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1 PROCESSING AND PRODUCTS Effects of Dietary Vitamin E Supplementation on Lipid Oxidation and Volatiles Content of Irradiated, Cooked Turkey Meat Patties with Different Packaging 1 D. U. AHN,2 J. L. SELL, C. JO, X. CHEN, C. WU, and J. I. LEE Animal Science Department, Iowa State University, Ames, Iowa ABSTRACT A study was conducted to determine the effects of dietary vitamin E supplementation on the storage stability and volatiles production in irradiated cooked turkey meat. Turkeys, raised with diets containing 25, 50, 75, or 100 IU of dl-a-tocopheryl acetate (TA)/ kg diet from 1 to 105 d of age, were fed with diets containing 25, 200, 400, or 600 IU of TA/kg diet from 105 to 122 d of age. Breast and leg meat patties were prepared, irradiated at 0 or 2.5 kgy dose, cooked to an internal temperature of 78 C, and stored in either vacuum or aerobic packaging. Thiobarbituric acid reactive substance (TBARS) values gradually decreased as the dietary TA increased and > 200 IU TA/kg diet treatments were helpful in maintaining low TBARS values in irradiated breast and leg meat patties during the 7-d storage period. With vacuumpackaging, irradiated cooked breast patties developed more oxidation than nonirradiated patties but the prooxidant effect of irradiation in cooked leg meat patties was not consistent. In aerobic-packaged cooked meat, irradiated patties had lower TBARS than nonirradiated patties in both breast and leg meat stored in oxygen permeable bags for 7 d. Propanal, pentanal, hexanal, 1-pentanol, and total volatiles were highly correlated with the TBARS values of meat. However, hexanal represented the lipid oxidation status of cooked meat better than any other volatiles component. The amount of hexanal and total volatiles in cooked breast and leg meat shows decreasing trends as dietary TA increased. In vacuum packaging, irradiated breast and leg meat had higher hexanal and total volatiles content than nonirradiated meat at both 0 and 7 d of storage. In aerobic packaging, the amount of hexanal and total volatiles greatly increased in both irradiated and nonirradiated meat patties during the 7-d storage periods. The results illustrated that the antioxidant effect of TA was not strong enough to control lipid oxidation and off-odor generation in cooked meat stored under aerobic conditions because the progress of lipid oxidation in cooked meat under aerobic condition is very rapid. However, the combination of dietary TA and vacuum packaging of cooked meat immediately after cooking could be a good strategy to minimize oxidation and volatiles production in cooked meat. (Key words: dietary vitamin E, turkey meat, irradiation, volatiles, lipid oxidation) 1998 Poultry Science 77: INTRODUCTION Vitamin E is one of the major antioxidants present in the cell membranes. Vitamin E protects membrane fatty acids and cholesterol from peroxidative damages caused by the reactive free radicals (Buckley et al., 1995; Liu et al., 1995). Free radicals generated by irradiation can destroy antioxidants in muscle, as well as reduce the storage stability and increase off-flavor production in meat (Thayer et al., 1993; Lakritz et al., 1995). Dietary Received for publication May 27, Accepted for publication January 12, Journal Paper Number J of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project Number 2794, and supported by Hoffmann-LaRoach, and the Hatch Act. 2 To whom correspondence should be addressed: duahn@iastate.edu supplementation of tocopheryl acetate has been shown to increase vitamin E in muscle tissues, and the antioxidant effect of the increased vitamin E in raw meat during storage is well documented (Wen et al., 1996; Sheldon et al., 1997). Irradiation is considered to be the most effective technology that can eliminate pathogenic bacteria in raw meat (Gants, 1996). Irradiation is allowed by Food and Drug Administration at 1.5 to 3 kgy to control pathogenic microorganisms such as Salmonella, Escherichia coli and Listeria in poultry meat and the irradiated poultry meats are available in certain supermarkets. In a review article, Brynjolfsson (1985) con- Abbreviation Key: MDA = malonaldehyde; TA = dl-a-tocopheryl acetate; TBARS = thiobarbituric acid reactive substance. 912

