Group Title: effect of postmortem electrical stimulation on the texture of hot-boned, chill-boned, and age-boned broiler breast fillets /
Title: The Effect of postmortem electrical stimulation on the texture of hot-boned, chill-boned, and age-boned broiler breast fillets
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Title: The Effect of postmortem electrical stimulation on the texture of hot-boned, chill-boned, and age-boned broiler breast fillets
Alternate Title: Broiler breast fillets
Physical Description: ix, 90 leaves : ill. ; 28 cm.
Language: English
Creator: Thompson, Leslie Dawn, 1959-
Publication Date: 1986
Copyright Date: 1986
 Subjects
Subject: Broilers (Poultry)   ( lcsh )
Chickens   ( lcsh )
Food Science and Human Nutrition thesis Ph. D
Dissertations, Academic -- Food Science and Human Nutrition -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis (Ph. D.)--University of Florida, 1986.
Bibliography: Bibliography: leaves 82-89.
Statement of Responsibility: by Leslie Dawn Thompson.
General Note: Typescript.
General Note: Vita.
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Bibliographic ID: UF00099334
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000566971
oclc - 14249231
notis - ACZ3419

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THE EFFECT OF POSTMORTEM ELECTRICAL STIMULATION ON THE
TEXTURE OF HOT-BONED, CHILL-BONED, AND AGE-BONED
BROILER BREAST FILLETS






BY






LESLIE DAWN THOMPSON


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA
















ACKNOWLEDGMENTS


The author would like to express her deep appreciation and

gratitude to Dr. D. M. Janky, committee chairman, for his assistance,

guidance, and patience during this study and throughout the author's

program. Thanks are also extended to Drs. R. L. West, J. F. Gregory,

S. A. Woodward, and H. E. Drummond for their willingness to serve on

the advisory committee, and for their guidance and suggestions during

this study.

Thanks are extended to Drs. R. L. West and D. K. Beede for the

use of their laboratory equipment and to Janet Eastridge, Gale Shultz,

and Estelle Hirchert for their technical advice and assistance.

The author would like to express her appreciation to Drs. D. M.

Janky and S. A. Woodward, Margaret Dukes, Elaine Batie, Linda Kelly,

Dean Bell and Vicky Dugan for their invaluable assistance during

processing. For help provided with the statistical analysis, the

author is most grateful to Margaret Dukes.

The author would like to express a debt of gratitude to Nancy

Daniel for the long hours of laboratory assistance which extended well

beyond the call of friendship.

Special thanks are extended to Cindy Zimmerman for her help and

cooperation in typing this manuscript under such extreme time

constraints.










Most of all, the author would like to express her deepest

appreciation and gratitude to her mother, Dorothy Thompson, for her

love, sacrifices, support, guidance and endless patience during the

author's seemingly never-ending education. It is to her and the

loving memory of the author's father, the late Maj. V. B. Thompson,

that this manuscript is dedicated.

















TABLE OF CONTENTS


Page

ACKNOWLEDGMENTS..................................................... ii

LIST OF TABLES..................................................... vi

ABSTRACT........................................... .... ...... .....viii

CHAPTERS

I INTRODUCTION.................. ........ ............... 1

II REVIEW OF THE LITERATURE................................5

Effects of Hot- and Chill-Boning on the Texture of
Poultry Meat........................................ 5
The Effects of Hot-Boning on the Texture of Bovine
Muscle............................................... 12
Effects of Electrical Stimulation on Meat Tenderness.....16
Effects of Electrical Stimulation on Palatability and
Appearance..................... ...........................20
Electrical Stimulation Methodology......................23

III PRELIMINARY STUDY: EFFECTS OF LOW VOLTAGE ELECTRICAL
STIMULATION AT VARIOUS DURATIONS ON THE TEXTURE OF
HOT-STRIPPED BROILER BREAST MEAT........................27

Introduction........................ .............27
Materials and Methods..................................30
Results and Discussion.................................32
Conclusions....... ............................34

IV EFFECTS OF ELECTRICAL STIMULATION AT VARIOUS DURATIONS
ON THE TEXTURE OF BROILER BREAST MEAT....................35

Introduction ................... .. .............. .......35
Materials and Methods..................................36
Results and Discussion.................................42
Conclusions.............................................58

V THE EFFECTS OF ELECTRICAL STIMULATION AT VARIOUS
VOLTAGES ON THE TEXTURE OF BROILER BREAST MEAT...........60










Introduction......................................... 60
Materials and Methods ...................................61
Results and Discussion.................................62
Conclusions.............................................78

VI SUMMARY AND CONCLUSIONS.................................79

REFERENCES....... .....................................82

BIOGRAPHICAL SKETCH .. ............ .................................90















LIST OF TABLES


Table Page

3-1 Mean shear values standard error of the means of
hot-boned broiler breast meat obtained from carcasses
stimulated with 45 volts for 0, 9, or 18 seconds............33

4-1 Shear values, pH, R-values, sarcomere lengths, and
fragmentation indexes of hot-boned, chill-boned,
and age-boned broiler breast meat obtained from
nonstimulated (control) carcasses..........................43

4-2 Mean shear values, pH, R-values, sarcomere lengths,
and fragmentation indexes standard error of the mean
of hot-boned broiler breast meat obtained from
carcasses stimulated with 240 volts for 0, 15, 30,
or 45 seconds............................................ ..49

4-3 Mean shear values, pH, R-values, sarcomere lengths,
and fragmentation indexes standard error of the mean
of chill-boned broiler breast meat obtained from
carcasses stimulated with 240 volts for 0, 15, 30,
or 45 seconds.............................................. 54

4-4 Mean shear values, pH, R-values, sarcomere lengths,
and fragmentation indexes standard error of the mean
of age-boned broiler breast meat obtained from
carcasses stimulated with 240 volts for 0, 15, 30,
or 45 seconds............................................ ..56

4-5 Percent water uptake, driploss, cookloss, and cooked
meat moisture of hot-boned, chill-boned, and age-boned
broiler breast meat obtained from carcasses stimulated
with 240 volts for 0, 15, 30, or 45 seconds.................57

5-1 Shear values, pH, R-values, sarcomere lengths, and
fragmentation indexes of hot-boned, chill-boned,
and age-boned broiler breast meat obtained from
nonstimulated (control) carcasses..........................63

5-2 Mean shear values, pH, R-values, sarcomere lengths,
and fragmentation indexes standard error of the mean
of hot-boned broiler breast meat obtained from
carcasses stimulated for 15 seconds with 0, 240, 530,
or 820 volts.......... .................................... 65












5-3 Mean shear values, pH, R-values, sarcomere lengths,
and fragmentation indexes standard error of the mean
of chill-boned broiler breast meat obtained from
carcasses stimulated for 15 seconds with 0, 240, 530,
or 820 volts.................................. ....... 70

5-4 Mean shear values, pH, R-values, sarcomere lengths,
and fragmentation indexes standard error of the mean
of age-boned broiler breast meat obtained from
carcasses stimulated for 15 seconds with 0, 240, 530,
or 820 volts ............................... ..... ........ 74

5-5 Percent water uptake, driploss, cookloss, and cooked
meat moisture of hot-boned, chill-boned, and age-boned
broiler breast meat obtained from carcasses stimulated
for 15 seconds with 0, 240, 530, and 820 volts..............77
















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

THE EFFECT OF POSTMORTEM ELECTRICAL STIMULATION ON THE
TEXTURE OF HOT-BONED, CHILL-BONED, AND AGE-BONED
BROILER BREAST FILLETS

BY

LESLIE DAWN THOMPSON

May, 1986


Chairman: Dr. D. M. Janky
Major Department: Food Science and Human Nutrition

Two experiments were conducted to determine the effects of

postmortem electrical stimulation of broiler carcasses (240V for 0,

15, 30, or 45 seconds; 0, 240, 530, or 820V for 15 seconds) on the

tenderness of broiler breast meat harvested immediately after feather

removal (hot-boned), after chilling (chill-boned), or after a 48-hour

aging period (age-boned).

Postmortem electrical stimulation of broiler carcasses,

regardless of the stimulation voltage or duration, had no significant

effect on the tenderness of hot-boned or age-boned broiler breast

meat. High voltage stimulation (820V) significantly improved the

tenderness of chill-boned broiler breast meat, producing an acceptably

tender product.

Electrical stimulation increased the rate of rigor development as

demonstrated by higher R-values and lower pH values of hot-boned and










chill-boned fillets from stimulated versus nonstimulated carcasses.

The ultimate pH or R-value of the meat was not affected by stimulation

treatment. High voltage stimulation (530 and 820) of carcasses caused

increased sarcomere lengths in hot-boned and chill-boned fillets.

Tenderness improvements associated with longer sarcomeres were

observed in the chill-boned fillets, but not in hot-boned fillets

where increased sarcomere lengths were offset by decreases in the

fragmentability of the myofibrils. The fragmentation index of chill-

boned fillets was not significantly affected by high voltage

stimulation (P<0.05) but was correlated to tenderness, indicating

increased fragmentability did play a role in tenderization.

Low voltage stimulation (240V) did not significantly affect the

fragmentation index of hot-boned or chill-boned fillets, or the

sarcomere lengths hot-boned fillets. Low voltage stimulation had an

inconsistent effect on sarcomere lengths, with increases in one

experiment but not the other.

Regardless of stimulation voltage or duration, electrical

stimulation did not significantly affect sarcomere lengths or

fragmentation indexes of age-boned poultry meat. The percent water

uptake, driploss, cookloss, or cooked meat moisture of hot-boned,

chill-boned, or age-boned was not significantly affected by electrical

stimulation.















CHAPTER I
INTRODUCTION


In the past decade there has been an increasing trend to market

whole fresh eviscerated broiler carcasses as further processed

products. Cut-up parts such as breast fillets, breasts, and

drumsticks that sell for premium prices compared to the whole carcass

are viewed as high value marketable products.

In the last few years, however, a dramatic change has occurred in

industry orientation, which is referred to as the "Third Great

Revolution" for the broiler industry. The industry has increased its

production of convenience food items for use at home in conventional

and microwave ovens. More importantly, the demand for deboned broiler

meat has increased tremendously as a result of the development of

restructured boneless product for use in the fast food industry.

Haffert (1984) estimated that by mid-1985 the demand for boneless meat

would expand by 2 million pounds per week in the U.S. as a result of

new product introductions in the fast food/takeout industry.

In an attempt to efficiently meet this increased demand for

deboned meat, many processors debone the meat immediately after

chilling. Consumer response has indicated that this technique causes

wide variation in the tenderness of the meat with a large portion of

the meat being unacceptably tough. This effect has been documented in

scientific literature (Sams, 1984; Lyon et al., 1985). Lyon et al.










(1985) demonstrated that a minimum aging period of 4 to 6 hours was

required to avoid the toughening that occurred with chill-boning.

Shelton (1985) estimated that, by the year 2000, 90% of poultry will

be marketed as cut-up or boned product, but tenderness problems

associated with chill-boning will force processors to adopt a minimum

4-hour aging period prior to boning. This aging period has resulted

and will result in increased production costs due to increased labor,

handling and storage requirements.

An alternate harvesting procedure has been suggested by D. Hamm

(1981, 1982) and Hamm and Thomson (1983), which they refer to as hot-

stripping, or the removal of a muscle or muscle system prior to

chilling (West, 1983). Current processing techniques involve

exsanguination, feather removal, evisceration, and chilling of the

whole carcass, followed by any desired processing and packaging. D.

Hamm's proposed technique involves the hot-boning of the defeathered,

but noneviscerated carcass. The breast, wing, and leg quarter would

be removed from the carcass for marketing while the remaining portions

would be rendered for use in poultry feeds. Hot-boning would result

in substantial savings compared to more conventional harvest for a

number of reasons. The evisceration line would be eliminated, thus

reducing the expense of the evisceration equipment and the personnel

involved in that portion of the line. The major savings, however,

would be in chilling and refrigeration. It is estimated that chilling

expenses would be cut by 55-60% by chilling only the premium priced

portions. The tonnage of meat requiring chilling would be reduced,










thus lowering the biochemical oxygen demand costs associated with the

chiller water (D. Hamm, 1982).

Like chill-boning, hot-boning has a deleterious effect on the

texture of poultry meat (de Fremery and Pool, 1960; Klose et al.,

1972; Lyon et al., 1973; Peterson, 1977; Sams, 1984; Stewart et al.,

1984b), which is even more severe than that found in chill-boned

meat. Results from numerous studies have indicated that some

tenderizing treatment is needed if hot- or chill-boning is to be

utilized successfully by the poultry industry. One possible method

involves the use of postmortem electrical stimulation.

Postmortem electrical stimulation is commonly used in the beef

and lamb industry today. This method has a long history of

experimentation dating back to the mid-1700s when Ben Franklin noted

that turkeys killed by electrocution were "uncommonly tender." Nearly

200 years later Harsham and Deatherage (1951), working with Kroger Co.

and Westinghouse, received a patent for the use of electrical

stimulation as a means of tenderizing beef. Their work went virtually

unnoticed until the 1970s when Carse (1973) utilized electrical

stimulation as a means of avoiding cold shortening in lambs.

Experimentation continued and the New Zealand lamb industry quickly

adopted the method as a means of avoiding cold and thaw shortening

that had been occurring in lambs that were frozen immediately after

slaughter for shipment overseas. The technique was soon adopted by

the beef industry as a means of hastening rigor development, thereby

reducing the risks of cold and thaw shortening, allowing for










hot-boning, reducing the occurrence of heat rings, and improving the

tenderness and color of meat (Pearson and Dutson, 1985).

Little work has been published examining the effects of

electrical stimulation on tenderness of poultry meat. Until recently

there was little reason for the broiler industry to be overly

concerned about the tenderness of poultry meat because it was

generally considered very tender. New consumer demands and processing

techniques designed to better serve the consumer and the processor

have created very real texture problems. Maki and Froning in 1984

stimulated turkey with 800 volts and found improvements in texture and

color compared to unstimulated controls. A British team, however,

found electrical stimulation of turkeys with 94 volts had virtually no

effect on the texture of the breast meat (Dransfield et al., 1984).

The objectives of this research project were to

1. examine the effect of electrical stimulation on the texture of
hot-boned, chill-boned and age-boned broiler breast meat;

2. establish an optimal stimulation voltage and duration in order
to achieve a maximum tenderness effect for each boning time;

3. examine some physical and biochemical changes that occur as a
result of electrical stimulation.
















