Combination of aerobic and vacuum packaging to control lipid oxidation and off-odor volatiles of irradiated raw turkey breast

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1 Meat Science 63 (2003) Combination of aerobic and vacuum packaging to control lipid oxidation and off-odor volatiles of irradiated raw turkey breast K.C. Nam, D.U. Ahn* Department of Animal Science, Iowa State University, Ames, IA , USA Received 11 February 2002; received in revised form 23 April 2002; accepted 23 April 2002 Abstract Effects of the combination of aerobic and anaerobic packaging on color, lipid oxidation, and volatile production were determined to establish a modified packaging method to control quality changes in irradiated raw turkey meat. Lipid oxidation was the major problem with aerobically packaged irradiated turkey breast, while retaining characteristic irradiation off-odor volatiles such as dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide was the concern for vacuum-packaged breast during the 10-day refrigerated storage. Vacuum packaging of aerobically packaged irradiated turkey breast meat at 1 or 3 days of storage lowered the amounts of S-volatiles and lipid oxidation products compared with vacuum- and aerobically packaged meats, respectively. Irradiation increased the a-value of raw turkey breast, but exposing the irradiated meat to aerobic conditions alleviated the intensity of redness. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Combination of aerobic/anaerobic packaging; Irradiation; Lipid oxidation; Off-odor; Color 1. Introduction One of the best emerging technologies to ensure the microbiological safety of meat is irradiation. Up to 3 kgy of irradiation is allowed for use in poultry meat (USDA, 1999). The main concern of irradiating meat, however, is the organoleptic quality changes that occur (Ahn et al., 1997). Ionizing radiation produces free radicals that can accelerate oxidative processes and produce radiolytic products from meat components (Woods & Pikaev, 1994). Previous studies showed that irradiation increased lipid oxidation in aerobically packaged meat and developed off-flavors (Ahn, Nam, Du, & Jo, 2001; Patterson & Stevenson, 1995). Jo and Ahn (2000) reported that the radiolytic degradation of amino acids, especially sulfur amino acids, was the main mechanism of off-odor production in irradiated meat. Therefore, both lipid oxidation products and radiolytic S-volatiles contributed to the overall off-flavor in irradiated raw meat. However, the characteristic irradiation off-odor was * Corresponding author. Tel.: ; fax: address: duahn@iastate.edu (D.U. Ahn). influenced much more by the sulfur-volatiles such as dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide than by lipid oxidation-dependent volatiles such as aldehydes (Ahn, Jo, Du, Olson, & Nam, 2000). The profiles and amounts of volatiles in irradiated meats showed that these S-volatiles were higher in vacuumpackaged than aerobically packaged meats because they were highly volatile under aerobic conditions (Ahn, Jo, Du et al., 2000, 2001). Therefore, aerobic packaging will be more beneficial in reducing the characteristic irradiation off-odor during refrigerated storage than vacuum packaging, unless lipid oxidation is a problem. The color of irradiated meat also depended upon packaging type. Turkey breast meat became pinker after irradiation (Lynch, MacFie, & Mead, 1991; Nam & Ahn, 2002), and the increased pink color was more intense and stable under vacuum than aerobic conditions (Luchsinger et al., 1996; Nam & Ahn, 2002). Thus, aerobic packaging was more desirable for the irradiated meat color than vacuum packaging, if lipid oxidation was not considered. Packaging is a critical factor that affects the quality of irradiated meat, and thus, modification of packaging methods can minimize the quality defect in irradiated meat. Exposing meat to aerobic conditions during /02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S (02)

