Effect of Optaflexx 45 (Ractopamine-HCl) on five-day retain shelf-life of muscles from the beef loin and round

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Effect of Optaflexx 45 (Ractopamine-HCl) on five-day retain shelf-life of muscles from the beef loin and round
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English
Creator:
Gonzalez, John Michael
Johnson, Dwain
Carr, Chad
Thrift, Todd
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.

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Effect of Optaflexx 45 (Ractopamine-HC1) on Five-Day Retail Shelf-Life
of Muscles from the Beef Loin and Round

John Michael Gonzalez, Dwain Johnson, Chad Carr, Todd Thrifti


Summary
The goal of this study was to evaluate the effects
of Optaflexx supplementation to steers during
the final 28 d of feeding on the shelf-life
properties of steaks from the round and loin.
Thirty-four steers were separated into four
harvest groups and fed at the University of
Florida Beef Teaching Unit. Within each
harvest group, steers were separated into two
pens. Both pens were fed a control diet of 85%
corn, 7.5% cottonseed hulls, and 7.5%
commercially produced protein/vitamin pellet.
When pens were visually 28 d from reaching a
pen average of 0.4 inch of backfat, pens were
supplemented with a top dress that contained 0
and 200 mg*hdl'*d'of Optaflexx. After d 28 of
supplementation for each harvest group, steers
were transported to the University of Florida
Meats Laboratory and harvested. Seventy-two
hours postmortem, the top round and knuckle
were removed from the right side of each
carcass. The Semimembranosus and Adductor
were separated from the top round and the
Rectus femoris and Vastus lateralis were
separated from the knuckle. Whole denuded
muscles were then vacuum packaged, wet aged
until day 13 postmortem, and cut into half-inch
steaks for five-day simulated retail display. Once
daily, steaks were subjectively evaluated for lean
color, fat color, and surface discoloration by an
eight-member trained visual panel. In addition,
steaks were also objectively measured for
L*a*b* values by a HunterLab MiniScan XE
spectrophotometer. Results of the study indicate
that L*, a*, and b* values were not affected
(P>0.05) by Optaflexx supplementation.


Additionally, visual panel scores revealed that
beef lean color and fat color was not
significantly (P>0.05) affected by Optaflexx
supplementation. However, visual panelists did
detect significant differences (P<0.05) between
treatments when evaluating surface
discoloration of the Vastus lateralis,
Semimembranosus, Rectus femoris, and
Adductor. Results of the study indicate that
supplementation of cattle with Optaflexx has a
detrimental effect on the shelf-life of steaks
0o igi,,,tig from the round.

Introduction
The supplement Optaflexx 45 (Ractopamine-
Hydrochloride) was approved by the FDA in
2003 for cattle fed in confinement during the last
24 to 42 d of feeding before slaughter. This
compound and the class of compounds it
belongs to, beta-agonists, are commonly referred
to as a "repartiontiong agent" due to their ability
to increase skeletal muscle accretion by
redirecting dietary nutrients away from adipose
tissue accretion to skeletal muscle growth
(Mersmann, 1979). Numerous studies with
swine and emerging data with cattle indicate
ractopamine elicits positive effects on both live
and carcass performance parameters. Optaflexx
commonly improves live performance by
increasing average daily gain, average daily feed
intake, and feed to gain ratio. In addition to the
live performance benefits, at the carcass level,
ractopamine can increase hot carcass weight and
ribeye area, decrease fat, and increase dressing
percentage by as much as 3.6% (Schroeder et al.,


'Department of Animal Sciences, University of Florida, Gainesville, FL


Supplementation with 200 mg*hd-l*d-'of Optaflexx 45 (Ractopamine-HCl) to steers during the
final 28 days of feeding prior to harvest did not affect L*,a*,b*, or visual panel beef lean and fat
color scores of muscles originating from the round during 5-day retail display. However, visual
panel steak surface discoloration scores indicated that Optaflexx 45 increases the rate of
discoloration in several muscles originating from the round.









2005; Winterholler et al., 2007). Therefore, in
today's market conditions of elevated feed
prices, the use of ractopamine to improve
average daily gain, gain to feed ratio, and
carcass characteristics becomes an attractive
option for producers as a means to lower the cost
of beef production.

