Effects of oleoresin tocopherol combinations on lipid oxidation, off-odor, and color of irradiated raw and cooked pork patties

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1 Meat Science 75 (2007) MEAT SCIENCE Effects of oleoresin tocopherol combinations on lipid oxidation, off-odor, and color of irradiated raw and cooked pork patties K.C. Nam 1, K.Y. Ko, B.R. Min, H. Ismail, E.J. Lee, J. Cordray, D.U. Ahn * Department of Animal Science, Iowa State University, Ames, IA , United States Received 28 February 2006; received in revised form 26 June 2006; accepted 26 June 2006 Abstract Lipid oxidation, color, and volatiles of double-packaged pork loins with various oleoresin or oleoresin tocopherol combinations were determined to establish the best oleoresin tocopherol conditions that can improve the quality of irradiated raw and cooked pork loins. Rosemary and a-tocopherol combination at 0.05% and 0.02% of meat weight, respectively, showed the most potent antioxidant effects in reducing both TBARS values and the amounts of volatile aldehydes in irradiated raw and cooked pork loins. The antioxidant combination, however, did not affect the production of sulfur volatiles responsible for irradiation off-odor and showed little effects on color changes in irradiated raw and cooked pork loins. Exposing double-packaged irradiated pork to aerobic conditions for 3 days during the 10-day storage was effective in controlling both lipid oxidation and irradiation off-odor, regardless of packaging sequences. Ó 2006 Published by Elsevier Ltd. Keywords: Oleoresin; Double packaging; Irradiation; Lipid oxidation; Off-odor; Pork loin 1. Introduction Food irradiation is proven to be the best technology in eliminating disease-causing pathogens from raw meat and poultry (Murano, 1995; Thayer, 1993). The chemical changes of meat and poultry by irradiation, however, are concern to consumers, and the meat industry is having difficulties in using the technology to achieve its food safety benefits. The generations of pink color (Millar, Moss, Mac- Dougall, & Stevenson, 1995; Nam & Ahn, 2002a) and offodor (Ahn, Nam, Du, & Jo, 2001; Patterson & Stevenson, 1995) are critical issues for irradiating pork because consumers associate the presence of pink color in cooked meat with undercooking or contamination, and off-odor with bacterial spoilage. The characteristic off-odor in irradiated meats was caused by the production of sulfur volatiles from * Corresponding author. Tel.: ; fax: address: duahn@iastate.edu (D.U. Ahn). 1 Present address: Exam. Div. of Food and Biological Resources, Korean Intellectual Property Office, Daejeon , Republic of Korea. sulfur-containing amino acids such as methionine and cysteine (Ahn, 2002; Jo & Ahn, 2000). The mechanism of pink color generation in irradiated pork or poultry was through the production of carbon monoxide from meat components (Lee & Ahn, 2004; Nam & Ahn, 2002b). The chemical changes in irradiated meats are initiated by the free radicals produced by irradiation, and the production of sulfur volatiles or carbon monoxide was caused by reactions between meat components and radiolytic free radicals (Ahn, 2002; Nam & Ahn, 2002b). Thus, antioxidants with free radical scavenging activities may help protect the irradiated pork from chemical changes. Various individual phenolic compounds separated from natural sources (e.g., gallate, sesamol) are proven to have very strong free radical scavenging capabilities, but are not permitted for use in foods as an antioxidant. Oleoresins extracted from various plants contain large amounts of phenolic antioxidants, however, are commercially available for use in meat products. a-tocopherol is permitted to use in meat at 0.02% level as a vitamin supplement or antioxidants. Thus, combination of oleoresins extracted /$ - see front matter Ó 2006 Published by Elsevier Ltd. doi: /j.meatsci