CHAPTER II
REVIEW OF THE LITERATURE


Effects of Hot- and Chill-Boning on the
Texture of Poultry Meat

Several investigators have noted that cutting carcasses into

parts or removing the muscle from the bone prior to rigor onset and

chilling (hot-boning), or immediately after chilling and prior to

rigor resolution (chill-boning), causes increased toughness in poultry

meat compared to meat boned after aging (de Fremery and Pool, 1960;

Klose et al., 1972; Lyon et al., 1973, 1985; Wyche and Goodwin, 1974;

Peterson, 1977; D. Hamm, 1983; Sams, 1984). Many poultry processors

currently utilize chill-boning in spite of the textural problems

encountered, but hot-boning or hot-stripping is an experimental

technique currently not in use by the industry. As opposed to age-

boning, the two techniques are more desirable ways for the processor

to obtain boned and cut-up parts, due to savings accrued through

reduced labor, handling and storage requirements (D. Hamm, 1982).

Although consumer demand and processor interest in boned meat have

only recently heightened, researchers have long examined the effects

of various prerigor and post-chill harvesting schemes on the texture

of poultry meat.

Lowe (1948) found that the tenderness of an uncut breast muscle

was considerably better than the tenderness of the opposite muscle

which was cut across the fibers prior to the onset of rigor, even










though the carcasses were aged for 24 hours prior to roasting. She

noted that if the muscle was cut after the onset of rigor the increase

in toughness did not occur. Klose et al. (1972) demonstrated that

toughness was induced in broiler breast meat by removing the wings at

the shoulder joint up to 2 hours postmortem. The hot-cut muscle had

shear values approximately twice that of muscle that was cut in a

similar manner after a 22-hour chilling period. Cutting the wing off

beyond the insertion of the breast muscle immediately after slaughter,

however, alleviated the toughening effect. Webb and Brunson (1972)

noted similar findings while examining the effects of line trimming on

tenderness. Cutting the breast muscle or cutting through the wing

joint substantially increased shear values of the Pectoralis

superficialis, while cutting the wing distal to the shoulder did not.

Klose et al. (1972) found that cutting carcasses into parts prior

to chilling significantly increased the shear values of light and dark

meat compared to carcasses that were cut-up after chilling and a 6

hour aging period. Similar results were obtained even if the hot-cut

parts were aged for up to 3 days postmortem prior to roasting. The

same trend was observed in commercially processed carcasses, but the

carcasses processed in the laboratory had much lower shear values than

those processed in the commercial setting. These differences were

attributed to a more extensive commercial picking regime compared to

that found in the laboratory.

Wyche and Goodwin (1974) found only small differences in the

shear values of light and dark meat obtained from hot-cut or chill-cut

(cut-up immediately after chilling) samples aged for 24 hours prior to










cooking, although taste panelists identified the hot-cut samples as

significantly tougher than the chill-cut samples. They also found

that shear values increased as the aging time after cutting increased

up to 4 hours, then declined and remained constant after 8 hours of

aging. Differences in the tenderness of hot-cut and chill-cut samples

were larger with shorter aging periods but after 24 hours the

differences were very small. The apparent conflict in the results

obtained by Klose et al. (1972) and Wyche and Goodwin (1974) could be

attributed to the use of different cutting procedures. Lyon et al.

(1973) found no differences in the shear values of breast meat

obtained from hot-cut or age-cut (aged 48 hours prior to cutting)

carcasses for five different commercial cutting procedures. However,

two other cutting methods, which involved transverse cuts across the

breast muscle, caused significant increases in toughness in hot-cut

samples compared to age-cut samples. Secondly, the time of chill-

boning was considerably different in the two studies. Lyon et al.

(1985) found that boning or cutting meat from carcasses 4 or more

hours postmortem significantly reduced shear values compared to those

of carcasses boned prior to this time.

Numerous studies have been conducted examining the causes of the

toughening associated with hot- and chill-boning. De Fremery and Pool

(1960) examined the effects of various treatments, such as hot-

stripping, mechanical stimulation, freezing, thawing, exhaustive

electrical stimulation, and irradiation on prerigor meat. All

treatments caused increased toughness compared to untreated samples,

and this toughness appeared to be related to a more rapid onset of










rigor mortis whether measured by breakdown of adenosine triphosphate

(ATP) or glycogen, drop in pH, or the loss of extensibility. It was

not clear if the toughening was directly attributed to ATP, glycogen,

or pH changes. In an attempt to partially answer this question

muscles were injected antemortem with sodium monobromate which caused

a rapid decrease in ATP but only small decreases in pH or glycogen.

Injected muscles were found to be as tender as untreated muscles, but

the ultimate pH of the treated muscle was much higher (> 6.5) than the

untreated (5.8). These results indicated that toughening was not

directly related to rapid ATP depletion but was related to changes in

glycogen levels and pH.

The influence of postmortem glycolysis on the tenderness of

poultry meat was examined by de Fremery and Pool (1963). Postmortem

glycolysis was prevented or minimized in fryers and turkey hens by

subcutaneous antemortem injection of epinephrine, injection of sodium

iodoacetate, or cooking immediately after slaughter. Antemortem

epinephrine injections caused a more rapid rate of postmortem ATP

depletion, and an increased rate of rigor onset compared to controls,

but breast meat from the injected carcasses had significantly lower

shear values than the controls. In a previous study, in 1960, de

Fremery and Pool suggested that toughness was induced by a more rapid

rate of rigor onset. They suggested that differences in tenderness

were related to the ultimate pH of the meat. The control birds, which

proceeded through normal postmortem glycolysis, had a significantly

lower pH of 5.71 compared to a pH of 6.56 in the epinephrine-treated

carcasses. Glycogen levels in the muscles of the treated carcasses











were drastically reduced prior to slaughter; thus the birds had less

substrate for glycolysis and did not produce typical amounts of lactic

acid, accounting for the substantially increased ultimate pH of the

treated carcasses.

Results similar to those found in the experiment conducted by de

Fremery and Pool (1960) were obtained when glycolysis was inhibited by

sodium iodoacetate, and cooking within 2 minutes postslaughter. The

shear values of the controls were significantly higher than those of

the treated carcasses. As in the previous experiment, the pH of the

muscle in which glycolysis was inhibited was higher than the pH of the

controls. Additionally, the carcasses which were cooked immediately

after slaughter had much lower shear values than carcasses cooked 1

hour postmortem.

Results from these two experiments by de Fremery and Pool (1960,

1963) indicated that the depletion of ATP did not directly affect the

texture of the muscle, but that textural changes were related to

changes that occurred in the muscle as a result of postmortem

glycolysis. Also, they demonstrated that a decrease in glycogen

levels in the muscles was not directly responsible for textural

changes that occurred postmortem, since in one experiment, glycogen

levels were depleted without an accompanying increase in toughness.

Khan and Nakamura (1970) used antemortem epinephrine injections

and unrestricted pre- and post-slaughter struggle as a means of

varying the amount of lactic acid found in broiler breast tissue after

slaughter. Antemortem injections of epinephrine served to deplete

glycogen stores, thus reducing lactic acid formation while










unrestricted struggle increased the amounts of lactic acid found after

slaughter. They found that as the lactic acid concentration in the

muscles 24 hours after slaughter increased, so did shear values as a

hyperbolic function, indicating that the texture of meat was related

to lactic acid concentration, thus the pH of the meat.

In order to relate changes in pH to the texture of hot-boned

meat, Peterson (1977) used antemortem sodium polyphosphate injections

to reduce lactic acid levels in hot-cut carcasses and compared them to

samples cut up after a 24-hour aging period. Hot-cut samples had

significantly higher shear values than the age-cut samples, but the

hot-cut samples from injected carcasses were as tender as the

controls. The differences in tenderness appeared to be related to the

ultimate pH of the breast muscle. As in the previously discussed

study by de Fremery and Pool (1963), it seemed that the toughening

effect was related to a lower ultimate pH, but Peterson suggested that

the rate of pH decline was responsible for textural changes, not just

the ultimate pH.

Stewart et al. (1983, 1984b) found that hot-boned or severed

(muscle was severed at the insertion) Pectoralis superficialis muscle

exhibited a slower rate of pH decline than intact muscle, even though

no difference in temperature existed between the three treatments.

The authors postulated that the slower rate of pH decline found in the

hot-boned and severed muscle resulted from severing muscle attachments

which allowed the muscle to undergo unimpeded contraction, decreasing

the need for ATP upon stimulation which, in turn, reduced the rate of

anaerobic glycolysis or the rate of pH decline.










Stewart et al. (1984a), in a second study, found that the shear

force of excised (prerigor) muscle was negatively and highly

correlated to the time of excision postmortem, as was the pH of the

excised muscle. The authors postulated, however, that the

relationship between pH at time of boning and shear value was not of a

direct cause and effect nature, but that they were related to similar

postmortem biochemical occurrences, particularly since the ultimate pH

of hot-boned muscle was similar to that of age-boned.

In another experiment, carcasses were chilled prior to excision

at 4 hours postmortem. Excised muscle had significantly higher pH and

shear values than control halves chilled and boned 24 hours postmortem

(Stewart et al., 1985a). In a similar experiment Lyon et al. (1985)

boned broiler breast halves at various times post-chill and found that

the most rapid pH decline occurred within 1 hour postmortem and that

pH and shear values decreased to control levels when boning occurred

at least 4 hours post-chill. Results from both experiments indicated

that chilling prior to boning slowed rigor development and increased

the holding time postmortem required to alleviate toughness caused by

chill-boning when compared to holding times for hot-boned (nonchilled)

muscle. It appeared that a holding period of at least 4 hours post-

chill was required to alleviate toughening found with chill-boning,

whereas a 2 to 4 hour holding period postmortem was required to

alleviate toughness in unchilled, hot-boned meat.










Effects of Hot-Boning on the Texture of Bovine Muscle

Kastner et al. (1973) and Falk et al. (1975) suggested that the

release of physical anatomical restraints prior to the onset of rigor

resulted in increased shortening upon the onset of rigor which in turn

increased toughness. Kastner et al. (1973) obtained shear values of

muscles from one side of a carcass held at 160C and hot-boned at 2, 5,

or 8 hours postmortem and compared these to values for muscle cut from

the other side of the carcass after 48 hour aging. Muscles boned at 2

and 5 hours postmortem were significantly tougher than the

corresponding controls, whereas muscle hot-boned at 8 hours was as

tender as the controls. The authors attributed this difference to the

fact that boning at 2 and 5 hours postmortem occurred prior to the

onset of rigor, but 8 hour boning occurred after the onset of rigor.

Jungk et al. (1967) found that maximum isometric tension development

related with rigor mortis occurred 3 to 5 hours postmortem, agreeing

with Kastner's hypothesis. Falk et al. (1975), in an evaluation of

hot-boned beef boned at 3, 5, and 7 hours postmortem, found no

significant differences between hot-boned and matching control sides

that were boned after a 48 hour aging period at 20C. Because the hot-

boned samples had a mean pH of 5.76 and a maximum rate of temperature

decline around 3 hours postmortem, the authors suggested that no

differences in tenderness were found because the carcasses were

already in rigor by 3 hours postmortem.

Tarrant (1977) examined the effects of hot boning on the rate of

glycolysis by removing the m. semimembranosus from beef carcasses

within one hour postmortem. The hot-boned muscle was held at 100C for










24 hours to avoid cold shortening while the control carcasses were

held at 30C. Temperature and pH were monitored at 1.5, 5, and 8 cm

from the surface of the muscle. It was found that hot-boning

increased the cooling rates of the hot-boned muscles over intact

muscles, by increasing the cooling rates at 5 and 8 cm, and slightly

decreasing the rate at the surface. By 6 hours postmortem the

temperature throughout the hot-boned muscle was approximately 14C,

while only the surface temperature of the intact muscle was decreased

to 140C. The initial pH of both muscles at 1 hour postmortem was

6.8. The rate of pH decline, however, was very different for the hot-

boned and intact muscles. Rates of pH decline up to 6 hours

postmortem for the hot-boned carcasses were 0.07, 0.11, and 0.07 pH

units/hour at 1.5, 5, and 8 cm, respectively, compared to 0.07, 0.16,

and 0.25 pH units/hour in the intact muscle. In the hot-boned muscles

the ultimate pH was reached in 24 hours while intact muscle reached

the ultimate pH in 6, 12, 24-48 hours at 8, 5, and 1.5 cm,

respectively. Hot-boning caused an immediate and significant decrease

in creatine phosphate at 5 and 8 cm, possibly a result of muscle

stimulation upon excision, but the ATP content immediately after

boning was similar to that in the intact muscle. Additionally, it was

shown that at both 8 and 5 cm from the muscle surface, hot-boned

muscle had much slower ATP depletion rates but a slightly increased

depletion rate at the muscle surface compared to the intact muscle.

The hot-boned muscle in general had a slow and uniform onset of rigor

mortis throughout the whole muscle, while the intact muscle had

varying rates of rigor onset with the interior having a higher










temperature and faster rate of rigor onset compared to the

intermediate depth. The outer portion of the intact muscle had a low

temperature and a relatively high pH, conditions which are associated

with cold shortening and increased toughness.

Tarrant's study demonstrated the profound influence of

temperature on postmortem rigor development. De Fremery and Pool

(1960) found that decreasing holding temperatures of prerigor poultry

meat from 400C to 10C caused a decline in the rate of ATP depletion,

or rigor development. Below 100C, however, the rate of ATP depletion

increased. Similar phenomena have been observed in prerigor bovine

muscle with the rates of ATP depletion decreasing as temperature

declined from 30 to 2C. Below 20C the ATP depletion rate

dramatically increased (Jolley et al., 1981). Locker and Hagyard

(1963) found that at 0 to 2C a rapid and extreme shortening of

isolated prerigor beef muscle occurred (47.7% of the original

length). Above 20C the extent of the shortening decreased reaching a

minimum between 14 and 190C.

Marsh and Leet (1966) documented the relationship between the

degree of muscle shortening and meat tenderness demonstrating that as

muscle shortened 20 to 40% of the original length, shear values

increased 3 to 4 times over values observed for nonshortened muscle.

When muscles were shortened more than 40%, however, shear values

decreased to those associated with nonshortened muscles leveling off

at 60% shortening. Tarrant (1977) demonstrated that hot-boning

resulted in more rapid and uniform cooling of muscle, compared to

intact muscles. Hot-boning allowed the meat to cool faster,









increasing the risk of achieving low temperatures (< 10C) prior to

the onset of rigor, thus resulting in cold shortening and the

accompanying increase in toughness.