2 390 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) irradiation and for certain periods of time during storage will help off-odor volatiles to escape from the meat. Therefore, an appropriate combination of aerobic- and vacuum-packaging conditions can be effective in minimizing both off-odor volatiles and lipid oxidation in irradiated raw turkey breast during storage. It may also be effective in reducing the generation of pink color in irradiated meat compared with vacuum packaging alone. The objectives of this study were to determine the effects of modified packaging conditions on lipid oxidation, volatiles, and color of irradiated raw turkey breast meat during refrigerated storage, and to find the best aerobic and vacuum packaging combination that can minimize quality defect of irradiated meat. 2. Materials and methods 2.1. Sample preparation Turkey breast muscles (Pectoralis major+minor) were separated from a total of 32 turkeys and sliced into 2-cm thick steaks. For modification of packaging conditions during the storage, the sliced samples were individually packaged in oxygen-permeable bags (polyethylene, Associated Bag Company, Milwaukee, WI) and irradiated at 3 kgy using a Linear Accelerator (Circe IIIR, Thomson CSF Linac, Saint-Aubin, France) at room temperature; 10 MeV of energy, 10 kw of power level, and 92.6 kgy/min of average dose rate were used. To confirm the target dose, alanine dosimeters attached to the top and bottom of sample were read using an 104 Electron Paramagnetic Resonance unit (EMS-104, Bruker Instruments Inc., Billerica, MA). The max./min. ratio was approximately 1.3. Then, a few of them were doubly vacuum-packaged in a larger vacuum bag (nylon/polyethylene, 9.3 ml O 2 /m 2 /24 h at 0 C; Koch, Kansas City, MO) after 1, 3, or 5 days of refrigerated storage until 10 days of storage for A1/V9 (aerobic for 1 day then vacuum for 9), A3/V7 (aerobic for 3 days then vacuum for 7), or A5/V5 (aerobic for 5 days then vacuum for 5) treatment, respectively. Nonirradiated aerobically packaged samples were used as a control. Irradiated aerobically and vacuum-packaged samples were prepared for references. Color, lipid oxidation, and volatile compounds of the samples were determined at 0 and 10 days of storage. The data of A1/V9, A3/V7, and A5/V5 at 0 days were represented by those of irradiated aerobically packaged samples Color measurement CIE color values were measured (AMSA, 1991) on the surface of samples using a LabScan color meter (Hunter Associated Labs, Inc., Reston, VA) that had been calibrated against black and white reference tiles covered with the same packaging materials as used for samples. The CIE L (lightness), a (redness), and b (yellowness) values were obtained using an illuminant A (light source). An average value from both top and bottom location on a sample surface was used for statistical analysis Analysis of 2-thiobarbituric acid reactive substances (TBARS) Lipid oxidation was determined by a TBARS method (Ahn, Olson, Jo, Chen, Wu & Lee, 1998). Minced sample (5 g) was placed in a 50-ml test tube and homogenized with 15 ml of deionized distilled water (DDW) using a Brinkman Polytron (Type PT 10/35, Brinkman Instrument Inc., Westbury, NY) for 15 s at high speed. The meat homogenate (1 ml) was transferred to a disposable test tube (13100 mm), and butylated hydroxytoluene (7.2%, 50 ml) and thiobarbituric acid/ trichloroacetic acid [20 mm TBAand 15% (w/v) 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 cooling for 10 min in cold water, the samples were vortexed and centrifuged at 3000g 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 DDW and 2 ml TBA/TCA solution. The amounts of TBARS were expressed as mg per kg of meat Analysis of volatile compounds Apurge-and-trap apparatus (Precept II and Purge & Trap Concentrator 3000, Tekmar-Dohrmann, Cincinnati, OH) connected to a gas chromatograph/mass spectrometer (GC Model 6890/MSD, HP 5973, Hewlett-Packard Co., Wilmington, DE) was used to analyze