JFS: Food Chemistry and Toxicology. Food Chemistry and Toxicology. Introduction Consumers and regulatory agencies are well aware of the dangers

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1 JFS: Prevention of Pinking, Off-odor, and Lipid Oxidation in Pork Loin Using Double Packaging K.C. NAM, B.R. MIN, S.C. LEE, J. CORDRAY, AND D.U. AHN ABSTRACT: Lipid oxidation, color, volatiles, and sensory evaluation of double-packaged pork loin were determined to establish a modified packaging method that can improve the quality of irradiated pork loins. Vacuum-packaged irradiated samples produced dimethyl sulfide and dimethyl disulfide responsible for irradiation off-odor, whereas lipid oxidation was promoted under aerobic conditions. Exposing double-packaged irradiated pork to aerobic conditions for 1 to 3 d was effective in controlling both lipid oxidation and irradiation off-odor, regardless of packaging sequence. Sensory panels could distinguish the decrease in irradiation off-odor intensities by modifying the packaging method. However, carbon monoxide heme pigments, responsible for the increased redness by irradiation, were not effectively controlled by double packaging alone. Keywords: double packaging, irradiation, lipid oxidation, off-odor, pork loin Introduction Consumers and regulatory agencies are well aware of the dangers of enteropathogenic Escherichia coli, Salmonella, and Listeria to human health. Irradiation provides the best method to control these pathogens in raw meat. The quality change in meat by irradiation, however, is a concern to the meat industry and to consumers. Pink color (Millar and others 1995; Nam and Ahn 2002) and off-odor (Patterson and Stevenson 1995; Ahn and others 2001) in poultry meat produced by irradiation persists throughout the storage period under vacuum conditions. The major volatile compounds responsible for off-odor in irradiated meats are sulfur compounds. Irradiation produces sulfur compounds via radiolytic degradation of sulfur-containing amino acids, such as methionine and cysteine (Jo and Ahn 2000; Ahn 2002). The prevention of pink color defects and off-odor in poultry and pork is critical for the use of irradiation in those meats because consumers associate the presence of a pink color with undercooked or contaminated meat, and off-odor with the formation of undesirable chemical compounds by irradiation. The color and odor changes in irradiated meat are highly dependent on packaging conditions. Under aerobic packaging conditions, most of the sulfur compounds produced by irradiation disappeared and color returned to normal after a few days of storage in irradiated turkey breast (Nam and Ahn 2003). Lipid oxidation, however, significantly increased when meat was irradiated and stored in aerobic packaging conditions (Ahn and others 2001). Therefore, an appropriate use of aerobic and vacuum-packaging conditions (so-called double-packaging) can be effective in minimizing lipid oxidation and off-odor volatiles in irradiated pork loin during storage, which also may affect pink color in irradiated pork. Two double-packaging strategies are devised: In MS Submitted 10/31/03, Revised 12/9/03, Accepted 12/19/03. Authors Nam, Min, Cordray, and Ahn are with the Animal Science Dept., Iowa State Univ., Ames, IA Author Lee is with Dept. of Food Science and Biotechnology, Kyungnam Univ., Korea. Direct inquiries to author Ahn ( duahn@iastate.edu). FCT214 JOURNAL OF FOOD SCIENCE Vol. 69, Nr. 3, 2004 Published on Web 3/25/2004 model nr 1, pork loins were double-packaged (aerobic bag inside and vacuum bag outside) and irradiated. A few days after irradiation, the outer vacuum bag was removed and then stored. In model nr 2, loins were aerobically packaged and irradiated. A few days after irradiation, the loins were vacuum-packaged