Davey and Gilbert (1974) demonstrated that the trigger for cold

shortening was the release of calcium ions. They found that muscle

fibers did not cold shorten in the presence of ethylenediaminetetra-

acidic acid (EDTA), and that calcium concentrations in the sarcoplasm

reached 10-5 M before cold shortening occurred.

Whiting (1980) demonstrated that at loC, muscle mitochondria lost

the ability to bind calcium and released calcium into the

sarcoplasm. Typically, the sarcoplasmic reticulum (SR) would

sequester the calcium lost from the mitochondria but the mitochondria

released more calcium than the SR could possibly sequester.

Additionally, workers have found that the calcium binding ability of

the SR declined with decreasing temperatures due to an inactivation of

the ATP-driven calcium pump that is responsible for regulating calcium

levels in the sarcoplasm. With the inactivation of the pump, calcium

levels in the sarcoplasm increased to the critical level cited by

Davey and Gilbert (1974), and calcium reacted with the troponin-

tropomyosin complex, initiating muscle contracture. If this occurred

early postmortem, appreciable levels of ATP were present, allowing for

muscle contracture in the prerigor muscle. As ATP levels declined

there was a further reduction in the ability of the ATP-driven calcium

pump in the SR to bind calcium. The calcium induced contraction would

utilize ATP, causing the rates of ATP depletion in muscles held at low











temperatures (approx. 2C) to be higher than rates found in muscle

held at higher temperatures.



Effects of Electrical Stimulation on Meat Tenderness

One of the first documented cases using electricity as a

tenderizing agent was reported by Benjamin Franklin in the 1700's,

when he noted that chickens and turkeys killed by electrocution were

"uncommonly tender" (Lopez and Herbert, 1975). Little work, however,

has been conducted using electrical stimulation as a tenderizer of

poultry muscle. Until recently, tenderness had not been a serious

concern in the poultry industry, but with the advent of new processing

techniques and a desire for greater uniformity in texture, methods to

promote tenderness have received greater attention.

De Fremery and Pool (1960) found that exhaustive electrical

stimulation of an excised Pectoralis superficialis muscle resulted in

accelerated rates of ATP disappearance and pH decline. The Pectoralis

superficialis muscles excised from six 11 week old broilers were

exhaustively stimulated, and it was found that the excised stimulated

muscle had higher shear values than the excised unstimulated

controls. The muscle was excised prior to stimulation and was

stimulated with voltages ranging from 20 to 360 volts for 15 to 30

minutes. Since the muscle was not physically restrained, electrical

stimulation probably increased the toughness of the meat through

extensive and exaggerated muscle shortening.

In contrast, Maki and Froning (1984) found that turkeys

stimulated with 800 volts after bleeding had significantly more tender










breast meat than unstimulated controls. The stimulated muscle was

also found to have longer sarcomere lengths and brighter color

compared to the controls.

Judging from the two studies, electrical stimulation must be

applied to the carcass while it is still intact to achieve tenderness

and electrical stimulation of poultry appears to have the potential to

improve poultry texture.

Postmortem electrical stimulation of lamb, pork, and beef

carcasses has been shown to induce tenderness and has been used

commercially (Carse, 1973; Grusby et al., 1976; Savell et al., 1977,

1978a, 1978b; Smith et al., 1977; Bouton et al., 1978). Researchers

have noted other effects of electrical stimulation in beef, lamb, and

pork. Consistently, electrical stimulation has induced an increase in

the rates of pH decline and onset of rigor (Carse, 1973; Bendall

et al., 1976; Grusby et al., 1976; Shaw and Walker, 1977; George

et al., 1980) and an increase in the rates of ATP depletion and lactic

acid accumulation (Bendall et al., 1976). One tenderizing mechanism

which was suggested from these observations was that electrical

stimulation reduced the effects of cold shortening by reducing

conditioning time (Carse, 1973; Bendall et al., 1976; Chrystall and

Hagyard, 1976). Locker and Hagyard (1963) showed that cold shortening

did not occur to a significant extent below a muscle pH of 6; thus

electrical stimulation hastened the time at which rapid, low

temperature cooling (< 20C) or freezing could occur.

Changes in the structural characteristics of electrically

stimulated meat, such as physical disruption of myofibrils or










sarcomere length, have been examined as possible factors contributing

to the tenderizing effect of electrical stimulation (Savell et al.,

1977, 1978a; Smith et al., 1977; Bouton et al., 1978, 1980, 1984;

George et al., 1980). In electrically stimulated beef, lamb, and goat

carcasses, sacromere length seemed to be unrelated to the tenderness

since there were no significant differences in sarcomere length

between stimulated and nonstimulated samples (Savell et al., 1977;

Smith et al., 1977; Salm et al., 1981; 1983). Other studies, however,

have shown conflicting or inconsistent results, with stimulated sides

having longer sarcomeres than controls (Bouton et al., 1978, 1980;

George et al., 1980). Bouton et al. (1984) clarified the conflicting

data by demonstrating that the mechanism of electrical stimulation

tenderization was related to the temperature at which rigor

occurred. At rigor temperatures < lbC electrical stimulation seemed

to reduce myofibrillar shortening, while at rigor temperature > 150C

electrical stimulation tenderization seemed unrelated to myofibrillar

shortening having an effect more similar to aging.

Savell et al. (1978a) noted several structural changes other than

sarcomere length that could have been responsible for the tenderizing

effect of electrical stimulation. Electrically stimulated samples had

contracture bands that displayed ill-defined I-bands and Z-lines.

Additionally, the sarcomeres adjacent to the contracture bands

appeared to be broken or stretched in some cases. The physical damage

was theorized to lead to less structural integrity and to be at least

a partial contributor to the improvement in tenderness.










Sorinmade et al. (1982) also found many changes in the

ultrastructure of electrically stimulated meat. Light and electron

micrographs revealed Longissumus muscle from electrically stimulated

sides examined 48 hr postmortem had superstretched myofibrils with

tearing around the Z-lines, and highly contracted myofibrils

characterized by ill-defined or narrow I-bands, no H-bands, and

indistinct A-bands. Approximately 30% of the tissue appeared to be

damaged, and the damage observed in this study appeared to be greater

than the damage observed in Savell's study in which the meat was

examined 24 hr postmortem. Sorinmade et al. (1982) suggested that the

difference was due to prolonged exposure to proteolytic enzymes

released from ruptured lysosomes upon exposure to a rapid decline in

pH at high temperatures. These workers also noted empty lysosomal

vesicles and fragmentation of myofibrils at the Z-lines.

Tenderization achieved by electrical stimulation, they concluded,

appeared to be a result of physical disruption of myofibrils and

possibly proteolysis.

In contrast, George et al. (1980) noted no myofibrillar damage

resulting from electrical stimulation upon histological examination of

meat aged for 48 hrs, but did find irregular bands of denatured

sarcoplasmic protein deposited on the myofibril surface in the fibers

of stimulated muscle that were similar to those found in pale soft

exudative pork. No significance was attached to this observation in

relationship to improved tenderness. Salm et al. (1981) observed

similar results upon examining the fragmentation index of electrically










stimulated and nonstimulated carcasses, finding no difference between

the two.

Smith et al. (1977) suggested that because the tenderizing effect

of electrical stimulation did not seem to be related exclusively to a

reduction in cold shortening or sarcomere length, a plausible cause of

tenderization was related to autolytic enzyme activity. The rapid

decrease in pH caused by electrical stimulation might rupture

lysosomal membranes releasing proteolytic enzymes, which are active

under conditions of high muscle temperature. Similarly, Salm et al.

(1983) found that electrical stimulation enhanced the degradation of

the myofibrillar proteins, actinin and troponin-T, and caused an

increase in the amount of a 30,000 dalton protein, evidence of

degradation of a myofibrillar protein.

Bouton et al. (1978) examined the possibility that some of the

tenderizing effect was related to changes in connective tissue

structure rather than myofibrillar structure. Using Instron

compression (IC) values, which are relatively sensitive to connective

tissue toughness, Bouton et al. (1978) found no significant

differences in IC values in stimulated and nonstimulated meat after

myofibrillar contribution to shear strength was removed by a pressure-

heat treatment.



Effects of Electrical Stimulation on
Palatability and Appearance

As well as affecting the texture of meat, electrical stimulation

has been shown to change some aspects of the sensory profiles of

meat. Savell et al. (1977, 1978b), Salm et al. (1981), and Hawrysh










and Wolfe (1983) reported no differences in flavor between stimulated

and nonstimulated beef or lamb carcasses, but conflicting results were

reported by Savell et al. (1977, 1978a), who found that Longissimus

muscle from electrically stimulated beef sides was rated more

flavorful by a 10-member taste panel than muscle from nonstimulated

sides. Palatability tests conducted on steaks aged for 1 day showed

heightened flavor desirability for those originating from electrically

stimulated carcasses as opposed to nonstimulated (Savell et al., 1981;

McKeith et al., 1982), but any flavor differences were negated by

longer aging periods (Savell et al., 1981). Conducting taste panels

after a 7 day aging period, Calkins et al. (1982) found no difference

in flavor desirability, flavor intensity, or presence of off-flavors

between steaks from electrically stimulated and nonstimulated beef

sides.

Calkins et al. (1982) did find, however, that inosine and inosine

monophosphate (IMP) levels at 12-24 hrs were higher in electrically

stimulated than in nonstimulated samples, but after a 7 day aging

period there were no significant differences in inosine or IMP levels

suggesting that fluctuations in these two compounds followed a similar

pattern to results from other studies regarding flavor changes in that

these compounds are factors contributing to flavor differences in non-

aged stimulated meat. Changes in ATP, adenosine diphosphate (ADP),

adenosine monophosphate (AMP), and creatine phosphate (CP) levels

appeared to have no contributing effect on the noted flavor

differences.










Decreased juiciness in electrically stimulated carcasses as

opposed to nonstimulated ones has been reported in beef frozen for 7-

21 days (Savell et al., 1978a, 1978b), but this is not a consistent

observation throughout the literature. Savell et al. (1977), Bouton

et al. (1980), Salm et al. (1981), and Salm et al. (1983) found no

significant difference in the juiciness of stimulated and

nonstimulated beef or lamb carcasses. In the latter three studies

there were no significant differences in cookloss, but there were

significantly greater cooklosses in the electrically stimulated

carcasses in the first two studies mentioned.

Electrical stimulation has also been shown to affect the color of

meat. Grusby et al. (1976) and Hawrysh and Wolfe (1983) noted no

color differences in Longissimus muscle removed from stimulated and

nonstimulated carcasses cooler aged for 48 hrs to 7 days. Smith

et al. (1977) reported similar observations on carcasses evaluated

after 3 days of aging, but color evaluation conducted only 23 hrs

postmortem showed that electrically stimulated carcasses had brighter

color and a lower occurrence of heat rings. Savell et al. (1978) and

Salm et al. (1981) also found better USDA color and fewer heat rings

in electrically stimulated sides evaluated 19-24 hours postmortem.

McKeith et al. (1982) also found an improvement in lean color in veal

carcasses evaluated 24 hrs postmortem. No deleterious color effects

as a result of electrical stimulation have been reported.

A few studies have been conducted to determine if electrical

stimulation has any affect on connective tissue as judged by trained

taste panelists. Savell et al. (1977, 1978b) found that panelists










rated connective tissue from electrically stimulated sides softer and

rated the meat as having less connective tissue for both beef and lamb

carcasses. In agreement with the latter finding Hawrysh and Wolfe

(1983) found that eight trained taste panelists could not detect any

differences between the connective tissue softness of stimulated or

nonstimulated Longissimus or Semitendenosus muscle evaluated 48 hrs

and 7 days postmortem.



Electrical Stimulation Methodology

A wide variety of voltages, currents, waveforms, duration times,

pulse lengths, and electrode types and placements have been used over

the course of research in electrical stimulation of meats, and no one

optimal methodology has evolved. The major stimulation variable

researchers have alluded to has been the voltage at which stimulation

occurs. Initially the use of high voltages was examined, with

voltages ranging from 3600V on sheep (Chrystall and Hagyard, 1976) to

700V (Bendall et al., 1976; George et al., 1980), 440V (Savell et al.,

1978a, 1978b), 320V (Grusby et al., 1976), and 250V (Carse, 1973) on

beef.

High voltages, however, pose major safety problems in a

processing facility and have been reported to cause extreme muscle

contraction and carcass distortion resulting in broken vertebrae and

vertebral joints, and muscle tearing in the back area (Bendall et al.,

1976; Chrystall and Hagyard, 1976). Because of these problems,

researchers have investigated the use of low voltage stimulation to

induce a tenderizing effect.










Carse (1973) found that electrical stimulation of lamb carcasses

with lower voltages (60-250V) caused significant tenderness

improvements compared to the tenderness of nonstimulated carcasses,

but he did find that the lower voltages resulted in a slower rate of

pH decline that affected the times at which low temperature cooling

and hot-boning could occur. Even lower voltages (120-20V) were used

by Savell et al. (1977), Shaw and Walker (1977), Bouton et al. (1978),

and Taylor and Marshall (1980). All found that low voltage electrical

stimulation induced a significant tenderizing effect and accelerated

the rate of decline of muscle pH. PH values from stimulated carcasses

taken at 1, 4, and 24 hrs postmortem were all significantly lower than

the corresponding unstimulated controls regardless of the voltage

applied (with one exception at 24 hrs where the pH was the same).

Different electrode types and placements have been used as well as

different waveforms and stimulation time schemes, including stepwise

voltage increases up to the desired peak voltage.

Authors utilizing low voltage stimulation generally have

concluded that low voltage stimulation was as effective in inducing

tenderness as higher voltages. Bouton et al. (1980) directly compared

three different voltage systems involving the use of a high voltage

(1100V), a low voltage (110V), and an extra low voltage (45V) to test

the efficacy of tenderness induction. These workers found that all

stimulation treatments significantly improved tenderness when compared

to nonstimulated controls for muscle removed 22 hrs postmortem, but

that the use of the high voltage system was more suitable for reducing

cold shortening effects than the low voltage treatments. Stimulation










was found to increase the rate of pH decline, with higher voltages

causing more rapid declines. Other important observations from this

study were that the high voltage system allowed the use of the rail as

a ground electrode while only one other contact electrode would have

been needed, but with the two low voltage systems, two or more

electrodes would need to be attached, one in the hind quarter and one

in the forequarter.

