The effect of dietary vitamin E and controlled atmosphere packaging on the storage life of beef

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1 The effect of dietary vitamin E and controlled atmosphere packaging on the storage life of beef G. G. Greer, S. D. M. Jones, B. D. Dilts, and W. M. Robertson Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, Alberta, Canada T4L 1W1. GreerG@em.agr.ca. Contribution no. 881, received 3 July 1997, accepted 10 November Greer, G. G., Jones, S. D. M., Dilts, B. D. and Robertson, W. M The effect of dietary vitamin E and controlled atmosphere packaging on the storage life of beef. Can. J. Anim. Sci. 78: The effects of dietary vitamin E upon colour, bacteriology and case life of beef was examined following extended storage of longissimus thoracis (LT) muscle in vacuum or in anoxic atmospheres containing 100% CO 2. The diets of treated steers were supplemented with 1000 IU of vitamin E animal 1 d 1 for 100 d. Animals were slaughtered in a research abattoir and after 24 h of postmortem aging the LT muscles were removed and assigned to a packaging treatment for storage for up to 11 wk at 2 C. Rib-eye steaks were cut and displayed under simulated retail conditions to give a surface temperature of 6 C after storage intervals of 0, 3, 6, 9 and 11 wk. Feeding treatment had no effect (P > 0.05) upon standard carcass and muscle quality traits or bacterial growth but increased carcass α-tocopherol levels from 2.89 µg g 1 in control animals to 5.18 µg g 1 in carcasses supplemented with vitamin E (P < ). The α-tocopherol concentration in LT muscles was unaffected (P > 0.05) by storage time for up to 11 wk in either packaging treatment. Dietary vitamin E increased a* values and reduced metmyoglobin accumulation after LT storage for up to 11 wk irrespective of package atmosphere. However, dietary vitamin E had no significant effect (P > 0.05) on the colour case life of steaks derived from the LT muscle after vacuum storage for 3 to 11 wk. Contrarily, vitamin E acted synergistically with the CO 2 packaging treatment to produce an increase in colour case life from 2.7 (control) to 5.4 d (vitamin E) after 6 wk of LT storage and from 2.4 (control) to 4.0 d (vitamin E) after 9 wk of LT storage (P < ). In combination with anoxic, CO 2 packaging, dietary vitamin E may play a role in assuring beef colour stability following extended periods of storage necessary for fresh beef export. Key words: Vitamin E, packaging, beef storage Greer, G. G., Jones, S. D. M., Dilts, B. D. et Robertson, W. M Effet de l apport de vitamine E dans l alimentation et de l emballage sous atmosphère modifiée sur la durée de conservation de la viande bovine. Can. J. Anim. Sci. 78: Nous avons examiné les effets de la vitamine E de provenance alimentaire sur la couleur, sur l état bactériologique et sur la conservabilité en présentoir de la viande bovine à la suite d un entreposage prolongé du muscle longissimus thoracis (LT) sous vide ou sous atmosphère anoxique contenant 100 % de CO 2. Les aliments des animaux traités étaient enrichis pendant 100 jours de UI de vitamine E par animal et par jour. Les bêtes étaient abattues dans un abattoir expérimental et après 24 h de maturation, le longissimus thoracis était enlevé et conditionné selon un des deux traitements de conservation pour une durée pouvant aller jusqu à 11 semaines. Après 0, 3, 6, 9 ou 11 semaines de conservation, la noix de côte était débitée en steacks qui étaient exposés dans des conditions simulées de présentation en magasin prévues pour donner à la viande une température en surface de 6 C. La complémentation en vitamine E des aliments n avait pas d effets significatifs (P > 0,05) sur les caractères qualitatifs standards de la carcasse et du muscle ni sur la croissance bactérienne. En revanche, la concentration d αtocophérol de la carcasse montait de 2,89 µg 1 chez les animaux témoins à 5,18 µg 1 chez ceux recevant le complément de vitamine E (P < 0,0001). Quel que soit le traitement de conditionnement, la concentration d αtocophérol du LT n était pas significativement modifiée (P < 0,05) par la durée de conservation, c est-à-dire au moins jusqu à 11 semaines. Parallèlement, durant la même période, la complémentation en vitamine E augmentait les valeurs a* et réduisait l accumulation de metmyoglobine du muscle LT, indépendamment du mode de conditionnement. Après 3 à 11 semaines de conservation sous vide, la complémentation en vitamine E ne provoquait pas d effets significatifs (P > 0,05) sur la durée de maintien de la couleur en présentoir des steack provenant du muscle LT. Par contre, dans la viande conditionnée sous atmosphère de CO 2, la vitamine E accroissait la durée de maintien de la couleur