However, within the muscle, the muscle fiber
isoform distribution is shifted from an oxidative
isoform to a glycolytic isoform (Gonzalez et al.,
2006). The shift toward more glycolytic muscle
fibers inherently reduces the ability of the
muscle to reduce metmyoglobin (brown,
discoloration) to oxymyoglobin (cherry red).
Therefore, it is expected that steaks originating
from Optaflexx supplemented cattle will have
reduced shelf-life in the retail display case.
Because color represents the single most
important visual component that determines if a
consumer will purchase a meat product (Hedrick
et al., 1994) the effect of Optaflexx on shelf-life
needs to be explored. Therefore, the objective of
our study was to investigate the effect of
Optaflexx on subjective and objective color
measurements during a five-day retail display
period.

Materials and Methods
Animals and Dietary Treatments
Thirty-four steers were selected from steers
housed at the University of Florida Beef
Teaching Unit. Upon selection, steers were
separated into four harvest groups based on time
until the cattle would reach a harvest endpoint of
0.4 inch of backfat. All cattle followed the same
implantation program consisting of a Ralgro
(Intervet, Millsboro, DE) implant followed by a
Revalor-S (Intervet, Millsboro, DE) implant.
Within each harvest group, steers were stratified
by weight and visual backfat thickness into two
pens. Steers were fed daily in concrete bunks
that provided 2.25 feet per head of bunk space.
Steers were fed a concentrate diet consisting of
85% corn, 7.5% cottonseed hulls, and 7.5%
commercially produced protein pellet (Jacko 52
medicated concentrate pellet, Lakeland Nutrition
Group, Lakeland, FL). This pellet was
comprised of 23 components including
cottonseed meal, dehydrated alfalfa meal, wheat
middlings, and various vitamins including


vitamin A, D3, and E. When pens were visually
28 d from reaching a pen average of 0.4 inch of
backfat, pens were supplemented with a top
dress that contained 0 and 200 mg-hd-'*d-'of
Optaflexx (Elanco Animal Health, Greenfield,
IN). Approximately two wk before the
beginning of the 28 d Optaflexx
supplementation period, both the control and
treatment pens were top dressed with a blank top
dress (33.33% corn meal, 50.83% alfalfa meal,
12.50% calcium carbonate, and 3.33% stable
feed fat) at a rate of 1 lb per head per day to
allow the steers time to adjust to the top dress.
Once the supplementation period began, the
control pen continued to receive the blank top
dress at a rate of 2 lb per head per day. The
treatment pens received 2 lb per head per day of
top dress designed to provide 200 mgohd-'*d-' of
Optaflexx. All top dressings were hand mixed
into the ration daily.

Harvesting and Sample Collection
Steers were harvested at the University of
Florida Meat Laboratory following the Humane
Methods of Slaughter Act of 1978. Seventy-two
hours postmortem, the bone-in strip loin,
knuckle, and top round were excised from the
right side of each carcass. Whole muscles were
removed from the subprimals including the the
Rectus Femoris (RF) and Vastus lateralis (VL)
from the knuckle; and the Adductor (ADD) and
Semimembranosus (SM) from the top round.
Whole muscles were placed in heat shrink
vacuum bags, vacuum packaged, and were wet
aged for 13 d postmortem at 33 30F.

Steak Cutting, Packaging, and Display
Following aging, muscles were removed from
their vacuum bags and cut into half-inch steaks.
Steaks were cut from the same end of each
muscle, perpendicular to the orientation of the
muscle fibers. Steaks from the LD and VL were
placed on 17S Styrofoam trays, steaks from the
ADD, GRA, and VL were placed on 1S
Styrofoam trays, and steaks from the SM were
placed on 10S Styrofoam trays. Each tray
contained a Dri-Loc 40 gram white meat pad
and was overwrapped with polyvinylchloride
film Steaks were displayed in a Hill coffin-style
retail case at 35 20F for 5 d. Cases were
illuminated with GE T8 Linear Fluorescent










lamps that emitted a case average of 106.7
footcandle with a 12 hour on, 12 hour off
lighting schedule. Steaks were rotated daily to
compensate for uneven temperature and light
distribution within the case.