the volatiles potentially responsible for the off-odor 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 analysis. The sample was purged with helium gas (40 ml/min) for 12 min at 40 C. Volatiles were trapped at 20 C using a Tenax/charcoal/silica trap column (Tekmar-Dohrmann), thermally desorbed (225 C) into a cryofocusing unit ( 90 C), and then thermally desorbed at 225 C into a GC column for 30 s. An HP-624 column (7.5 m, 250 mm i.d., 1.4 mm nominal), an HP-1 column (52 m, 250 mm i.d., 0.25 mm nominal), and an HP-Wax column (7.5 m, 250 mm i.d., 0.25 mm nominal) combined with zero dead-volume column connectors (Hewlett Packard Co.) were used to improve the separation of volatiles. A

3 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) ramped oven temperature was used (0 C for 2.5 min, increased to 15 C at 2.5 C/min, increased to 45 Cat 5 C/min, increased to 110 C at 20 C/min, and increased to 200 Cat10 C/min for 3.25 min). Liquid nitrogen was used to cool the oven below ambient temperature. Helium was the carrier gas at a constant pressure of 20.5 psi. The ionization potential of MS was 70 ev, and the scanned mass range was m/z. Identification of volatiles was achieved by comparing mass spectral data of samples with those of the Wiley library (Hewlett-Packard Co.). Selected standards were used to verify the identities of some volatiles. Each peak area was integrated using the ChemStation TM software (Hewlett Packard Co.) and reported as the amount of volatiles released (total ion counts10 4 ) Statistical analysis The experiments were performed by four replications and designed to determine the effects of modified packaging methods and storage time on color, lipid oxidation, and volatile compounds of the irradiated samples during the 10 days of storage. Analysis of variance was used by the generalized linear model procedure of SAS software (SAS Institute, 1995); Student- Newman Keul s multiple range test was used to compare the mean values of the treatments. Mean values and standard error of the means (SEM) were reported (P<0.05). 3. Results and discussion 3.1. Color changes Irradiation made turkey breast meat redder, and the increased redness was more distinct in irradiated vacuum-packaged than aerobically packaged meats (Table 1). Nam and Ahn (2002) attributed the increased red color in irradiated turkey meat to the formation of carbon monoxide myoglobin (CO Mb) complex. Compared with oxymyoglobin, CO Mb complex is not easily oxidized to brown metmyoglobin, because of the strong binding of CO to the iron-porphyrin in myoglobin molecule (Sorheim, Nessen, & Nesbakken, 1999). The redness of irradiated aerobically packaged turkey breast was lower than vacuum-packaged breast, but it was still higher than that of the nonirradiated control. After 10 days of storage, the redness of aerobically or doubly packaged turkey breast was not changed, whereas that of vacuum-packaged breast significantly increased. Therefore, exposing irradiated meat to aerobic conditions was effective in reducing pink color in irradiated turkey breast meat. Although the binding affinity of CO myoglobin is 200-fold stronger than O 2 (Stryer, 1981), the continuous challenge from oxygen Table 1 Color values of irradiated raw turkey breast meat with different packaging during refrigerated storage ab Storage NonIr Irradiated SEM Aerobic Aerobic A5/V5 c A3/V7 d A1/V9 e Vacuum L-value Day a 45.8aby 45.8aby 45.8aby 45.8aby 43.6by 0.5 Day x 51.8x 51.6x 51.0x 48.8x 0.9 SEM a-value Day 0 2.5cx 3.5b 3.5b 3.5b 3.5b 4.9ay 0.2 Day cy 3.3b 3.1b 4.0b 4.0b 5.6ax 0.3 SEM b-value Day y 4.4y Day x 6.4x SEM a Different letters (a c) within a row are significantly different (P<0.05). n=4. b Different letters (x,y) within a column with same color value are significantly different (P<0.05). c Aerobically packaged for 5 days and then vacuum packaged for 5 days. d Aerobically packaged for 3 days and then vacuum packaged for 7 days. e Aerobically packaged for 1 day and then vacuum