de 2,7 (témoin) à 5,4 j (vit E) après 6 semaines de conservation et de 2,4 à 4 j après 9 semaines (P < 0,0001). Combiné avec l emballage en anoxie sous 100 % CO 2, l apport de vitamine E dans l alimentation pourrait contribuer à maintenir la coloration de la viande bovine durant les périodes prolongées de conservation requises pour les exportations de viande fraîche. Mots clés: Vitamine E, emballage, conservation de la viande bovine Preservative packaging (modified or controlled) and low temperature storage have the potential to extend the storage life of raw meat including colour stability (Gill and Molin 1991; Nesom-Fleet et al. 1993). Unfortunately, beef can undergo a transient degradation in colour under these conditions (Gill and McGinnis 1995). Also, when beef is removed from the oxygen-depleted atmosphere and placed under the aerobic conditions of retail display, colour rapidly deteriorates in direct proportion to the time of prior storage in a modified atmosphere. Thus, the colour case life of beef can 57 be reduced as much as 50% after 2 wk of storage in a vacuum or controlled atmosphere (Greer et al. 1993). If preservative packaging is to become a commercially viable method of distributing non-frozen raw beef to remote markets, colour stability must be assured during storage, Abbreviations: CFU, colony forming units; DMb, deoxymyoglobin; IU, international unit; LL, longissimus lumborum; LT, longissimus thoracis; MMb, metmyoglobin

2 58 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 1. Effect of vitamin E on carcass and meat quality attributes z Control Vitamin E Measurement mean mean SE P Live weight gain (kg) Live slaughter weight (kg) Hot carcass weight (kg) Hot carcass (g kg 1 of livewt.) Liver (g kg 1 of livewt.) Cooler shrinkage (g kg 1 ) Grade fat (mm) Carcass y α-tocopherol (µg g 1 ) LL ph, 45 min LL ph, ultimate LL temperature Steak drip loss (µg g 1 ) Maximum shear value (kg) z Data are least squares means and standard errors for 20 animals treatment 1. y m. sternomandibularis. upon pack opening and during retail display. Currently available commercial oxygen scavengers are not a feasible means of reducing transient discolouration (Gill and McGinnis 1995). However, α-tocopherol has been reported to stabilize the oxymyoglobin complex (Lanari et al. 1994) and there is considerable evidence that the result is an improvement in the colour case life of fresh pork (Asghar et al. 1991), beef (Faustman et al. 1989a; Arnold et al. 1993a), veal (Shorland et al. 1981), and lamb (Wulf et al. 1995). These beneficial effects are without impact upon the growth of meatborne pathogens or spoilage bacteria (Chan et al. 1994; Smith et al. 1994). More recent studies by Chan et al. (1995, 1996) showed that elevated α-tocopherol did not mask bacterial spoilage. Research with beef cattle has confirmed that feeding vitamin E in finishing diets can elevate α-tocopherol in subprimal (Sherbeck et al. 1995) and retail cuts (Morgan et al. 1993). The result was decreased surface discolouration, a 64 88% reduction in product that had to be marked down and a 2 3 d extension of retail case life. It was also of interest that vitamin E supplementation could produce a dosedependent increase in the α-tocopherol content of ground beef and extend the colour stability of this highly colourunstable retail product by up to 42 h (Lavelle et al. 1995). Despite this convincing body of evidence to support the view that dietary vitamin E can improve colour stability, there are not many published reports that have examined beef colour stability during storage for periods of time required for the sea export, distribution and display in remote export markets. One of few published studies has shown that dietary supplementation with vitamin E could extend the storage life of beef during vacuum storage (3 wk) and subsequent retail display in modified atmosphere (Taylor et al. 1994). Although anoxic packaging systems containing elevated levels of CO 2 could be employed to extend storage life to several months (Gill 1989) there are few reports (Allen et al. 1996) on the combined effects of dietary vitamin E and this form of controlled atmosphere packaging. The current research was designed to more fully characterize the effects of dietary vitamin E supplementation upon beef quality, colour stability, bacterial spoilage and case life during and following periods of storage (up to 3 mo) that would give the required flexibility for fresh product to be distributed to foreign markets. A comparison was made of the current commercial practice of vacuum packaging to the more optimal packaging system using a controlled atmosphere containing CO 2 (Gill 1989). MATERIALS AND METHODS Feeding Treatments