and then stored. The objective of this study was to determine the effect of doublepackaging conditions on lipid oxidation, volatiles, and color of irradiated pork loins during refrigerated storage. This study can provide information that can control the quality defects in irradiated pork because controlling pink color and off-odor production can improve consumer acceptance of irradiated pork. Materials and Methods Sample preparation Pork loin (longissimus dorsi) muscles from 8 different animals were purchased from a local packing plant and all surface fat was trimmed. The lean muscles were sliced into 2-cm-thick steaks and packaged as follows: (1) oxygen-permeable bags (polyethylene, 4 6, 2 mil; Assoc. Bag Co., Milwaukee, Wis., U.S.A.); (2) oxygen-impermeable vacuum bags (nylon/polyethylene, 9.3 ml O 2 /m 2 /24 h at 0 C; Koch, Kansas City, Mo., U.S.A.); (3) double-packaged: pork loins were individually packaged in oxygen-permeable bags 1st, and then a number of aerobically packaged loins were vacuumpackaged in a larger oxygen-impermeable bag. The packaged meat samples were irradiated at 2.5 kgy using a linear accelerator (Circe IIIR; Thomson CSF Linac, Saint-Aubin, France) with 10 MeV of energy, 10.2 kw of power level, and 88.9 kgy/min of average dose rate. For double-packaging model nr 1, the outer vacuum bags were removed after 3 d (V3/A7), 5 d (V5/A5), 7 d (V7/A3), or 9 d (V9/A1) of storage, respectively, during the 10 d of storage at 4 C. Therefore, 7 different treatments consisted of nonirradiated vacuumpackaged, irradiated aerobically-packaged, irradiated vacuumpackaged, and 4 irradiated double-packaged pork. For double-packaging model nr 2, aerobically packaged and irradiated loins were stored at 4 C for 1 d, 3 d, 5 d, or 7 d, and then vacuum Institute of Food Technologists Further reproduction without permission is prohibited

2 packaged (A1/V9, A3/V7, A5/V5, or A7/V3, respectively). vacuum-packaged, irradiated under aerobic, and irradiated under vacuum conditions were also prepared as controls. Lipid oxidation, color, gas, oxidation-reduction potential, and volatiles of the samples were determined after 0 d and 10 d of storage. Sensory evaluation was conducted at 10 d. flows were 400 and 35 ml/min, respectively. The compounds detected were identified using standard gases (CO; Aldrich, Milwaukee, Wis., U.S.A.; CH 4 and CO 2 ; Praxair, Danbury, Conn., U.S.A.). An integrated peak area was converted to a concentration (ppm) in the headspace (14 ml) of 10 g meat from the concentration of CO 2 in air (330 ppm). 2-Thiobarbituric acid-reactive substances Lipid oxidation was determined by a 2-thiobarbituric acid reactive substances (TBARS) method (Ahn and others 1998). Minced sample (5 g) was placed in a 50-mL test tube and homogenized with 15 ml deionized distilled water (DDW) using a Brinkman Polytron (Type PT 10/35; Brinkman Instrument, Inc., Westbury, N.Y., U.S.A.) for 15 s at high speed. The meat homogenate (1 ml) was transferred to a disposable test tube ( mm), and 50 L butylated hydroxytoluene (7.2% in ethanol) and 2 ml of thiobarbituric acid/ trichloroacetic acid (20 mm TBA and 15%, w/v, TCA) solution were added. The mixture was vortex-mixed and then incubated in a 90 C water bath for 15 min. After cooling, the samples were vortexmixed and centrifuged at 3000 g for 15 min. The absorbance of the resulting upper layer was read at 531 nm against a blank (1 ml DDW + 2 ml TBA/TCA). The amounts of TBARS were expressed as mg of malondialdehyde (MDA) per kg of meat. Color measurement CIE color values were measured on the sample surface using a LabScan colorimeter (Hunter Associate Labs, Inc., Reston, Va., U.S.A.) 