Subjective and Objective Color Analysis
Subjective color measurements were collected
using an eight-member experienced panel.
Panelists evaluated steaks for beef lean color (8
= extremely bright cherry red; 1 = extremely
dark red), fat color (5 = yellow; 1 = white), and
surface discoloration (7 = total [100%]
discoloration; 1 = no [0%] discoloration) daily
for 5 days. Objective color measurements, L*,
a*, b* reflectance data, of the samples were
taken using a HunterLab MiniScan XE.
Spectrophotometric measurements were
captured using illuminant A and 100 standard
observer. Before each data collection period, the
MiniScan was calibrated on both a black and
white tile. Two measurements per steak were
obtained to represent the average color of the
entire steak.

Statistics
Data was analyzed using carcass as the
experimental unit. Objective, and subjective
color data was analyzed as a split-plot design
with repeated measures. Harvest group and
treatment was considered the whole plot and
muscle was considered the sub-plot. Day was
the repeated measure with animal within
treatment as the subject. All measured variables
were analyzed with the PROC MIXED
procedure of SAS (SAS Inst. Inc., Carry, NC,
2002). Pair-wise comparisons between the least
square means of the factor levels were computed
using the PDIFF option of the LSMEANS
statement. Differences were considered
significant at an alpha = 0.05 and tendencies at
an alpha = 0.10.

Results
Objective color data for all steaks are presented
in Table 1. Supplementing Optaflexx did not
affect the darkness (L*), redness (a*), and
yellowness (b*) of the steaks during the entire
display period. Visual panel scores of the six
muscles indicate that Optaflexx
supplementation did not affect either beef lean


color or fat color (Table 2). Surface
discoloration scores for all muscles are located
in Figure 1. Historically, a discoloration score
higher than a value of 2 is when consumers will
begin to discriminate between packages of meat
and be less willing to purchase discolored
product. Noticeable differences can be observed
between muscles, with some muscles having a
better shelf-life than other muscles. Optaflexx
did not affect (P > 0.05) surface discoloration
scores from d 0 to d 3 of the display period in
the Semimembranosus, Rectus femoris, or the
Vastus lateralis. However, Vastus lateralis
steaks from Optaflexx animals had more
surface discoloration on d 4 (P = 0.05) and
maintained greater surface discoloration on d 5
(P = 0.07). Similarly, Rectus femoris and
Semimembranosus steaks from Optaflexx
supplemented steers exhibited higher surface
discoloration (P = 0.009 and P = 0.04,
respectively) than control steaks at d 5. The
Adductor steaks discolored rapidly, with
Optaflexx steaks scoring higher (P = 0.05) than
control by d 2. The Adductor is identified as
having a very short shelf-life (approximately
three days). Therefore, this result indicates that
shelf-life in this muscle was decreased by 1 d by
supplementing Optaflexx.

Implications
In the retail display case, consumers visually
evaluate numerous factors when considering
which product to purchase. These factors include
portion size, leanness, ease of preparation, and
color. Historically, color is the single most
important visual component that determines if a
consumer will purchase a meat product. The
oxidation state of myoglobin, the heme-
containing protein that stores oxygen in the
muscle, determines the color that a consumer
sees when purchasing meat. As the myoglobin
is exposed to oxygen it is converted into
oxymyoglobin, which is typically the bright
cherry red color that the consumer desires.
However, as meat ages, oxymyoglobin
experiences oxidation and the formation of
metmyoglobin occurs. As more metmyoglobin
is formed the amount of discoloration observed
by a consumer increases. Literature indicates
that as the amount of oxidative muscle fibers in
muscle decreases, the ability of the muscle to










reduce metmyoglobin to oxymyoglobin
decreases. In the current study, we did observe
an Optaflexx-induced shift of muscle fibers to
more glycolytic fibers (data not shown). The
observed shift caused the Optaflexx
supplemented steaks to have decreased shelf-life
at the end of each steak's respective life. With
the results, we estimate that supplementing
Optaflexx reduces the amount of days that
steaks are available for sale by 1 to 2 d.
Therefore, the negative effect that Optaflexx
elicits on steak surface discoloration requires
attention and consideration when deciding
whether to use this growth enhancing
technology.






