Experiments were conducted in two identical trials involving pens of 10 steers for each of the two feeding regimes outlined below. Thus, a total of 40 yearling steers (Charolais Maine Anjou) weighing 440 ± 44 kg (SD) were utilized for the entire study. Although the magnitudes of treatment effects were not the same in both trials, the trends in treatment effects were similar and trials were pooled in the final analyses. Cattle were fed prior to the experiment on a commercial farm diet of barley silage (85% of dry matter) with a pelleted barley supplement (15% of dry matter). The steers were weighed at the beginning of the study and randomly assigned to feeding treatments. Two treatments were compared: A control diet of 50% barley silage plus 50% barley pelleted concentrate and the same diet supplemented with 1000 IU of vitamin E animal 1 d 1 (Hoffmann-La Roche, High River, High River, AB, Canada). This level of dietary supplementation was selected by the supplier and has been successfully used to promote a significant increase in muscle colour stability. The vitamin E was added as a top dressing to the feed. All cattle were fed for 100 d and pen intakes were recorded daily. Carcass and Meat Quality Measurements Animals were slaughtered in a research abattoir at slaughter weights depicted in Table 1. The warm carcass sides were weighed and then spray-chilled four times per hour for 1 min with water pre-chilled to 1 C for the first 6 h of chilling before being chilled in a cooler at 1 C with an air speed of 1 m s 1 to a total time of 18 h. Carcass and meat quality traits were determined by published methods (Jones and Robertson 1988). After chilling, a portion of the LL from the left carcass side from the 13th rib to the 5th lumbar vertebra was then

3 GREER ET AL. VITAMIN E AND BEEF STORAGE IN CONTROLLED ATMOSPHERES 59 Table 2. The effect of vitamin E and LT storage time on the appearance case life of steaks z Wk in Vacuum CO 2 storage Control Vitamin E SE P Control Vitamin E SE P z Data are least squares means for 8 rib-eye steaks treatment 1 storage interval 1. excised, vacuum packaged and stored at 1 C for 5 d to give a total aging period of 6 d. After aging, a steak of 35 mm thickness was cut into three equal size pieces which were placed in 0.9% saline and cooked in a 80 C water bath to an internal temperature of 72 C, then immersed immediately in ice water for min, to arrest the cooking process. The pieces were stored overnight at 4 C. Cores of 19 mm diameter were removed from each piece using a cork borer, and then sheared in a Warner Bratzler shear cell attached to an Instron Model 4301 Materials Testing System (Instron, Canton, Massachusetts 02021) with a 1 kn load cell, and crosshead speed of 50 mm min 1. Maximum shear force was averaged over the three cores from each steak. Packaging Treatments and Storage The LT muscle was removed from the rib area (6 12th rib) of both sides of each carcass after 24 h of postmortem aging at 1 C. Muscles from alternate, paired sides were assigned to one of two packaging treatments: vacuum or CO 2. Rib-eye muscles to be vacuum packaged were placed in barrier bags with an oxygen transmission rate of cc m 2 24 h 1 (Winpak Ltd., Winnipeg, MB), evacuated and sealed using a Multivac. Rib-eye muscles to be packaged in a controlled CO 2 atmosphere were placed in an oxygen impermeable foil laminate in an atmosphere containing 2.5 L of CO 2 kg 1 of meat and packaged using a Captron III system as previously described (Greer et al. 1993). Under these conditions residual oxygen levels were <300 ppm. Packaged rib-eye muscles were stored at 2 C and examined at 0, 3, 6, 9 and 11 wk. Retail Display After each 2 to 3 wk interval of vacuum storage, 4 LT muscles per packaging treatment per feed treatment were cut into rib-eye steaks then randomized within treatment. Steaks were over-wrapped with an oxygen permeable polyvinyl chloride film (Vitafilm Choice Wrap, Goodyear Canada Inc., Toronto, ON) with an oxygen transmission rate of 8000 cc m 2 24 h 1. Retail packages were placed in a fan-circulated, horizontal type retail case illuminated 12 h d 1 with incandescent lighting that gave an intensity of 750 lx at the steak surface. The average surface temperature of steaks during retail display was 5.6 C. A detailed description of this retail environment has been published (Greer and Jeremiah 1980). Sensory Evaluation and Case Life LT and steak discolouration and retail acceptance were evaluated after each storage or display interval by an experienced 5-member sensory panel. The subjective, hedonic scales were: discolouration (1 = no surface discolouration; 7 = complete surface discolouration); retail appearance (1 = extremely undesirable; 