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 by an illuminant A (light source). Two random readings from both top and bottom locations on a sample surface were used for statistical analysis. Oxidation-reduction potential A ph/ion meter (Accumet 25; Fisher Scientific, Fair Lawn, N.J., U.S.A.) was used to measure oxidation-reduction potential (ORP). A platinum electrode filled with an electrolyte solution (4 M KCl saturated with AgCl) was tightly inserted into the center of the block of meat sample. To minimize the effect of air, the smallest pore possible was made in the sample by a cutter before inserting the electrode. A temperature-reading sensor was also inserted to compensate for the effect of temperature. ORP readings (mv) were recorded at exactly 2 min after inserting the electrode into a sample. Gas The method of Nam and Ahn (2002) was modified to detect gases in meat samples. Minced meat sample (10 g) was placed in a 24- ml screw-cap glass vial with a Teflon fluorocarbon resin/silicone septum (I-Chem Co., New Castle, Del., U.S.A.). The vial was microwaved at 1.55 kw for 10 s to release gas compounds from the meat. After 5 min of cooling in room temperature, the headspace gas (200 L) was withdrawn using an airtight syringe and injected into a split inlet (9:1) of a gas chromatograph (GC; HP 6890; Hewlett Packard Co., Wilmington, Del., U.S.A.). A Carboxen-1006 Plot column (30 m 0.32-mm inner dia; Supelco, Bellefonte, Pa., U.S.A.) was used and an oven temperature was programmed (initial temperature, 80 C; increased to 120 C at 20 C/min). Helium was the carrier gas at a constant flow of 1.8 ml/min. A flame-ionizing detector connected to a nickel catalyst (Hewlett Packard Co.) was used for detection and the temperatures of inlet, detector, and nickel catalyst were set at 130, 280, and 375 C, respectively. Detector air and hydrogen Volatiles A dynamic headspace analysis was performed using a Solartek 72 Multimatrix-Vial Autosampler/Sample Concentrator 3100 (Tekmar-Dohrmann, Cincinnati, Ohio, U.S.A.) connected to a gas chromatograph-mass spectrometer (GC-MS) (HP 6890/HP 5973, Hewlett-Packard Co.) according to the method of Ahn and others (2001). Minced sample (3 g) was placed in a 40-mL vial, He (40 psi) was flushed for 3 s, and a Teflon fluorocarbon resin/silicone septum (I-Chem Co.) was capped airtight. The maximum waiting time in a loading tray (4 C) was less than 2 h to minimize oxidative changes before analysis. The meat sample was purged with He (40 ml/min) for 14 min at 40 C. Volatiles were trapped using a Tenax/charcoal/ silica column (Tekmar-Dohrmann) and desorbed for 2 min at 225 C, focused in a cryofocusing module ( 80 C), and then thermally desorbed into a column for 60 s at 225 C. An HP-624 column (7.5 m, 0.25-mm inner dia, 1.4 m nominal), an HP-1 column (52.5 m, 0.25-mm inner dia, 0.25 m nominal), and an HP-Wax column (7.5 m, mm inner dia, 0.25 m nominal) were connected. Ramped oven temperature was used to improve volatile separation. The initial oven temperature of 0 C was held for 1.5 min. After that, the oven temperature was increased to 15 C at 2.5 C per min, increased to 45 C at 5 C per min, increased to 110 C at 20 C per min, and then increased to 170 C at 10 C per min and held for 2.25 min at that temperature. Constant column pressure at 20.5 psi was maintained. The ionization potential of mass spectrometer (MS) was 70 ev, and the scan range was 19.1 to 350 m/z. Identification of volatiles was achieved by the Wiley library (Hewlett-Packard Co.). The area of each peak was integrated using ChemStation TM software (Hewlett-Packard Co.) and the total peak area (total ion counts 10 4 ) was reported as an indicator of volatiles generated from the samples. Sensory evaluation A 12-member sensory panel evaluated the intensity of off-odor. Training sessions were conducted to familiarize panelists with the irradiation off-odor and rancid odor. Panelists were trained with meat samples