Literature Cited
Gonzalez et al. 2008. J. Anim. Sci. 86:3568.
Mersmann, Harry J. 1998. J. Anim. Sci. 76:160.
Schroeder et al. 2005. J Anim. Sci. 83(Suppl. 1):111(Abstr.).
Winterholler et al. 2007. J. Anim. Sci. 85:413.


















Table 1. LSMEANS of HunterLab MiniScan XE L*, a*, and b* values from steaks originating
from the round of steers fed with (RAC) and without (CON) ractopamine-HCI displayed under
simulated retail display conditions for 5 days


Item Day
L*1 0
1
2
3
4
5
SEM
a*2 0
1
2
3
4
5
SEM
b*3 0
1
2
3
4
5


Muscle
Adductor Rectus femoris
CON RAC CON RAC
49.1 49.3 47.9 47.7
46.3 46.1 45.7 46.9
45.4 45.2 43.8 44.4
45.5 44.7 43.7 44.4
43.4 44.2 42.5 42.4
44.9 43.5 43.6 43.6
1.6 1.6
32.8 32.3 32.4 30.4
28.3 27.1 30.9 28.6
24.9 24.2 28.6 26.7
22.7 22.1 27.1 25.1
22.3 21.1 25.9 25.0
20.8 19.5 24.8 22.8
1.4 1.4
30.6 30.1 29.2 27.3
28.6 27.6 29.5 27.2
26.5 26.2 28.2 26.3
25.6 25.5 27.3 25.5
25.5 24.9 27.1 25.7
25.0 24.6 25.9 24.6


Semimembranosus
CON RAC
43.5 42.7
42.8 40.8
42.0 41.5
41.5 40.4
41.3 40.1
41.3 40.0
1.6


34.7
33.6
32.0
30.9
29.9
28.5

32.5
32.2
31.3
30.6
29.8
29.1


34.0
34.4
31.7
30.4
29.1
27.6

31.9
33.3
31.1
30.7
29.8
29.0


Vastus lateralis
CON RAC
44.4 44.5
42.1 41.8
41.7 41.8
41.2 41.8
41.1 40.8
41.0 41.0
1.6


34.7
35.9
33.4
32.2
31.4
30.0

31.5
33.6
31.5
30.8
30.1
29.3


33.7
35.6
31.4
29.3
29.4
27.7

30.5
33.1
29.7
28.4
28.5
27.6


SEM 1.1 1.1 1.1 1.1
1 Lightness: 100 = White; 0 = Black.
2 Redness: 60 = Red; -60 = Green.
3 Yellowness: 60 = Yellow; -60 = Blue.









Table 2. LSMEANS of visual panel scores for steaks from the round displayed under simulated
retail display conditions for 5 days from cattle fed with and without ractopamine-HCI
Muscle
Adductor Rectus femoris Semimembranosus Vastus lateralis
Item Day CON RAC CON RAC CON RAC CON RAC
Beef 0 5.5 5.4 5.8 5.6 5.4 5.4 5.6 5.3
Lean 1 4.5 4.3 5.7 5.2 5.0 4.7 5.1 5.0
Color1 2 4.1 3.9 5.6 5.4 5.0 4.6 4.9 4.9
3 3.9 3.7 5.6 5.3 4.7 4.4 5.0 4.6
4 3.6 3.3 5.3 5.3 4.5 4.2 4.9 4.7
5 3.4 3.2 5.5 5.3 4.5 4.1 5.0 4.5
SEM 0.3 0.3 0.3 0.3
Fat 0 1.9 1.9 1.8 1.8 1.9 1.9 1.9 1.8
Color2 1 2.0 2.0 2.0 2.0 2.0 2.1 2.0 2.0
2 2.0 2.1 2.0 2.1 2.1 2.1 2.1 2.0
3 2.0 2.0 2.1 2.0 2.0 2.1 2.0 2.0
4 2.4 2.5 2.2 2.2 2.2 2.2 2.2 2.2
5 2.7 2.6 2.3 2.4 2.3 2.4 2.2 2.4
SEM 0.1 0.1 0.1 0.1
18 = Extremely bright cherry-red; 7 = Bright cherry-red; 6 = Moderately bright cherry-red; 5 =


Slightly bright cherry-red; 4 = Slightly dark cherry-red; 3 =
Extremely dark red.
25 = Yellow; 4 = Moderately yellow; 3 = Slightly yellow; 2


Adductor Discoloration Scores


6-


31-



0
0 1 2 3 4 5
Day
Semimembranosus Discoloration Scores


Moderately dark red; 2 = Dark red; 1

= Creamy white; 1 = White.