packaged for 9 days. under aerobic conditions should have replaced CO Mb ligand to MbO 2, which oxidized easily to metmb and decreased pink color intensity. Grant and Patterson (1991) also reported that irradiated meat color could be discolored at the presence of oxygen. There was no difference in color a-values among doubly packaged samples with different exposure time to aerobic conditions, and even aerobic exposure for 1 day after irradiation was effective in reducing the redness. However, none of the aerobic/vacuum packaging combinations ( double packaging ) could lower color a-values of irradiated turkey meat to the level of the nonirradiated control Lipid oxidation Vacuum-packaged meat was more resistant to lipid oxidation than aerobically packaged meat irrespective of irradiation dose at 0 days, but irradiation accelerated lipid oxidation during the 10-days storage (Table 2). At day 10, the TBARS of irradiated turkey breast meat was commensurate with the exposing time to aerobic conditions. This showed that the increased lipid oxidation was mainly problematic only when irradiated turkey breast meat was aerobically stored, and the presence of oxygen was the most critical factor influencing lipid oxidation during the storage of irradiated meat. Although the TBARS of doubly packaged meats were still higher than those of the vacuum-packaged meats,

4 392 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) Table 2 TBARS values of irradiated raw turkey breast meat with different packaging during refrigerated storage ab Storage NonIr Irradiated SEM Aerobic Aerobic A5/V5 c A3/V7 d A1/V9 e Vacuum (mg / kg meat) Day ay 0.65ay 0.65ay 0.65ay 0.65ay 0.34b 0.03 Day bx 2.63ax 1.97bx 1.33cx 0.92cdx 0.43d 0.16 SEM a Different letters (a d) within a row are significantly different (P<0.05). n=4. b Different letters (x,y) within a column are significantly different (P<0.05). c Aerobically packaged for 5 days and then vacuum packaged for 5 days. d Aerobically packaged for 3 days and then vacuum packaged for 7 days. e Aerobically packaged for 1 day and then vacuum packaged for 9 days. they were significantly lower than those of the aerobically packaged meats with or without irradiation. Therefore, 1 3 days of aerobic packaging of irradiated raw turkey breast meat during the 10 days did not cause any problem in lipid oxidation Off-odor volatiles Table 3 shows that irradiation produced many new volatiles and increased the amounts of a few volatiles found in nonirradiated turkey breast meat. Specific volatiles generated by irradiation include methanethiol, methylthio ethane, dimethyl disulfide, dimethyl trisulfide, propanal, 3-methyl butanal, pentanal, and toluene. The amount of total volatiles in turkey breast with vacuum packaging was only about half that of the aerobically packaged meat, indicating that considerable amounts of volatiles were evaporated during the storage period under aerobic conditions. The predominant volatile of nonirradiated control meat was dimethyl sulfide, but the amount was not changed much by irradiation. The composition of S-volatiles in irradiated turkey meat differs greatly depending on the packaging methods used. For example, the ratio of dimethyl sulfide to dimethyl disulfide was 10:1 in aerobically packaged turkey breast, while the ratio was changed to 1:1 in vacuum-packaged irradiated turkey breast. All of these S-compounds are regarded as major volatiles responsible for the characteristic irradiation off-odor, which is different from the rancidity produced by lipid oxidation products. Ahn, Jo, and Olson (2000) described the irradiation odor in raw pork as a barbecued corn-like odor. 