irradiated at high dose (10 kgy) and containing specific chemical compounds found in the volatiles of previous studies. Samples (3 g) stored for 10 d were placed in a coded 40-mL sample vial and capped with a septum (I-Chem Co.). The samples were incubated for 1 h at 22 C before serving. According to the modified method of Jones and others (1989), 4 different samples with the same packaging method were presented to each panelist in isolated booths at each separate session. Panelists were instructed to smell the samples at random and to record the intensity of irradiation off-odor and rancid odor on a 15-cm line scale anchored from not detectable to strongly intense. Statistical analysis The experiment was a completely randomized design and 7 different treatments were compared with 4 replications. Data were analyzed by the procedure of generalized linear model using SAS software (SAS Inst. 1995): Student-Newman-Keul s multiple range test was used to compare the mean values of treatments. Mean values and standard error of the means (SEM) were reported (P < 0.05). URLs and addresses are active links at Vol. 69, Nr. 3, 2004 JOURNAL OF FOOD SCIENCE FCT215

3 Table 1 2-Thiobarbituric acid reactive substances (TBARS) values of irradiated raw pork loin with different packaging conditions during refrigerated storage (expressed as mg of malondialdehyde per kg of meat) a 0 d 0.12cy 0.23ay 0.21ay 0.21az 0.21ay 0.21ay 0.16b d c 0.15ex 0.44ax 0.33cx 0.37bx 0.31cdx 0.28dx 0.17e d d 0.15ex 0.46ax 0.38bx 0.29cy 0.22dy 0.24dy 0.17e 0.01 SEM a Means with different letters (a e) within a row are significantly different (P < 0.05), n = 4. Means with different letters (x z) within a column are significantly different (P < 0.05). SEM = standard error of the means. b Vm/An: Stored under vacuum and aerobic conditions for m days and n days,respectively. Table 2 a* values of irradiated raw pork loin with different packaging conditions during refrigerated storage a 0 d 6.6c 8.2b 11.1ax 11.2ax 10.7a 10.5ax 10.6a d c 7.0c 8.9b 9.0by 10.9ax 10.8a 10.1abx 10.0ab d d 6.1c 8.7b 8.4by 8.1by 9.2ab 8.5by 10.1a 0.4 SEM a Means with different letters (a c) within a row are significantly different (P < 0.05), n = 4. Means with different letters (x,y) within a column are significantly different (P < 0.05). SEM = standard error of the means. b Vm/An: Stored under vacuum and aerobic conditions for m days and n days, respectively. Table 3 ORP of irradiated raw pork loin with different packaging conditions during refrigerated storage a (mv) 0 d 43 a 0 a 202 by 202 by 202 by 202 by 225 by d c 80c 21a 8abx 17abx 26abcx 61bcx 67bcx d d 55b 9a 4ax 40bx 43bx 41bx 69bx 10 SEM a Means with different letters (a c) within a row are significantly different (P < 0.05), n = 4. Means with different letters (x,y) within a column are significantly different (P < 0.05). ORP = oxidation-reduction potential; SEM = standard error of the means. b Vm/An: Stored under vacuum and aerobic conditions for m days and n days, respectively. Results and Discussion Lipid oxidation Irradiation increased TBARS, but vacuum conditions prevented lipid oxidation of pork loin (Table 1). The TBARS values of aerobically packaged pork loin were much higher than those of the vacuum-packaged meat after 10 d of storage. The TBARS values of double-packaged meats ranked between the aerobically and the vacuum-packaged ones. Double-packaged loins with model nr 2 (aerobically then vacuum-packaged) had lower TBARS values than those with model nr 1 (vacuum-packaged and then aerobically packaged), showing that lipid oxidation was accelerated as storage time increased. During the refrigerated storage, exposed time to aerobic conditions was the most critical factor determining the degree of lipid oxidation, and the TBARS values of pork loins at day 10 