PROCESSING AND PRODUCTS. Double-Packaging Is Effective in Reducing Lipid Oxidation and Off-Odor Volatiles of Irradiated Raw Turkey Meat 1

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1 PROCESSING AND PRODUCTS Double-Packaging Is Effective in Reducing Lipid Oxidation and Off-Odor Volatiles of Raw Turkey Meat 1 K. C. Nam and D. U. Ahn 2 Department of Animal Science, Iowa State University, Ames, Iowa ABSTRACT The effects of double packaging on lipid pounds (methanethiol, dimethyl sulfide, dimethyl disulfide, oxidation, color, and volatile production were determined to establish a modified packaging method to improve quality changes in irradiated raw turkey meat. Sliced raw and dimethyl trisulfide), mainly responsible for the irradiation off-odor, during storage. Exposure of doublepackaged irradiated turkey meats to aerobic conditions turkey breast and thigh meats were aerobically, vacuumor double (vacuum and aerobic)-packaged, electron beam test was effective in controlling both lipid oxidation-de- by removing outer vacuum bags a few days before the irradiated at 2.5 kgy, and then stored under refrigerated pendent (aldehydes) and radiolytic off-odor (S-compounds) volatiles. The a* values of raw turkey breast temperature. For the double-packaged samples, the outer and thigh meats increased by irradiation regardless of vacuum bags were removed after 5, 7, or 9dofrefriger- ated storage. 2-Thiobarbituric acid-reactive substances packaging conditions. The a* value of double-packaged meats was lower than that of the vacuum-packaged meats (TBARS) values, volatile compounds, and color values of but was not significant. Thus, the use of double-packaging the samples were determined after 10 d of storage. alone was not enough to reduce the pink color of irradiated raw turkey meat. When lipid oxidation and irradia- Irradiation and aerobic packaging promoted production of aldehydes (propanal and hexanal) related to lipid oxidation in turkey breast and thigh meats. Vacuumpackaged irradiated samples retained S-volatile comtion off-odor should be minimized without any additional additives, however, double packaging is an excellent method to be used for turkey meats. (Key words: double packaging, irradiation, lipid oxidation, off-odor, turkey meat) 2003 Poultry Science 82: INTRODUCTION Irradiation is a feasible method for controlling pathogenic and putrefying microorganisms in raw meat. The quality changes in irradiated meat, however, are a concern for the meat industry and the consumer. Previous reports indicate that irradiation increases lipid oxidation in aerobically packaged meat, and several off-odor volatile compounds are newly generated or increased in meat after irradiation (Patterson and Stevenson, 1995; Ahn et al., 2001). Ahn et al. (2000b) suggested that volatile compounds responsible for off-odor in irradiated meat are produced by the radiolysis of protein and lipid molecules and are distinctively different from those of lipid oxidation. The color of meat is one of the most important quality parameters that determines consumer acceptance of meat. Reports show that turkey breast meat becomes pink after irradiation (Millar et al., 1995; Nam and Ahn, 2002). The increased pink color in irradiated raw turkey breast is more intense and stable under vacuum than aerobic conditions (Luchsinger et al., 1996; Nam and Ahn, 2002). Although irradiated meat can be microbiologically safer than nonirradiated meat, consumers will not buy irradiated meat unless its quality, including color and odor, is acceptable. The color and odor changes in meat by irradiation are highly dependent upon packaging conditions. Lipid oxidation is a significant problem in irradiated meat when it is stored aerobically, because oxygen is essential for lipid oxidation and plays an important role in determining the secondary reactions of free radicals with meat components (Merritt et al., 1975; Katusin-Razem et al., 1992). Off-odor, however, is more problematic in vacuumpackaged meats (Ahn et al., 2000a), because sulfur com Poultry Science Association, Inc. Received for publication February 11, Accepted for publication December 18, Journal Paper No. J of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA Project No. 3706, and supported by State of Iowa funds. 