Rectus Femoris Discoloration Scores


b


IaRAC


0 1 2 3 4 5
Day
Vastus Lateralis Discoloration Scores


b
a





0 1 2 3 4 5
Day


4
3

0
t I2


b
a
I RC


0 1 2 3 4 5
Day


Figure 1. Surface discoloration scores from steaks originating from the round of steers fed with and without
ractopamine-HCl displayed under simulated retail display conditions for 5 day. Means within a row with different
letters are significantly different (P < 0.05). 1 = No discoloration (0%); 2 = Slight discoloration (1-19%); 3 = Small
discoloration (20-39%); 4 = Modest discoloration (40-59%); 5 = Moderate discoloration (60-78%).




Full Text

PAGE 1

Summary The goal of this study was to evaluate the effects of Optaflexx supplementation to steers during the final 28 d of feeding on the shelf life properties of steaks from the round and loin. Thirty four steers were separated into four harvest groups and fed at the University of Florida Beef Teaching Unit. Within each harvest group, steers were separated into two pens. Both pens were fed a control diet of 85% corn, 7.5% cottonseed hulls, and 7.5% commercially produced protein/vitamin pellet. When pens were visually 28 d from reaching a pen average of 0.4 inch of backfat, pens were supplemented with a top dress that contained 0 1 1 of Optaflexx After d 28 of supplementation for each harvest group, steers were transported to the University of Florida Meats Laboratory and harvested. Seventy two hours postmortem, the top round and knuckle were removed from the right side of each carcass. The Semimembranosus and Adductor were separated from the top round and the Rectus femoris and Vastus later alis were separated from the knuckle. Whole denuded muscles were then vacuum packaged, wet aged until day 13 postmortem, and cut into half inch steaks for five day simulated retail display. Once daily, steaks were subjectively evaluated for lean color, fat color, and surface discoloration by an eight member trained visual panel. In addition, steaks were also objectively measured for L*a*b* values by a HunterLab MiniScan XE spectrophotometer. Results of the study indicate that L*, a*, and b* values were no t affected (P>0.05) by Optaflexx supplementation. Additionally, visual panel scores revealed that beef lean color and fat color was not significantly (P>0.05) affected by Optaflexx supplementation. However, visual panelists did detect significant diff erences (P<0.05) between treatments when evaluating surface discoloration of the Vastus lateralis, Semimembranosus, Rectus femoris, and Adductor. Results of the study indicate that supplementation of cattle with Optaflexx has a detrimental effect on the s helf life of steaks originating from the round. Introduction The supplement Optaflexx 45 (Ractopamine Hydrochloride) was approved by the FDA in 2003 for cattle fed in confinement during the last 24 to 42 d of feeding before slaughter. This compound and the class of compounds it belongs to, beta agonists, are commonly referred to increase skeletal muscle accretion by redirecting dietary nutrients away from adipose tissue accretion to skeletal muscle grow th (Mersmann, 1979). Numerous studies with swine and emerging data with cattle indicate ractopamine elicits positive effects on both live and carcass performance parameters. Optaflexx commonly improves live performance by increasing average daily gain, av erage daily feed intake, and feed to gain ratio. In addition to the live performance benefits, at the carcass level, ractopamine can increase hot carcass weight and ribeye area, decrease fat, and increase dressing percentage by as much as 3.6% (Schroeder et al., Effect of Optaflexx 45 (Ractopamine HCl) on Five Day Retail Shelf Life of Muscles from the Beef Loin and Round John Michael Gonzalez, Dwain Johnson, Chad Carr, Todd Thrift 1 1 1 of Optaflexx 45 (Ractopamine HCl ) to steers during the final 28 days of feeding prior to harvest did not affect L*,a*,b*, or visual panel beef lean and fat color scores of muscles originating from the round during 5 day retail display. However, visual panel steak surface discoloration sc ores indicated that Optaflexx 45 increases the rate of discoloration in several muscles originating from the round. 1 Department of Animal Sciences, University of Florida, Gainesville, FL