were proportional to the days under aerobic conditions. Thus, lipid oxidation can be a concern in irradiated meat when it is only aerobically packaged. Color changes Irradiation changed the color of raw pork loin reddish pink, as indicated by the colorimeter values (Table 2). The increase in redness (a* values) by irradiation was more distinctive in vacuumpackaged pork loins than in aerobically packaged ones. Therefore, packaging conditions were important in determining color changes in pork loin during the irradiation process. The redness of irradiated pork loin was very stable during the 10-d refrigerated storage irrespective of packaging method. At day 10, the a* values of irradiated pork loins were significantly higher than those of nonirradiated pork. A few double-packaged pork loins (A3/V7, A5/V5) had significantly lower a* values than irradiated vacuum-packaged ones during storage, but the values were still higher than those of nonirradiated vacuum-packaged control. Therefore, the double-packaging method alone was not enough to control redness in pork loin induced by irradiation. L* values in pork loins were little influenced by irradiation, and b* values showed an increasing trend but the results were inconsistent (data not shown). Nam and Ahn (2002) reported that the color of irradiated turkey breast became pinker due to carbon monoxide myoglobin complex formation, which was induced by the production of carbon monoxide and reducing conditions by irradiation. This mechanism of color changes in irradiated turkey breast can be similarly applied to that FCT216 JOURNAL OF FOOD SCIENCE Vol. 69, Nr. 3, 2004 URLs and addresses are active links at

4 Table 4 Gas production of irradiated raw pork loin with different packaging conditions during refrigerated storage a Carbon monoxide (ppm) 0 d 0b 121ax 123ax 123ax 123ax 123a 121ax 8 10 d c 0c 84aby 66by 86aby 108abx 114a 107abxy d d 0c 50by 56by 80aby 65by 117a 95aby 11 SEM Methane (ppm) 0 d 0b 4b 38ax 38ax 38ax 38ax 41ax 2 10 d c 0c 4c 3cy 4cy 5cy 14by 49ax 1 10 d d 0b 0b 0by 0by 0by 0bz 24ay 1 SEM Carbon dioxide (%) 0 d 3.1ax 1.3bx 3.1ax 3.1ax 3.1ax 3.1ax 3.4a d c 1.6bcy 0.8cxy 0.7cy 0.9cy 1.5bcy 2.3abxy 2.8a d d 2.5ax 0.6by 0.7by 0.7by 0.5bz 1.4by 3.2a 0.5 SEM a Means with different letters (a c) within a row are significantly different (P < 0.05), n = 4. Means with different letters (x,y) within a column are significantly different (P < 0.05). SEM = standard error of the means. b Vm/An: Stored under vacuum and aerobic conditions for m days and n days, respectively. of irradiated pork loin because the contents of heme pigments in those muscles are relatively low. Irradiation decreased the ORP of pork loin under vacuum-packaged conditions (Table 3). Swallow (1984) reported that hydrated electrons, radiolytic free radicals, could be produced by irradiation and act as a very powerful reducing agent. However, the ORP values of irradiated pork loins increased after 10 d in contrast to the decrease in nonirradiated meat, showing that stronger oxidizing conditions were generated in irradiated meat by oxidizing free radicals such as superoxide and hydroperoxyl radical during storage (Woods and Pikaev 1994). Irradiation produced a few gas compounds (Table 4), one of which was carbon monoxide that could be a ligand of heme pigments in irradiated pork loin and thus increase redness. The production of carbon monoxide was little influenced by packaging conditions regardless of storage, indicating that most of the carbon monoxide produced was bound to heme pigments in meat throughout storage. Off-odor volatiles Many new volatile compounds were generated and a few volatiles already present in nonirradiated pork loins increased by irradiation (Table 5). The amount of total volatiles produced in irradiated pork loin was 3 