2 To whom correspondence should be addressed: duahn@iastate.edu. Abbreviation Key: a* = redness; b* = yellowness; L* = lightness; MDA = malonedialdehyde; TBARS = 2-thiobarbituric acid reactive substances; TBA = thiobarbituric acid; TCA = trichloroacetic acid; V5-A5 = vacuum packaged for 5 d then aerobically packaged for 5 d; V7-A3 = vacuum packaged for 7 d then aerobically packaged for 3 d; V9-A1 = vacuum packaged for 9 d then aerobically packaged for 1 d. 1468

2 DOUBLE PACKAGING AND IRRADIATED TURKEY MEAT QUALITY 1469 pounds, the main volatiles responsible for off-odor in irradiated meat, are highly volatile and easily evaporate under aerobic conditions during storage. However, sulfur compounds stay in meat during storage under vacuum conditions (Ahn et al., 2001). Modifying packaging conditions may minimize the quality deterioration of irradiated meat. An appropriate combination of aerobic- and vacuum-packaging conditions can be effective in minimizing lipid oxidation and off-odor volatiles in irradiated turkey breast during storage. It may also be effective in reducing pink color in irradiated meat. The term double packaging was used in this study to describe a packaging method in which meat pieces were first individually packaged in oxygen-permeable bags and then a few of them were vacuum packaged in a larger vacuum bag. After a certain period of storage, the outer vacuum bag was removed, and the meat was stored until the last day of storage. The concept of double packaging was developed as an attempt to minimize odor and color problems in irradiated raw meat without adding any additives. Current Food and Drug Administration USDA regulations allow no additives added to meat before irradiation. When a new petition is approved, however, this double-packaging concept can be used in combination with other additives such as antioxidants in raw and ready-to-eat cooked meat products. The objective of this study was to determine the effectiveness of double-packaging conditions on lipid oxidation, volatiles, and color of irradiated turkey breast and thigh meat during refrigerated storage. MATERIALS AND METHODS Sample Preparation and Irradiation Large White turkeys (n = 32; 16 wk old) were slaughtered, then carcasses were chilled in ice water for 3 h and drained in a cold room. Breast and leg muscles were deboned from the carcasses 24 h after slaughter. Skin and visible fat were removed. Breast or thigh muscles from eight birds were pooled and used as a replication. The muscles were sliced into 2 cm thick steaks and individually packaged in oxygen-permeable bags 3 (polyethylene, 4 6, 2 mil) or oxygen-impermeable vacuum bags 4 (nylonpolyethylene, 9.3 ml O 2 /m 2 per 24 h at 0 C). The meat samples were irradiated at 2.5 kgy using a linear accelerator 5 with 10 MeV of energy, 10 kw of power level, and 88.1 kgy/min of average dose rate. vacuumpackaged samples were used as a control. Alanine dosimeters were attached to the top and bottom surfaces of a sample and were read using a 104 Electron Paramagnetic Resonance Instrument 6 to check the absorbed dose. For 3 Associated Bag Company, Milwaukee, WI. 4 Koch, Kansas City, MO. 5 Circe IIIR; Thomson CSF Linac, Saint-Aubin, France. 