2 DIETARY VITAMIN E ON OXIDATION AND VOLATILES OF COOKED TURKEY 913 cluded that irradiating foods with doses up to the sterilizing doses of 56 kgy does not introduce harmful effects. One of the major concerns in irradiating meat, however, is its effect on meat quality, mainly related to the free radicals reaction and off-odor generated by irradiation. Irradiation could produce a large amount of hydroxyl radical in meat because over 75% of muscle cells are composed of water (Thakur and Singh, 1994). Lipid radicals will be formed via the free radical reactions, and lipid hydroperoxides will be formed when oxygen is available. Reineccius (1979) suggested that carbonyl compounds are important for irradiation odor and the intensity of irradiation odor is dependent upon oxygen content during irradiation. Al-Kahtani et al. (1996) and Hampson et al. (1996) reported that gamma irradiation at 1.5 to 10 kgy dosages increased thiobarbituric acid values in turkey breast and fish muscles. Irradiation-induced oxidative chemical changes are dose dependent, and the presence of oxygen has a significant effect on the rate of oxidation (Katusin- Razem et al., 1992; Thayer et al., 1993). Lynch et al. (1991) reported that irradiated turkey breast fillet produced a set of unpleasant odor notes when stored in oxygen-impermeable film and were different from those developed from corresponding nonirradiated samples. Heath et al. (1990) and Hashim et al. (1995) also showed that irradiating uncooked chicken meat produced a characteristic bloody and sweet aroma that remained after the meat was cooked. Merritt (1966) suggested that the volatile compounds responsible for the off-odor in irradiated meat are produced by the radiation impact on the protein and lipid molecules and are different from those of lipid oxidation. Patterson and Stevenson (1995) showed that dimethyltrisulfide is the most potent off-odor compound in irradiated raw chicken meat. However, Shahidi et al. (1991) reported that irradiation had no detrimental effect on the flavor of vacuum-packaged raw meat and cured meat, and Shamsuzzaman et al. (1992) showed that electron beam treatment had little effect on the odor and flavor of the reheated meat with sous-vide treatment. At present, however, little information is available on the nature and off-odor generation mechanisms in irradiated meat, especially at low-dose irradiation (< 10 kgy). The antioxidant effect of tocopherol is not strong enough to control lipid oxidation in cooked meat during storage (Ajuyah et al., 1993; Ahn et al., 1995; Winne and Dirinck, 1996); however, it may play an important role in the final quality of cooked meat products. The initial oxidation status of cooked meat is determined by the degree of lipid oxidation in raw meat before cooking. Also, the progress of lipid oxidation in cooked meat during storage would also be highly dependent on the 3Thomson CSF Linac, Cedex, Saint-Aubin, France. 4Burker Instruments, Inc., EPR division, Bellerica, MA Burker Analytische Messtechnik, Silberstreifen, Germany. 6Koch, Kansas City, MO amount of primary lipid oxidation products in raw meat. Therefore, increased vitamin E in tissues by the dietary supplementation may protect raw meat from oxidation during and after irradiation, and the low lipid oxidation conditions can be maintained when combined with proper packaging methods after cooking. The objective of this study was to determine the effects of dietary vitamin E supplementation on 1) the storage stability of irradiated cooked turkey meat with different packaging, and 2) volatiles development in irradiated cooked turkey meat during storage. MATERIALS AND METHODS Dietary Treatments and Sample Preparations Male Large White turkeys were fed diets containing 25, 50, 75, or 100 IU of dl-a-tocopheryl acetate (TA)/kg from 1 to 105 d of age. At 105 d, two pens of turkeys previously fed 25, 50, 75, or 100 IU of TA were randomly assigned diets containing 200, 400, or 600 IU of TA/kg diet to increase tissue vitamin E content in the short term. Each of the 200, 400, and 600 IU TA treatments was fed to eight pens of poults, eight poults per pen, from 105 to 122 d of age. Turkeys fed 25 IU of TA/kg diet from 1 to 122 d were used as a control. At the end of the trial, 2 birds per pen and the 8t turkeys on the 25 IU diet (a total of 56 birds) were selected and slaughtered following USDA guidelines (USDA, 1982). Carcasses were chilled in ice water for 3 h and then drained in a cold room. Breast and leg muscles were deboned from the carcasses 24 h after slaughter. Skin and visible fat were removed from the breast and leg meat, and the meat was ground twice through a 3-mm plate. Breast and leg meats from two birds from the same pen were pooled and used as a replication. Twelve breast and 12 leg meat patties (approximately 100 g each) were prepared from each of the pooled ground breast and pooled leg meats representing each pen. The breast and leg meat patties were put on laminated foam trays and wrapped with oxygen permeable plastic film and irradiated with accelerated electrons to a average dose of 0- or 2.5-kGy (127 kgy/min) by using a Linear Accelerator3 (Model Circe IIIR). Dosimeters4 (Alanine) were placed on surface and base of patties being irradiated, and the dosimeters were read using an Electroparamagnetic Resonance5 (EMS-104). The temperatures of the meat were kept at 2-4 C during irradiation and after irradiation. Twenty-four hours after irradiation, the patties were cooked in an electric oven (300 C) to an internal temperature of 78 C, chilled for 3 h at 4 C, and then packaged. Half of the cooked meats was vacuumpackaged in oxygen-impermeable nylon/polyethylene bags6 (O 2 permeability, 9.3 ml O 2 /m2/24 h at 0 C), and the other half was aerobic-packaged in oxygen-permeable bags. The patties were stored in a refrigerator for 7 d. The thiobarbituric acid reactive substances (TBARS) values of

3 914 cooked meat were measured at 0, 3, and 7 d, and volatiles were measured at 0 and 7 d of storage at 4 C. Zero-day samples were analyzed 3 h after cooking. Lipid Oxidation Lipid peroxidation of cooked turkey meat was determined by the modified method of Buege and Aust (1978). A 5-g meat sample was placed in a 50-mL test tube and homogenized with 15 ml of deionized distilled water by using a Brinkman Polytron (Type PT 10/35)7 for 15 s at speed 7 to 8. Meat homogenate (1 ml) was transferred to a disposable test tube ( mm) and butylated hydroxyanisole (50 ml, 7.2%) and 2 ml of a solution of 20 mm thiobarbituric acid/15% trichloroacetic acid were added. The mixture was vortexed and then incubated in a boiling water bath for 15 min to develop color. After color development, the samples were cooled in cold water for 10 min and then centrifuged for 15 min at 2,000 g. The absorbance of the resulting supernatant solution was determined at 531 nm against a blank containing 1 ml double distilled water and 2 ml thiobarbituric acid/ trichloroacetic acid solution. The TBARS numbers were expressed as milligrams malonaldehyde (MDA) per kilogram of meat. Volatiles Analysis A purge-and-trap apparatus connected to a gas chromatograph was used to quantify and characterize the volatiles potentially responsible for the off-odor in irradiated meat. Tekmar Precept II and Purge-and-Trap Concentrator were used to purge and trap volatiles from the samples. A Hewlett Packard gas chromatograph (Model 6890)9 equipped with flame ionization detector was used to analyze volatiles. In preparation for volatiles analysis, minced cooked meat (2 g) was weighed into a sample vial (40 ml), an oxygen absorber (Ageless type ZPT-30)10 was added, and the vial was capped tightly with a Teflon-lined open-mouth cap and was placed in a refrigerated (3 C) sample tray. The sample was purged by using a auto sampling unit (Precept II) equipped with a robotic arm. The sample was heated to 32 C and then purged with helium gas (40 ml/min) for 11 min. Volatiles were trapped by using a Tenax/Silica gel/charcoal column,8 and desorbed for 2 min at 220 C. A split inlet (split ratio, 29:1) was used to inject volatiles into a gas chromatograph column (DB-Wax capillary column, mm i.d., 30 m, and 1 mm film thickness), and ramped oven temperature conditions (32 C for 0.5 min, increased to 40 C at 40 C/min, increased to 100 C at 7Brinkman Instruments Inc., Westbury, NY Tekmar-Dohrmann, Cincinnati, OH Hewlett Packard Co., Wilmington, DE Mitsubishi Gas Chemical America, Inc., New York, NY J & W Scientific, Folsom, CA Chromatography Research Supplies, Inc., Addison, IL AHN ET AL. 30 C/min, increased to 180 C at 20 C/min, and