times higher than that of the nonirradiated control. At 0 d, sulfur (S)-containing volatiles, 2-propanone, and ethanol were the most predominant volatiles in irradiated pork loin. Among the detected S-volatiles, methanethiol, dimethyl sulfide, methylthio ethane, and dimethyl disulfide could be responsible for the characteristic irradiation off-odor. Ahn and others (2000a) 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 were the result of compounding effects of volatiles from lipid oxidation and radiolysis of various amino acid side chains. The amounts of S-volatiles in irradiated pork loin were highly dependent on packaging conditions. Higher amounts of S-volatiles were found in vacuum-packaged or double-packaged pork loin than in aerobically packaged ones, indicating that considerable amounts of S-compounds were evaporated under aerobic conditions during Table 5 Volatile compounds of irradiated raw pork loin with different packaging conditions at day 0 a Compound Vacuum Aerobic Double Vacuum SEM Total ion counts 10 4 Acetaldehyde Methanethiol 0c 887c 3886a 2238b 342 Pentane 0c 526a 349b 349b 27 Dimethyl sulfide 0b 610b 2771a 2345a Propanone Hexane 0b 723a 232b 217b 132 Ethanol Methylthio ethane Propanol Butanone 74c 930a 350b 417b 97 Benzene Heptene Heptane Pentanone Dimethyl disulfide 37c 773c 1761b 2678a 290 Toluene Octane Hexanal Total 4894b 15207a 14241a 14274a 1457 a Means with different letters (a c) within a row are significantly different (P < 0.05), n = 4. SEM = standard error of the means. the process of irradiation and post-irradiation handling. For the meat that will be consumed fresh (lipid oxidation is not a problem), therefore, aerobic packaging is more beneficial than vacuum-packaging in terms of reducing irradiation off-odor. The amounts of dimethyl sulfide and dimethyl disulfide in aerobically packaged pork loin were only 26% and 29% of the vacuum-packaged one, respectively. Lipid oxidation products in irradiated pork loin at 0 d were minimal, and only aerobically packaged pork loin had a trivial amount of hexanal. After 10 d of refrigerated storage, the volatiles profile of irradiated pork loin was highly dependent on packaging conditions (Tables 6 and 7). The greatest amounts of total volatiles were detected in vacuum-packaged pork loin because many S-volatiles still URLs and addresses are active links at Vol. 69, Nr. 3, 2004 JOURNAL OF FOOD SCIENCE FCT217

5 Table 6 Volatile compounds of irradiated raw pork loin with double-packaging model 1 at day 10 a Compound Vacuum Aerobic V3/A7 b V5/A5 c V7/A3 d V9/A1 e Vacuum SEM Total ion counts 10 4 Pentane 38b 997a 597ab 564ab 613ab 450ab 367ab Propanone Carbon disulfide 300a 0b 0b 0b 0b 0b 0b 18 Hexane 412b 3012a 2784a 743b 560b 317b 220b 357 Dimethyl sulfide 0b 0b 0b 0b 0b 37b 133a 24 2-Propanol Butanone 0c 390a 203b 204b 296b 254b 221b 24 1-Heptene Heptane Pentanone S-methyl ethanethioate 0b 0b 0b 0b 0b 62b 268a 28 Dimethyl disulfide 0b 0b 0b 0b 0b 387b 1108a 154 Toluene Octene 0b 120a 103a 56ab 87a 0b 0b 18 Octane Octene Hexanal 0c 169a 122ab 31bc 57bc 63bc 0c 21 Dimethyl trisulfide 0b 0b 0b 0b 0b 54b 246a 33 Total 2621c 7674a 6627a 4243b 4534b 4046b 5379ab 729 a Means with different letters within a row are significantly different (P < 0.05), n = 4. b Vacuum-packaged for 3 d then aerobically packaged for 7 d. c Vacuum-packaged for 5 d then aerobically packaged for 5 d. d Vacuum-packaged for 7 d then aerobically packaged for 3 d. e Vacuum-packaged for 9 d then aerobically packaged for 1 d. Table 7 Volatile compounds of irradiated raw pork loin with double-packaging model nr 2 at day 10 a Compound Vacuum Aerobic A7/V3 b A5/V5 c A3/V7 d A1/V9 e Vacuum SEM Total ion counts 10 4 Pentane 58b 645a 601a 566a 524a 527a 345a 69 2-Propanone Carbon disulfide 45a 0b 0b 0b 0b 0b 0b 4 Hexane 412b 