6 Bruker Instruments, Inc., Billerica, MA. 7 Brinkman Instrument, Inc., Westbury, NY. 8 Hunter Associated Labs, Inc., Reston, VA. 9 Takmar-Dohrmann, Cincinnati, OH. 10 Hewlett-Packard Co., Wilmington, DE. the double-packaged samples, the outer vacuum (V) bags were removed after 5 d (V5-A5), 7 d (V7-A3), or 9 d (V9- A1) of refrigerated storage in a cold room (4 C). Lipid oxidation, color, and volatile compounds of the samples were determined after 0 and 10 d of storage. Analysis of 2-Thiobarbituric Acid Reactive Substances Values Lipid oxidation was determined by 2-thiobarbituric acid-reactive substances (TBARS) method (Ahn et al., 1998). Minced sample (5 g) was placed in a 50-mL test tube and homogenized with 15 ml of deionized, distilled water using a Brinkman Polytron Type PT 10/35 7 for 15 s at high speed. The meat homogenate (1 ml) was transferred to a disposable test tube ( mm), and butylated hydroxytoluene (7.2%, 50 µl) and thiobarbituric acid (TBA)-trichloroacetic acid (TCA) [20 mm TBA and 15% (wt/vol) TCA] solution (2 ml) were added. The mixture was vortexed and then incubated in a 90 C water bath for 15 min to develop color. After being cooled for 10 min in cold water, the samples were vortexed and centrifuged at 3,000 g for 15 min at 5 C. The absorbance of the resulting upper layer was read at 531 nm against a blank prepared with 1 ml deionized, distilled water and 2 ml TBA-TCA solution. The amounts of TBARS were expressed as milligrams of malonedialdehyde (MDA) per kilogram of meat. Color Measurement The CIE color values were measured on the sample surface using a LabScan color meter 8 that had been calibrated against black and white reference tiles covered with the same packaging materials as used for samples. The CIE lightness (L*), redness (a*), and yellowness (b*) values were obtained using an illuminant A (light source). An average value from both top and bottom locations on a sample surface was used for statistical analysis. Analysis of Volatile Compounds A purge-and-trap apparatus 9 (Precept II and Purge & Trap Concentrator 3000) connected to a gas chromatograph-mass spectrometer 10 was used to analyze volatiles produced in samples (Ahn et al., 2001). Minced sample (3 g) was placed in a 40-mL sample vial, and the vials were then flushed with helium gas (40 psi) for 5 s. The maximum holding time of a sample in a refrigerated (4 C) loading tray was less than 4 h to minimize oxidative changes during the waiting period before starting the analysis (Ahn et al., 1999). The meat sample was purged with helium gas (40 ml/min) for 11 min at 40 C. Volatiles were trapped using a Tenax-charcoal-silica column 9 and desorbed for 2 min at 220 C, focused in a cryofocusing module ( 90 C), and then thermally desorbed into a column for 30 s at 220 C. An HP-624 column (7.5 m, 0.25 mm i.d., 1.4 µm nominal), an HP-1 column 10 (52.5 m, 0.25 mm i.d., 0.25 µm

3 1470 NAM AND AHN nominal), and an HP-Wax column (7.5 m, mm i.d., 0.25 µm nominal) were connected using zero dead-volume column connectors 11 and used for volatile analysis. Ramped oven temperature was used to improve volatile separation. The initial oven temperature of 0 C was held for 2.50 min. After that, the oven temperature was increased to 15 C at2.5 C per min, increased to 45 C at 5 C per min, increased to 110 C at20 C per min, and then increased to 200 Cat10 C per min and was held for 5.25 min at that temperature. Constant column pressure at 20.5 psi was maintained. The ionization potential of the mass selective detector 10 (Model 5973) was 70 ev, and the scan range was 18.1 to 350 m/z. Identification of volatiles was achieved by comparing mass spectral data of samples with those of the Wiley Library. 10 Standards, when available, were used to confirm the identification by the mass selective detector. The area of each peak was integrated using ChemStation software, 10 and the total peak area was reported as an indicator of volatiles generated from the meat samples. Statistical Analysis A completely randomized design was used to determine the effects of double packaging on color, lipid oxidation, and volatile profiles of the irradiated samples during storage. Data were analyzed by the procedure of generalized linear model using SAS software (SAS Institute, 1995): Student-Newman-Keul s multiple-range test was used to compare the mean values of treatments. Means and standard error