held for 1 min) were used. Inlet temperature was 180 C, and detector temperature was 220 C. Helium was used as a carrier gas and column flow was 5.8 ml/min. Detector air, hydrogen, and make-up gas (helium) flows were set at 30, 30, and 28 ml/min, respectively. Individual peaks were identified by the retention time of volatile standards. Standard kits (aldehyde-ketones, alcohols, hydrocarbons, and alkenes C6 C10) were purchased from Chromatography Research Supplies,12 and a total of 44 standards (9 aldehydes, 11 alcohols, 8 ketones, and 16 hydrocarbons) were used to identify peaks in meat volatiles. The area of each peak was integrated by using ChemStation software,9 and the total peak area (pa*sec) was reported as an indicator of volatiles generated from the meat samples. Statistical Analysis The experiment was designed primarily to determine the effect of high level dietary vitamin E (> 200 IU TA/kg of diet) on the lipid peroxidation and off-odor production of irradiated cooked turkey breast and leg meat stored in packaging film with different oxygen permeability (oxygen-permeable or oxygen-impermeable wrap). Breast and leg meat data were analyzed independently by SAS software (SAS Institute, 1989). Analyses of variance were conducted to test dietary TA effect within irradiation and storage time, irradiation effect within storage time and dietary TA, and storage effect within dietary TA and irradiation. The Student-Newman-Keuls multiple range test was used to compare differences among mean values. Mean values and SEM were reported. RESULTS AND DISCUSSION TBARS Values of Cooked Meat In nonirradiated breast, TBARS values of vacuumpackaged cooked breast meat patties gradually decreased as the dietary TA increased at all storage times (Table 1). High level dietary TA (> 200 IU TA/kg of diet) treatments were also effective in maintaining low TBARS in irradiated breast during storage. However, the difference between the TBARS of irradiated breast meat from toms fed 200 or 400 IU dietary TA/ kg was not consistent. Irradiated meat developed more lipid oxidation than nonirradiated. The TBARS values of vacuum-packaged cooked breast remained relatively low throughout the 7-d storage period. The TBARS values of leg meat were much higher than those of the breast (Tables 1 and 2) because leg meat patties had higher fat content than breast meat (1.74% for breast and 6.45% for leg meat patties) as reported by Ahn et al. (1995). High level dietary TA (> 200 IU TA/kg of diet) treatments were helpful in maintaining low TBARS values in cooked leg meat for 3 d but the prooxidant effect of irradiation in cooked leg meat patties was not consistent (Table 2). Unlike in cooked breast meat patties, the TBARS

4 DIETARY VITAMIN E ON OXIDATION AND VOLATILES OF COOKED TURKEY 915 TABLE 1. Effect of dietary vitamin E, irradiation, and storage time (4 C) on the thiobarbituric acid reactive substances (TBARS) values of vacuum-packaged cooked turkey breast meat patties Dietary vitamin E Day 0 1 Day 3 Day 7 Control IR 2 SEM Control IR SEM Control IR SEM (IU/kg) (mg MDA 3 /kg meat) x 1.19 x x 1.23 x b,x 1.63 a,x y 0.88 x y 0.76 y y 1.02 y b,yz 1.04 a,x b,z 0.82 a,y z 0.74 z b,z 0.61 a,y b,z 0.44 a,z z 0.59 z 0.04 SEM a,bvalues within a row of same storage period with no common superscript differ significantly (P < 0.05). x zvalues within a column with no common superscript differ significantly (P < 0.05). 10 d samples were analyzed 3 h after cooking (n = 4). 2Patties were irradiated (IR) at 0 or 2.5 kgy (avg.) and then cooked. 3MDA = malonaldehyde. values of cooked leg meat patties increased significantly during the 7-d storage period. The baseline TBARS values (0 d) of cooked breast and leg meat patties in this study are relatively high and the high baseline TBARS values in this study were caused by the relatively long chilling time before analysis. The baseline TBARS values of cooked turkey breast and leg meat patties in our previous studies (Ahn et al., 1992, 1993) were 0.7 to 0.8 and increased to about 1.4 to 1.6 during 2-h chilling period. Most of the oxidation products in cooked meat were produced by oxygen contact with the cooked meat during the 3-h chilling period after cooking. In aerobic-packaged conditions, both cooked breast and leg meat patties developed