7 = extremely desirable). Retail case life was quantified by assuming that rejection would occur at the times in days that scores for retail appearance declined to 3.5 on the subjective scale (Greer et al. 1993). At each evaluation time 4 LT muscles feed treatment 1 packaging treatment 1 were assessed and 8 rib-eye steaks feed treatment 1 packaging treatment 1 were evaluated at each display interval. The same samples were also examined for bacterial numbers as described below. Bacteriology Samples for bacteriological analysis were obtained by excising 10 cm 2 of surface tissue from LT muscles or steaks. The LT muscles were sampled at the anterior and posterior ends and the lateral surfaces. Steaks were sampled at a single location only. Following appropriate dilution samples were surface plated on MRS agar (Difco Laboratories, Detroit, MI, USA) to determine total anaerobes and on Plate Count Agar (Difco) to determine total aerobes (Greer and Jones 1991). Colour and Metmyoglobin Estimates Eight rib-eye steaks per treatment were cut from random locations from the LT, over-wrapped in O 2 -permeable film and stored in a retail display case for 12 d. On day 0 and each successive day, 3 measurements were made across the surface of each steak, and averaged, using a MacBeth Model spectrophotometer (Prism Instruments, Whitbey, ON) to obtain reflectance values at 20-nm intervals between 360 and 740 nm, as well as CIE (1976) L*, a*, b* values. Reflectance values (R) at 474, 525, 572 and 610 nm were obtained by linear interpolation and K/S values were calculated for each wavelength. K/S = (1 R) 2 /2R, with R expressed as a decimal. K/S values were determined similarly for 100% MMb, by immersing steaks in 1.0% potassium ferricyanide for 1 min, packaging in O 2 -permeable film and storage at 1 C for 16 h. For deoxymyoglobin, steaks were placed in 10% sodium hydrosulfite for 2 min, vacuum packaged for 1.5 h at 20 C, repackaged in O 2 -permeable film and scanned immediately. Methods for meat colour evaluation were according to AMSA guidelines (Hunt et al. 1991). Estimation of the relative concentration of MMb was calculated as follows:

4 60 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 1. The effect of vitamin E and vacuum storage time on the a* values of beef rib-eye steaks during retail display. Beef LT muscles were stored for 0 (1a), 3 (1b), 6 (1c), 9 (1d) or 11 wk (1e) in vacuum at 2 C before the fabrication of retail steaks. Data are the means of eight steaks treatment 1.

5 GREER ET AL. VITAMIN E AND BEEF STORAGE IN CONTROLLED ATMOSPHERES 61 %MMb = (K/S 572 K/S 525 for 100% DMb) (K/S 572 K/S 525 for sample) (K/S 572 K/S 525 for 100% DMb) (K/S 572 K/S 525 for 100% MMb) 100 Muscle -Tocopherol Concentrations Tissue levels of α-tocopherol were determined using high performance liquid chromatography according to the methods described by Asghar et al. (1991). Analyses were performed on 10-g samples of m. sternomandibularis obtained 24 h post-slaughter (trial 1 and trial 2) and 10-g samples of LT muscle after various intervals of storage in modified atmospheres at 2 C (one trial only). A reverse phase novapak C18 column with 100% methanol (mobile phase) was used to isolate the α-tocopherol with UV detection at 280 nm. The α-tocopherol content of the m. sternomandibularis was determined to reflect carcass α-tocopherol at 24 h postmortem while that of the LT muscle was determined to assess stability during storage in vacuum or CO 2. Statistical Analyses All data were analyzed using the GLM (General Linear Model) procedure of the SAS Institute, Inc. (1985). For carcass and meat quality traits, data were analyzed using a oneway analysis of variance with feed treatment as the main effect. Within each packaging treatment, bacterial numbers, a* values, percent MMb and case life were analyzed using a two-way analysis of variance with feed treatment and retail display time as the main effects. Means were separated with linear contrasts with a single degree of freedom (P 0.05). RESULTS Carcass and Meat Quality Supplementation with vitamin E increased (P < ) the α-tocopherol content (m. sternomandibularis) from 2.89 µg g 1 (range was 1.27 to 4.05 µg g 1 ) in control carcasses to 5.18 µg g 1 (range was 2.65 to 8.67) in carcasses from animals fed vitamin E (Table 1). Feeding treatment had no effect (P > 0.05) upon performance, carcass characteristics or standard meat quality attributes. There was a trend (P = ) for the 1.30 kg reduction in shear value of the vitamin E treatment group to be different than the control group. Effect of Extended Storage (a) LT-α-TOCOPHEROL. There was no consistent change (P > 0.05) in α-tocopherol with storage time and similar levels of α-tocopherol