of the means (SEM) are reported (P < 0.05). RESULTS AND DISCUSSION Lipid Oxidation Irradiation promoted lipid oxidation of turkey meat, but the increased lipid oxidation was problematic only when the irradiated meat was aerobically packaged and stored (Table 1). The differences in TBARS between aerobically and vacuum- or double-packaged turkey breast meat were minimal at d 0, but the TBARS of aerobically packaged turkey breast meat became significantly higher than those of vacuum-packaged meat after 10 d of storage. The TBARS of double-packaged meat was between the aerobically packaged and vacuum-packaged meats and showed an increasing trend as the exposure time to aerobic conditions increased. turkey thigh meat showed a greater degree of lipid oxidation than breast meat (Table 1). The TBARS of aerobically packaged irradiated turkey thigh meat were about four times higher than those of the breast meat. According to our experience with sensory tests, a considerable proportion of consumers could detect rancid offodor when the TBARS value is 1 mg MDA/kg meat or 11 J&W Scientific, Folsom, CA. higher. When irradiated turkey thigh meat was aerobically packaged and stored for 10 d, lipid oxidation was a problem. Vacuum-packaged thigh meat was within the critical limit (< 1.0 mg MDA/kg meat). If lipid oxidation is the major quality concern, vacuum or V9-A1 double packaging (9 d vacuum packaging and then 1 d aerobic packaging) is desirable for the refrigerated storage of irradiated turkey breast and thigh meats. Color Changes Raw turkey breast meat was more pink after irradiation (Table 2). The a* values of raw turkey breast meat increased significantly after irradiation irrespective of packaging types. Nam and Ahn (2002) reported that the turkey breast meat color becomes more pink due to formation of carbon monoxide-myoglobin and that pink color indicates a defect if it persists after cooking. The pink color generated by irradiation was more stable under vacuum than under aerobic conditions (Lynch et al., 1991; Nam and Ahn, 2002). Although the a* values of irradiated turkey breast meats decreased under all packaging conditions during the storage, the vacuum-packaged meat had higher a* values than aerobically packaged meat after 10 d of storage. The a* values of double-packaged meats were lower than those of the vacuum-packaged meats, but the differences were not significant. Therefore, the use of double packaging alone was not enough to reduce the pink color of irradiated turkey meat to the level of nonirradiated meat. The L* values of turkey breast decreased after irradiation but gradually increased during storage regardless of packaging conditions. The b* value of aerobically packaged turkey breast increased after irradiation and then remained high during storage. The redness of raw turkey thigh meat also increased significantly after irradiation regardless of packaging conditions (Table 3). Double-packaged thigh meats had lower a* values than vacuum-packaged meats, but the difference was not significant as in breast meats. The b* value of aerobically packaged irradiated turkey thigh meat was significantly higher than that of the vacuum-packaged thigh. Off-Odor Volatiles Many volatile compounds were newly generated, or the amounts of volatiles already present in nonirradiated raw turkey breast increased significantly by irradiation (Table 4). The amount of total volatiles in irradiated turkey breast was higher than that of the vacuum-packaged nonirradiated control at d 0. The amounts of S-compounds and hexanal also increased significantly after irradiation. The biggest difference between aerobically and vacuum-packaged irradiated turkey breast was found in S-compounds. The amount of dimethyl sulfide in aerobically packaged turkey breast meat was higher than that in vacuum-packaged meat, whereas dimethyl disulfide and dimethyl trisulfide were much higher in vacuumpackaged than in aerobically packaged irradiated meat