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 (Ahn, Jo, Du et al., 2000). Jo and Ahn (2000) also found that 2,3-dimethyl disulfide was produced from irradiated oil emulsion containing methionine. This different composition of S-volatiles as well as their absolute amount may have significant effect Table 3 Volatile profile of irradiated raw turkey breast meat with different packaging at day 0 a Aerobic Aerobic Vacuum 2-Methyl-1-propene 0b 133a 153a 8 Methanethiol 0b 226b 1280a 79 1-Pentene 0c 125a 74b 11 Pentane 310b 717a 455b 64 2-Pentene 0b 43a 0b 1 Propanal 0b 80a 0b 5 Dimethyl sulfide Hexene 0b 69a 55a 4 Hexane 183c 472a 284b 15 Methylthio ethane 0b 75a 67a 3 Benzene 0b 195a 222a 11 3-Methyl butanal 0b 71a 62a 4 1-Heptene 0c 205a 124b 10 Heptane 51c 264a 122b 11 Pentanal 0b 58a 63a 6 Dimethyl disulfide 0c 430b 4266a 295 Toluene 0b 1254a 1339a 68 1-Octene 0b 66b 259a 26 Octane 289c 658b 837a 48 2-Octene 0c 69b 178a 3 3-Methyl-2-heptene 0b 0b 233a 11 Dimethyl trisulfide 0b 84b 814a 39 Total 5436c 9857b 17,772a 694 a Different letters (a c) within a row are significantly different (P<0.05). n=4. on the descriptive characteristics of the irradiation offodor because each S-volatile has its own characteristic odor note and threshold. Dimethyl disulfide produced more stringent and stronger odor than dimethyl sulfide. Therefore, the odor of vacuum-packaged meat would be more stimulating than that of aerobically packaged meat because of high dimethyl disulfide in the meat. After 10 days of refrigerated storage, volatile profiles of irradiated turkey breast were highly dependent upon packaging conditions (Table 4). The greatest amounts of total volatiles and S-volatiles were detected in

5 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) vacuum-packaged irradiated turkey breast meat. Significantly,the amount of S-volatiles was inversely related to the exposure time to aerobic conditions. On the other hand, the total amount of aldehydes in irradiated turkey breast increased with the time in aerobic conditions and agrees with TBARS (Table 2). The amount of total S- volatiles in irradiated turkey breast meat with A3/V7 (aerobic conditions for 3 days and then vacuum packaging for 7 days) double packaging was only about 10% that of vacuum packaged, and the amount of total aldehydes was 22% of aerobically packaged meat. The amount of total ketone, however, was proportional to the time with aerobic conditions irrespective of irradiation dose. The major aldehydes produced in aerobically packaged irradiated turkey breast at 10 days were propanal, pentanal, and hexanal, and considerable amounts of these aldehydes were found in A5/V5 (aerobic conditions for 5 days then vacuum conditions for 5 days) doubly packaged irradiated samples (Table 5). Ketones such as 2-propanone and 4-pentanone were produced mainly in aerobically packaged turkey breast meat regardless of irradiation dose, and 2-propanone was the most representative volatile compound in nonirradiated aerobically packaged turkey meat after 10 days of storage (Table 5). S-volatiles in vacuum-packaged irradiated turkey breast meat at day 10 consisted of dimethyl sulfide Table 4 Volatile profile of irradiated raw turkey breast meat with different packaging at day 10 a Aldehydes 72e 1503a 1103b 340c 177d 165d 20 Ketones 12396a 11,338a 9863ab 9273ab 8930b 5867c 243 S-compounds 1136e 1167e 1870d 2607c 5462b 25,311a 87 Hydrocarbons 2596c 4761ab 6189ab 7341a 3462b 4983b 37 Others 98a 47a 52a 0b 0b 0b 6 Total 16,302b 18,825b 19,087b 16,743b 18,037b 36,336a 97 a Different letters (a e) within a row are significantly different (P<0.05). n=4. Table 5 The content of aldehydes, ketones, and other volatiles in irradiated raw turkey breast meat with different packaging at day 10 a Aldehydes Propanal 72b 983a 865a 269b 125b 106b 57 Butanal 0c 73a 51b 0c 0c 0c 2 3-Methyl butanal 0b 37a 0b 0b 0b 0b 1 Pentanal 0c 157a 139a 71b 52b 59b 16 Hexanal 0b 253a 48b 0b 0b 0b 23 Ketones 2-Propanone 12,117a 11,141ab 9696ab 9138b 8772b 5802c Butanone 128b 197a 167ab 135b 158ab 65c 12 3-Pentanone 151a 0b 0b 0b 0b 0b 8 Others Acetate, ethyl ester 47a 0b 0b 0b 0b 0b 3 2-Ethyl furan 51a 47a 52a 0b 0b 0b 5 Total 12,566a 12,888a 11,018b 9613c 9107c 6032d 84 a Different letters (a c) within a row are significantly different (P<0.05). n=4.

6 394 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) Table 6 Sulfur-containing volatiles of irradiated raw turkey breast meat with different packaging at day 10 a Methanethiol 0b 0b 0b 0b 0b 1505a 91 Dimethyl sulfide 1033d 1024d 1774cd 2576c 5346b 15,101a 316 Carbon disulfide 103a 103a 62b 0c 0c 0c 4 Methylthio ethane 0b 0b 0b 0b 0b 47a 1 Dimethyl disulfide 0b 40b 34b 31b 116b 8020a 91 Dimethyl trisulfide 0b 0b 0b 0b 0b 638a 22 Total 1136e 1167e 1870d 2607c 5462b 25,311a 87 a Different letters (a e) within a row are significantly different (P<0.05). n=4. Table 7 Hydrocarbons of irradiated raw turkey breast meat with different packaging at day 10 a 2-Methyl-1-propene 0e 77d 90d 150c 199b 528a 16 Butane 71b 209a 212a 192a 0c 0c 18 1-Pentene 49c 111bc 180a 107bc 66bc 130ab 17 Pentane 1633ab 2202a 2518a 1615ab 835bc 467c Pentene 0d 115b 204a 116b 55c 133b 12 3-Methyl pentane 0b 51a 0b 0b 0b 0b 3 1-Hexene 0c 71b 76b 53b 54b 110a 7 Hexane Benzene 49c 61bc 118b 126b 131b 222a 17 1-Heptene 0c 158a 154a 107b 90b 71b 11 Heptane 130c 261ab 351a 234bc 139c 75d 30 Toluene 40d 370c 355c 430c 563b 713a 25 1-Octene 0d 44d 214b 145c 168bc 434a 16 Octane 101e 202d 557b 368c 484b 898a 31 2-Octene 76c 101bc 285a 166b 144bc 265a 19 3-Methyl-2-heptene 0c 89b 156b 109b 162b 529a 19 Total 2596c 4761ab 6189ab 7341a 3462b 4983b 37 a Different letters (a e) within a row are significantly different (P<0.05). n=4. and dimethyl disulfide as at day 0 (Table 6). The main difference between 0 and 10 day stored vacuumpackaged irradiated meats was the amount of dimethyl disulfide and dimethyl sulfide, which increased two-fold over the storage time. Dimethyl trisulfide, methanethiol, and methanethiol ethane were found in only vacuumpackaged irradiated turkey breast. Under aerobic conditions, on the other hand, almost all S-compounds, except for dimethyl sulfide, evaporated during the 10- day storage period and clearly suggested that aerobic packaging was more beneficial than vacuum packaging in reducing S-volatiles responsible for the irradiation off-odor. Aerobic packaging, however, promoted lipid oxidation in turkey breast meat as evidenced by the increased aldehydes and TBARS (Tables 2 and 5). When both lipid oxidation and S-volatiles responsible for irradiation off-odor should be considered, therefore, doubly packaging turkey breast meat was far more beneficial than the aerobic or vacuum packaging alone. Turkey breast meat with A3/V7 double packaging (aerobic conditions for 3 days then vacuum conditions for 7 days) had only 17% dimethyl sulfide and 0.4% dimethyl disulfide of vacuum-packaged irradiated turkey breast, and other S-volatiles (methanethiol, methylthiol ethane, and dimethyl trisulfide) were not detected. In aerobically packaged nonirradiated turkey

7 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) breast meat, dimethyl sulfide and carbon disulfide were the predominant S-volatiles at day 10. The doublepackaging effect on the production of many of the hydrocarbons in turkey breast at day 10 was inconsistent. The amounts of butane, pentane, 3-methylpentane, 1-heptene and heptane, however, showed decreasing trends, and 2-methyl-1-propene, toluene, 1- octene, and 3-methyl-2-heptene had increasing trends as the exposure time to oxygen decreased (Table 7). The amounts of benzene, toluene, 1-octene, octane, and 3- methyl-2-heptene were higher in irradiated than nonirradiated meats. Thus, these hydrocarbons may also have a certain effect on the irradiation off-odor. The specific evaluation of each volatile compound to the irradiation off-odor is beyond the scope of this work. 4. Conclusion Irradiating and storing turkey breast meat for 1 3 days under aerobic conditions and then storing under vacuum conditions (A1/V9 or A3/V7 double packaging) could minimize irradiation off-odor by volatilizing S- volatile compounds. Vacuum packaging was required to minimize lipid oxidation during the remaining storage period. This double packaging can be an efficient way to minimize the quality changes in poultry breast meat caused by irradiation without adding any additives. However, this modified packaging method involves with some extra costs, labor, and time, and more efficient and convenient modification of this concept will be needed. Acknowledgements Journal Paper No. J of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA Project No. 3706, supported by State of Iowa funds. References Ahn, D. U., Jo, C., Du, M., Olson, D. G., & Nam, K. C. (2000). Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions. Meat Science, 56, Ahn, D. U., Jo, C., & Olson, D. G. (2000). Analysis of volatile components and the sensory characteristics of irradiated raw pork. Meat Science, 54, Ahn, D. U., Nam, K. C., Du, M., & Jo, C. (2001). Volatile production in irradiated normal, pale soft exudative (PSE), and dark firm dry (DFD) pork under different packaging and storage conditions. Meat Science, 57, Ahn, D. U., Olson, D. G., Jo, C., Chen, X., Wu, C., & Lee, J. I. (1998). Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production, and color in raw pork patties. Meat Science, 47, Ahn, D. U., Sell, J. L., Jeffery, M., Jo, C., Chen, X., Wu, C., & Lee, J. I. (1997). Dietary vitamin E affects lipid oxidation and total volatiles of irradiated raw turkey meat. Journal of Food Science, 62, AMSA. (1991). Guidelines for Meat Color Evaluation. Chicago, IL: National Live Stock and Meat Board. Grant, I. R., & Patterson, M. F. (1991). Effect of irradiation and modified atmosphere packaging on the microbiological and sensory quality of pork stored at refrigeration temperatures. International Journal of Food Science and Technology, 26, Jo, C., & Ahn, D. U. (2000). Production volatile compounds from irradiated oil emulsions containing amino acids or proteins. Journal of Food Science, 65, Luchsinger, S. E., Kropf, D. H., Garcia-Zepeda, C. M., Hunt, M. C., Marsden, J. L., Rubio-Canas, E. J., Kastner, C. L., Kuecher, W. G., & Mata, T. (1996). Color and oxidative rancidity of gamma and electron beam-irradiated boneless pork chops. Journal of Food Science, 61, Lynch, J. A., MacFie, H. J. H., & Mead, G. C. (1991). Effect of irradiation and packaging type on sensory quality of chilled-stored turkey breast fillets. International Journal of Food Science and Technology, 26, Nam, K. C., & Ahn, D. U. (2002). Carbon monoxide-heme pigment complexes are responsible for the pink color in irradiated raw turkey breast meat. Meat Science, 60, Patterson, R. L., & Stevenson, M. H. (1995). Irradiation-induced offodor in chicken and its possible control. British Poultry Science, 36, SAS Institute, Inc. (1995). SAS/STAT user s guide. Cary, NC: SAS Institute. Sorheim, O., Nessen, H., & Nesbakken, T. (1999). The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide. Meat Science, 52, Stryer, L. (1981). Biochemistry. New York, NY: Freeman and Co. USDA. (1999). USDA issues final rule on meat and poultry irradiation: Backgrounder. Washington, DC: US Dept. of Agriculture Available: Woods, R. J., & Pikaev, A. K. (1994). Interaction of radiation with matter. In R. J. Woods, & A. K. Pikaev (Eds.), Applied radiation chemistry: radiation processing (pp ). New York: John Wiley & Sons.