lipid oxidation rapidly (Tables 3 and 4). After 3 d of storage, the TBARS values of irradiated and nonirradiated breast meat reached 3.7 to 5.0 range depending on dietary TA and irradiation conditions. High level dietary TA treatments (> 200 IU TA/kg of diet) significantly slowed the development of lipid oxidation in irradiated and nonirradiated cooked turkey breast meat during the 3-d storage, but the antioxidant effect of dietary TA was not strong enough. The TBARS values of cooked breast meat patties increased to a range of 4.7 to 6.0 after 7 d of storage, but the antioxidant effect of dietary TA was no longer observed. Although the TBARS values of nonirradiated cooked breast meat patties at 0 d were lower than or not different from those of irradiated, they were higher than those of irradiated after 7 d of storage (Table 3). The TBARS values of aerobic-packaged leg meat increased very rapidly during the first 3-d storage but decreased after that (Table 4). As in breast meat, irradiated leg meat patties had lower TBARS than nonirradiated patties stored in oxygenpermeable bags. The data presented in Tables 1 to 4 indicate that irradiation had no direct effect on the TBARS values of cooked meat during storage. Dietary TA at 600 IU significantly reduced the TBARS values of irradiated cooked leg meat after 7-d storage. However, all the aerobic-packaged cooked leg meat patties had very high TBARS values after 7 d of storage, and the differences in TBARS values related to the dietary TA may not have much meaning in terms of meat quality. Tissue vitamin E is not significant enough to prevent lipid oxidation in cooked meat during storage (Ajuyah et al., 1993). However, vitamin E can play an important role TABLE 2. Effect of dietary vitamin E, irradiation, and storage time (4 C) on the thiobarbituric acid reactive substances (TBARS) values of vacuum-packaged cooked turkey leg meat patties Dietary vitamin E Day 0 1 Day 3 Day 7 Control IR 2 SEM Control IR SEM Control IR SEM (IU/kg) (mg MDA 3 /kg meat) x 3.18 x x 3.41 x x 4.55 x y 1.25 y y 1.90 y a,y 2.60 b,y a,y 1.73 b,z yz 1.53 y z 2.25 y y 1.55 z b,z 1.43 a,y a,z 2.34 b,y 0.12 SEM a,bvalues within a row of same storage period with no common superscript differ significantly (P < 0.05). x zvalues within a column with no common superscript differ significantly (P < 0.05). 10 d samples were analyzed 3 h after cooking (n = 4). 2Patties were irradiated (IR) at 0 or 2.5 kgy (avg.) and then cooked. 3MDA = malonaldehyde.

5 916 AHN ET AL. TABLE 3. Effect of dietary vitamin E, irradiation, and storage time (4 C) on the thiobarbituric acid reactive substances (TBARS) values of aerobic-packaged cooked turkey breast meat patties Dietary vitamin E Day 0 1 Day 3 Day 7 Control IR 2 SEM Control IR SEM Control IR SEM (IU/kg) (mg MDA 3 /kg meat) x 1.19 x x 5.04 x a 4.79 b y 0.88 x xy 4.48 y a 4.82 b b,yz 1.04 a,x y 3.86 z a 4.84 b b,z 0.61 a,y xy 3.66 z a 4.69 b 0.23 SEM a,bvalues within a row of same storage period with no common superscript differ significantly (P < 0.05). x zvalues within a column with no common superscript differ significantly (P < 0.05). 10 d samples were analyzed 3 h after cooking (n = 4). 2Patties were irradiated (IR) at 0 or 2.5 kgy (avg.) and then cooked. 3MDA = malonaldehyde. in the quality of cooked meat. Ahn et al. (1992, 1993) showed that the storage stability of cooked meat can be maintained if the meat is vacuum-packaged immediately after cooking. Wen et al. (1996) reported that tissue vitamin E is a highly efficient antioxidant and can maintain low baseline lipid peroxidation levels in raw meat. If dietary TA and vacuum packaging immediately after cooking are combined, the oxidative quality of cooked meat can be maintained throughout normal storage periods. Volatiles from Cooked Meat Figure 1 shows typical chromatograms of volatiles in cooked turkey meat with different degrees of lipid oxidation. Aldehydes were the major components in cooked oxidized meat, and the content of alcohols also gradually increased as the lipid oxidation of meat increased. As reported previously (Ahn et al., 1992, 1993), the inclusion of oxygen was the most critical factor that influenced the development of lipid oxidation in cooked meat. Also, during volatiles analysis, presence of oxygen in sample vials