In an attempt to elucidate the pathways of high (850V peak) and

low voltage (45V peak) stimulation, Morton and Newbold (1982) used

curare to inhibit the functional nervous system in anesthetized

sheep. Electrical stimulation regardless of voltage was found to

accelerate glycolysis in control (nonanesthetized, exsanguinated

sheep) and anesthetized exsanguinated sheep, but curare injections

prior to slaughter negated the effect low voltage stimulation had on

glycolysis acceleration. The authors concluded that for low voltage

stimulation to be effective in accelerating glycolysis, a functional

nervous system is required, but that high voltages can exert their

effect by directly depolarizing the cell membrane. It is essential,

therefore, that low voltage stimulation occurs very soon after death

for complete effectiveness.

In an effort to further define optimal stimulation conditions,

Chrystall and Devine (1978) observed the effects of various voltages,

frequencies, pulse shapes, polarities, and stimulation periods on the

effectiveness of electrical stimulation. The researchers found that

electrical stimulation hastened the onset of rigor in a two-stage

process. The initial stage occurred during stimulation resulting in a










rapid and dramatic decrease in pH of .5 to .7 pH units. The second

stage occurs upon cessation of stimulation causing a much slower rate

of pH decline compared to the first stage. The pH decline in the

second stage, however, is still twice as fast as the decline in

nonstimulated muscle. At a constant voltage (200V) frequency had a

sizable effect on the magnitude of the pH fall in the first stage.

Frequencies of 5 to 16.6 pulses/sec caused the largest drop in pH

during the stimulation period (.7 pH units). Pulse shapes on

polarities seemed to have little effect on the rate of pH decline in

either stage. In this study a stimulation duration of 120 sec,

regardless of voltage, was more effective in inducing a more rapid pH

decline than shorter stimulation periods.
















CHAPTER III
PRELIMINARY STUDY:
EFFECTS OF LOW VOLTAGE ELECTRICAL STIMULATION AT
VARIOUS DURATIONS ON THE TEXTURE OF HOT-STRIPPED BROILER BREAST MEAT


Introduction

Harvesting cut-up or boned meat prior to evisceration (hot-boned)

or immediately after chilling (chill-boned), as opposed to harvesting

after a 4-6 hour aging period (age-boned), is more desirable for

processors due to savings accrued through reduced labor, storage, and

handling requirements. Hot-boning and chill-boning, however, have a

detrimental effect on the texture of light and dark broiler meat

(de Fremery and Pool, 1960; Klose et al., 1972; Lyon et al., 1973;

Peterson, 1977; Stewart et al., 1984a; Lyon et al., 1985). Results

from these studies have indicated that some treatment to induce

tenderness is needed if hot-boning is to be adopted for use in the

industry or if utilization of chill-boning is to be continued by the

industry. One possible method of improving the texture of hot-boned

and chill-boned poultry involves the use of electrical stimulation.

Postmortem electrical stimulation is a standard practice in beef

and lamb processing today. This method has had a long history of

experimentation but was not adopted until the 1970s by the New Zealand

lamb industry as a means of avoiding cold and thaw shortening in lambs

that were frozen immediately after slaughter for shipment overseas.

The technique was later adopted by the beef industry as a means of










hastening rigor development, reducing cold shortening, allowing for

hot-boning, reducing the occurrence of heat rings, and improving color

and texture of meat (Pearson and Dutson, 1985).

No one optimal methodology of stimulation has evolved thus far.

Many early studies utilized high voltages ranging from 3,600 to 250

volts. The use of high voltages, however, has posed major safety

problems in a processing facility and caused extreme muscle

contracture and carcass distortion resulting in broken joints and

muscle tearing (Bendall et al., 1976; Chrystall and Hagyard, 1976).

Because of these problems researchers have investigated the use of low

voltage stimulation to induce a tenderness response.

Experimentation with low voltages (120 to 20 volts) resulted in

significant tenderness improvements and increased rates of pH decline

over nonstimulated carcasses, but higher stimulation voltages resulted

in more rapid pH declines (Carse, 1973; Bouton et al., 1980). Bouton

et al. (1980) concluded that low voltage stimulation (45 volts) was as

effective as higher voltages in inducing tenderness, but higher

voltages were more suitable in reducing the effects of cold shortening

due to accelerated rates of glycolysis. In this same study workers

found that using high voltages allowed for the use of the rail as the

ground and only one other ground electrode. Low voltage systems,

however, required the use of two or more contact electrodes to

overcome the resistance of the carcass.

Morton and Newbold (1982) found that the use of low voltage

stimulation had a limited effect on accelerating glycolysis if applied

late in the processing scheme. Using anesthetized sheep and curare










injections, the authors found that low voltage stimulation required a

functional nervous system to be effective, but high voltage

stimulation exerted its effect by directly depolarizing the muscle

cell membranes. It is generally recommended that low voltage

stimulation be applied within 10 minutes after death for complete

effectiveness (Savell, 1985).

At the time this preliminary study was undertaken little work had

been published examining the effects of postmortem electrical

stimulation on the texture of poultry meat. De Fremery and Pool

(1960) removed the Pectoralis superficialis from six 11 week old

chickens and stimulated one fillet from each carcasses for 30 minutes

with voltage gradually increasing from 20 volts to 390 volts. The

current was pulsed on for 0.1 second at 1 second intervals. The

stimulated muscles had higher shear values (5.5 kg) than the

nonstimulated controls (3.7 kg). In a second experiment these workers

found that electrical stimulation of hot-stripped fillets with 90

volts increased the rates of ATP depletion and pH decline over the

nonstimulated fillets.

The objectives of this experiment were to determine if low

voltage stimulation for relatively short durations would improve the

tenderness of hot-boned broiler breast meat. Because low voltage

electrical stimulation was effective in inducing a tenderness response

in beef, and because of the problems of carcass distortion and safety

associated with high voltage stimulation, a relatively low voltage of

45 volts was selected for this preliminary experiment examining the

effects of postmortem electrical stimulation on the tenderness of










hot-boned broiler breast meat. Since electrical stimulation of

excised breast fillets caused increased toughness in the breast meat,

(de Fremery and Pool, 1960) whole carcasses were stimulated. The

stimulation was applied immediately after exsanguination, since Morton

and Newbold (1982) concluded that a functional nervous system was a

prerequisite for the effective use of low voltage stimulation.



Materials and Methods

Processing Scheme

Male Cobb, feather-sexed broilers, 49 days of age, reared on a

commercial-type broiler diet were fasted for 12 hours, and then cooped

8/coop for a total of 36 birds. Six birds per replication were hung

by the shanks on shackles, individually identified by duplicate wing

bands, and electrically stunned using a Cervin model FS stunner on

setting 4 and killed by exsanguination. Following a 90 second

bleeding period, the carcasses were subjected to the stimulation

treatments using a Koch low voltage electrical stimulator (45

volts). Two carcasses per replication were electrically stimulated

for 0, 9, and 18 seconds by placing an electrode around the neck while

the rail/shackle system functioned as the ground. The feathers were

removed by subscalding the carcasses in an Ashley scalder at 600C for

45 seconds and picking in a commercial rotary drum picker for 25

seconds.

Following feather removal, the carcasses were hot-boned.

Carcasses were suspended from the shackle by the neck; after removal

of the skin from the breast, the humeral-scapular joint was severed










and the Pectoralis superficialis muscles with the wings attached were

stripped from the carcass by firmly pulling downward on the wings.

The fillets were chilled in ice slush for one hour, allowed to

drain for 10 minutes, and ice packed. Following a 24-hour holding

period at 20C, paired fillets were bagged together and held at -230C,

for 12 days for subsequent cooking and shear evaluation.

Cooking Procedure

Paired fillets with the wings attached were cooked by replication

on roasting racks in foil-lined and covered stainless steel pans, in a

rotary hearth oven at 1770C to an internal temperature of 820C.

Internal temperature was monitored using copper constant thermocouples

placed in the thickest portion of the breast. Cooked fillets were

cooled to room temperature, wrapped by replication in aluminium foil,

and held overnight at 70C for shear force evaluation.

Shear Force Evaluation

Duplicate samples (1 x 1 x 2-3 cm) were obtained from the

anterior portion of each fillet, with the long dimension paralleling

muscle fibers. Samples were sheared perpendicular to the muscle

fibers in a standard 10-blade shear compression cell. A Food

Technology Corporation Texture Test System shear instrument, equipped

with a 136 kg force transducer and a TG-4A Texturegage, was used with

a descent speed of 0.7 cm/sec. Data were converted to kg force/g

sample and the four shear values from each carcass were averaged.










Statistical Analysis

Means for each treatment were calculated along with standard

error of the means (Steel and Torrie, 1960).



Results and Discussion

The mean shear value of breast meat obtained from nonstimulated

carcasses was similar to values previously reported by Sams (1984) and

was higher than the shear values observed for the breast meat from the

stimulated carcasses (Table 3-1). Low voltage stimulation of

carcasses, however, did not reduce shear values to an acceptable

tenderness level below the 8 kg force/g sample suggested by Simpson

and Goodwin (1974). It is possible that stimulation with higher

voltages and/or longer stimulation durations might cause even greater

improvements in tenderness since higher voltages have been shown to be

more effective in hastening rigor thus avoiding toughening associated

with hot-boning (Bouton et al., 1980).

The lack of a more pronounced tenderizing effect with 45V may

have resulted because the nervous system of poultry is rendered

nonfunctional within minutes after death. Morton and Newbold (1982)

observed in sheep that high voltage stimulation directly depolarizing

the sarcolemma causing muscle contraction, but low voltage stimulation

depolarized the nervous system causing the nervous system to initiate

muscle contraction, not the externally applied voltage. If the

functional capabilities of the nervous system are impaired prior to or

during stimulation the effectiveness of the low voltage stimulation

treatment would be reduced.





33









Table 3-1. Mean shear values standard error of the means of hot-
boned broiler breast meat obtained from carcasses
stimulated with 45 volts for 0, 9, or 18 seconds




Stimulation duration (sec.)

0 9 18



Shear value 11.9 0.74 9.2 0.64 9.2 0.65





34




Conclusions

Results from this experiment indicated that low voltage

stimulation caused a slight improvement in the tenderness of hot-boned

broiler breast meat with the stimulation durations utilized.

Subsequent experiments need to focus on the use of higher voltages and

various stimulation durations. Additionally, biochemical and physical

parameters, such as ATP levels, pH, sarcomere lengths, and myofibril

fragmentation should be examined in order to determine a clearer

picture of the effects of electrical stimulation on the poultry meat.
















CHAPTER IV
EFFECTS OF ELECTRICAL STIMULATION AT VARIOUS DURATIONS
ON THE TEXTURE OF BROILER BREAST MEAT


Introduction

Data from the preliminary study, discussed in Chapter III,

demonstrated that low voltage (45V) postmortem electrical stimulation

caused a slight improvement in the tenderness of hot-boned broiler

breast meat. Bouton et al. (1980), however, found that high voltage

stimulation of beef was more effective in reducing the effects of hot-

boning than was low voltage stimulation. Haki and Froning (1984)

observed that stimulating turkeys with 800 volts improved the

tenderness of aged turkey breast meat.

The use of high voltage, however, has been associated with muscle

tearing, and broken and disjointed bones in beef carcasses (Bendall

et al., 1976; Chrystall and Hagyard, 1976). Broken and disjointed

bones and torn muscles could result in lowered U.S.D.A. grades in

broiler carcasses and parts, detract from the overall product

appearance, and ultimately cause economic losses. A medium range

stimulation voltage (240V) was chosen for use in the second

experiment, possibly avoiding broken bones, disjoints and muscle

damage associated with higher voltages.

The purpose of this experiment was to determine if electrical

stimulation with medium voltage improves the texture of hot-boned,

chill-boned, or age-boned broiler breast meat and to determine an










optimal stimulation duration at a given voltage in order to achieve a

maximum tenderness response.



Materials and Methods

Two trials were conducted utilizing a stimulation voltage of

240V. Three of 12 carcasses per replication (5 replicates/trial) were

subjected to one of four stimulation durations: 0, 15, 30, and 45

seconds. One carcass from each stimulation treatment was either hot-

boned, chill-boned, or age-boned.

Basic Processing, Electrical Stimulation, and Boning

On two separate days (2 trials), 52 and 53 day-old male Cobb,

feather-sexed, broilers reared on a commercial type broiler diet were

weighed to obtain a uniform weight range, fasted for 9 hours, and

cooped 10/coop for a total of 120 birds (60/trial). Twelve birds per

replication were hung by the shanks on shackles, individually

identified with duplicate wing bands, and electrically stunned using a

Cervin model FS stunner set on setting 4, and killed by

exsanguination. Following a 90 second bleeding period, the carcasses

were subjected to the stimulation treatments using the same Cervin

Stunner on the highest setting producing 340 ma and equipped with a

rheostat to produce a constant voltage of 240V. The carcasses were

electrically stimulated by using the shackle/rail system as the ground

and placing the kill knife on the skin at the back of the neck near

the last cervical vertebra, and pulsing the current on for 2 seconds

and off for 1 second, as typically practiced in the beef industry

(Savell, 1985), until the total time of 15, 30, or 45 seconds had










elapsed. Stimulation caused pronounced muscle contraction with the

maximum initially observed response declining after 12-15 seconds of

stimulation. Generally by the end of a 45 second stimulation period

the degree of response was minimal with only slight visual evidence of

muscle contraction.

After electrical stimulation the feathers were removed by

subscalding the carcasses in an Ashley scalder at 60C for 45 seconds

and picking in a commercial rotary drum picker for 25 seconds.

Following feather removal, one carcass from each stimulation

treatment (4 total carcasses/rep) was hot-boned. Carcasses were

suspended from the shackle by the neck; after removing the skin from

the breast, the humeral-scapular joint was severed and both Pectoralis

superficialis muscles with the wings attached were stripped from the

carcass by firmly pulling downward on the wings. The left Pectoralis

superficialis was weighed and chilled. The right Pectoralis

superficialis was immediately divided into sections and frozen in

liquid nitrogen for pH and R-value analysis. Due to insufficient

liquid nitrogen storage facilities, samples for fragmentation index

and sarcomere length analysis were stored at -230C, conditions similar

to those used by Culler et al. (1978) and Calkins et al. (1980).

Concurrently, the remaining 8 carcasses were eviscerated using

standard procedures, rinsed, and weighed.