3012a 612b 308bc 313bc 367bc 269bc 111 Dimethyl sulfide 0b 0b 0b 0b 0b 0b 133a 24 2-Propanol 197b 221ab 248ab 304a 249ab 307a 274ab 20 2-Butanone 0c Heptene Heptane Pentanone 0b 65ab 102a 72ab 70ab 53ab 47ab 16 S-methyl ethanethioate 0b 0b 0b 0b 0b 0b 268a 28 Dimethyl disulfide 0b 0b 0b 0b 0b 0b 1108a 154 Toluene Octene Octane Octene 219a 0b 0b 34b 18b 31b 297a 33 Hexanal 0b 130a 110a 102a 102a 53ab 0b 24 Dimethyl trisulfide 0b 0b 0b 0b 0b 0b 246a 33 Total 2986c 6886a 4892b 4168b 3851b 4646ab 5883a 823 a Means with different letters (a c) within a row are significantly different (P < 0.05), n = 4. SEM = standard error of the means. baerobically packaged for 7 d then vacuum-packaged for 3 d. c Aerobically packaged for 5 d then vacuum-packaged for 5 d. d Aerobically packaged for 3 d then vacuum-packaged for 7 d. eaerobically packaged for 1 d then vacuum-packaged for 9 d. remained under vacuum conditions. Dimethyl disulfide was the most predominant volatile compound in vacuum-packaged pork loins. No S-volatiles were detected in most double-packaged pork loins. S-volatiles such as dimethyl disulfide, dimethyl trisulfide, and S-methyl ethanethioate were found in the V9/A1 double-packaging model nr 1 as well as vacuum-packaged samples. On the other hand, those S-volatiles were not detected in the A1/V9 doublepackaging model nr 2. It seems that double-packaging model nr 2 is better than model nr 1 in removing S-volatiles because the production of S-volatiles is critical in the middle of the irradiation process rather than storage. However, exposing double-packaged irradiated pork to aerobic conditions for 3 d was enough to eliminate the sulfur compounds responsible for irradiation off-odor, regardless of packaging sequences. Aerobic packaging was effective in eliminating S-volatiles but increased lipid oxidation in pork loins (Table 1). Therefore, doublepackaging treatments such as exposing the irradiated meat to aerobic conditions for 1 to 3 d and then keep them in vacuum condi- FCT218 JOURNAL OF FOOD SCIENCE Vol. 69, Nr. 3, 2004 URLs and addresses are active links at

6 Table 8 Sensory characteristics of irradiated raw pork loin with different packaging conditions (double-packaging model nr 1) at day 10 a Table 9 Sensory characteristics of irradiated raw pork loin with different packaging conditions (double-packaging model nr 2) at day 10 Off-odor b Vacuum Aerobic V7/A3 c Vacuum SEM Irradiation odor 1.0d 3.8c 9.5b 11.3a 0.6 Rancid odor a Means with different letters within a row are significantly different (P < 0.05), n = 12. SEM = standard error of the means. b 0.0: not detectable, 15.0: highly intense. c Vacuum-packaged for 7 d then aerobically packaged for 3 d. a Off-odor b Vacuum Aerobic A3/V7 c Vacuum SEM Irradiation odor 1.3c 4.4b 5.6b 12.4a 1.0 Rancid odor a Means with different letters within a row are significantly different (P < 0.05), n = 12. SEM = standard error of the means. b 0.0: not detectable, 15.0: highly intense. c Aerobically packaged for 3 d then vacuum-packaged for 7 d. tions for the remaining period should be used to control both irradiation off-odor and lipid oxidation in irradiated pork loins. Sensory characteristics Pork loins from double-packaging model nr 1 (V7/A3) and nr 2 (A3/V7) were selected, and the sensory characteristics were compared with those from aerobic and vacuum-packaged ones (Tables 8 and 9). Most panelists easily distinguished the characteristic irradiation odor. The intensity of irradiation odor in irradiated vacuum-packaged pork was ranked the highest, double-packaged loins in the middle, and aerobically packaged the lowest. The result of the irradiation odor intensity was very consistent with the amount of S-volatiles detected in the pork at 10 d (Table 6 and 7), showing that S-volatiles are representative compounds