4 DOUBLE PACKAGING AND IRRADIATED TURKEY MEAT QUALITY 1471 TABLE 1. 2-Thiobarbituric acid reactive substance values of irradiated raw turkey meat under different packaging conditions during refrigerated storage 1 Storage Vacuum Aerobic V5-A5 V7-A3 V9-A1 Vacuum SEM (mg MDA/kg meat) Breast Day c 0.63 ay 0.48 by 0.48 by 0.48 by 0.52 by 0.03 Day d 2.34 ax 1.68 bx 1.35 bx 0.96 cx 0.71 cx 0.11 SEM Thigh Day by 1.09 ay 0.58 b 0.58 b 0.58 b 0.53 by 0.01 Day cx 8.17 ax 3.42 bx 2.14 bc 1.26 cx 0.90 cx 0.53 SEM a c Different letters within a row are significantly different (P < 0.05), n = 4. x,y Different letters within a column with same meat are significantly different (P 0.05). 1 MDA = malonedialdehyde; V5-A5 = vacuum packaged for 5 d then aerobically packaged for 5 d; V7-A3 = vacuum packaged for 7 d then aerobically packaged for 3 d; V9-A1 = vacuum packaged for 9 d then aerobically packaged for 1 d. TABLE 2. Color values of irradiated raw turkey breast meat under different packaging conditions during refrigerated storage 1 Storage Vacuum Aerobic V5-A5 V7-A3 V9-A1 Vacuum SEM L* value Day x 46.8 y 45.5 y 45.5 y Day by 52.8 ax 50.3 abx 49.8 abx 48.6 b 51.4 ab 1.0 SEM a* value Day b 8.4 ax 8.4 ax 8.4 ax 8.4 ax 8.7 ax 0.4 Day c 4.4 by 5.9 ay 5.0 aby 5.7 ay 6.1 ay 0.3 SEM b* value Day bx 15.0 ax 12.6 bx 12.6 bx 12.6 bx 13.1 bx 0.4 Day by 9.5 ay 9.4 ay 7.6 by 8.2 aby 7.4 by 0.4 SEM a c Different letters within a row are significantly different (P < 0.05), n = 4. x,y Different letters within a column with same color value are significantly different (P < 0.05). 1 L* = lightness; a* = redness; b* = yellowness; V5-A5 = vacuum packaged for 5 d then aerobically packaged for 5 d; V7-A3 = vacuum packaged for 7 d then aerobically packaged for 3 d; V9-A1 = vacuum packaged for 9 d then aerobically packaged for 1 d. TABLE 3. Color values of irradiated raw turkey thigh meat under different packaging conditions during refrigerated storage 1 Storage Vacuum Aerobic V5-A5 V7-A3 V9-A1 Vacuum SEM L* value Day a 37.2 b 33.8 by 33.8 by 33.8 by 37.1 by 1.6 Day x 41.7 x 42.2 x 43.8 x 1.4 SEM a* value Day b 19.3 ax 16.7 ax 16.7 ax 16.7 ax 17.0 ax 1.0 Day b 11.2 by 13.5 ab 12.9 ab 12.6 aby 14.1 ay 0.7 SEM b* value Day bx 21.3 ax 13.3 b 13.3 b 13.3 b 15.9 bx 0.8 Day by 16.6 ay 14.7 ab 13.4 ab 12.5 b 11.4 by 0.9 SEM a,b Different letters within a row are significantly different (P 0.05), n = 4. x,y Different letters within a column with same color value are significantly different (P 0.05). 1 L* = lightness; a* = redness; b* = yellowness; V5-A5 = vacuum packaged for 5 d then aerobically packaged for 5 d; V7-A3 = vacuum packaged for 7 d then aerobically packaged for 3 d; V9-A1 = vacuum packaged for 9 d then aerobically packaged for 1 d.

5 1472 NAM AND AHN TABLE 4. Volatiles profile of irradiated raw turkey breast meat at d 0 under different packaging conditions Compound Vacuum Aerobic Vacuum SEM 2-Methyl-1-propene 0 b 0 b 342 a 12 Butane 0 b 288 a 0 b 11 Pentane 253 b 3,315 a 3,034 a 224 Dimethyl sulfide 3,963 b 22,973 a 4,312 b 1,652 Hexane Heptene 0 b 590 a 662 a 34 Heptane 34 b 543 a 582 a 30 Dimethyl disulfide 0 b 2,153 b 16,600 a 3,395 Toluene 0 b 2,492 a 2,604 a Octene 0 b 0 b 677 a 41 Octane 827 c 1,848 b 2,776 a Octene 0 b 0 b 575 a 18 3-Methyl-2-heptene 0 b 0 b 575 a 18 Hexanal 328 b 915 a 883 a 74 Dimethyl trisulfide 0 b 780 b 5,266 a 877 Total 5,531 b 36,448 a 39,535 a 4,214 a c Different letters within a row are significantly different (P 0.05), n = 4. at d 0. All of these S-compounds are regarded as major volatiles responsible for the characteristic irradiation offodor and are different from rancid odor produced by lipid oxidation products. Hashim et al. (1995) showed that irradiating raw chicken breast and thigh produced a characteristic bloody and sweet aroma that remained after the thighs were cooked, but was not detectable after the breasts were cooked. Ahn et al. (2000a) described the irradiation odor in raw pork as a barbecued