Carcasses and hot-boned fillets were immersion chilled

separately, in tap water using a two stage process to simulate

commercial time-temperature conditions (15 minutes at 210C, followed

by 30 minutes in 1C ice-slush). A 3:1 water to carcass or fillet










ratio was maintained (Mickelberry et al., 1962), and to improve the

cooling rate, carcasses/fillets were agitated in the chilling medium

by moving wire baskets containing carcasses or fillets up and down.

Carcasses/fillets were hung by the wings, rinsed, and drained for

5 minutes prior to weighing to determine percent water uptake. Both

Pectoralis superficialis muscles from one carcass from each

stimulation treatment (4 carcasses/rep) were removed and sampled as

described for hot-boned fillet harvesting and sampling. The hot- and

chill-boned fillets, and the remaining intact carcasses (4

carcasses/rep) were packed in ice, and held for 48 hours at 20C prior

to weighing for determination of percent driploss. Remaining intact

aged carcasses (one/stimulation treatment) were boned and sampled as

previously described.

Cooking Procedure and Percent Cookloss

Wings were removed from all left-side fillets: new

identification bands were attached and fillets were weighed. Fillets

were cooked, by replication, on roasting racks in foil-lined and

covered stainless steel pans in a rotary hearth oven at 1770C to an

internal temperature of 820C. Internal temperature was monitored

using copper constantan thermocouples equipped with a digital display

and placed in the thickest portion of the breast. Cooked fillets were

cooled to room temperature (250C), reweighed to determine percent

cookloss, wrapped in foil, and held overnight at 70C for shear force

evaluation.










Shear Force and Cooked Moisture

Duplicate samples (1 x 1 x 2-3 cm) were obtained from the

anterior portion of each fillet with the long dimension paralleling

muscle fibers. Samples were sheared perpendicular to the direction of

the muscle fibers in a standard 10-blade shear compression cell. A

Food Technology Corporation Texture Test System shear instrument,

equipped with a 136 kg force transducer and at TG-4A Texturegage was

used with a descent speed of 0.7 cm/sec. Data were converted to kg

force/g sample and averaged for each fillet. Meat from each fillet

was chopped, packaged in Whirl-pak bags, and held at -230C for 2-3

weeks for moisture evaluation (AOAC, 1970). Moisture evaluation, as

well as percent cookloss, water uptake and driploss were determined to

detect possible changes in the water-holding capacity of the meat,

which could effect the functional properties or tenderness of the

meat. Additionally, percent water uptake and droploss were monitored

to determine if electrical stimulation caused problems regarding

compliance with U.S.D.A. chilling regulations. The U.S.D.A.

regulations allow a maximum 8% water uptake in ice-packed broilers

sent directly to nearby consumer markets, or 12% if shipped and

rehandled in distant markets (Brant et al., 1982).

PH Determination

Liquid nitrogen frozen samples (4-5 g) obtained from the caudal

end of the right-side fillets at the time of boning were removed from

liquid nitrogen, wrapped in butcher paper, and pulverized with a

hammer. A 1:10 (w/v) solution of meat powder and approximately 70C

0.005 M sodium iodoacetate were blended in a 100 ml stainless steel










cup at medium-high speed (approximately 14,600 rpm) using a Virtis 23

homogenizer for 30 seconds prior to solution pH determination using a

Corning Model 125 pH equipped with a Fisher combination, protected

polymer body, gel filled pH electrode (Sams, 1984).

R-Value

R-values were determined using procedures described by Khan and

Frey (1971) and Honikel and Fischer (1977) on liquid nitrogen frozen

samples (3-4 g) from each right-side fillet. Approximately 3 g of the

meat powder, obtained as described for the pH samples, was homogenized

in 20 ml of 1 M perchloric acid for 1 minute using a Virtis 23

homogenizer at 14,600 rpm. After gravity filtration (Fisher P8 filter

paper), 0.1 ml of the acid filtrate was added to 4 ml of 0.1 M

phosphate buffer. Absorbances at 250 and 260 nm were obtained using a

Hitachi Perkin-Elmer spectrophotometer at a slit width of 0.5 nm, and

R-values or absorbance ratios for each sample were calculated as

A250/A260.

Sacromere Length

Frozen samples (10-15 g) from the medial area of each right-side

fillet were cubed and homogenized in 25 ml of cold 0.25 M sucrose

using a Virtis 23 homogenizer at 11,500 rpm for 10-15 seconds until

fiber separation was noted. Two drops of the homogenate were placed

on a microscopic slide, covered with a cover slip, and placed in the

path of a helium-neon laser (wavelength = 632.8 nm). The sacromere

length was determined using methods and the equation described by

Cross et al. (1980).










Fragmentation Index

The fragmentation index (FI) was determined by adapting

procedures used for beef as outlined by Calkins and Davis (1978) and

Davis et al. (1980). In a preliminary study using the method outlined

by Davis et al. (1980), few differences in fragmentation index were

found in broiler breast meat with shear values ranging from 3.5 to

18.0 kg force/g sample. The homogenization treatment outlined for use

with beef was too severe for poultry meat, and as a result the

majority of the homogenate passed through the 250 pm filter screen.

In subsequent preliminary trials the length of the homogenization

period and speed (rpms) were varied using a Virtis homogenizer or a

Waring blender. In some trials a larger screen size, 500 ^m, was used

instead of the 250 pm screen suggested by Davis et al. (1980).

Eventually, a procedure utilizing the 250 0m screen and a Waring

blender produced fragmentation indexes that were related to the shear

values of broiler breast meat.

To determine fragmentation index, frozen samples (5-6 g) obtained

at the time of boning from the anterior portion of each right-side

fillet were chopped into 5 mm cubes, weighed to the nearest 0.0001 g,

and homogenized with 50 ml of 0.25 M sucrose, 0.02 M KC1 solution at

high speed for 30 seconds with a Waring blender. The homogenate was

vacuum filtered through a tared 250 pm nylon screen to approximately

the same dryness. After air drying for ten minutes on Fisher P8

filter paper, the weight of residue was determined and fragmentation

index was calculated using the following formula:

FI = 1000 x (Residue weight/Original sample weight).










Statistical Analysis

Data within each boning treatment were analyzed using analyses of

variance, Duncan's Multiple Range test, and, where appropriate,

orthogonal comparisons (Steel and Torrie, 1960) utilizing the General

Linear Model system available in the Statistical Analysis Systems

package (SAS, 1982). Shear force, pH, R-value, sarcomere length, and

fragmentation index data were tested for correlations over the entire

experiment, within boning treatments, and within boning-stimulation

treatments using programs available in SAS, and standard error of the

means were calculated for each boning-stimulation treatment (SAS,

1982). Data from both trials were combined since there were no

significant trial x treatment interactions.


Results and Discussion

Data in Table 4-1 reflect shear values, pH, R-values, sarconere

lengths, and fragmentation indexes of the nonstimulated control

samples for each boning treatment, demonstrating the relationships

between the three boning treatments for each of the parameters. It

was not the major focus of the research to examine the tenderness

differences between the various boning treatments for they have been

previously documented (Sams, 1984), but to examine the effects of

electrical stimulation on tenderness within a boning treatment. These

data established reference values for the various parameters, in order

to determine the effects of electrical stimulation, particularly for

those parameters for which little published data pertaining to poultry

meat exists. These data will be used to briefly review the physical















Table 4-1. Shear values, pH, R-values, sarcomere lengths, and fragmentation indexes of hot-
boned, chill-boned, and age-boned broiler breast meat obtained from nonstimulated
(control) carcasses




Boning Shear value pH R-value* Sarcomere Fragmentation**
treatment (kg force/ length index
g sample) (Iim)


Hot-boned 15.7 1.38*** 6.08 0.04 0.92 0.03 1.63 0.03 404 47

Chill-boned 9.9 + 1.83 6.00 0.07 1.02 0.05 1.60 0.05 385 45

Age-boned 4.2 0.63 5.71 0.06 1.37 0.01 1.79 0.04 255 66


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means standard error of the mean.










and biochemical differences between the boning treatments and to

discuss some postmortem changes that occur as muscle is converted to

meat.

Harvesting of broiler breast fillets immediately after picking

(hot-boned) or immediately after chilling (chill-boned) caused a

dramatic increase in toughness, and increased variations associated

mean shear values compared to harvesting after a 48-hour aging period

(age-boned) (Table 4-1), a trend that has been well documented in the

literature (Sams, 1984; Stewart et al., 1984a; Lyon et al., 1985;

Dawson et al., 1986). According to Simpson and Goodwin (1974) poultry

meat with a shear value of 8 kg force/g sample or above is

unacceptably tough. Hot-boned and chill-boned fillets produced

unacceptably tough products with shear values above 15 and 9 kg

force/g sample, respectively.

As the time between slaughter and boning increased there was a

corresponding decrease in muscle pH and an increase in R-values (Table

4-1). The increasing R-values with delayed boning reflected

postmortem changes that occurred primarily in the ratio of IMP to

ATP. The R-value is an indicator of the relative amounts of IMP,

inosine, and hypoxanthine to adenine nucleotides, as detected by

absorbance of an acid extract of muscle tissue at 250 nm/260nm,

respectively, and is not an absolute quantification of IMP and ATP

levels. Adenine diphosphate, AMP, inosine, and hypothanxine are

present in much smaller concentrations than ATP and IMP and have only

a small effect on the R-value of meat. A pure ATP solution had an

absorbance ratio of approximately 0.80, and a pure IMP preparation had










a ratio of approximately 1.70. Calkins et al. (1982) reported that

the R-value (A250/A260) of aged beef was 1.35, similar to the value

reported in Table 4-1 for age-boned breast meat.

After death during rigor development, muscle cells attempt to

maintain antemortem ATP levels, but ATP is rapidly depleted because

cells rapidly lose the ability to regenerate ATP due to the

dysfunction of the mitochondria under the anaerobic conditions that

develop as a result of the loss of the circulatory system. Some ATP

is generated by conversion of CP and ADP to ATP. Creatine phosphate

is rapidly used up and ATP is produced through anaerobic glycolysis

which results in the accumulation of lactic acid in the tissues and

the typical decrease in postmortem muscle pH seen in Table 4-1. As

muscle progress through normal postmortem rigor development, ATP is

depleted resulting in the formation of AMP. Adenosine monophosphate

is deaminated forming IMP, thus as rigor progresses ATP levels

decrease while IMP levels increase. Eventually IMP is

dephosphorylated forming inosine and inosine is hydrolyzed forming

hypoxanthine (Hultin, 1976). Over the course of rigor development, as

mentioned across the three boning treatments, pH was positively and

significantly (P<0.01) correlated to shear values, and R-values were

negatively and significantly (P<0.01) correlated to shear values with

correlation coefficients of 0.37 and -0.65, respectively, agreeing

with data published by Khan and Frey (1971).

Khan and Frey (1971) reported that monitoring the postmortem

change in the ratio of IMP/ATP spectrophotometrically was useful in

determining the state of rigor mortis. They found that changes in the










R-value over time corresponded to the development of rigor mortis,

with R-values increasing as rigor developed and leveling off at a

maximum once maximum rigor contraction occurred.

Khan and Frey (1971) reported that the ultimate pH and R-value of

poultry muscle was achieved within 24 and 48 hours, respectively.

Since age-boning occurred 48 hours postmortem, the pH and R-values

obtained in this experiment (Table 4-1) reflected the ultimate levels

achieved in typically processed meat and were similar to pH values

reported by Stewart et al. (1984a) in poultry and R-values reported by

Honikel and Fisher (1977) in beef.

As the time of boning increased, the sarcomere lengths increased,

which corresponded to decreases in shear values. Additionally,

sarcomere lengths were negatively and significantly correlated to

shear values when data from all three boning treatments were analyzed

(P<0.01, r=-0.50). The degree of muscle contraction or muscle

shortening has been shown to be one factor relating to the tenderness

of meat (Marsh and Leet, 1966), and sarcomere lengths have been used

as a simple means of estimating the degree of contraction (Howard and

Judge, 1968). Herring et al. (1967) reported a negative and

curvilinear relationship between shear values and sarcomere lengths in

beef muscle. In their study, sarcomere lengths of approximately 1.6

~m corresponded to high shear values between 18-14 kg force/g sample,

and longer sarcomere lengths (2.0 pm) corresponded to considerably

lower shear values, as found in the data in Table 4-1.

Increased muscle shortening with the boning of prerigor meat, as

seen in hot-boned and chill-boned fillets (Table 4-1), has been










attributed to the release of physical anatomical restraints prior to

rigor, allowing for unimpeded muscle contraction resulting in

increased shortening during rigor development (Kastner et al., 1973;

Falk et al., 1975).

Janky et al. (1983) reported sarcomere lengths for aged carcasses

of approximately 2.0 um, while values in this study were somewhat

shorter (1.8 um). These differences might have been due to the use of

different methods to determine the sarcomere lengths. Janky et al.

(1983) utilized an oil immersion microscopic method while the laser

diffraction method was utilized in this study. Cross et al. (1980)

reported that the laser diffraction method measured many more

sarcomeres than the oil immersion method, allowing for a more

representative average than that found using the microscopic

technique, which could account for the differences observed between

the two experiments.

Myofibril fragmentation is another factor that has been found to

be related to the tenderness of meat. Myofibril fragmentation has

been used as an indication of structural weakening of myofibrils

generally believed to be associated with structural changes occurring

at or near the Z-lines (Davey and Gilbert, 1969; Sayre, 1970), a loss

of adhesion between adjacent myofibrils, and a general loss of tensile

strength in the myofibrils (Davey and Gilbert, 1969), possibly caused

by myofibrillar protein hydrolysis with endogenous lysosomal enzymes

(Hultin, 1976). Fragmentability of myofibrils has been related to the

tenderness of poultry (Sayre, 1970), and beef (Culler et al., 1978),

with tougher meat having a greater resistance to fragmentation. As










the time of boning increased, the muscles had lower fragmentation

indexes (increased fragmentability) which corresponded to decreased

shear values (Table 4-1). Across the three boning treatments,

fragmentation indexes and shear values were significantly and

positively correlated (P<0.01, r=0.63). Culler et al. (1978) reported

that fragmentation index accounted for a maximum of 50% of the

variability in the tenderness of loin steaks and that it appeared to

be a more important factor in the tenderness of aged meat than

sarcomere lengths.