were found in the muscle after 11 wk of storage at 2 C for either the feed or atmosphere treatments. The amount of α-tocopherol in the LT muscles from vitamin E fed animals was always greater than that of the control group. During storage in CO 2, the α-tocopherol concentration ranged from 1.32 to 2.72 µg g 1 in the control muscles and 3.27 to 4.98 µg g 1 in the muscles from the vitamin E fed animals. During storage in vacuum, the α-tocopherol concentration ranged from 1.84 to 2.91 µg g 1 in the control muscles and from 3.42 to 5.17 µg g 1 in the muscles from vitamin E fed animals. (b) BACTERIAL GROWTH ON LT MUSCLE. Irrespective of feeding treatment (vitamin E vs. Control) or storage atmosphere (vacuum vs. CO 2 ), anaerobic bacteria grew at a similar rate (P > 0.05) during 11 wk of LT storage at 2 C (data not shown). (c) SUBJECTIVE DISCOLOURATION OF LT MUSCLE. During storage in vacuum or CO 2 the rate of discolouration of the LT muscle surface was usually unaffected by vitamin E treatment (P > 0.05). However, there was a more rapid discolouration of LT muscles stored in vacuum when compared with those in the CO 2 atmosphere. The difference was statistically significant (P < 0.05) after 9 and 11 wk of storage at 2 C. On the basis of appearance, CO 2 -stored LT muscles remained acceptable to the sensory panel for the duration of the storage interval (11 wk) while vacuum packaged LT muscles had deteriorated to the point of rejection within 7 to 8 wk. There were no apparent differences in the colour of LT muscles when control and vitamin E treatments were compared (data not shown). Retail Display In general, dietary supplementation with vitamin E had no consistent effects on the growth of aerobic bacteria on retail rib-eye steaks following any period of storage of the intact LT muscle (P > 0.05, data not shown). However, bacterial numbers increased with time of storage in CO 2 or vacuum and with time on retail display. This was evident for both packaging treatments (CO 2 vs. vacuum) and feeding treatments (control vs. vitamin E). In addition, there was a trend (P < 0.05) for higher numbers of bacteria from displayed steaks cut from LT muscles stored in vacuum than CO 2. This was most evident in the first 6 wk of storage in trial 1, where some statistically significant differences were determined (P < 0.05). The effects of vitamin E and packaging treatment on the appearance case life of rib-eye steaks are compared for up to 11 wk of storage in vacuum or CO 2 (Table 2). Prior to storage in modified atmosphere, the colour case life of rib-eye steaks was longer for steaks cut from LT muscles from vitamin E supplemented steers. However, the magnitude of this difference was only significant for muscle assigned to the vacuum packaging treatment (P < 0.05) where vitamin E extended case life by more than 3 d. Since these differences were not determined prior to packaging, they could not be ascribed to vacuum or CO 2 treatment effects. For all treatments, steak colour case life deteriorated progressively with LT muscle storage. Generally, the case life of rib-eye steaks was longer for LT storage in CO 2 than in vacuum. During extended storage, the only significant (P < 0.001) increase in retail case life that could be attributed to dietary vitamin E was following 6 and 9 wk of storage in CO 2. At these times, a 2 to 3 d increase in rib-eye case life was related to the vitamin E treatment (Table 2). a* Values The a* values are compared during the retail display of ribeye steaks from LT muscles derived from animals fed the control diet or the diet supplemented with vitamin E and

6 62 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 2. The effect of vitamin E and CO 2 storage time on the a* values of beef rib-eye steaks during retail display. Beef LT muscles were stored for 0 (2a), 3 (2b), 6 (2c), 9 (2d) or 11 wk (2e) in 100% CO 2 at 2 C before the fabrication of retail steaks. Data are the means of eight steaks treatment 1.

7 GREER ET AL. VITAMIN E AND BEEF STORAGE IN CONTROLLED ATMOSPHERES 63 Fig. 3. The effect of vitamin E and vacuum storage time on the percentage of metmyoglobin in rib-eye steaks during retail display. Beef LT muscles were stored for 0 (3a), 3 (3b), 6 (3c), 9 (3d) or 11 wk (3e) in vacuum at 2 C before the fabrication of retail steaks. Data are the means of eight steaks treatment 1.

8 64 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 4. The effect of vitamin E and CO 2 storage time on the percentage of metmyoglobin in rib-eye steaks during retail display. Beef LT muscles were stored for 0 (4a), 3 (4b), 6 (4c), 9 (4d) or 11 wk (4e) in 100% CO 2 at 2 C before the fabrication of retail steaks. Data are the means of eight steaks treatment 1.

