, cooking times, cooking losses,

and palatability. The microwave oven used in this study

operated at 2450 MHz and on power levels of "high" (553

watts) or "simmer" (237 watts). Conventionally cooked roasts

were prepared using a still-air electric oven set at 1630C.

Roasts were cooked uncovered in the conventional oven and

were loosely covered with waxed paper when cooked in the

microwave oven. When compared to the conventional oven less

time was required to cook frozen or thawed roasts to the same

internal temperature when the roasts were cooked in the

microwave oven regardless of power level. Energy consumption

data indicated that about half as much electricity was

required to cook roasts in a microwave oven as compared to

conventional oven cookery. In addition, there was no

difference in the amount of electrical energy used between


"high" and "simmer" power levels. Cooking losses included

drip and volatile components and when added together yielded

a total cooking loss. Roasts cooked conventionally from the

frozen state had less drip (3%) and volatile losses (30.3%)

than microwave cooked roasts which had 5.6% and 36.4%,

respectively, for drip and volatile losses at high power and

8.4% and 29.2%, respectively, on low power. Roasts cooked

from the thawed state had less drip (8.3%) and volatile

losses (23.2%) than microwave cooked roasts which had 15.0%

and 26.4%, respectively, on high power. Total cooking losses

were significantly higher for roasts cooked at the "high"

microwave power level than for those cooked in a conventional

oven. However, when roasts were cooked at the "simmer"

microwave power level, the total loss was not significantly

different from those cooked in the conventional oven.

Sensory evaluation scores and shear force values for roasts

cooked from the thawed state did not differ for overall

acceptability, flavor, juiciness, and tenderness due to

microwave cooking method ("high" or "simmer") versus

conventional cooking. Roasts prepared from the frozen state,

regardless of cooking method had lower scores compared to

scores for thawed roasts. There was no difference between

conventional and microwaved "simmer" cooked roasts prepared

from the frozen state for sensory characteristics. However,

shear force values were lower for conventionally cooked

roasts than for roast cooked at either microwave power level.


In general, roasts cooked from the frozen state using "high"

microwave power had lower (less desirable) sensory scores

when compared to all other cooking methods.

Moore and coworkers (1980) studied differences among top

round steaks cooked by dry or moist heat in a conventional or

a microwave oven. The authors used a Gardner Color

Difference Meter to access the degree of doneness of each

steak and concluded that steaks were heated more evenly by

conventional dry heat than by conventional moist or by

microwave dry or moist heat. In addition, cooking time,

evaporative cooking losses, total moisture content, and

sensory juiciness and tenderness scores were less, and total

and drip cooking losses, and ether extract were greater for

steaks cooked by microwaves than for conventionally cooked


Korschgen and Baldwin (1980) compared the quality of

beef rib roasts cooked by manually cycling a microwave oven

on and off so as to simulate the automatic cycling control

for microwave energy. Both microwave cooking methods were

compared to conventionally cooked beef rib roasts as a

control. Sensory panel scores indicated that regardless of

cooking method used, all roasts were deemed acceptable in

flavor and juiciness. Mean sensory scores for tenderness

indicated significantly lower (less desirable) scores for

roasts cooked by the manual pulsing procedure compared to

conventionally cooked roasts. There was no difference in


tenderness scores for automatically cycled microwave energy

compared to conventional cooking. Energy requirements were

lower and total cooking losses were higher for meat prepared

by microwave power regardless of cycling method (Korschgen

and Baldwin, 1980). The authors concluded that automatic

cycling permitted equilibration of heat developed within the

product. This transfer of heat within the product is due to

conduction from one region of the roast to another.

The issue of bacteria in food surviving in large numbers

after thermal processing by microwave radiation compared to

conventional hot air processing was studied by Sawyer and

coworkers (1984). The purpose of their study was to

determine the effect of plastic wrapping on the internal

end-point temperature and on the survival of bacteria in food

subjected to thermal processing in a microwave oven. Single

serving sized portions of chicken drumsticks, ham slices and

pork loin slices were cooked from the frozen state in a

microwave oven using 630 watts of power. Microbiological

counts of wrapped-vented and unwrapped foods were made before

and after microwave processing for Staphylococcus aureus

surface inoculated on to chicken drumsticks and ham slices.

Salmonella senftenberg surface inoculated on to ham and pork

slices indicated that wrapping did not have a statistically

significant effect on internal end-point temperature or on

counts of bacteria per gram of product tested. Wrapping

generally provided a slight improvement in microbial quality

when mean counts were considered. Schiffmann (1981) and

Ohisson (1983) both indicated that the increased occurrence

of bacteria surviving in foods processed in microwave ovens

was due to a lack of a uniform microwave field. The lack of

field uniformity results in hot and cold spots occurring

within the microwave oven.

Zimmermann (1983) studied the effects of microwave

thermal processing on the survival of Trichinella spiralis,

the causative agent of trichinosis. In this study the author

indicated the difficulty in attaining 76.70C throughout a

pork roast when subjected to microwave thermal processing.

Zimmermann (1983), in an attempt to cook pork roasts in a

microwave oven to 76.70C, failed to do so 149 out of 189

attempts when following the oven manufactures and pork

industry recommendations. Zimmermann (1983) suggested that

low wattage cooking at 50% or less would give any trichina

present longer exposure to heat and, thus, provide an

approach to safe cooking methods. In this study some roasts

were still infective after cooking at 30% power for 46.2

min/kg.' This research futhur emphasizes the lack of

uniformity in heat distribution in microwave cooked products.

In a recent report, Welke et al. (1986) evaluated the

effect of microwave, convection and conventional cooking

methods on the texture of top round roasts when epimysial

tissue from one to eight year old animals was physically

inserted into the roasts (approximately 2000 g each).