Postmortem electrical stimulation of carcasses with 240 volts for

intervals to 45 seconds did not improve the tenderness of hot-boned

fillets (Table 4-2). Postmortem electrical stimulation of beef has

been shown to offset the undesirable increase in toughness caused by

hot-boning even when meat was boned as early as 1 hour postmortem

(Cross and Tennent, 1980). Dransfield et al. (1985), however, found

that postmortem electrical stimulation of turkeys did not improve

tenderness, as typically found in beef.

The pH at the time of hot-boning was not significantly affected

by electrical stimulation with all pH values above 6 (Table 4-2).

Numerous workers have reported that electrical stimulation increases

the rate of pH decline in beef and lamb muscles producing lowered pH

over that observed for nonstimulated controls (Carse, 1973; Chrystall

and Devine, 1978). After death, during rigor development, muscle

cells attempt to maintain antemortem ATP levels using aerobic

mechanisms and by converting CP and ADP to ATP, but eventually ATP is

produced through anaerobic glycolysis which results in the















Table 4-2. Mean shear values, pH, R-values, sarcomere lengths, and fragmentation indexes
standard error of the mean of hot-boned broiler breast meat obtained from
carcasses stimulated with 240 volts for 0, 15, 30, or 45 seconds



Stimulation Shear value pH R-value* Sarcomere Fragmentation**
duration (kg force/ length index
(sec.) g sample) (vm)


0 15.7a 1.38*** 6.08a 0.04 0.92a + 0.03 1.63a 0.03 404a 47

15 15.2a 1.61 6.11a 0.04 0.98ab 0.02 1.62a 0.05 502a + 67

30 15.7a 1.69 6.07a 0.05 1.03b 0.02 1.53a 0.06 511a 66

45 15.2a 1.37 6.06a + 0.05 1.02b + 0.04 1.59a + 0.01 526a 77


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means within a column with different superscripts are significantly different
(P<0.05).










accumulation of lactic acid in the muscle tissues and a typical

decrease in postmortem muscle pH (Hultin, 1976). Electrical

stimulation hastens these processes by causing muscle contraction,

thus a more rapid depletion of ATP, CP, and accumulation of lactic

acid compared to nonstimulated muscle. In the present study, however,

hot-boning occurred within 10 minutes of electrical stimulation so it

is possible that muscle from stimulated carcasses had not accumulated

significantly greater amounts of lactic acid than nonstimulated

muscle, causing a lack of significant differences in pH between the

treatments.

Electrical stimulation produced a significant increase in the

R-value (Table 4-2) with the 30 and 45 second durations being more

effective in increasing the rate of postmortem rigor development. As

the meat progresses through normal postmortem rigor development, ATP

is depleted resulting in the formation of AMP. Adenosine

monophosphate is deaminated forming IMP, thus as rigor progresses, ATP

levels decrease while IMP levels increase. Khan and Frey (1971) have

reported that monitoring the postmortem change in the ratio of ATP/IMP

spectrophotometrically was useful in determining the state of rigor.

They found that changes in the R-values over time corresponded to the

development of rigor mortis, with maximum rigor contraction occurring

at the point of a stable and minimum R-value. From data in Table 4-2,

it was evident that electrical stimulation increased the rate of rigor

development compared to nonstimulated meat and that lengthening the

duration of stimulation increased the rate of rigor development. The

R-value appeared to be a much more sensitive indicator of the










progression of early postmortem rigor development than pH, since no

significant differences in pH at the time of boning were observed, but

significant differences were found in the R-values.

There were no significant differences in sarcomere lengths

between any of the treatments (Table 4-2), which corresponded to a

lack of significant differences in the shear values. Herring et al.

(1967) reported a negative and curvilinear relationship between shear

values and sarcomere lengths in beef muscle. Since no significant

shear value differences existed it was not surprising that differences

in sarcomere lengths were not found since the two were correlated in

earlier studies.

Electrical stimulation treatment had no significant effect on the

fragmentation index of hot-boned broiler breast meat (Table 4-2).

Also, no significant differences were found when an orthogonal

comparison between the stimulated and nonstimulated controls was

conducted (P<0.89). Fragmentability of myofibrils has been related to

tenderness of poultry (Sayre, 1970) and beef (Culler et al., 1978),

with tougher meat having a greater resistance to fragmentation. Since

there were no significant differences in shear values between the

treatments it is reasonable that no differences in fragmentation

indexes were found.

The lack of a tenderness response in hot-boned, prerigor, breast

meat obtained from electrically stimulated carcasses was well

supported by observed data obtained for pH, sarcomere length, and

fragmentation index, and could be due to several factors. Electrical

stimulation has been used as a tool to induce more rapid onset of











rigor mortis thus allowing for hot-boning and rapid chilling. In this

study, hot-boned fillets, from stimulated and nonstimulated carcasses,

were removed from the carcasses prior to full rigor development as

evidenced by the lack of muscle stiffness, and relatively high pH

values and low R-values. Removing the prerigor meat from the bone

released physical anatomical restraints allowing for unimpeded

contraction while the meat is progressing into rigor. The act of hot-

boning also provided the meat with a stimulus, inducing contraction to

occur. The low values (1.6 um) for sarcomere lengths reflected this

increase in the degree of contraction, and shorter sarcomeres have

been related to increased toughness (Herring et al., 1967).

Electrical stimulation probably failed to illicit a tenderness

response since boning occurred so soon after stimulation and prior to

full rigor development. Even though the rate of rigor development was

increased by electrical stimulation, as reflected by larger R-values,

rigor development was not complete, therefore, hot-boning still acted

as a toughening agent. An orthogonal comparison between nonstimulated

control and stimulated also revealed there were no significant

differences (P>0.89). Analyzing data within the hot-boning treatment

pH was significantly correlated with shear values (r=-0.42, P<0.01)

and fragmentation indexes with pH (r=-0.54, P<0.01), indicating that

tenderness of meat boned prior to rigor development is related to the

pH at which boning occurs, and the fragmentability of the myofibrils

is also related to pH.

Postmortem electrical stimulation of carcasses with 240 volts did

not significantly improve the tenderness of broiler breast meat boned










immediately after chilling (chill-boned) (Table 4-3). Using the

criteria established by Simpson and Goodwin (1974) the meat was still

unacceptably tough but samples from carcasses stimulated for 15 and 45

seconds approached this critical point of 8.0 kg force/g sample.

The rate of rigor development was significantly affected by

electrical stimulation as reflected in a significant increase in R-

value and decrease in pH at the time of chill-boning (Table 4-3). The

pH nor R-values were not significantly different for the nonstimulated

and 15 second stimulated samples, but 30 seconds of stimulation

produced a significant increase in the rate of rigor development.

Electrical stimulation did not significantly affect the sarcomere

lengths or fragmentation indexes of the chill-boned meat, but there

was a trend toward longer sarcomere lengths with stimulation as

demonstrated in an orthogonal comparison of fillets from nonstimulated

vs. stimulated carcasses (P<0.11), which corresponds with the shear

data (Table 4-3). Within the chill-boned treatment, sarcomere lengths

and FI were significantly correlated with shear values (r=-0.28,

P<0.08; r=0.55, P<0.01). Additionally, sarcomere lengths and

fragmentation indexes were correlated with both pH and R-values. This

indicated that the tenderness of chill-boned fillets is related to the

point of rigor development at which boning occurs, and that sarcomere

lengths and fragmentation indexes both were valid indicators of

tenderness, within the boning time.

Broiler breast meat deboned approximately 48 hours postmortem

(age-boned), as expected, was very tender as indicated by the low

shear values, and electrical stimulation did not significantly















Table 4-3. Mean shear values, pH, R-values, sarcomere lengths, and fragmentation indexes
standard error of the mean of chill-boned broiler breast meat obtained from
carcasses stimulated with 240 volts for 0, 15, 30, or 45 seconds




Stimulation Shear value pH R-value* Sarcomere Fragmentation**
duration (kg force/ length index
(sec.) g sample) (nm)


0 9.9a 1.83k** 6.00a 0.07 1.02a 0.05 1.60a + 0.05 385a 45

15 8.2a + 1.06 5.94ab + 0.05 1.12ab + 0.03 1.63a + 0.03 389a + 49

30 9.0a 1.51 5.83b 0.05 1.18b 0.04 1.70a 0.04 372a 50
45 8.3a 1.28 5.89b + 0.07 1.22b 0.02 1.71a 0.05 346a 38


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means within a column with different superscripts are significantly different
(P<0.05).










increase tenderness regardless of the stimulation duration (Table

4-4). In agreement with these findings, there were also no

significant differences in the fragmentation indexes or sarcomere

lengths between any of the treatments.

Electrical stimulation did not produce any significant

differences in the pH, or R-values of age-boned meat regardless of the

duration of stimulation (Table 4-4). Khan and Frey reported that pH

and R-values reached their ultimate levels within 24 and 48 hours

postmortem, respectively. Since the age-boned fillets were aged for

48 hours prior to boning and sampling, no differences in pH or R-

values would be expected because the ultimate pH and ATP

concentrations would have already been achieved. Electrical

stimulation increased the rate of rigor development, but electrical

stimulation does not alter the ultimate pH (Pearson and Dutson, 1985),

or the ultimate concentration of ATP, ADP, AMP, CP, IMP, or inosine

(Calkins et al., 1982) of meat.

Electrical stimulation had no significant effect on the water

holding capacity (WHC) of hot-boned, chill-boned or age-boned meat as

reflected in the percent water uptake, driploss, cookloss, cooked

moisture of the meat (Table 4-5). Whiting et al. (1981) and Terrell

et al. (1981) found that electrical stimulation had no significant

effect on the WHC of lamb or beef, respectively. The values obtained

in this experiment for water uptake and driploss were somewhat higher

than values previously reported (Sams, 1984), but the differences

could be accounted for by the use of slightly different agitation

techniques during chilling. The differences in water uptake,
















Table 4-4. Mean shear values, pHl, R-values, sarcomere lengths, and fragmentation indexes
standard error of the mean of age-boned broiler breast meat obtained from
carcasses stimulated with 24U volts for 0, 15, 30, or 45 seconds




Stimulation Shear value pll R-value* Sarcomere Fragmentation**
duration (kg force/ length index
(sec.) g sample) (i pn)


0 4.2a 0.63*** 5.71a 0.06 1.37a 0.01 1.79a 0.04 255a 66

15 3.8a 0.38 5.72a 0.06 1.39a + 0.01 1.78a 0.03 245a 38

30 4.0a 0.44 5.67a 0.05 1.40a 0.02 1.84a 0.06 213a 19

45 3.7a 1.10 5.68a 0.05 1.40a t 0.02 1.83a 0.05 279a 42


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means within a column with different superscripts are significantly different
(P<0.05).











Table 4-5. Percent water uptake, driploss, cookloss, and cooked meat
moisture of hot-boned, chill-boned, and age-boned broiler
breast meat obtained from carcasses stimulated with 240
volts for 0, 15, 30, or 45 seconds



Boning Stimulation %
treatment duration Water Driploss Cookloss Cooked
(sec.) uptake moisture


Hot-boned 0 9.83a* 7.30a 32.28a 67.89a
15 9.93a 6.39a 30.87a 68.46a
30 9.75a 6.37a 30.78a 67.97a
45 8.84a 5.98a 31.77a 67.64a



Chill-boned 0 6.94a 2.90a 30.16a 68.29a
15 5.60a 1.08a 27.36a 68.54a
30 6.68a 3.05a 28.32a 68.35a
45 5.50a 0.94a 28.92a 68.62a



Age-boned 0 5.33a 1.36a 26.39a 68.88a
15 6.06a 1.30a 26.60a 68.47a
30 4.65a 1.01a 26.63a 68.35a
45 5.12a 1.36a 28.08a 68.33a


with different


Means within a column and a boning treatment
superscripts are significantly different (P<0.05).










driploss, and cookloss between hot-boned fillets and the other two

boning treatments resulted because the hot-boned fillets were chilled

as fillets without the skin, while the chill- and age-boned fillets

were obtained from chilled carcasses. Hot-boned fillets had a greater

surface area/unit weight in contact with the chilling medium thus

increasing the amount of water uptake. Since there was a greater

water uptake in the tissue there was a corresponding increase in

driploss and cookloss. The carcasses from which chill-boned and age-

boned fillets were obtained, whether stimulated or not, had water

uptake well below the 8 or 12% limits imposed by the U.S.D.A. for ice-

packed broilers (Brant et al., 1982). The hot-boned fillets, however,

had water uptake close to the 12% limit for ice-packed fillets to be

transported to and rehandled in distant markets, and exceeded the 8%

water uptake limit for ice-packed poultry sent to nearby markets.

Commercially, it may be necessary to reduce the time period allowed

for chilling or reduce the amount of agitation during chilling to

reduce percent water uptake in order to stay within U.S.D.A. limits if

the product is ice-packed. If the processor wishes to chill-pack or

freeze the fillets soon after processing, processors would be required

to further limit water uptake in order to stay within U.S.D.A.

regulations.



Conclusions

Postmortem electrical stimulation of broiler carcasses with 240

volts for as long as 45 seconds did not significantly improve the

tenderness of hot-boned, chill-boned, or age-boned broiler breast










meat. Electrical stimulation increased the rate of rigor development

as indicated by more rapid pH declines, and increased R-values.

Electrical stimulation, however, did not alter the ultimate pH or R-

values found in the age-boned fillets. Electrical stimulation did not

significantly affect the sarcomere length or the fragmentation index

of fillets obtained from any of the boning treatments.

Across the three boning treatments, sarcomere lengths,

fragmentation index, pH, and R-values were significantly correlated to

shear values. Within the three boning treatments, however,

fragmentation index was the only variable significantly correlated

with shear values within each of the boning treatments. Values for pH

were correlated with shear values within the hot-boned treatments,

sarcomere lengths with shear values within chill-boned fillets, and

pH, R-values, sarcomere lengths, and fragmentation index were all

corerlated with shear values within the age-boned treatment. Within

boning-simulation treatments very few significant correlations between

shear values, and pH, R-value, sarcomere lengths, or fragmentation

indexes existed. This indicates that pH, R-values (indicators of

rigor development), or sarcomere lengths and meat tenderness were

related to physiological changes that occur in muscle during rigor

development, but did not necessarily have a cause and effect

relationship. Stewart et al. (1985b) had similar findings for the

relationship between tenderness and pH values.
