9 GREER ET AL. VITAMIN E AND BEEF STORAGE IN CONTROLLED ATMOSPHERES 65 following periods of storage in vacuum (Fig. 1) or CO 2 (Fig. 2). During the retail display of rib-eye steaks following any period of vacuum or CO 2 storage the a* values decreased with time on display for either feeding treatment. The reduction in a* values tended to be delayed in steaks from animals fed dietary vitamin E and a* values were generally higher than control steaks at all retail display times (except at the 3 wk storage interval). For steaks derived from vacuum packaged LT muscles (Fig. 1) the difference in a* values was significant after all vacuum storage intervals (P < 0.05). There were a significant retail display time effect (P < 0.05) and consistent display time treatment interactions (P < 0.05), since the magnitudes of treatment effects were not similar on each display day. In a similar fashion, a* values tended to be higher (P < 0.05) during the retail display of vitamin E steaks from the CO 2 packaging treatment than those of steaks from animals fed control diets (Fig. 2). The magnitude of these differences was most pronounced after 6 and 9 wk of storage in CO 2 and larger than differences observed with meat derived from vacuum packaged product at the same storage interval. As observed following vacuum storage, significant display time (P < 0.05) and display time treatment effects (P < 0.05) were determined. Although not shown, vitamin E treatment was also found to limit the increase in hue angle. Percent Metmyoglobin The accumulation of metmyoglobin is compared during the retail display of rib-eye steaks from LT muscles derived from animals fed the control diet with the diet supplemented with vitamin E and following periods of storage in vacuum (Fig. 3) or CO 2 (Fig. 4). During the retail display of rib-eye steaks following any period of vacuum or CO 2 storage, the percent metmyoglobin increased with display time for either feeding treatment (P < 0.05). However, the magnitude and rate of metmyoglobin accumulation was less in steaks from animals fed dietary vitamin E at most storage times. For steaks derived from vacuum packaged LT muscles (Fig. 3) the differences in percent metmyoglobin were significant at 0, 6 and 11 wk only (P < 0.05). Significant display time treatment effects (P < 0.05) were attributable to differences in the magnitude of treatment effects on each day. In a similar fashion, percent metmyoglobin measured at the steak surface was lower (P < 0.05) during the retail display of vitamin E steaks from the CO 2 packaging treatment than that found on steaks from animals fed control diets (Fig. 4). Differences were significant (P > 0.05) after 0, 3, 6 and 9 wk but not 11 wk of LT storage in CO 2. The extent of these differences was greatest after 6 and 9 wk of CO 2 storage. As described above, significant display time treatment interactions (P < 0.05) were attributable to variation in the extent of the differences on each display day. There were unexpected large differences in the percent metmyoglobin after 5 d of retail display in the steaks derived from vacuum packaged LT muscle (Fig. 3c). Thus, the rates of accumulation of metmyoglobin were similar for vitamin E and control treatments for up to 4 d of display after which metmyoglobin accumulation ceased or actually decreased in the vitamin E treatment after reaching a level of about 50%. However, the panel had already rejected the meat on the basis of appearance after 2 to 3 d so this unexplained result had no impact upon storage life. DISCUSSION The data reported herein support the body of published evidence that dietary vitamin E can increase tissue levels of α- tocopherol and stabilize pigments without detrimental effects on performance, carcass and meat quality traits and bacteriology (Arnold et al. 1993b; Smith et al. 1994; Chan et al. 1996). Data from the present study suggest that dietary vitamin E can be utilized in conjunction with controlled atmosphere packaging to improve the colour of retail ribeye steaks after 6 and 9 wk of subprimal storage in 100% CO 2. This suggestion is substantiated by increased a* values, reduced metmyoglobin formation and a 2- to 3-d increase in retail case life as assessed by the subjective panel evaluation of the acceptability of lean colour. Vitamin E and controlled CO 2 packaging appeared to act synergestically. Thus, colour stability and storage life for steaks derived from vitamin E supplemented cattle was generally improved after LT storage in CO 2 in comparison with vacuum storage. Indeed, with LT vacuum storage for any storage interval from 3 to 11 wk at 2 C, vitamin E supplementation was not found to improve the retail case life of cut steaks in comparison to those derived from animals fed the control diets. The a* colour coordinates (green to red) have been highly correlated with panel assessment of discolouration (Chan et al. 1995) in trials with dietary vitamin E. In the present study, increased colour case life attributable to vitamin E had no