had a significant influence on lipid oxidation and volatiles production while the samples were waiting for volatiles analysis. Without eliminating oxygen from the sample vial, it was impossible to evaluate the amounts and profiles of volatiles in cooked meat correctly. To resolve this dilemma, a bag of oxygen absorber was added (Ageless 30 to 50) to each of the sample vials along with cooked meat sample, resulting in stabilization of samples from developing lipid oxidation and volatiles production. The correlation coefficients shown in Table 5 indicate that propanal, pentanal, hexanal, 1-pentanol, and total volatiles were highly correlated with lipid oxidation of meat (TBARS values). Also, propanal, pentanal, hexanal, 1-pentanol, and total volatiles were highly correlated to each other. This relationship indicated that any one or all of these components could be used to accurately predict the oxidation status of cooked meat accurately. However, hexanal represented the lipid oxidation status of cooked meat better than any other volatiles components in our cooked meat study. Figure 2 presents the summary of hexanal produced in the cooked breast and leg meat patties with different irradiation and packaging conditions. In vacuum- TABLE 4. Effect of dietary vitamin E, irradiation, and storage time (4 C) on the thiobarbituric acid reactive substances (TBARS) values of aerobic-packaged cooked turkey leg meat patties Dietary vitamin E Day 0 1 Day 3 Day 7 Control IR 2 SEM Control IR SEM Control IR SEM (IU/kg) (mg MDA 3 /kg meat) x 3.18 x a 9.29 b x y 1.25 y a 7.52 b,y a,y 1.73 b,z a 8.29 b a 6.98 b,y y 1.55 z a 6.53 b,y 0.28 SEM a,bvalues within a row of same storage period with no common superscript differ significantly (P < 0.05). x zvalues within a column with no common superscript differ significantly (P < 0.05). 10 d samples were analyzed 3 h after cooking (n = 4). 2Patties were irradiated (IR) at 0 or 2.5 kgy (avg.) and then cooked. 3MDA = malonaldehyde.

6 DIETARY VITAMIN E ON OXIDATION AND VOLATILES OF COOKED TURKEY 917 FIGURE 1. Gas chromatogram of volatiles from cooked turkey meat. A) Vacuum-packaged nonirradiated cooked breast meat at Day 0; B. Aerobicpackaged nonirradiated cooked breast meat after 7 d of storage. TABLE 5. Correlation coefficient 1 (r 2 ) between thiobarbituric acid reactive substances (TBARS) value, major volatile components, and total volatiles of cooked turkey meat 2 Retention 2-Methyl Total 1.54 min 1-Heptene Propanal propanal Butanone Pentanal Hexanal 1-Pentanol volatiles TBARS Retention Heptene Propanal Methyl propanal n-butanone Pentanal Hexanal Pentanol Correlation coefficient (r 2 ) > ± 0.06 is significant at P < Data obtained from both breast and leg meat patties of all packaging, irradiation, and storage conditions were pooled and used for the calculation of correlation coefficients. (n = 320).

7 918 AHN ET AL. FIGURE 2. The amount of hexanal produced in the cooked breast and leg meat patties with different irradiation and packaging conditions. = nonirradiated, 0 d; = irradiated, 0 d; o = nonirradiated, 7 d; ÿ = irradiated, 7 d. Different letters within a same dietary TA are significantly different (P < 0.05). Breast-vacuum packaging: 25 IU dietary TA, SEM = 10.20; 200 IU dietary TA, SEM = 6.53; 400 IU dietary TA, SEM = 3.54; 600 IU dietary TA, SEM = Breast-aerobic packaging: 25 IU dietary TA, SEM = 14.30; 200 IU dietary TA, SEM = 17.70; 400 IU dietary TA, SEM = 11.87; 600 IU dietary TA, SEM = Leg-vacuum packaging: 25 IU dietary TA, SEM = 12.23; 200 IU dietary TA, SEM = 11.81; 400 IU dietary TA, SEM = 13.64; 600 IU dietary TA, SEM = Leg-aerobic packaging: 25 IU dietary TA, SEM = 16.66; 200 IU dietary TA, SEM = 19.47; 400 IU dietary TA, SEM = 20.44; 600 IU dietary TA, SEM = 24.76). packaged cooked breast, irradiated meat had a higher hexanal content than nonirradiated meat at both 0- and 7-d storage. The amount of hexanal was increased in vacuum-packaged breast meat during the 7-d storage in most dietary TA treatments. Except for an increase of hexanal content in irradiated breast meat from toms on the 600 IU dietary TA, the amount of hexanal in cooked meat tended to decrease as dietary TA increased (Figure 2A). In aerobic-packaged cooked breast, the amount of hexanal dramatically increased in both irradiated