CHAPTER V
EFFECTS OF ELECTRICAL STIMULATION AT VARIOUS VOLTAGES
ON THE TEXTURE OF BROILER BREAST MEAT


Introduction

Results from the third experiment demonstrated that electrical

stimulation with 240 volts regardless of the stimulation duration did

not induce tenderness in hot-boned, chill-boned, or age-boned broiler

breast fillets. Maki and Froning (1984) reported that electrical

stimulation of turkeys at 800 volts improved the tenderness of breast

meat, but Dransfield et al. (1985) found that stimulation of turkeys

with only 94 volts did not improve tenderness. Because of a lack of

tenderness response in poultry using 45 and 240 volts, the effect of

utilizing even higher stimulation voltages was examined in the second

experiment. Because no tenderness response occurred using the longer

stimulation durations for any of the boning treatments in the previous

experiment (Chapter IV), the shortest duration of 15 seconds was

selected for use in the third experiment.

The purpose of this study was to examine the effects of

electrical stimulation at various voltages on the texture of hot-

boned, chill-boned, and age-boned broiler breast meat and to determine

an optimal stimulation voltage to induce a maximum tenderness response

for a given stimulation duration for each boning treatment.










Materials and Methods

Basic Processing, Electrical Stimulation, and Boning

On two separate days (2 trials) 59 and 60 day-old male

Cobb,feather-sexed broilers reared on a commercial type broiler diet

were weighed to obtain a uniform weight range, fasted for 12 hours,

and cooped 10/coop for a total of 120 birds (60/trial). Twelve birds

per replication were processed, electrically stimulated, and boned as

described in Chapter IV, except three carcasses were nonstimulated

controls, while the remaining carcasses were subjected to stimulation

for 15 seconds at 240, 530, or 820 volts. One carcass from each

stimulation treatment was either hot-boned, chill-boned, or age-boned,

for a total of 10 birds/treatment (boning time and voltage).

Analyses

Shear force, percent water uptake, driploss, cookloss, and cooked

meat moisture, pH, sarcomere length, fragmentation index, and R-values

were determined as outlined previously in Chapter IV.

Statistical Analysis

Data within each boning treatment were analyzed using analyses of

variance, Duncan's Multiple Range Test (Steel and Torrie, 1960) and,

where appropriate, orthogonal comparisons utilizing the General Linear

Model system available in the Statistical Analysis Systems package

(SAS, 1982). Shear force, pH, R-value, sarcomere length, and

fragmentation index data were tested for correlations over the entire

experiment, within boning treatments, and within boning-stimulation

treatments using programs available in SAS, and standard error of the

means were calculated for each boning-stimulation treatment (SAS,










1982). Data from both trials were combined since there were no

significant trial x treatment interactions.



Results and Discussion

Shear values similar to those found in the previous experiment

(Chapter IV) were obtained, with hot-boned and chill-boned broiler

breast meat producing an unacceptably tough product compared to

fillets that were age-boned (Table 5-1). As the time of boning

increased, pH values decreased, and R-values and sarcomere lengths

increased, and correlations of shear force and pH, R-values or

sarcomere lengths were significant across the three boning treatments

(r=0.55, -0.63, and -0.58, respectively; P<0.01) trends that were

observed in the previous experiment. The differences in the pH and R-

values between the two experiments for the hot-boned and chill-boned

fillets could be related to differences in antemortem stress, and

degree of starvation prior to slaughter. Shrimpton (1960) found that

the degree of antemortem struggle affected the glycogen levels found

in the muscle and subsequently affected the rate of postmortem

glycolysis. Additionally, longer feed withdrawal periods had a

tendency to decrease the rate of pH decline and caused considerable

variation in the rate of pH decline compared to birds fed prior to

slaughter.

The fragmentation index data (Table 5-1) did not follow the same

trends that were evident in the previous experiment (Chapter IV)

although shear values and fragmentation indexes were positively and

significantly correlated over the entire experiment, as in Chapter IV















Table 5-1. Shear values, pH, R-values, sarcomere lengths, and fragmentation indexes of hot-
boned, chill-boned, and age-boned broiler breast meat obtained from nonstimulated
(control) carcasses




Boning Shear value pH R-value* Sarcomere Fragmentation**
treatment (kg force/ length index
g sample) (um)


Hot-boned 13.6 0.94*** 6.28 0.04 0.93 0.04 1.46 0.06 264 39

Chill-boned 9.4 1.17 6.12 0.04 0.90 0.04 1.50 0.05 354 47

Age-boned 3.7 0.22 5.69 0.04 1.33 0.07 1.80 0.04 204 32


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means standard error of the mean.










(r=0.41, P<0.01). This difference was probably due to the large

variation in the data, which arose from difficulties in controlling

the degree of thaw in the samples prior to homogenization. Samples

that remained frozen prior to homogenization produced higher

fragmentation indexes than samples that were thawed. In the previous

experiment, the samples were held in the freezer until homogenization

while the samples in this experiment were allowed to thaw for

approximately 15 minutes prior to homogenization.

Electrical stimulation for 15 seconds regardless of the voltage

utilized did not significantly improve the tenderness of hot-boned

broiler breast meat (P<0.05) (Table 5-2). However, orthogonal

comparison of fillets from nonstimulated vs. stimulated carcasses

revealed a trend for stimulation to increase the shear values of hot-

boned broiler breast meat (P < 0.12). Utilization of high voltages

(530 and 820V) significantly increased the rate of postmortem rigor

development as indicated by significantly lower pH values and

significantly higher R-values compared to fillets from nonstimulated

and low voltage stimulated (240V) carcasses (Table 5-2).

Electrical stimulation of beef has been utilized to improve

tenderness by hastening the onset of rigor so that cold shortening

could be avoided and hot-boning utilized (Carse, 1973; Cross and

Tennent, 1980). Savell et al. (1978b) demonstrated that electrical

stimulation could be used to avoid toughness problems caused by rapid

processing, but that electrical stimulation also improved the

tenderness of conventionally processed beef. Much work has been

published examining the effects of various voltages ranging from













Table 5-2. Mean shear values, pH, R-values, sarcomere lengths, and fragmentation indexes
standard error of the mean of hot-boned broiler breast meat obtained from
carcasses stimulated for 15 seconds with 0, 240, 530, or 820 volts



Stimulation Shear value pH R-value* Sarcomere Fragmentation**
voltage (kg force/ length index
(v) g sample) ( rn)

0 13.6a 0.94*** 6.28a 0.04 0.93a 0.04 1.46a 0.06 264a 39

240 16.3a 1.59 6.15ab 0.05 0.92a 0.02 1.60b 0.02 363ab 49

530 16.2a 1.38 6.05b 0.05 1.00ab 0.04 1.55b 0.03 409b 57

820 16.2a 1.64 6.06b 0.03 1.04b 0.03 1.62b 0.02 413b 70


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means within a column with different superscripts are significantly different
(P<0.05).










20 to 3,600V, and even very low voltages were effective in inducing

tenderness in beef (Taylor and Marshall, 1980). High voltage systems,

however, were recommended for use in conjunction with hot-boning or

rapid chilling because as the voltage increases there is a

corresponding increase in the rate of rigor onset (Carse, 1973; Bouton

et al., 1980) which decreases the length of the holding time required

prior to rapid chilling or boning. Even though voltages as high as

820 volts were utilized in this study, the tenderness of the hot-boned

meat was not improved, in spite of a significant increase in the rate

of rigor development.

In this experiment, hot-boned fillets from stimulated and

nonstimulated carcasses, were removed from the carcasses prior to full

rigor development, as evidenced by relatively high pH values, low R-

values, and a lack of muscle stiffness. Removing the prerigor meat

from the bone releases physical anatomical restraints allowing for

unimpeded muscle contraction while the muscle is progressing into

rigor. The act of hot-boning also provides the meat with a stimulus,

inducing contraction to occur. The low sarcomere length values

reflect this increase in the degree of contraction (Table 5-2), which

has been related to increased toughness (Herring et al., 1967).

Cold shortening also may have contributed to toughening

associated with hot-boning and the smaller shear values associated

with the fillets obtained from nonstimulated carcasses. The hot-boned

fillets were subjected to low temperatures (10C) within 20 minutes of

boning and it is likely that the fillets were progressing into rigor

at this time causing the cold shortening. Locker and Hagyard (1963)










found that subjecting isolated prerigor beef to temperatures between 0

and 20C caused rapid and extreme shortening compared to muscle held at

higher temperatures. Marsh and Leet (1966) demonstrated that this

shortening caused an increase in the toughness of the meat. Since the

nonstimulated carcasses had a slower rate of rigor development (Table

5-2), ATP was available for muscle contraction possibly causing a more

severe form of cold shortening than that observed in the fillets from

stimulated carcasses as evidenced by the significantly shorter

sarcomere lengths (Table 5-2) for the nonstimulated compared to the

stimulated carcasses. This extreme shortening found in the

nonstimulated fillets caused a slight improvement in tenderness.

Marsh et al. (1974) found that micrographs of severely contracted

muscle were not uniform, with zones of severely shortened sarcomeres

and, in contrast, regions which were physically disrupted or

stretched. They concluded that severe shortening actually caused

tenderization as a result of physical disruption of the fibers. Marsh

and Leet (1966) documented the tenderizing effect, finding that up to

40% shortening increased the toughness in beef, but shortening to a

greater extent caused a linear decrease in shear values.

The hypothesis of severe shortening inducing tenderization in the

nonstimulated fillets was substantiated by the fragmentation index

data (Table 5-2). As earlier stated, the severe shortening found in

the nonstimulated fillets could have caused physical fibril disruption

which would decrease the fragmentation index of the myofibrils since

fragmentation index is an indicator of structural weakening of the

myofibrils. Boning the nonstimulated fillets at high pH's (>6.15)










resulted in extremely shortened sarcomeres producing slight

tenderization caused by fibril disruption, as evidenced by low

fragmentation indexes. Electrical stimulation prevented the extreme

shortening, reducing any minor tenderization caused by extreme

shortening.

An additional reason for the lack of a tenderness response in

fillets from electrically stimulated carcasses may be related to a

lack of an enzymatic response. Dutson et al. (1980) suggested

autolytic proteolysis, caused by the lysosomal enzymes,

3-glucuronidase and cathepsin-C, as one mechanism for the

tenderization response caused by electrical stimulation. In beef,

electrical stimulation produces a condition of low pH while the

temperature of the muscle is still relatively high. Under these

conditions, lysosomal enzymes degraded myofibrillar proteins (Schwartz

and Bird, 1977). In this experiment the fillets were deboned while

the pH was still relatively high, and within 10-15 minutes the fillets

were chilled, preventing the development of optimal conditions needed

for the action of the lysosomal enzymes.

Calcium-activated factor (CAF) is another enzyme that has been

associated with meat tenderization. Marsh et al. (1981) found that

holding beef at relatively high temperatures at a neutral pH promoted

the development of tenderness, suggesting that an enzyme or enzyme

system active at neutral pH and high temperatures could have been

responsible for some tenderness development during rigor. Purified

preparations of CAF degraded the myofibrillar proteins, tropomyosin,

troponin-I, troponin-T, the Z-line, and the gap filaments (Locker










et al., 1977). It would seem unlikely, however, that CAF had an

active role in tenderization in this experiment since CAF is not

active below pH 6.5 (Dayton et al., 1975). Rapid pH declines in hot-

boned meat, whether stimulated or not, produced conditions

unconclusive to CAF activity.

Within the hot-boned treatment, sarcomere length was the only

variable significantly correlated with shear values (r=-.33, P<0.01),

indicating that pH, R-values, and fragmentation indexes did not have a

direct cause and effect relationship with shear values, but that

differences in tenderness were more closely associated with sarcomere

lengths than the other variables. Changes occurring in sarcomere

length and fragmentation index, however, were significantly correlated

with pH, indicating that the degree of contraction and myofibril

fragmentability in prerigor meat is related to the development of

rigor mortis, and that tenderness in hot-boned meat was indirectly

related point during rigor development at which the fillets were

boned, and the myofibril fragmentation did have some role in

tenderness but large variation in the data obscured any significant

differences in fragmentation indexes between treatments.

In chill-boned broiler breast meat, no significant improvement in

tenderness was observed when carcasses were stimulated at 240, or 530

volts, but a significant tenderness improvement occurred when

carcasses were stimulated at 820 volts (Table 5-3). Stimulation with

820 volts reduced the average shear value of chill-boned meat to a

level below the value of 8 kg/g suggested by Simpson and Goodwin as a

threshold for unacceptability in tenderness. Many processors have














Table 5-3. Mean shear values, pH, R-values, sarcomere lengths, and fragmentation indexes
standard error of the mean of chill-boned broiler breast meat obtained from
carcasses stimulated for 15 seconds with 0, 240, 530, or 820 volts




Stimulation Shear value pH R-value* Sarcomere Fragmentation**
voltage (kg force/ length index
(v) g sample) (ijm)


0 9.4a 1.17*** 6.12a + 0.04 0.90a 0.04 1.50a + 0.05 354a + 47

240 9.2a + 0.97 5.91b + 0.06 1.07ab 0.07 1.60ab + 0.03 304a 58

530 8.2a 0.94 5.96b + 0.06 1.17b 0.06 1.64b 0.05 206a 41

820 6.5b 0.84 5.83b + 0.06 1.12b + 0.06 1.68b + 0.03 301a 44


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means within a column with different superscripts are significantly different
(P<0.05).










been chill-boning meat in spite of the tenderness problems

encountered. Results from this study indicated that postmortem

electrical stimulation could be used to solve the tenderness

problem. Electrical stimulation systems should be fairly easy to

implement in current processing schemes, particularly with a

stimulation duration as short as 15 seconds. Some processors are

currently poststunning carcasses after bleeding to reduce variation in

tenderness due to struggling of misstunned birds. Postslaughter

stunning devices utilized equipment similar to preslaughter stunning

devices which operate at 800 volts. Processors would need to make

modifications increasing the length of the poststun period from 1 or 2

seconds to 15 seconds in order to achieve the desired response.

Electrical stimulation significantly reduced the pH at the time

of chill-boning, and there was a trend toward lower pH values as the

stimulation voltage increased (Table 5-3). The increase in the rate

of the rigor development was also evident in the increase in R-values

as stimulation voltage increased. As the stimulation voltage

increased, there was a corresponding significant increase in sarcomere

lengths. As earlier discussed, longer sarcomere lengths have been

found to correlate to lower shear values (Herring et al., 1967), a

trend evident in chill-boned fillets, with shear values significantly

and negatively correlating to sarcomere lengths (r=-0.32, P<0.05).