PAGE 2

2005; Winterholler et al., 2007). Therefore, in prices, the use of ractopamine to improve average daily gain, gain to feed ratio, and carcass characteristics becomes an attractive option for producers as a means to lower the cost of beef production. However, within the muscle, the muscle fiber isoform distribution is shifted from an oxidative isoform to a glycolytic isoform (Gonzalez et al., 2006). The shift toward more glycolytic muscle fibers inherentl y reduces the ability of the muscle to reduce metmyoglobin (brown, discoloration) to oxymyoglobin (cherry red). Therefore, it is expected that steaks originating from Optaflexx supplemented cattle will have reduced shelf life in the retail display case. Because color represents the single most important visual component that determines if a consumer will purchase a meat product (Hedrick et al., 1994) the effect of Optaflexx on shelf life needs to be explored. Therefore, the objective of our study was to investigate the effect of Optaflexx on subjective and objective color measurements during a five day retail display period. Materials a nd Methods Animals and Dietary Treatments Thirty four steers were selected from steers housed at the University of Flor ida Beef Teaching Unit. Upon selection, steers were separated into four harvest groups based on time until the cattle would reach a harvest endpoint of 0.4 inch of backfat. All cattle followed the same implantation program consisting of a Ralgro (Intervet Millsboro, DE) implant followed by a Revalor S (Intervet, Millsboro, DE) implant. Within each harvest group, steers were stratified by weight and visual backfat thickness into two pens. Steers were fed daily in concrete bunks that provided 2.25 feet per head of bunk space. Steers were fed a concentrate diet consisting of 85% corn, 7.5% cottonseed hulls, and 7.5% commercially produced protein pellet ( J acko 52 medicated concentrate pellet, Lakeland Nutrition Group, Lakeland, FL) This pellet was comprised of 23 components including cottonseed meal, dehydrated alfalfa meal, wheat middlings and various vitamins including vitamin A, D 3 and E. When pens were visually 28 d from reaching a pen average of 0.4 inch of backfat, pens we re supplemented with a top 1 1 of Optaflexx (Elanco Animal Health, Greenfield, IN). Approximately two wk before the beginning of the 28 d Optaflexx supplementation period, both the control and treatment pens were top dressed with a blank top dress (33.33% corn meal, 50.83% alfalfa meal, 12.50% calcium carbonate, and 3.33% stable feed fat) at a rate of 1 lb per head per day to allow the steers time to adjust to the top dress. Once the supplementation period began, the control pen continued to receive the blank top dress at a rate of 2 lb per head per day. The treatment pens received 2 lb per head per day of 1 1 of Optaflexx All top dressings were hand mixed into the rat ion daily. Harvesting and Sample Collection Steers were harvested at the University of Florida Meat Laboratory following the Humane Methods of Slaughter Act of 1978. Seventy two hours postmortem, the bone in strip loin, knuckle, and top round were exci sed from the right side of each carcass. Whole muscles were removed from the subprimals including the the Rectus Femoris (RF) and Vastus lateralis (VL) from the knuckle; and the Adductor (ADD) and Semimembranosus (SM) from the top round. Whole muscles were placed in heat shrink vacuum bags, vacuum packaged, and were wet aged for 13 d postmortem at 33 3F. Steak Cutting, Packaging, and Display Following aging, muscles were removed from their vacuum bags and cut into half inch steaks. Steaks were cut from the same end of each muscle, perpendicular to the orientation of the muscle fibers. Steaks from the LD and VL were placed on 17S Styrofoam trays, steaks from the ADD, GRA, and VL were placed on 1S Styrofoam tr ays, and steaks from the SM were placed on 10S Styrofoam trays. Each tray contained a Dri Loc 40 gram white meat pad and was overwrapped with polyvinylchloride film Steaks were displayed in a Hill coffin style retail case at 35 2F for 5 d Cases were illuminated with GE T8 Linear Fluorescent