corn-like odor. Ahn et al. (2000b) reported that S-containing volatiles, such as 2,3-dimethyl disulfide produced by the radiolytic degradation of sulfur amino acids, were responsible for the off-odor in irradiated pork, and their amounts were highly dependent upon irradiation dose. They also assumed that the off-odor volatiles in irradiated pork TABLE 5. Volatiles profile of irradiated raw turkey breast meat at d 10 under different packaging conditions 1 were the result of compounding effects of volatiles from lipid oxidation and radiolysis of various amino acid side chains (Ahn et al., 2001). Jo and Ahn (2000) also found that 2,3-dimethyl disulfide was produced from irradiated oil emulsion containing methionine. turkey thigh meat had higher total volatiles compared with breast meat, but their volatile profiles were similar to those of breast meat (Tables 4 and 5). The amount of hexanal in turkey thigh meat was much higher than that in turkey breast, which was consistent with the TBARS results (Table 1). Several hydrocarbons such as 2-methyl-l-propene, butane, 1-octene, and octane were detected more in irradiated vacuum-packaged turkey thigh meat than in aerobically packaged meat. Significantly more dimethyl disulfide or dimethyl trisulfide was Compound Vacuum Aerobic V5-A5 V7-A3 V9-A1 Vacuum SEM Butane 0 c 0 c 525 ab 467 a 602 a 0 c 34 Methanethiol 0 b 0 b 0 b 0 b 523 b 1,509 a 128 Pentane 293 d 4,486 b 5,502 a 3,683 bc 2,981 c 4,038 bc 340 Propanal 0 b 797 a 0 b 0 b 0 b 0 b 1 Dimethyl sulfide 4,275 b 0 b 907 b 3,127 ab 10,420 a 10,724 a 2,048 Hexane 125 c 762 b 700 b 1,001 a 696 b 1,113 a 53 Heptane 32 b 737 a 584 a 587 a 0 b 0 b 60 Dimethyl disulfide 31 c 0 c 0 c 0 c 1,764 b 4,395 a 238 Toluene 6 d 0 d 752 c 728 c 1,086 b 1,398 a 38 1-Octene 0 b 0 b 0 b 0 b 0 b 1,061 a 15 Octane 1,115 c 825 c 1,292 c 1,984 b 2,289 ab 2,676 a Octene 0 b 0 b 0 b 0 b 0 b 715 a 14 3-Methyl-2-heptene 527 b 0 b 0 b 0 b 0 b 885 a 22 Hexanal 174 b 8,628 a 7,539 a 2,857 b 1,208 b 1,398 b 930 Dimethyl trisulfide 0 c 0 c 0 c 0 c 847 b 1,670 a 72 Total 6,583 c 17,237 b 17,804 b 14,437 b 22,419 b 31,582 a 2,282 a d Different letters within a row are significantly different (P < 0.05), n = 4. 1 V5-A5 = vacuum packaged for 5 d then aerobically packaged for 5 d; V7-A3 = vacuum packaged for 7 d then aerobically packaged for 3 d; V9-A1 = vacuum packaged for 9 d then aerobically packaged for 1 d.

6 DOUBLE PACKAGING AND IRRADIATED TURKEY MEAT QUALITY 1473 TABLE 6. Volatiles profile of irradiated raw turkey thigh meat at d 0 under different packaging conditions Compound Vacuum Aerobic Vacuum SEM 2-Methyl-1-propene 0 c 358 b 446 a 20 Butane 0 b 521 a 594 a 44 1-Pentene 0 c 658 b 1,010 a 45 Pentane 548 c 7,234 b 10,414 a 705 Dimethyl sulfide 3,039 b 12,076 a 11,203 a 1,350 1-Hexene 0 b 0 b 702 a 26 Hexane 379 c 1,491 b 2,295 a 77 Benzene 0 b 688 a 723 a 38 1-Heptene 0 c 1,536 b 1,864 a 80 Heptane 62 c 1,136 b 1,795 a 91 Dimethyl disulfide 0 b 1,138 a 2,339 a 1,769 Toluene 0 b 1,484 a 1,676 a Octene 0 b 0 b 1,147 a 23 Octane 1,894 c 4,584 b 6,544 a Octene 0 b 0 b 651 a 10 3-Methyl-2-heptene 0 b 0 b 681 a 12 Hexanal 1,338 4,455 3,243 1,480 Dimethyl trisulfide 0 b 0 b 1,289 a 464 Total 7,262 c 37,366 b 48,616 a 3,830 a c Different letters within a row are significantly different (P < 0.05), n = 4. detected in irradiated thigh meats with vacuum packaging than in irradiated turkey breast. The volatiles profile of irradiated turkey breast meat was highly dependent upon packaging conditions during irradiation and storage (Table 5). The greatest amounts of total volatiles and hydrocarbons such as toluene, 1- octene, and octane were detected in vacuum-packaged turkey breast meat. The amount of dimethyl sulfide was significantly increased, and methanethiol was newly generated under V9-A1 double-packaging and vacuum-packaging conditions. Considerable proportions of dimethyl disulfide and dimethyl trisulfide (26 and 32% of 0 d values, respectively), however, still