Results from this study (Table 5-3) were consistent with findings of

Maki and Froning (1984) who found that electrical stimulation with 800

volts improved the tenderness of turkey breast meat and caused an

increase in sarcomere lengths over nonstimulated carcasses.










Although fragmentation indexes were not significantly different

between the treatments (P<0.05), correlations between shear values and

fragmentation indexes were significantly correlated (r=0.42, P<0.01)

indicating that improvements in tenderness in the fillets stimulated

at 820V were related to increased fragmentability. Sayre (1970) and

Culler et al. (1978) demonstrated that the fragmentability of

myofibrils was related to the tenderness of poultry and beef,

respectively, with tougher meat having a greater resistance to

fragmentation.

Sonaiya et al. (1982) observed that the improvement in tenderness

of electrically stimulated beef carcasses over nonstimulated carcasses

appeared to be related to myofibril disruption as indicated by

increases in the fragmentability of the myofibrils. Savell et al.

(1978a) and Sorinmade et al. (1982) found ill-defined I-bands, Z-

lines, contracture bands, and stretch sarcomeres in electrically

stimulated meat, that was not evident in nonstimulated control

muscles. Savell et al. (1978a) suggested this led to a loss of

structural integrity and increased tenderness. The lack of a

significant myofibril fragmentability response with electrical

stimulation at the a=0.05 level was related to the large amount of

variation in the data caused by problems associated with controlling

the degree of thaw in samples prior to homogenization.

As with hot-boned meat, pH and R-values were not significantly

correlated with shear values but sarcomere lengths were significantly

correlated to pH, R-values, and shear force values (r=-0.38, P<0.02;

r=0.39, P<0.02; r=-0.32, P<0.05, respectively). Fragmentation index










was also significantly and negatively correlated with shear values.

Results indicated that tenderness improvements in chill-boned fillets

with electrical stimulation at 820 volts were related to increased

sarcomere lengths and decreased fragmentation indexes. Increasing

sarcomere lengths appeared to be related to increases in the rate of

rigor development caused by high voltage stimulation (820V).

Decreases in shear values related to decreases in fragmentation

indexes, however, did not appear to be directly caused by changes in

pH or R-value but instead could have been a direct result of physical

fiber disruption caused by more severe muscle contractions at higher

voltages since pH and R-values were not correlated to fragmentation

indexes. Additional evidence for this hypothesis is found in

correlations between shear values and fragmentation indexes within

boning-stimulation treatments. Shear values from nonstimulated chill-

boned fillets were not significantly correlated with fragmentation

indexes (r=0.09, P<0.80). Shear values and fragmentation indexes,

however, were significantly correlated within each of the stimulated,

chill-boned treatments (240V: r=0.64, P<0.05; 530V: r=0.58, P<0.01;

530V: r=0.45, P<0.10).

Unlike the results obtained for the chill-boned meat, there was

no significant improvement in the tenderness of the age-boned fillets

even with the use of high voltage stimulation (820V) (Table 5-4). It

is possible that stimulation increased the tenderness of age-boned

poultry meat, as found in red meats, but such low shear values

approached the lower limit of detectability for the shear method used

in this experiment, which has been reported to be 2 to 3 kg force/g














Table 5-4. Mean shear values, pH, R-values, sarcomere lengths, and fragmentation indexes
standard error of the mean of age-boned broiler breast meat obtained from
carcasses stimulated for 15 seconds with 0, 240, 530, or 820 volts



Stimulation Shear value pH R-value* Sarcomere Fragmentation**
voltage (kg force/ length index
(v) g sample) ( nm)

0 3.7a 0.22*** 5.69a 0.04 1.33a 0.07 1.80a 0.04 204a 32

240 3.9a 0.31 5.67a 0.06 1.44a + 0.01 1.76a + 0.03 186a + 38

530 4.0a 0.36 5.70a 0.05 1.42a 0.01 1.75a 0.02 215a 59

820 3.6a + 0.22 5.80a 0.08 1.41b 0.01 1.82a 0.03 168a 45


R-value = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

** Fragmentation index = 1000 x (residue wt./sample wt.).

*** Means within a column with different superscripts are significantly different
(P<0.05).










sample (Janky et al., 1982). As the lower limit of shear force was

approached, the reduction in toughness became insignificant because

the variation between samples within a stimulation treatment remained

constant but the difference between treatment means was reduced.

Electrical stimulation did not produce any significant

differences in the pH or R-values of age-boned meat regardless of the

stimulation voltage (Table 5-4). Khan and Frey (1971) reported that

pH and R-values reached their ultimate levels within 24 and 48 hours

postmortem, respectively. Since the age-boned fillets were aged 48

hours prior to boning, no differences in the pH of R-values would be

expected because the pH and ATP levels would have already been

achieved. Electrical stimulation increased the rate of rigor

development, as evidenced by lower pH and higher R-values in

stimulated hot-boned and chill-boned fillets, but electrical

stimulation did not alter the ultimate pH (Pearson and Dutson, 1985),

or the ultimate concentration of ATP, ADP, AMP, CP, IMP, or inosine

(Calkins et al., 1982) of meat.

Electrical stimulation had no significant effect on the sarcomere

lengths or fragmentation indexes of age-boned breast fillets, which

corresponds to the shear value data (Table 5-4). As previously

discussed, longer sarcomere lengths (Herring et al., 1967) and lower

fragmentation indexes (Culler et al., 1978) have been associated with

improved meat tenderness.

Values of pH were significantly correlated to shear values

(r=-0.37, P
treatment. This indicates that ultimate pH levels are related to the









tenderness of age-boned meat as demonstrated by shear values and

sarcomere lengths, but the differences in the tenderness of age-boned

meat, regardless of stimulation voltage are so small they are

insignificant.

Electrical stimulation, regardless of the voltage, had no

significant effect on the WHC of hot-boned broiler breast meat as

reflected in the nonsignificant differences in percent water uptake,

driploss, cookloss, or cooked meat moisture (Table 5-5). The same was

true for the chill-boned and age-boned fillets with two exceptions

(Table 5-5). Chill-boned fillets from carcasses stimulated at 820

volts had significantly higher driploss than nonstimulated controls.

There was a numeric, but nonsignificant, trend in this study for the

carcasses that were stimulated with 820 volts to have a slightly

increased water uptake compared to carcasses from the other

treatments. It would then follow that the 820 volt carcasses would

have an increased driploss. It was unlikely that this was truly a

significant effect related to the stimulation treatment, because there

was a large amount of variation between individual carcasses within

the same treatment. The same was true for the significant increase in

driploss for age-boned carcasses stimulated with 530 volts. These

carcasses had an increased but nonsignificant water uptake, so it

would follow that there would be proportionately higher driploss,

since the amount of driploss was proportional to the amount of water

picked up during chilling (Kiker and Farr, 1975).












Table 5-5. Percent water uptake, driploss, cookloss, and cooked meat
moisture of hot-boned, chill-boned, and age-boned broiler
breast meat obtained from carcasses stimulated for 15
seconds with 0, 240, 530, and 820 volts



Boning Stimulation %
treatment voltage Water Driploss Cookloss Cooked
(V) uptake moisture


Hot-boned 0 11.56a* 8.34a 27.19a 69.64a
240 11.30a 7.65a 27.22a 69.02a
530 10.51a 7.36a 24.97a 70.42a
820 11.12a 6.74a 27.28a 68.80a



Chill-boned 0 5.10a 0.74a 20.98a 70.21a
240 5.40a 1.79ab 25.05a 69.53a
530 5.42a 1.24ab 25.66a 69.56a
820 6.36a 2.22b 23.97a 69.76a



Age-boned 0 5.68a 2.10a 23.80a 70.39a
240 5.48a 2.05a 25.80a 70.00a
530 7.41a 3.42b 25.00a 70.27a
820 5.63a 1.97a 23.38a 70.17a


with different


Means within a column and a boning treatment
superscripts are significantly different (P<0.05).










Conclusions

In summary, postmortem electrical stimulation of broiler

carcasses with 820 volts improved the tenderness of fillets boned

immediately after chilling, and it appeared that tenderization was

related to increased sarcomere lengths and myofibril fragmentability.

An improvement in texture was not noted in hot-boned or age-boned

fillets. There was a significant increase in sarcomere lengths of

hot-boned fillets from stimulated carcasses, but this increase did not

lead to the improvement in texture as expected. The increase in

sarcomere lengths appeared to be offset by a substantial decrease in

the fragmentability of stimulated meat. Postmortem electrical

stimulation increased the rate rigor development and there was a trend

for higher voltages to have an even greater effect on this rate

increase. Correlations between shear values and pH or R-values, as

discussed earlier, tended to indicate that there was not a direct

relationship between pH and shear values upon examining the data from

the three different boning treatments and within boning-stimulation

treatments. Stewart et al. (1984a) suggested that the development of

tenderness and pH in poultry meat were related to similar biochemical

processes but their relationship was not of a direct cause and effect

nature. The same appeared to be true for the R-value.
















SUMMARY AND CONCLUSIONS


Electrical stimulation, regardless of the stimulation duration or

voltage, had no significant effect on the tenderness of hot-boned or

age-boned broiler breast meat. However, high voltage (820V)

postmortem electrical stimulation of broiler carcasses significantly

improved the tenderness of broiler breast meat that had been harvested

immediately after chilling, producing an acceptably tender product.

Processors have been utilizing chill-boning in order to efficiently

meet the increased demand for boned meat, in spite of the toughness

problems encountered with the technique. Boned meat and cut-up parts

are high value marketable products compared to whole ready-to-cook

carcasses. Shelton (1985) estimated that, by the year 2000, nearly

90% of poultry meat will be marketed as cut-up or boned product, but

that the tenderness problems associated with chill-boning will force

processors to adopt a minimum 4 hour aging period prior to boning.

This aging requirement has resulted in and will result in increased

production costs due to increased labor, handling, and storage

requirements.

The use of high voltage postmortem electrical stimulation could

be applied to reduce the toughness problems associated with chill-

boning and could save processors from instituting or continuing to use

a minimum 4 hour aging period prior to boning. Electrical stimulation

systems would be fairly easy to implement in current processing










schemes, particularly with stimulation durations as short as 15

seconds. Some processors have been utilizing a type of electrical

stimulation, applied to the carcass after bleeding, referred to as

poststunning. Poststunning has been used to reduce variation in

tenderness that is caused by struggling of misstunned birds and has

been accomplished using 800 volts, the same voltage used for

electrical stunning. Processors only may need to make modifications

increasing the length of the poststun period from 1 or 2 seconds to 15

seconds to achieve the desired tenderness response.

Postmortem electrical stimulation increased the rate of rigor

development as demonstrated by higher R-values and lower pH values in

hot-boned and chill-boned fillets from stimulated carcasses compared

to fillets from nonstimulated carcasses. Increasing stimulation

voltage and duration caused an increase in the rate of rigor

development. Electrical stimulation, however, did not affect the

ultimate pH or R-value of the breast meat as demonstrated by a lack of

significant difference in R-values or pH values between stimulated and

nonstimulated age-boned meat. Results tended to indicate that there

was not a direct relationship between pH and shear values upon

examining the data from the three boning treatments. As Stewart

et al. (1984a) suggested, the development of tenderness in poultry

meat was related to similar processes but their relationship was not

of a direct cause and effect nature. The same appeared to be true for

the R-values.

High voltage electrical stimulation (530 and 820) of carcasses

caused an increase in the sarcomere lengths of hot-boned and










chill-boned breast fillets. Improvements in tenderness associated

with longer sarcomeres were observed in chill-boned fillets, but not

in hot-boned fillets where increased sarcomere lengths appeared to be

offset by significant decreases in the fragmentability of the

myofibrils. The fragmentability of chill-boned fillets was not

significantly effected by high voltage stimulation (P<0.05), but was

correlated to tenderness indicating the increased fragmentability did

play a role in tenderization.

Low voltage stimulation (240V) did not affect the fragmentation

index of hot- or chill-boned fillets or the sarcomere lengths of hot-

boned fillets, regardless of stimulation duration. Low voltage

stimulation had an inconsistent effect on the sarcomere lengths of

chill-boned fillets with increases observed in one experiment but not

the other.

Regardless of the stimulation voltage or duration, electrical

stimulation did not significantly effect the sarcomere lengths or

fragmentation indexes of age-boned meat.

Electrical stimulation had no significant effect on the water

holding capacity of poultry meat as demonstrated by a lack of

significant differences in percent water uptake during chilling of

carcasses or hot-boned fillets, the driploss of hot-boned and chill-

boned fillets or whole carcasses, or the percent cookloss and cooked

moisture of the hot-, chill-, or age-boned fillets regardless of the

stimulation duration or voltage.
















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89





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BIOGRAPHICAL SKETCH


The author, Leslie Thompson, was born April 9, 1959, in Pasadena,

Texas. During her youth, the author traveled and lived throughout the

U.S. and the Phillipines with her parents, Major and Mrs. V. B.

Thompson, eventually attending Newberry Park High School in Thousand

Oaks, California. In 1977, she graduated from Crestview Senior High

School in Crestview, Florida. She attended the University of Florida

receiving a Bachelor of Science in Agriculture degree in August of

1980, and a Master of Science degree with specialization in poultry

products technology in August of 1983. Currently, the author is a

doctoral candidate pursuing a Ph.D. in food science and human

nutrition at the University of Florida.

During her college career she was a member of the Poultry Science

Club, serving as Treasurer and Vice President; Alpha Zeta; Ganma Sigma

Delta; and the University of Florida Horse Teaching Unit. As an

undergraduate and master's candidate she was employed part-time at the

University of Florida Poultry Research Unit, and during her Ph.D.

program the author received a teaching/research assistantship from the

Poultry Science Department.

The author was the recipient of the Wallace-Hi-Line Hatcheries

Scholarship, Ohio State Scholarship, Beta Club Scholarship, and the

Julian S. Moore Memorial Merit Award for Outstanding Undergraduate.

Professional memberships include the Institute of Food Technologists

and Poultry Science Association.










I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation for the degree
of Doctor of Philosophy.




Douglas M fJanky, Chairrn
Professor of Food Science and man
Nutrition



I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation for the degree
of Doctor of Philosophy.




Roger 1.)West
Professor of Animal Science



I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation for the degree
of Doctor of Philosophy.




Jdsse F. Gregory, III
Associate Professor of Food Science
and Human Nutrition



I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation for the degree
of Doctor of Philosophy.



^)('f'-~CL LC'i<~- Ct L-
Scott A. Woodward
Assistant Professor of Poultry
Science




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