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lamps that emitted a case average of 106.7 footcandle with a 12 hour on, 12 hour off lighting schedule. Steaks were rotated daily to compensate for uneven temperature and light distribution within the case. Subjec tive and Objective Color Analysis Subjective color measurements were collected using an eight member experienced panel. Panelists evaluated steaks for beef lean color (8 = extremely bright cherry red; 1 = extremely dark red), fat color (5 = yellow; 1 = wh ite), and surface discoloration (7 = total [100%] discoloration; 1 = no [0%] discoloration) daily for 5 days. Objective color measurements, L*, a*, b* reflectance data, of the samples were taken using a HunterLab MiniScan XE. Spectrophotometric measureme nts were captured using illuminant A and 10 standard observer. Before each data collection period, the MiniScan was calibrated on both a black and white tile. Two measurements per steak were obtained to represent the average color of the entire steak. Statistics Data was analyzed using carcass as the experimental unit. Objective, and subjective color data was analyzed as a split plot design with repeated measures. H arvest group and treatment was considered the whole plot and muscle was considered the s ub plot. Day was the repeated measure with animal within treatment as the subject. All measured variables were analyzed with the PROC MIXED procedure of SAS (SAS Inst. Inc., Carry, NC, 2002). Pair wise comparisons between the least square means of the fa ctor levels were computed using the PDIFF option of the LSMEANS statement. Differences were considered significant at an alpha = 0.05 and tendencies at an alpha = 0.10. Results Objective color data for all steaks are presented in Table 1. Supplementing Optaflexx did not affect the darkness (L*), redness (a*), and yellowness (b*) of the steaks during the entire display period. Visual panel scores of the six muscles indicate that Optaflexx supplementation did not affect either beef lean color or fat color (Table 2). Surface discoloration scores for all muscles are located in Figure 1. Historically, a discoloration score higher than a value of 2 is when consumers will begin to discriminate between packages of meat and be less willing to p urchase discolored product. Noticeable differences can be observed between muscles, with some muscles having a better shelf life than other muscles. Optaflexx did not affect ( P > 0.05) surface discoloration scores from d 0 to d 3 of the display period in the Semimembranosus Rectus femoris or the Vastus lateralis However, Vastus lateralis steaks from Optaflexx animals had more surface discoloration on d 4 ( P = 0.05) and maintained greater surface discoloration on d 5 ( P = 0.07). Similarly, Rectus femo ris and Semimembranosus steaks from Optaflexx supplemented steers exhibited higher surface discoloration ( P = 0.009 and P = 0.04, respectively) than control steaks at d 5. The Adductor steaks discolored rapidly, with Optaflexx steaks scoring higher ( P = 0.05) than control by d 2 The Adductor is identified as having a very short shelf life (approximately three days). Therefore, this result indicates that shelf life in this muscle was decreased by 1 d by supplementing Optaflexx Implications In the retail display case, consumers visually evaluate numerous factors when considering which product to purchase. These factors include portion size, leanness, ease of preparation, and color. Historically, color is the single most important visual comp onent that determines if a consumer will purchase a meat product. The oxidation state of myoglobin, the heme containing protein that stores oxygen in the muscle, determines the color that a consumer sees when purchasing meat. As the myoglobin is exposed to oxygen it is converted into oxymyoglobin, which is typically the bright cherry red color that the consumer desires. However, as meat ages, oxymyoglobin experiences oxidation and the formation of metmyoglobin occurs. As more metmyoglobin is formed the amount of discoloration observed by a consumer increases. Literature indicates that as the amount of oxidative muscle fibers in muscle decreases, the ability of the muscle to

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reduce metmyoglobin to oxymyoglobin decreases. In the current study, we did obs erve an Optaflexx induced shift of muscle fibers to more glycolytic fibers (data not shown). The observed shift caused the Optaflexx supplemented steaks to have decreased shelf life the results, we estim ate that supplementing Optaflexx reduces the amount of days that steaks are available for sale by 1 to 2 d. Therefore, the negative effect that Optaflexx elicits on steak surface discoloration requires attention and consideration when deciding whether to use this growth enhancing technology. Literature Cited Gonzalez et al. 2008. J. Anim. Sci. 86:3568 Mersmann, Harry J. 1998. J. Anim. Sci. 76:160 Schroeder et al. 2005. J Anim. Sci. 83(Suppl. 1):111(Abstr.). Winterholler et al. 2007. J. Anim. Sci. 8 5:413