remained in the meat under vacuum-packaging conditions after 10 d of storage (Table 5). These changes in the composition of S-compounds during storage suggested that dimethyl disulfide and dimethyl trisulfide might be degraded into dimethyl sulfide during storage under V9-A1 double-packaging and vacuum-packaging conditions. Under aerobic conditions, almost all S-compounds disappeared during the 10-d storage period. Therefore, aerobic packaging was more effective than vacuum packaging in reducing volatiles responsible for the irradiation offodor. However, aerobic packaging promoted lipid oxidation in meats as evidenced by the increased amounts of propanal and hexanal as well as TBARS (Tables 1 and 4 to 7). When lipid oxidation and irradiation off-odor were considered, double packaging of turkey breast meat was more desirable than aerobic or vacuum packaging alone. The volatile characteristics of double-packaged turkey breast were somewhere between the aerobically and vacuum-packaged meats depending upon the number of days in vacuum and aerobic conditions. Among the double-packaged treatments, V7-A3 double-packaged (vacuum conditions for 7 d and then aerobic conditions for 3 d) turkey breast meat was the most desirable in reducing irradiation off-odor and lipid oxidation. After 10 d of storage, the amount of dimethyl disulfide in V7-A3 double packaging was only 29% of the vacuum packaging, and the other S-volatiles (methanethiol, dimethyl sulfide, and dimethyl trisulfide) were not detected. The amounts of propanal and hexanal also decreased to 0 and 33% of the aerobically packaged turkey breast, respectively. Turkey breast with V5-A5 double packaging (5 d of vacuum packaging and then 5 d of aerobic conditions) produced significant amounts of lipid oxidation products such as propanal and hexanal, and V9-A1 double packaging had large amounts of S-compounds in the meat. turkey thigh meats produced more volatiles than breast meat after 10 d of storage, and lipid oxidation was a greater concern in irradiated turkey thigh than in breast (Table 7). Greater amounts of propanal and hexanal were produced in irradiated turkey thigh than in breast, and 3-methyl butanal, pentanal, and heptanal, which were not found in irradiated breast meat, were also detected in aerobically packaged irradiated thigh meat. Unlike in breast meat, aerobically packaged turkey thigh meat had more total volatiles than vacuum-packaged meat. The amounts and profiles of S-compounds in irradiated turkey thigh meat at d 10 were similar to those in breast. As in turkey breast, irradiated vacuum-packaged turkey thigh meat contained large amounts of S-compounds, and aerobically packaged thigh meats had lipid oxidation problems at d 10. Turkey thigh meat with V7- A3 double packaging (7 d vacuum packaging and then 3 d aerobic conditions) had less S-compounds than vacuum-packaged meat and had smaller lipid oxidation products than aerobically packaged meat. The amounts of dimethyl sulfide and dimethyl disulfide in V7-A3 doublepackaged irradiated thigh meat were 50 and 35% of the

7 1474 NAM AND AHN TABLE 7. Volatiles profile of irradiated raw turkey thigh meat at d 10 under different packaging conditions 1 Compound Vacuum Aerobic V5-A5 V7-A3 V9-A1 Vacuum SEM Butane 0 c 495 b 509 b 512 b 765 a 0 c 26 Methanethiol 0 c 0 c 0 c 0 c 494 b 1,920 a 45 Pentane 708 e 20,199 a 13,036 b 7,269 c 6,166 c 3,562 d 615 Propanal 0 d 6,146 a 2,545 b 1,642 c 0 d 0 d 334 Dimethyl sulfide 3,461 c 256 c 2,804 c 11,865 b 14,629 b 23,587 a 1,145 Hexane 290 d 1,778 b 2,488 a 1,754 b 1,403 bc 1,096 c 113 Butanal 0 b 901 a 0 b 0 b 0 b 0 b 10 3-Methyl butanal 0 b 922 a 0 b 0 b 0 b 0 b 27 1-Heptene 0 d 1,227 a 827 b 693 bc 821 b 613 c 37 Heptane 69 1, Pentanal 0 d 11,149 a 3,958 b 1,371 c 661 cd 0 d 272 Dimethyl disulfide 10 d 0 d 473 c 792 c 1,582 b 4,476 a 131 Toluene 0 d 562 c 547 c 824 b 1,029 a 968 a 34 1-Octene 0 b 0 b 0 b 0 b 0 b 657 a 30 Octane 1,755 c 2,650 bc 2,439 bc 4,954 ab 4,499 a 2,785 bc Octene 443 b 914 a 0 c 0 c 0 c 0 c 23 3-Methyl-2-heptene 616 a 604 a 0 b 0 b 0 b 0 b 38 Hexanal 65 e 82,197 a 62,278 b 23,349 c 13,064 d 3,283 e 2,809 Heptanal 0 b 1,512 a 0 b 0 b 0 b 0 b 51 Dimethyl trisulfide 0 c 0 c 0 c 0 c 906 b 1,696 a 54 Total 7,421 d 142,798 a 92,861 b 55,677 c 46,978 c 45,266 c 3,408 a e Different letters within a row are significantly different (P < 0.05), n = 4. 1 V5-A5 = vacuum packaged for 5 d then aerobically packaged for 5 d; V7-A3 = vacuum packaged for 7 d then aerobically packaged for 3 d; V9-A1 = vacuum packaged for 9 d then aerobically packaged for 1 d. vacuum-packaged irradiated meat, respectively, and no methanethiol or dimethyl trisulfide was detected. The amounts of propanal, pentanal, and hexanal in V7-A3 double-packaged irradiated turkey thigh meat were 26, 12, and 28%, respectively, of the aerobically packaged irradiated thigh meat, and 3-methyl butanal and heptanal were not detected. Therefore, exposing the double-packaged irradiated turkey meat to aerobic conditions by removing the outer vacuum bag 3 d before selling or consuming is desirable to reduce S-volatiles and minimize lipid oxidation in turkey breast meats. For irradiated thigh meat, at least 5 d exposure to aerobic conditions is needed to remove off-odor volatiles. Exposure of the thigh meat to aerobic conditions for 5 d or longer, however, caused lipid oxidation. Therefore, double packaging alone was not enough to solve both the lipid oxidation and off-odor problems simultaneously in irradiated thigh meat. REFERENCES Ahn, D. U., C. Jo, and D. G. Olson Volatile profiles of raw and cooked turkey thigh as affected by purge temperature and holding time before purge. J. Food Sci. 64: Ahn, D. U., C. Jo, and D. G. Olson. 2000b. Analysis of volatile components and the sensory characteristics of irradiated raw pork. Meat Sci. 54: Ahn, D. U., C. Jo, M. Du, D. G. Olson, and K. C. Nam. 2000a. Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions. Meat Sci. 56: Ahn, D. U., D. G. Olson, C. Jo, X. Chen, C. Wu, and J. I Lee., Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production, and color in raw pork patties. Meat Sci. 47: Ahn, D. U., K. C. Nam, M. Du, and C. Jo Volatile production in irradiated normal, pale soft exudative (PSE) and dark firm dry (DFD) pork under different packaging and storage conditions. Meat Sci. 57: Hashim, I. B., A. V. A. Resurrecccion, and K. H. MacWatters Disruptive sensory analysis of irradiated frozen or refrigerated chicken. J. Food Sci. 60: Jo, C., and D. U. Ahn. 2000, Production volatile compounds from irradiated oil emulsions containing amino acids or proteins. J. Food Sci. 65: Katusin-Razem, B., K. W. Mihaljevic, and D. Razem Timedependent post irradiation oxidative chemical changes in dehydrated egg products. J. Agric. Food Chem. 40: Luchsinger, S. E., D. H. Kropf, C. M. Garcia-Zepeda, M. C. Hunt, J. L. Marsden, E. J. Rubio-Canas, C. L. Kastner, W. G. Kuecher, and T. Mata Color and oxidative rancidity of gamma and electron beam-irradiated boneless pork chops. J. Food Sci. 61: Lynch, J. A., H. J. H. MacFie, and G. C. Mead Effect of irradiation and packaging type on sensory quality of chilledstored turkey breast fillets. J. Food Sci. Technol. 26: Merritt, Jr. C., P. Angelini, E. Wierbicki, and G. W. Shuts Chemical changes associated with flavor in irradiated meat. J. Agric. Food Chem. 23: Millar, S. J., B. W. Moss, D. B. MacDougall, and M. H. Stevenson The effect of ionizing radiation on the CIELAB color co-ordinates of chicken breast meat as measured by different instruments. Int. J. Food Sci. Technol. 30: Nam, K. C., and D. U. Ahn Carbon monoxide-heme pigment complexes are responsible for the pink color in irradiated raw turkey breast meat. Meat Sci. 61: Patterson, R. L., and M. H. Stevenson Irradiation-induced off-odor in chicken and its possible control. Br. Poult. Sci. 36: SAS Institute SAS/STAT User s Guide. SAS Institute Inc., Cary, NC.