responsible for the irradiation odor. Hashim and others (1995) reported 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 and others (2000b) described the irradiation odor in raw pork as a barbecued corn-like odor. Nam and others (2002) reported that during the training sessions, panelists came to a consensus to describe the irradiation odor from pork as sulfury, boiled sweet corn, or steamed or rotten vegetables. On the other hand, panelists could not recognize rancid odor because the degree of lipid oxidation of irradiated raw pork was not high enough to produce detectable rancid odor and was masked by the strong irradiation odor. Conclusions The double-packaging method (exposing the irradiated pork to aerobic conditions for a few days and then keeping the pork in vacuum conditions for the remaining storage) was better than vacuum or aerobic packaging in controlling lipid oxidation and irradiation off-odor in pork loin. Although double-packaging model nr 2 (irradiating meat under aerobic packaging conditions and then storing it under vacuum-packaging conditions a few days later) was better than double-packaging model nr 1 (irradiating meat under vacuum-packaging conditions and then removing the outer vacuum bags a few days before use) in reducing off-odor volatiles, their differences were relatively small. Acknowledgments This work was supported by the Natl. Pork Board. The NASA FTCSC funded the purchase of the Solartek 72 Multimatrix-Vial Autosampler used for the volatile analysis in this study. References Ahn DU Production of volatiles from amino acid homopolymers by irradiation. J Food Sci 67(7): Ahn DU, Jo C, Olson DG. 2000a. Analysis of volatile components and the sensory characteristics of irradiated raw pork. Meat Sci 54(2): Ahn DU, Jo C, Du M, Olson DG, Nam KC. 2000b. Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions. Meat Sci 56(2): Ahn DU, Nam KC, Du M, Jo C Volatile production in irradiated normal, pale soft exudative (PSE) and dark firm dry (DFD) pork under different packaging and storage conditions. Meat Sci 57(4): Ahn DU, Olson DG, Jo C, Chen X, Wu C, Lee JI Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production, and color in raw pork patties. Meat Sci 47(1): Hashim IB, Resurrecccion AVA, MacWatters KH Disruptive sensory analysis of irradiated frozen or refrigerated chicken. J Food Sci 60(4): Jo C, Ahn DU Production volatile compounds from irradiated oil emulsions containing amino acids or proteins. J Food Sci 65(4): Jones RC, Dransfield E, Crosland AR, Francombe MA Sensory characteristics of British sausages: relationships with composition and mechanical properties. J Sci Food Agric 48(1): Millar SJ, Moss BW, MacDougall DB, Stevenson MH 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(6): Nam KC, Ahn DU Carbon monoxide-heme pigment complexes are responsible for the pink color in irradiated raw turkey breast meat. Meat Sci 61(1): Nam KC, Ahn DU Combination of aerobic and vacuum packaging to control lipid oxidation and off-odor volatiles of irradiated raw turkey breast. Meat Sci 63(3): Nam KC, Prusa KJ, Ahn DU Addition of antioxidant to improve quality and sensory characteristics of irradiated pork patties. J Food Sci 67(7): Patterson RL, Stevenson MH Irradiation-induced off-odor in chicken and its possible control. Br Poultry Sci 36(3): SAS Inst SAS/STAT user s guide. Cary, N.C.: SAS Inst. Swallow AJ Fundamental radiation chemistry of food components. In: Bailey AJ, editor. Recent advances in the chemistry of meat. London: The Royal Society of Chemistry. P Woods RJ, Pikaev AK Interaction of radiation with matter. In: Woods RJ, Pikaev AK, editors. Applied radiation chemistry: radiation processing. New York: John Wiley & Sons, Inc. p URLs and addresses are active links at Vol. 69, Nr. 3, 2004 JOURNAL OF FOOD SCIENCE FCT219