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Table 1. LSMEANS of HunterLab MiniScan XE L*, a*, and b* values from steaks originating from the round of steers fed with (RAC) and without (CON) ractopamine HCl displayed under simulated retail display conditions for 5 days M uscle Adductor Rectus femoris Semimembranosus Vastus lateralis Item Day CON RAC CON RAC CON RAC CON RAC L* 1 0 49.1 49.3 47.9 47.7 43.5 42.7 44.4 44.5 1 46.3 46.1 45.7 46.9 42.8 40.8 42.1 41.8 2 45.4 45.2 43.8 44.4 42.0 41.5 41.7 41.8 3 45.5 44.7 43.7 44.4 41.5 40.4 41.2 41.8 4 43.4 44.2 42.5 42.4 41.3 40.1 41.1 40.8 5 44.9 43.5 43.6 43.6 41.3 40.0 41.0 41.0 SEM 1.6 1.6 1.6 1.6 a* 2 0 32.8 32.3 32.4 30.4 34.7 34.0 34.7 33.7 1 28.3 27.1 30.9 28.6 33.6 34.4 35.9 35.6 2 24.9 24.2 28.6 26.7 32.0 31.7 33.4 31.4 3 22.7 22.1 27.1 25.1 30.9 30.4 32.2 29.3 4 22.3 21.1 25.9 25.0 29.9 29.1 31.4 29.4 5 20.8 19.5 24.8 22.8 28.5 27.6 30.0 27.7 SEM 1.4 1.4 1.4 1.4 b* 3 0 30.6 30.1 29.2 27.3 32.5 31.9 31.5 30.5 1 28.6 27.6 29.5 27.2 32.2 33.3 33.6 33.1 2 26.5 26.2 28.2 26.3 31.3 31.1 31.5 29.7 3 25.6 25.5 27.3 25.5 30.6 30.7 30.8 28.4 4 25.5 24.9 27.1 25.7 29.8 29.8 30.1 28.5 5 25.0 24.6 25.9 24.6 29.1 29.0 29.3 27.6 SEM 1.1 1.1 1.1 1.1 1 Lightness: 100 = White; 0 = Black. 2 Redness: 60 = Red; 60 = Green. 3 Yellowness: 60 = Yellow; 60 = Blue.

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Table 2. LSMEANS of visual panel scores for steaks from the round displayed under simulated retail display conditions for 5 days from cattle fed with and without ractopamine HCl Muscle Adductor Rectus femoris Semimembranosus Vastus lateralis Item Day CON RAC CON RAC CON RAC CON RAC Beef 0 5.5 5.4 5.8 5.6 5.4 5.4 5.6 5.3 Lean 1 4.5 4.3 5.7 5.2 5.0 4.7 5.1 5.0 Color 1 2 4.1 3.9 5.6 5.4 5.0 4.6 4.9 4.9 3 3.9 3.7 5.6 5.3 4.7 4.4 5.0 4.6 4 3.6 3.3 5.3 5.3 4.5 4.2 4.9 4.7 5 3.4 3.2 5.5 5.3 4.5 4.1 5.0 4.5 SEM 0.3 0.3 0.3 0.3 Fat 0 1.9 1.9 1.8 1.8 1.9 1.9 1.9 1.8 Color 2 1 2.0 2.0 2.0 2.0 2.0 2.1 2.0 2.0 2 2.0 2.1 2.0 2.1 2.1 2.1 2.1 2.0 3 2.0 2.0 2.1 2.0 2.0 2.1 2.0 2.0 4 2.4 2.5 2.2 2.2 2.2 2.2 2.2 2.2 5 2.7 2.6 2.3 2.4 2.3 2.4 2.2 2.4 SEM 0.1 0.1 0.1 0.1 1 8 = Extremely bright cherry red; 7 = Bright cherry red; 6 = Moderately bright cherry red; 5 = Slightly bright cherry red; 4 = Slightly dark cherry red; 3 = Moderately dark red; 2 = Dark red; 1 = Extremely dark red. 2 5 = Yellow; 4 = Moderately yellow; 3 = Slightly yellow; 2 = Creamy white; 1 = White.