effect on the microbial condition (Chan et al. 1996). It has also been well documented that supplemental vitamin E delays metmyoglobin accumulation during the display of a number of beef cuts following limited periods of storage (1 to 3 wk) in vacuum (Faustman et al. 1989b; Arnold et al. 1993b; Mitsumoto et al. 1994). Comparable results have also been observed during the retail display of beef cuts stored in modified atmospheres (70% 0 2, 30% CO 2 ) preceded by 7 and 21 d of vacuum storage (Taylor et al. 1994). Extended colour display life for beef derived from vitamin E supplemented cattle has been confirmed (Smith et al. 1994; Sherbeck et al. 1995). In addition, Arnold and associates (1993b) determined an increase in display life of 2 to 3 d for beef derived from vitamin E supplemented cattle after both 7 and 21 d of aging in vacuum. There are no known studies where subprimal cuts have been stored for periods of time in 100% CO 2 comparable to that of the current work (i.e. 11 wk). However, Garber et al. (1996) concluded that supplementation with vitamin E did not limit metmyoglobin or lipid oxidation in beef gluteus medius after 92 d of vacuum storage and subsequent retail display. An important aspect of the present investigation was the inherent variability in carcass and tissue α-tocopherol content. Under the experimental condition described herein,

10 66 CANADIAN JOURNAL OF ANIMAL SCIENCE dietary vitamin E supplementation of feedlot steers (1000 IU d 1 for 100 d) produced about a 70 90% increase in the α-tocopherol content of the carcass as determined in the neck muscle (m. sternomandibularis) at 24 h post-mortem. However, tissue levels of α-tocopherol in vitamin E fed cattle were exceedingly variable and ranged from 2.65 to 8.87 µg g 1 of muscle depending on the animal examined. Although other researchers have reported increases of a similar magnitude in the tissue concentration of α-tocopherol following dietary supplementation with vitamin E (Faustman et al. 1989b; Arnold et al. 1993a,b), this level of variability among experimental animals has not often been noted. Allen et al. (1996) did attribute a lack of treatment effects to α- tocopherol variability in modified atmosphere packaged beef. It is conceivable that variation could be attributable to differences in vitamin E intake which appears to be difficult to control (Arnold et al. 1993a) or inherent animal variation in the metabolism of vitamin E. Also, differences in the design of feed treatments (premix vs. top dressing; individual vs. pen feeding) would have an impact. In the current study, vitamin E was fed as a top dressing and observation confirmed that some animals within a pen were more aggressive feeders than others. This work was not designed to relate the animal-to-animal variation in α-tocopherol to the resultant variability in a* values, percent metmyoglobin or case life. The limited sampling that was reported was undertaken only to assess the stability of α-tocopherol in LT muscles during extended storage in vacuum or carbon dioxide. The α-tocopherol content in the LT muscle of vitamin E treated cattle ranged from 3.42 to 5.17 µg g 1 during storage for up to 11 wk and there were no significant changes with storage time. Chan et al. (1996) reported that a threshold concentration of α-tocopherol of 4 µg g 1 was necessary for a maximum reduction in metmyoglobin concentration. The α-tocopherol levels of some of the meat used in the current study were below this threshold. This could explain why dietary vitamin E was found to extend the case life of rib-eye steaks after 6 and 9 wk of LT storage but not after 3 wk of LT storage. It could also account for the wide variation in case life prior to storage. In summary, the present findings may have important implications for the export of beef to remote markets where colour stability is a concern. A major concern is the extreme variation in carcass and muscle α-tocopherol following vitamin E supplementation. Future studies should be designed to further evaluate dosing strategies to ensure that under practicable conditions in commercial feedlots all animals have sufficient intake of vitamin E to consistently assure colour stability. ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support of Hoffmann-LaRoche Ltd. and the Agriculture and Agri-Food Canada s Matching Investment Initiative program. The technical assistance of R. Dyck, S. Landry, D. Tonkin, J. Colyn and P. LePage was greatly appreciated. The clerical assistance of L. Verquin is also gratefully acknowledged. Allen, P., Doherty, A. M., Buckley, D. J., Kerry, J., O Grady, M. N. and Monahan, F. J Effect of oxygen scavengers and vitamin E supplementation on colour stability of MAP beef. Proc. 42 Int. Cong. Meat Sci. Technol. pp Arnold, R. N., Arp, S. C., Scheller, K. K., Williams, S. N. and Schaefer, D. M. 1993a. Tissue equilibration and subcellular distribution of vitamin E relative to myoglobin and lipid oxidation in displayed beef. J. Anim. Sci. 71: Arnold, R. N., Scheller, K. K., Arp, S. C., Williams, S. N. and Schaefer, D. M. 1993b. Dietary alpha-tocopherol acetate enhances beef quality in Holstein and beef breed steers. J. Food Sci. 58: Asghar, A., Gray, J. I., Booren, A. M., Gomaa, E. A., Abourzied, M. M. and Miller, E. R Effect of supranutritional dietary vitamin E levels on subcellular deposition of alphatocopherol in the muscle and on pork quality. J. Sci. Food Agric. 