and nonirradiated meat patties during the 7-d storage periods. Irradiation produced higher hexanal in 0-d breast meat from toms fed > 400 IU of dietary TA/kg but had no effect in 7-d samples. As in the vacuum-packaged breast meat, the amount of hexanal gradually decreased as the level of dietary TA increased (Figure 2B). In vacuum-packaged cooked leg meat (Figure 2C), the amount of hexanal in nonirradiated meat, except for 600 ID dietary TA treatment, remained unchanged during the 7-d storage period. Hexanal content in irradiated leg meat, however, was significantly increased during the 7 d of storage. The amount of hexanal in irradiated meat at Day 7 was significantly higher than that of the nonirradiated meat at Day 0 and Day 7. In aerobic-packaged cooked leg meat (Figure 2D), the amount of hexanal in both control and irradiated meat increased by about twofold during the 7-d storage period. Irradiation had no effect on the hexanal content of aerobic-packaged leg meat. High level

8 DIETARY VITAMIN E ON OXIDATION AND VOLATILES OF COOKED TURKEY 919 FIGURE 3. The amount of total volatiles produced in the cooked breast and leg meat patties with different irradiation and packaging conditions. = nonirradiated, 0 d; = irradiated, 0 d; o = nonirradiated, 7 d; ÿ = irradiated, 7 d. Different letters within a same dietary TA are significantly different (P < 0.05). Breast-vacuum packaging: 25 IU dietary TA, SEM = 18.49; 200 IU dietary TA, SEM = 12.14; 400 IU dietary TA, SEM = 9.85; 600 IU dietary TA, SEM = Breast-aerobic packaging: 25 IU dietary TA, SEM = 21.43; 200 IU dietary TA, SEM = 25.11; 400 IU dietary TA, SEM = 19.67; 600 IU dietary TA, SEM = Leg-vacuum packaging: 25 IU dietary TA, SEM = 20.76; 200 IU dietary TA, SEM = 21.74; 400 IU dietary TA, SEM = 21.41; 600 IU dietary TA, SEM = Leg-aerobic packaging: 25 IU dietary TA, SEM = 24.75; 200 IU dietary TA, SEM = 26.85; 400 IU dietary TA, SEM = 27.80; 600 IU dietary TA, SEM = dietary TA (> 200 IU TA/kg of diet) reduced hexanal content in both vacuum and aerobic-packaged cooked leg meat, but the decrease in hexanal content caused by dietary TA may not have significant meaning for the flavor of aerobic-packaged cooked meat after 7 d of storage. As expected from the correlation coefficient between hexanal and total volatiles shown in Table 5, the changes in total volatiles by the dietary TA, irradiation, and storage were very similar to those observed with hexanal (Figure 3). In vacuum-packaged cooked breast, irradiated meat had higher total volatiles content than nonirradiated except for the irradiated meat from toms fed 25 IU TA/kg of diet at Day 0. The amount of total volatiles in meat stored for 7 d was the same or higher than that of the 0-d samples in both irradiated and nonirradiated meat. The changes of total volatiles by the dietary TA also followed the same pattern as hexanal in vacuumpackaged breast meat. (Figure 3A). In aerobic-packaged cooked breast, the amount of total volatiles increased twoto fourfold during the 7-d storage periods, but irradiation had a negligible effect on the amount of total volatiles in cooked breast meat after 7 d of storage (Figure 3B). In vacuum-packaged cooked leg meat (Figure 3C), the amount of total volatiles in irradiated meat increased significantly, but small changes (significant only with 600 IU TA/kg of diet) were observed in nonirradiated meat during the 7-d storage period. In aerobic-packaged

9 920 cooked leg meat (Figure 3D), the amount of total volatiles in leg meat increased significantly during the 7-d storage period but was not as large as in aerobic-packaged breast meat. Irradiation had no consistent effect on the total volatiles content of aerobic-packaged leg meat, but a high level dietary TA (> 200 IU TA/kg of diet) significantly reduced the total volatiles content of aerobic-packaged cooked leg meat after 7 d of storage. Aldehydes are frequently used as a warmed-over indicator for cooked meat, but hexanal was recommended as the best single volatile component that can be used as an indicator for warmed-over flavor in cooked meat (St. Angelo et al., 1987; Konopka et al., 1995). Data on volatiles indicated that hexanal constituted approximately 50 to 70% of total aldehydes in cooked meat. 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