Results of their study were that Warner-Bratzler shear values

for old epimysial tissue cooked in the microwave oven was

lower than shear values for old epimysial tissue cooked by

convection or conventional ovens (5.0, 7.7, and 8.4 kg,

respectively). Roasts cooked by the microwave method

required significantly shorter cooking times than did roasts

cooked by convection or conventional methods (97, 146, or 186

min, respectively). Microwave and convection cooked roasts

cooked to an internal temperature of 630C experienced an 80C

post-cooking temperature rise over a 30-min period, whereas

conventionally cooked roasts were heated to an end-point

temperature of 710C. These authors suggested that lower

shear values from epimysial tissue from old animals for the

microwave method was due to an increase in collagen

hydrolysis when compared with convection and conventional

cooking methods. This supports the work of Law et al.

(1967), McCrae and Paul (1974) and Hutton et al. (1981), but

is in contrast to the theories of Van Zante (1973), Roberts

and Lawrie (1974) and Peckham and Freeland-Graves (1979) who

suggested that use of the microwave oven does not allow time

for collagen solubilization and tenderization. Factors to be

considered when producing a microwavable meat product are fat

percentage within the product and post-cooking temperature

rise. The effect of cooking method on fat percentage and

cooking yields for ground beef patties was reported by Berry

and Leddy (1984). Beef patties from ground round, ground


chuck and regular ground beef containing 14, 19, and 24% fat,

respectively, were cooked by six different methods and

analyzed for compositional differences. Percentage of

cooking yield, fat, and moisture of cooked patties were

significantly affected by the interaction of fat level and

cooking method. Except for patties cooked by broiling or

convection heating, patty yields decreased with increasing

fat levels. Microwave cooking always produced patties

containing the least fat and caloric content in comparison

with other methods since cooking losses were greater.

The duration and extent of post-cooking temperature

elevation in microwave cooking were reported by Ruyack and

Paul (1972), Sawyer (1985), and Welke et al. (1986). Ruyack

and Paul (1972) cooked choice beef semitendinosus muscles in

a 915 MHz, 1600 W microwave oven and reported a 20C/min

post-cooking temperature elevation in roasts covered with a

polyester film and an 1.60C/min increase in uncovered roasts.

Sawyer (1985) reported that experimental product processed in

a hot air oven did not exhibit post-cooking temperature

elevations. However, chicken frankfurters processed in a

microwave oven at 50% power had a 2.10C greater post-cooking

temperature elevation than frankfurters processed at 100%

power. It was concluded that the extent of post-cooking

temperature rise may be related to power level used during

processing. Thus, post-cooking temperature elevation may be

more commonly associated with microwave heating than with


conventional heating when time of processing is kept constant

(Ruyack and Paul, 1972).

When beef is cooked in a microwave oven, water heats the

solid material. However, the surface temperature never

reaches a temperature greater than 1000C. This temperature

is not high enough to denature fully oxymyoglobin, thus the

surface never becomes dark brown. Also, the meat seldom

develops the flavor and aroma of meat cooked in a

conventional oven (Walker, 1987).

Even though microwave technology has made great strides

forward in the areas of increased speed, convenience and

futuristic computerized programmed appliances, this technical

sophistication has not been matched by the development of

beef entrees compatible with the microwave oven. A recent

survey indicated that one-third of the microwave oven owners

prepare more than three-quarters of their meals in their

microwave ovens and another one-fourth prepare more than half

of their meals that way (Taki, 1986). While consumers are

cooking more meals in their microwave ovens, research

indicates that the incidence of cooking meat entrees is

seldom (Taki, 1986).



As a result of changing life styles, consumers are

demanding convenience in meat entrees. One possibility is a

ready-to-cook roast beef product reformed from denuded chuck

muscle that can be cooked with microwave energy. Previous

work has indicated that microwave cooking of meat results in

greater cooking losses and less palatable meat than

conventional methods (Korschgen and Baldwin, 1976; Nykvist

and Decareau, 1976; Sawyer, 1985). Nykvist and Decareau

(1976) indicated that early research efforts on microwave

roasting of beef did not take into consideration the high

post-cooking temperature rise (PCTR) associated with

microwave roasting. As a result, roasts were often

overcooked when compared to controls, and therefore deemed

lower in palatability.

Moore et al. (1980) indicated that conventional oven

roasting of top round steaks with moist heat produced a 20C

post-cooking temperature rise compared to a 100C increase for

moist microwave cooking. Drew and coworkers (1980)


acknowledged that preliminary experiments had to be conducted

to establish the extent to which PCTR occurred in association

with microwave cookery (no values given) prior to conducting

their research. Sawyer (1985) identified the presence of an

extensive PCTR, which was highly variable in duration and

intensity, in food entrees subjected to microwave heating.

Experimental products were cooked in a microwave or a

conventional hot air oven and tested for PCTR. Some of the

products included chicken frankfurters, pork roast, turkey

roast, and cake cones. Experimental products processed in a

conventional hot air oven did not exhibit a PCTR. However,

microwave heating produced PCTR of 8.50C + 6.50C, 2.90C +

1.20C, 6.10C + 3.70C, and 0, respectively. The time required

for each of these PCTR values to occur varied from as little

as 45 sec for chicken frankfurter to 16.2 min for turkey

roast. From these results it was suggested that PCTR was

more likely to occur in products processed with microwave

power, dependent on the type of product heated and possibly

the power level used. The author concluded that the duration

and intensity to which PCTR occurs should be given

consideration when commercial products are to be processed in

microwave ovens, or when developing mathematical models of

microwave cooking/heating procedures (Sawyer, 1985).

Nykvist and Decareau (1976) and Decareau (1985) allude

to the presence of a large temperature gradient existing

between the interior and the outer regions of a meat product