57: Chan, W. K. M., Hakkarainen, K., Faustman, C., Schaefer, D. M. and Scheller, K. K Effect of dietary vitamin E on microbial growth and discoloration of beef. Proc. 40th Int. Cong. Meat Sci. Technol. S-IVA.45. Chan, W. K. M., Hakkarainen, K., Faustman, C., Schaefer, D. M., Scheller, K. K. and Liu, Q Color stability and microbial growth relationships in beef as affected by endogenous α-tocopherol. J. Food Sci. 60: Chan, W. K. M., Hakkarainen, K., Faustman, C., Schaefer, D. M., Scheller, K. K. and Liu, Q Dietary vitamin E effect on color stability and sensory assessment of spoilage in three beef muscles. Meat Sci. 42: Faustman, C., Cassens, R. G., Schaefer, D. M., Buege, D. R. and Scheller, K. K. 1989a. Vitamin E supplementation of Holstein steer diets improves sirloin steak color. J. Food Sci. 54: Faustman, C., Cassens, R. G., Schaefer, D. M., Buege, D. R. and Scheller, K. K. 1989b. Improvement of pigment and lipid stability in Holstein steer beef by dietary supplementation with vitamin E. J. Food Sci. 54: Garber, M. J., Roedes, R. A., Davidson, P. M., Pumfrey, W. M. and Schelling, G. T Dose-response effects of vitamin E supplementation on growth performance and meat characteristics in beef and dairy steers. Can. J. Anim. Sci. 76: Gill, C. O Packaging meat for prolonged chilled storage: the Captech process. Br. Food J. 91: Gill, C. O. and McGinnis, J. C The effects of residual oxygen concentration and temperature on the degradation of the colour of beef packaged under oxygen-depleted atmospheres. Meat Sci. 39: Gill, C. O. and Molin, G Modified atmospheres and vacuum packaging. Pages in J. J. Russell and G. W. Gould, ed. Food preservatives. Blackie and Son Ltd., Glasgow, UK. Greer, G. G. and Jeremiah, L. E Influence of retail display temperature on psychrotrophic bacterial growth and beef case life. J. Food Prot. 34: Greer, G. G. and Jones, S. D. M Effects of lactic acid and vacuum packaging on beef processed in a research abattoir. Can. Inst. Food Sci. Technol. J. 24: Greer, G. G., Dilts, B. D. and Jeremiah, L. E Bacteriology and retail case life of pork after storage in carbon dioxide. J. Food Prot. 56: Hunt, M. C., Acton, J. C., Benedict, R. C., Calkins, C. R., Cornforth, D. P., Jeremiah, L. E., Olson, D. G., Salm, C. P., Savell, J. W. and Shivas, S. D Guidelines for meat color evaluation. American Meat Science Association Committee on Guidelines for Meat Color Evaluation. Jones, S. D. M. and Robertson, W. M The effects of spray-chilling carcasses on the shrinkage and quality of beef. Meat

11 GREER ET AL. VITAMIN E AND BEEF STORAGE IN CONTROLLED ATMOSPHERES 67 Sci. 24: Lanari, M. C., Cassens, R. G., Schaefer, D. M. and Scheller, K. K Effect of dietary vitamin E on pigment and lipid stability of frozen beef: A kinetic analysis. Meat Sci. 38: Lavelle, C. L., Hunt, M. C. and Kropf, D. H Display life and internal cooked color of ground beef from vitamin E supplemented steers. J. Food Sci. 60: Mitsumoto, M., Arnold, R. N., Schaeffer, D. M. and Cassens, R. G Improvement of pigment and lipid stability in ground and sliced beef longissimus with dietary vitamin E supplementation. 40th Int. Cong. Meat Sci. Technol. S-IVA.46. Morgan, J. B., Saunders, S., Gerken, C., Sherbeck, J. and Smith, G. C Vitamin E supplementation: Effects on fresh beef shelf life. Meat Focus Internat. 2: Nesom-Fleet, S. K., Greer, G. G., Jeremiah, L. E. and Wolfe, F. H The bacteriology and case-life of retail-ready beef after extended storage in carbon dioxide. Proc. 39th Int. Cong. Meat Sci. Technol. S8P13.WP. SAS Institute, Inc SAS user s guide: Statistics. SAS Institute, Cary, NC. Sherbeck, J. A., Wulf, D. M., Morgan, J. B., Tatum, J. D., Smith, G. C. and Williams, S. N Dietary supplementation of vitamin E to feedlot cattle affects beef retail display properties. J. Food Sci. 60: Shorland, F. B., Igene, J. O., Pearson, A. M., Thomas, J. W., McGuffey, R. K. and Aldridge, A. E Effects of dietary fat and vitamin E on the lipid composition and stability of veal during frozen storage. J. Agric. Food Chem. 29: Smith, G. C., Morgan, J. B., Sofos, J. N., Tatum, J. D. and Schmidt, G. R Quality and shelf-life of beef from animals fed supplemental vitamin E. Proc. 40th Int. Cong. Meat Sci. Technol. S-IVA.43. Taylor, A. A., Vega, L., Wood, J. D. and Angold, M Extending colour life of MA packed beef by supplementing feed with vitamin E. Proc. 40th Int. Cong. Meat Sci. Technol. S-IVA.44 Wulf, D. M., Morgan, J. B., Sanders, S. K., Tatum, J. D., Smith, G. C. and Williams, S Effects of dietary supplementation of vitamin E on storage and case life properties of lamb retail cuts. J. Anim. Sci. 73: