Volatile production in irradiated normal, pale soft exudative (PSE) and dark rm dry (DFD) pork under di erent packaging and storage conditions $

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1 Meat Science 57 (2001) 419±426 Volatile production in irradiated normal, pale soft exudative (PSE) and dark rm dry (DFD) pork under di erent packaging and storage conditions $ D.U. Ahn *, K.C. Nam, M. Du, C. Jo Department of Animal Science, Iowa State University, Ames, IA , USA Received 18 July 2000; received in revised form 18 September 2000; accepted 18 September 2000 Abstract Normal, pale soft exudative (PSE) and dark rm dry (DFD) pork Longissimus dorsi muscles were vacuum packaged, irradiated at 0 or 4.5 kgy and stored at 4 C for 10 days. Volatile production from pork loins was determined at Day 0 and Day 10 of storage at 4 C. With both aerobic and vacuum packaging, irradiation increased the production of sulfur-containing volatiles (carbon disul de, mercaptomethane, dimethyl sul de, methyl thioacetate and dimethyl disul de) in all three pork conditions at Day 0 but did not increase hexanal the major indicator volatile of lipid oxidation. The PSE pork produced the lowest amount of total sulfur-containing volatiles in both aerobically and vacuum-packaged pork at Day 0. The majority of sulfur-containing volatiles produced in meat by irradiation disappeared during the 10-day storage period under aerobic packaging conditions. With vacuum packaging, however, all the volatiles produced by irradiation remained in the packaging bag during storage. Irradiation had no relationship with lipid oxidation-related volatiles (e.g. hexanal) in both aerobic and vacuum-packaged raw pork. The DFD muscle was very stable and resistant to oxidative changes in both irradiated and nonirradiated pork during storage, suggesting that irradiation can signi cantly increase the utilization of raw DFD pork and greatly bene t the pork industry. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Meat conditions; Irradiation; Volatiles; Packaging; O -odor; Lipid oxidation 1. Introduction The e ect of irradiation on the catalysis of lipid oxidation and the development of o - avor in normal, pale soft exudative (PSE) and dark rm dry (DFD) pork may differ. Also, the membrane structure of PSE pork is leaky because of high protein denaturation (Fisher, Hamm, & Honikel, 1979; Warriss & Brown, 1987). Through the holes generated by the denatured membrane proteins, water molecules can easily get into membrane bilayers. Along with the water, irons and free amino acids con ned inside cellular materials under normal conditions may also migrate into membrane bilayers and promote oxidative reactions when free radicals are available. Hydroxyl $ Journal Paper No. J of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA Project No. 3322, and supported by the Food Safety Consortium. * Corresponding author. Tel.: ; fax: address: duahn@iastate.edu (D.U. Ahn). radicals can be formed from water molecules in all meat conditions upon irradiation, and the reaction of hydroxyl radicals is site speci c because of their short half-life (10 6 sec) (Diehl, 1995; Thakur & Singh, 1994). Therefore, the distribution of water and the site where hydroxyl radicals formed are critical for the irradiation-dependent reaction. The distribution and proportion of free and bound water in normal, PSE and DFD pork are di erent (Forrest, Aberle, Hedrick, Judge, & Merkel 1975). It is hypothesized that PSE meat would be more susceptible to oxidative changes and produce more o - avor volatiles than normal and DFD pork when irradiated. Volatile compounds responsible for o -odor in irradiated meat are produced by the impact of radiation on protein and lipid molecules and are distinctly di erent from those characteristics of lipid oxidation. Recent ndings in this area (Patterson & Stevenson, 1995) support and extend this concept. These investigators studied odor volatiles in irradiated chicken meat and found that dimethyltrisul de is the most potent o -odor compound, followed by cis-3- and trans-6-nonenals, oct /01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S (00)

2 420 D.U. Ahn et al. / Meat Science 57 (2001) 419±426 en-3-one and bis(methylthio-)methane. These studies also provided evidence to support the concept that the changes that occur following irradiation are distinctly di erent from those of warmed-over avor in oxidized meat. Thayer, Fox and Lakritz (1993) reported that irradiation dose, processing temperature and packaging conditions strongly in uence the microbial load and the nutritional quality of meat. Irradiation-induced oxidative chemical changes are dose dependent, and the presence of oxygen has a signi cant e ect on the development of oxidation and odor intensity (Merritt, Angelini, Wierbicki, & Shuts, 1975). Hashim, Resurrecccion, and McWatters (1995) reported that irradiating uncooked chicken thigh and breast produced a characteristic ``bloody and sweet'' aroma that remained after the thighs were cooked but was not detectable after the breasts were cooked. The chromatograms of raw irradiated meat suggested that lipid oxidation can be responsible for only part of the o -odor in irradiated meat (Ahn, Olsen, Lee, Jo, Wu, & Chen, 1998; Ahn, Jo, & Olson, 1999a), and other mechanisms such as radiolysis of proteins played an important role in the production of o -odor volatiles in irradiated meat (Jo & Ahn, 2000). The objective of this research was to determine the e ects of irradiation on volatile characteristics of normal, pale soft exudative and dark rm dry pork during storage with di erent packaging conditions. 2. Materials and methods 2.1. Sample preparation Three conditions of pork loin (Longissimus dorsi) muscles Ð Normal, PSE and DFD Ð were purchased from a local packing plant, sliced to 3-cm thick steaks and either packaged in oxygen-permeable zipper bags (46, 2 MIL, Associated Bag Company, Milwaukee, WI) or vacuum-packaged ( 1.0 bar, at 4 C) in oxygenimpermeable nylon/polyethylene bags (9.3 ml O 2 /m 2 /24 hat0 C; Koch, Kansas City, MO) using a Multi Vac vacuum packager (AG-800, Wolfertschwenden/Allgau, Germany). Half of the steaks from the oxygen permeable and oxygen impermeable bags were stored overnight at 4 C and then irradiated using a Linear Accelerator (Circe IIIR, Thomson CSF Linac, Saint-Aubin, France). The target doses of irradiation were 0 and 4.5 kgy. The energy and power level used were 10 MeV and 10 kw, respectively, and the average dose rate was 92.0 kgy/ min. The max/min ratio was approximately 1.12 for 2.5 kgy and 1.15 for 4.5 kgy. To con rm the target dose, two alanine dosimeters per cart were attached to the top and bottom surfaces of the sample. The alanine dosimeter was read using a 104 Electron Paramagnetic Resonance Instrument (Bruker Instruments Inc., Billerica, MA). The irradiated pork steaks were stored at 4 C for 10 days, and the volatile characteristics of the steaks were determined after 0 and 10 days of storage. Precept II and Purge-and-Trap Concentrator 3000 (Tekmer-Dohrmann, Cincinnati, OH) connected to gas chromatography (GC; 6890, Hewlett-Packard Co., Wilmington, DE) was used to quantify and characterize the volatiles responsible for the o - avor in the pork with di erent irradiation doses and meat conditions Dynamic headspace GC/mass spectrometry Volatiles were analyzed using a dynamic headspace GC/mass spectrometry method. Two grams of minced pork loin sample was placed in a sample vial (40 ml) and then one pack of oxygen absorber (Ageless Type Z-100, Mitsubishi Gas Chemical America, Inc., New York, NY) was added. Four replications per treatments were analyzed. The sample vial was ushed (40 C) with helium gas (99.999%) for 5 s at 40 psi, capped tightly with a Te on-lined, open-mouth cap and placed in a refrigerated (4 C) sample-tray. The maximum holding time for samples before volatile analysis was less than 10 h to minimize oxidative changes during the sample holding time (Ahn, Jo, & Olson, 1999b). Samples were purged with helium gas (40 ml/min) for 15 min. Volatiles were trapped at 20 C using a Tenax/Silica gel/ Charcoal column (Tekmar-Dorham) and desorbed for 2 min at 220 C. The desorbed volatiles were concentrated at 100 C using a cryofocusing unit, and then thermally desorbed and injected (30 s) into a capillary GC column. An HP-624 (7.5 m, 0.25 mm i.d., 1.4 mm nominal) and an HP-1 (52.5 m, 0.25 mm i.d., 0.25 mm nominal, Hewlett-Packard Co.) were connected using a zero deadvolume column connector (J&W Scienti c, Folsom, CA). Ramped oven temperature was used to improve volatile separation. The initial oven temperature, 0 C was held for 2.50 min. After that the oven temperature was increased to 10 Cat2.5 C per min, increased to 80 Cat10 C/min, increased to 150 Cat20 C/min and then increased to 180 Cat10 C/min. Constant column pressure at 20 psi was maintained. The ionization potential of the mass selective detector was 70eV and the scan range was 33.1± 300 m/z. Identi cation of volatiles was achieved by comparing mass spectral data of samples with those of the Wiley library (Hewlett-Packard Co.). Standards, when available, were used to con rm the identi cation by the mass selective detector. The area of each peak was integrated using ChemStation software (Hewlett- Packard Co.), and the total ion counts10 4 was reported as an indicator of volatiles generated from the meat samples Statistical analysis The e ects of irradiation on the volatiles of normal, PSE and DFD pork with di erent packaging and storage

3 D.U. Ahn et al. / Meat Science 57 (2001) 419± time were analyzed statistically by analysis of variance using SAS 1 software (SAS Institute, 1985). The Student- Newman-Keuls multiple range test was used to compare di erences in volatile content among irradiated meats within a packaging and storage combination (P<0.05). The e ect of irradiation, meat condition, packaging and storage on each volatile was also determined statistically. Mean values, S.E.M. and probabilities for treatment e ects were reported. 3. Results and discussion 3.1. Volatiles of aerobically packaged pork Irradiation had a signi cant impact on the amount and pro le of volatiles in pork. At Day 0, aerobically packaged irradiated pork produced a greater number of volatiles than the nonirradiated pork (Table 1). Butane, propane, mercaptomethane, dimethyl sul de, methyl thioacetate and dimethyl disul de, not detected in nonirradiated pork, were produced by irradiation in all three pork conditions. Among the volatiles produced by irradiation, mercaptomethane, dimethyl disul de, methyl thioacetate and dimethyl disul de Ð sulfurcontaining volatile compounds Ð were the major ones. The productions of butane, mercaptomethane, dimethyl sul de, methyl thioacetate and dimethyl sul de were the highest in irradiated normal pork and the lowest in irradiated PSE pork in most cases. Carbon disul de, another sulfur-containing volatile compound, was found in both irradiated and nonirradiated pork, but its concentration also increased signi cantly after irradiation in all three pork conditions. The production of carbon disul de was the highest in irradiated PSE pork and the lowest in nonirradiated DFD pork. The total content of sulfur-containing volatiles in irradiated normal pork was about 2-fold higher than the contents in the PSE or DFD pork, suggesting that normal pork would produce stronger irradiation odor than PSE or DFD pork. The greater production of sulfur-containing volatiles in irradiated normal pork compared with the PSE or DFD pork could be related to the water content/activity of the meat, but cannot prove it at this Table 1 Relative production of volatiles of aerobically packaged pork Longissimus dorsi muscle at 0 days of storage at 4 C a Volatile compound 0 kgy 4.5 kgy S.E.M. Normal PSE DFD Normal PSE DFD Peak area (pas) 10 4 Butane 0 c 0 c 0 c 136 a 76 b 87 b 8 Acetaldehyde 962 bc 688 bc 1818 a 506 bc 1093 b 356 c 153 Propane 0 c 0 c 0 c 87 b 142 a 77 b 10 Mercaptomethane 0 d 0 d 0 d 3024 a 676 c 1345 b 80 Pentane 321 ab 224 b 286 ab 581 a 206 b 144 b 67 Furan 41 b 51 b 58 ab 72 ab 93 a 72 ab 9 Ethanol 956 a 692 a 789 a 233 b 98 b 52 b 80 Dimethyl sul de 0 b 0 b 0 b 682 a 136 b 562 a 45 Carbon disul de 185 cd 130 cd 65 d 422 b 1162 a 352 b 67 3-Methyl pentane 31 b 0 c 0 c 48 b 97 a 0 c 6 1-Hexene 29 b 0 b 0 b 74 a 25 b 0 b 6 Hexane 170 b 145 b 167 b 323 a 247 ab 160 b 29 1-Propanol 117 a 6 0b 72 b 19 c 25 c 0 c 10 Diacetyl 323 a 141 b 363 a 43 b 36 b 26 b 37 2-Butanone 283 bc 431 ab 182 c 513 a 53 c 145 c 59 3-Methyl butanal 28 ab 0 b 17 ab 45 a 27 ab 32 ab 7 1-Heptene 26 c 0 d 0 d 125 a 71 b 33 c 9 Heptane 148 b 124 b 71 b 284 a 196 ab 86 b 35 2-Pentanone 93 a 119 a 17 b 0 b 0 b 0 b 9 Methyl thioacetate 0 c 0 c 0 c 402 a 36 c 295 b 24 Pentanal 74 ab 66 ab 31 b 103 a 55 ab 25 b 13 Dimethyl disul de 0 b 0 b 0 b 612 a 30 b 130 b 38 1-Octene Octane 1226 a 1353 a 1297 a 1305 a 1139 a 526 b Octene Octene 5 b 0 b 0 b 31 a 26 a 0 b 3 Hexanal Nonane Total volatiles 5242 bc 4390 c 5400 bc 9862 a 5899 b 4571 c 419 a Di erent letters within a row are di erent (P<0.05). n=4. PSE, pale, soft, exudative; DFD, dark, rm, dry; S.E.M., standard error of the mean.

4 422 D.U. Ahn et al. / Meat Science 57 (2001) 419±426 point. Hashim et al. (1995) characterized the odor of irradiated meat as a bloody and sweet and Heath, Owens, Tesch and Hannah (1990) described it as a hot fat, burned oil, or burned feathers odor. The amount of acetaldehyde was the highest in nonirradiated DFD but the lowest in irradiated DFD pork. Propane was the highest in irradiated PSE pork. The content of pentane, hexane and heptane, a group of chemicals presumably associated with radiolytic degradation of lipids, was higher in irradiated normal pork than in nonirradiated normal pork and also was higher than the irradiated and nonirradiated PSE and DFD pork, respectively. As previously reported (Ahn, Olson, Jo, Love, & Jin, 1999), the concentrations of alkenes such as 1-hexene and 1-heptene in pork from a same meat condition Ð except for 1-hexene in DFD pork Ð increased signi cantly after irradiation, but the amounts were small. Octane content in irradiated DFD pork was lower than in any other irradiated or nonirradiated pork. The amounts of ethanol, 1-propanol, diacetyl and 2-pentanone in all three pork conditions decreased signi cantly after irradiation, but the amounts were small compared with the sulfur-containing compounds. Hexanal, an o - avor volatile typically associated with oxidative changes to linoleic acid, was detected only in irradiated and nonirradiated normal meat. Changes in other volatiles in all three pork conditions after irradiation were either small or inconsistent. Most sulfur and carbonyl compounds have low odor thresholds and were considered as important to irradiation odor (Angelini, Merritt, Mendelshon, & King 1975). Batzer and Doty (1955) reported that methyl mercaptan and hydrogen sul de were important to irradiation odor, and Patterson and Stevenson (1995) found that dimethyl trisul de was the most potent o odor compound, followed by cis-3- and trans-6-nonenals, oct-1-en-3-one, and bis(methylthio-)methane in irradiated chicken meat. Dimethyl trisul de was detected in irradiated pork loin in our previous work (Ahn, Jo, & Olson, 1999a), but no noticeable amount of dimethyl trisul de was found in this study. This indicated that the sulfur-containing compounds would be the major volatile components responsible for the characteristic odor in irradiated pork. This study also provided evidence to support the concept that the changes that occur following irradiation are distinctly di erent from those of warmed-over avor in oxidized meat. After 10 days of storage in the aerobic packaging condition, the amount of total volatiles decreased by Table 2 Relative production of volatiles of aerobically packaged pork Longissimus dorsi muscle after 10 days of storage at 4 C a Volatile compound 0 kgy 4.5 kgy S.E.M. Normal PSE DFD Normal PSE DFD Peak area (pas) 10 4 Butane 38 b 26 b 27 b 80 a 91 a 44 b 10 Acetaldehyde 197 b 164 b 434 a 235 ab 357 ab 257 ab 50 Mercaptomethane Pentane Furan 26 a 0 b 0 b 33 a 29 a 26 a 2 Ethanol 64 b 61 b 70 a 112 b 77 b 32 b 56 Dimethyl sul de 0 b 0 b 0 b 749 a 336 b 873 a 102 Carbon disul de 139 b 11 b 112 b 216 ab 246 a 215 ab 25 3-Methyl pentane Hexene 22 b 0 c 0 c 22 b 31 a 0 c 2 Hexane Propanol Diacetyl 76 b 188 b 515 a 73 b 143 b 127 b 32 2-Butanone 217 c 139 c 173 c 379 b 200 c 707 a 45 3-Methyl butanal 21 bc 0 c 34 b 27 bc 93 a 18 bc 7 1-Heptene 39 ab 0 b 0 b 49 a 60 a 55 a 11 Heptane 121 ab 59 b 54 b 145 a 172 a 162 a 18 2-Pentanone 166 a 57 b 62 b 0 c 0 c 0 c 12 Methyl thioacetate 0 c 0c 0c 194 a 45 bc 79 b 2 Pentanal Octene 46 b 271 a 27 b 53 b 97 b 88 b 21 Octane Octene Octene 13 a 24 a 0 b 18 a 19 a 0 b 3 Hexanal Nonane 30 a 41 a 0 b 38 a 53 a 37 a 6 Total volatiles 2300 b 2500 b 2724 b 4180 a 4123 a 4184 a 192 a Di erent letters within a row are di erent (P<0.05). n=4. PSE, pale, soft, exudative; DFD, dark, rm, dry; S.E.M., standard error of the mean.

5 D.U. Ahn et al. / Meat Science 57 (2001) 419± ±60% in all pork but irradiated DFD pork. As in 0- day pork, mercaptomethane, dimethyl sul de and methyl thioacetate were found only in irradiated pork, and 2-pentanone in nonirradiated pork (Tables 1 and 2). This indicated that storage time had no e ect on the production of these compounds. Propane and dimethyl disul de, found in irradiated meat at Day 0, were not detected after 10 days of storage in aerobic conditions. The amounts of other volatiles such as acetaldehyde, mercaptomethane, furan and ethanol signi cantly decreased in all three pork conditions after 10 days of storage, but the decrease of mercaptomethane was the most signi cant (Table 2). The amount of methyl thioacetate in irradiated DFD pork, and that of octane in all pork except irradiated DFD, also decreased signi cantly over the 10- day storage in aerobic conditions. The content of dimethyl sul de was the only sulfur compound that increased signi cantly after 10 days of storage in aerobic conditions. This result suggests that some of these compounds escaped from the packaging bags and others converted to other compounds via the chemical or enzymatic reactions during storage. Hexanal was produced in all three pork conditions, except nonirradiated DFD pork after 10 days of storage in aerobic conditions. Irradiation did not increase hexanal production in all three pork conditions, but the storage time did in aerobically packaged pork (Table 2). Luchsinger et al. (1996) showed that 2-thiobarbituric acid reactive substances (TBARS) values of both chilled and frozen boneless pork chops were stable, regardless of display day, dose and irradiation sources. Ahn et al. (1998) reported that hexanal is the volatile compound that best represents the lipid oxidation status in meat. This indicated that DFD pork is less susceptible to oxidative changes during storage. The amount of 3-methyl pentane in irradiated DFD pork also increased during storage Volatiles of vacuum-packaged pork Volatile pro les of vacuum-packaged pork at Day 0 (Table 3) were similar to those of the aerobically packaged pork (Table 1) except for minor di erences. In addition to butane, propane, mercaptomethane, dimethyl sul de, methyl thioacetate and dimethyl disul de, a few other volatiles were detected only in vacuum-packaged irradiated pork at Day 0 (Tables 1 and 3). The productions Table 3 Relative production of volatiles of vacuum-packaged pork L. dorsi muscle at 0 days of storage at 4 C a Volatile compound 0 kgy 4.5 kgy S.E.M. Normal PSE DFD Normal PSE DFD Peak area (pas) 10 4 Butane 0 c 0 c 0 c 96 a 67 b 64 b 3 Acetaldehyde 1261 ab 877 bc 1651 a 326 c 699 bc 462 c 161 Propane 0 b 0 b 0 b 86 a 15 a 85 a 13 Mercaptomethane 0 c 0 c 0 c 2185 a 739 bc 1408 b 247 Pentane 235 bc 332 ab 160 c 419 a 436 a 190 c 33 Furan Ethanol 761 a 587 a 667 a 104 b 95 b 0 b 51 Dimethyl sul de 0 d 0 d 0 d 759 b 354 c 978 a 29 Carbon disul de 0 d 82 bc 55 cd 189 a 124 ab 145 ab 18 3-Methyl pentane 0 b 0 b 0 b 0 b 45 a 0 b 2 1-Hexene 0 b 0 b 0 b 53 a 43 a 0 b 4 Hexane 115 b 131 b 88 b 183 a 204 a 135 b 14 1-Propanol 43 b 64 a 42 b 16 cd 24 bc 0 d 6 Diacetyl 204 a 72 b 181 a 0 c 0 c 44 bc 13 2-Butanone 201 ab 232 a 103 b 120 b 134 ab 196 ab 25 3-Methyl butanal 17 bc 0 c 22 bc 41 b 114 a 26 bc 8 1-Heptene 14 b 0 b 0 b 97 b 871 a 38 b 45 Heptane 95 b 105 b 57 b 178 a 189 a 91 b 14 2-Pentanone 46 a 53 a 0 b 0 b 0 b 0 b 3 Methyl thioacetate 0 b 0 0 b 187 a 153 a 137 a 16 Pentanal Dimethyl disul de 0 c 0 c 0 c 239 a 55 c 145 b 4 1-Octene 119 b 78 b 66 b 328 a 81 b 66 b 31 Octane 18 ab 992 ab 619 b 1089 ab 1163 a 849 ab Octene 13 b 0 b 138 a 28 b 29 b 21 b 14 3-Octene 0 0 b 0 b 20 a 21 a 0 b 1 Nonane 0 c 18 b 0 c 39 a 26 ab 0 c 5 Total volatiles 4142 d 3735 d 3933 d 6916 a 5709 b 5159 c 201 a Di erent letters within a row are di erent (P<0.05). n=4. PSE, pale, soft, exudative; DFD, dark, rm, dry; S.E.M., standard error of the mean.

6 424 D.U. Ahn et al. / Meat Science 57 (2001) 419±426 of butane, mercaptomethane, dimethyl sul de and dimethyl disul de were the highest in irradiated normal pork and the lowest in irradiated PSE pork as in aerobically packaged pork at Day 0 (Table 1). Irradiation increased the production of 1-hexene, 3-octene and nonane in normal and PSE pork. But irradiation decreased the amounts of ethanol, 1-propanol, diacetyl and 2-pentanone signi cantly. Irradiated normal pork produced the highest amounts of butane, carbon disul de and 1-octene; nonirradiated DFD pork had the highest acetaldehyde; irradiated DFD pork produced the lowest pentane, ethanol and 1-propanol; and irradiated PSE pork had the highest 3-methyl butanal. Hexanal was not detected from any of the vacuum-packaged pork (Table 3). The changes of volatiles in pork after10 days of storage in vacuum packaging were di erent from those in aerobic packaging. Total volatile content of nonirradiated pork decreased but that of the irradiated pork increased signi cantly (Table 4). Unlike in aerobically packaged pork, the amounts of all sulfur-containing volatile compounds except for mercaptomethane and carbon disul de increased signi cantly. Among the sulfur compounds, the increase of dimethyl sul de in irradiated pork during the 10-day storage was the most dramatic (4- to 6- fold increase from the Day 0, Tables 3 and 4), but those of methyl thioacetate and dimethyl disul de were also signi cant. Irradiated normal pork produced the highest amount of total sulfur-containing volatile compounds and DFD pork had the lowest of the three pork conditions. The amounts of acetaldehyde and 2-butanone in irradiated meat increased but that of ethanol in nonirradiated pork decreased after storage. Hexanal was found in both irradiated and nonirradiated normal and PSE pork, and the production of nonane increased signi cantly after 10 days of storage in vacuum-packaged pork (Table 4) Correlations The production of volatiles was strongly in uenced by meat condition and irradiation. Storage time had less e ect than meat condition and irradiation on the content of many volatile compounds, but packaging of raw Table 4 Relative production of volatiles of vacuum-packaged pork Longissimus dorsi muscle after 10 days of storage at 4 C a Volatile compound 0 kgy 4.5 kgy S.E.M. Normal PSE DFD Normal PSE DFD Peak area (pas) 10 4 Butane 0 c 0 c 0 c 331 a 271 a 197 b 20 Acetaldehyde 272 ab 57 b 135 b 367 a 278 ab 108 b 42 Propane 0 c 0 c 0 c 111 a 110 a 68 b 8 Mercaptomethane 0 b 0 b 0 b 1692 a 1655 a 1684 a 116 Pentane 205 cd 96 d 109 d 637 a 382 b 309 bc 42 Furan 13 b 0 c 0 c 29 a 34 a 25 a 2 Ethanol 269 ab 131 b 0 b 397 a 100 b 62 b 68 Dimethyl sul de 0 b 0 b 0 b 4877 a 1612 b 3562 a 454 Carbon disul de 211 b 124 c 77 c 292 a 186 b 204 b 16 3-Methyl pentane 110 ab 149 a 68 b 104 ab 71b 39 b 18 1-Hexene 0 c 0 c 0 c 89 a 35 b 10 c 6 Hexane 130 bc 88 c 144 bc 290 a 201 b 173 bc 22 1-Propanol 130 a 38 b 13 b 68 b 20 b 13 b 15 Diacetyl 123 a 152 a 29 b 63 b 23 b 117 a 15 2-Butanone 346 b 308 b 208 c 760 a 196 bc 322 b 66 3-Methyl butanal 16 c 0 c 0 c 91 b 129 a 17 c 11 1-Heptene 0 d 0 d 0 d 191 a 66 b 37 c 7 Heptane 65 c 45 c 42 c 273 a 137 b 83 bc 18 2-Pentanone 329 a 124 b 50 c 0 c 0 c 0 c 13 Methyl thioacetate 0 b 0 b 0 b 410 a 259 a 374 a 61 Pentanal 31 b 34 b 0 b 79 a 48 b 25 b 5 Dimethyl disul de 0 c 0 c 0 c 358 ab 235 b 473 a 41 1-Octene 30 c 196 b 17 c 141 b 537 a 139 c 23 Octane Octene 0 b 0 b 0 b 30 a 25 a 20 a 3 3-Octene 0 c 0 c 0 c 25 a 17 b 10 c 2 Hexanal 22 b 26 b 0 b 128 a 78 ab 0 b 19 Nonane 42 ab 50 ab 17 bc 58 a 48 ab 10 c 8 Total volatiles 3062 c 2184 c 1424 c a 7635 b 8880 b 413 a Di erent letters within a row are di erent (P<0.05). n=4. PSE, pale, soft, exudative; DFD, dark, rm, dry; S.E.M., standard error of the mean.

7 D.U. Ahn et al. / Meat Science 57 (2001) 419± Table 5 Statistical signi cance of e ects of meat condition, irradiation dose, storage time and packaging on volatile production from pork L. dorsi muscle a Volatile compound Probability Meat condition (d.f.=2) Irradiation (d.f.=1) Storage (d.f.=1) Packaging (d.f.=1) Butane Acetaldehyde Propane Mercaptomethane Pentane Furan Ethanol Dimethyl sul de Carbon disul de Methyl pentane Hexene Hexane propanol Diacetyl Butanone Methyl butanal Heptene Heptane Pentanone Methyl thioacetate Pentanal Dimethyl disul de Octene Octane Octene Octene Hexanal Nonane Total volatiles a n=36 for meat condition e ect; n=48 for irradiation, storage and packaging e ect. meat had the least e ect on most of the volatiles found in this study. Among the volatiles found in irradiated and nonirradiated pork (Tables 1±4), the production of all the volatile compounds except for acetaldehyde, dimethyl sul de and carbon disul de were in uenced by meat condition; 3-pentanol, 3-methyl pentane, 2-butanone, 1- octene, octane, 3-octene and hexanal were in uenced by irradiation; and pentane, ethanol, dimethyl sul de, carbon disul de, 1-propanol, 3-methyl butanal, heptane, methyl thioacetate, dimethyl disul de and total volatiles were in uenced by storage time. Butane, propane, mercaptomethane, dimethyl sul de, hexane, heptane, 2- octene, and hexanal in pork were in uenced by packaging methods. Irradiation was the only factor that in uenced the production of all ve sulfur-containing volatile compounds in pork. The production of hexanal, the major volatile related to oxidative changes in meat, was not in uenced by irradiation but by meat condition, storage and packaging methods (Table 5). Ahn, Jo and Olson (1999a) also reported that irradiation did not increase lipid oxidation in meat, and Nam, Ahn, Du, Jo, and Jo (2000) and Nam, Du, Jo, and Ahn (2000) showed that irradiation and storage time had no e ect on the TBARS of vacuum- and aerobic-packaged normal, PSE and DFD pork. 4. Conclusion Irradiation increased the production of sulfur-containing volatiles (carbon disul de, mercaptomethane, dimethyl sul de, methyl thioacetate and dimethyl disul de), but not lipid oxidation products (aldehydes), in all three pork conditions regardless of packaging conditions. With vacuum packaging, lipid oxidation and volatile production of irradiated PSE and irradiated DFD pork were not di erent from normal pork. Most of the sulfurcontaining volatiles produced in meat by irradiation escaped during storage under aerobic packaging conditions. The DFD muscle was very stable and resistant to oxidative changes. Irradiation and storage of meat in vacuum packaging may be desirable for long-term storage but may reduce the acceptance of irradiated meat because of the sustaining o -odor volatiles. Therefore, irradiation of DFD pork in aerobic packaging for shortterm storage can be an option for the increased utilization

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