2 62 K.C. Nam et al. / Meat Science 75 (2007) from various spices (dill, basil, garlic, onion, and rosemary) with a-tocopherol may increase the antioxidant effect of oleoresins. The color and odor changes in irradiated meats are highly dependent upon packaging conditions. Under aerobic packaging conditions, most of the sulfur volatiles in irradiated turkey breast disappeared and the pink color returned to normal after a few days of aerobic storage (Nam & Ahn, 2003b). On the other hand, irradiation generates hydroxyl radicals that can initiate lipid oxidation, but lipid oxidation became a potential quality problem only when the meats were exposed to aerobic conditions (Ahn et al., 2001). Double-packaging, which exposes the vacuum packaged meat to aerobic conditions for 2 3 days during storage, was effective in minimizing lipid oxidation, pink color defect and sulfur-volatile production in irradiated pork loin during storage (Nam, Min, Lee, Cordray, & Ahn, 2004). Double-packaging was proven to be effective in reducing both color and off-odor problems in turkey breast without adding any additives, but combination of double-packaging and antioxidants was more effective than double-packaging alone in controlling lipid oxidation and irradiation off-odor (Nam & Ahn, 2003a). The objective of this study was to select the best oleoresin tocopherol combinations to control lipid oxidation, off-odor, and color in irradiated pork loins. 2. Materials and methods 2.1. Sample preparation Pork loin (Longissimus dorsi) muscles (3 days after slaughter) from 8 different animals (Berkshire, female, approximately 105 kg live weight) were purchased from the Meat Laboratory at Iowa State University (Ames, IA) and ground through a 5-mm plate. Loins from two animals were pooled, ground and used as a replication (4 replications). Oleoresin from dill, basil, garlic, onion, or rosemary (0.05% of meat wt.) singly or in combination with tocopherol (0.02%) was added to ground pork, mixed for 2 min in a kitchen mixer, and then patties were prepared. The patties were individually packaged in oxygen-permeable plastic bags (polyethylene, 4 6, 2 mil; Associated Bag Company, Milwaukee, WI), 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. Half of the aerobically packaged patties were stored at 4 C and lipid oxidation of the patties was determined at Day 0 and Day 10 of storage. The other half of the patties were cooked in a 176 C electric oven to an internal temperature of 75 C at Day 0, stored in oxygen-permeable plastic bags at 4 C, and analyzed for lipid oxidation after 0 and 3 days of storage. Irradiated and nonirradiated ground pork patties with none added were used as controls. Two oleoresin or oleoresin tocopherol combinations that provide the best control for lipid oxidation in irradiated raw and cooked meat were selected and used for the next study, which determines the effect of antioxidant (oleoresin tocopherol)/double-packaging combinations on the quality changes in irradiated raw and cooked ground pork loins during storage. Pork loins were ground through a 5-mm plate, mixed with selected oleoresin tocopherol combinations, and then patties were prepared. The patties were packaged, irradiated (2.5 kgy), and stored at 4 C according to two double-packaging models: for double-packaging model A3/V7, patties were individually packaged in oxygen-permeable bags (polyethylene, 4 6, 2 mil), irradiated at 2.5 kgy, and then stored at 4 C. After 3 days of storage, the aerobically packaged patties were packaged again with oxygen impermeable vacuum bags (nylon/polyethylene, 9.3 ml O 2 /m 2 /24 h at 0 C; Koch, Kansas City, MO), and then stored at 4 C for another 7 days. For V7/A3 double-packaging model, patties were individually packaged in oxygen-permeable bags first, and then vacuum-packaged in oxygen-impermeable bags (nylon/polyethylene, 9.3 ml O 2 /m 2 /24 h at 0 C). The doubly packaged patties were irradiated and then stored at 4 C. After 7 days of storage, the outer vacuum bags of the patties were removed and then patties were exposed to aerobic conditions for 3 days. Nonirradiated and irradiated vacuum-packaged patties were used as controls. The patties were cooked immediately after irradiation in a 176 C electric oven to an internal temperature of 75 C. Lipid oxidation, color, and volatiles of the cooked patties were determined at 0 day and 10 days of storage Thiobarbituric acid reactive substances (TBARS) Lipid oxidation was determined by a modified TBARS method of Buege and Aust (1978). 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, NY) for 15 s at high speed. The meat homogenate (1 ml) was transferred to a disposable test tube ( mm), and 50 ll 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 vortex-mixed and centrifuged at 3000g for 15 min. The absorbance of the resulting upper layer was read at 532 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 values CIE color values were measured on the sample surface using a LabScan colorimeter (Hunter Associate Labs, Inc., Reston, VA) that had been calibrated against black

3 K.C. Nam et al. / Meat Science 75 (2007) 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. Table 1 TBARS values of raw pork loin affected by irradiation, oleoresins, and tocopherol during refrigerated storage Irradiation Oleoresin a a-tocopherol 0 day 10 day SEM (mg MDA/kg meat) 0 kgy Control 0.24bx 1.50cy kgy Control 0.21bx 1.78cy kgy Dill 0.19bx 0.68dy kgy Basil 0.45ax 2.74by kgy Garlic 0.39ax 4.19ay kgy Onion 0.22bx 1.32cy kgy Rosemary 0.18bx 0.29dy kgy Dill 0.02% 0.16bx 0.36dy kgy Basil 0.02% 0.21bx 0.71dy kgy Garlic 0.02% 0.30bx 2.50by kgy Onion 0.02% 0.19bx 0.37dy kgy Rosemary 0.02% 0.18bx 0.36dy 0.02 SEM Mean values with different letters (a d) within a column are significantly different (P < 0.05). a Added at 0.05%. Table 2 TBARS values of cooked pork loin affected by irradiation, oleoresins, and tocopherol during refrigerated storage Irradiation Oleoresin a a-tocopherol 0 day 3 day SEM (mg MDA/kg meat) 0 kgy Control 1.13ax 3.19ay kgy Control 1.11ax 3.19ay kgy Dill 1.03ax 2.72bcy kgy Basil 1.15ax 3.18ay kgy Garlic 1.08ax 2.85aby kgy Onion 0.93abx 2.48cy kgy Rosemary 0.52dx 1.43dey kgy Dill 0.02% 0.59dx 1.49dey kgy Basil 0.02% 0.70cdx 1.59dy kgy Garlic 0.02% 0.79bcx 1.71dy kgy Onion 0.02% 0.62cdx 1.19efy kgy Rosemary 0.02% 0.56dx 1.02fy 0.02 SEM Mean values with different letters (a f) within a column are significantly different (P < 0.05). a Added at 0.05%. Table 3 TBARS values of irradiated raw pork patties affected by oleoresin + tocopherol and packaging during refrigerated storage Irradiation Antioxidant a Packaging 0 day 10 day SEM (mg MDA/kg meat) 0 kgy Control Vacuum a kgy Control Vacuum a kgy Onion + tocopherol A3/V7 b b kgy Onion + tocopherol V7/A3 c b kgy Rosemary + tocopherol A3/V b kgy Rosemary + tocopherol V7/A b 0.01 SEM Mean values with different letters (a, b) within a column are significantly different (P < 0.05). a Oleoresin tocopherol combination added at % of meat wt. b Aerobically packaged for 3 days first and then vacuum-packaged for 7 days. c Vacuum-packaged for 7 days first and then aerobically packaged for 3 days.

4 64 K.C. Nam et al. / Meat Science 75 (2007) Volatile compounds (volatiles) A dynamic headspace analysis was performed using a Solartek 72 Multimatrix-Vial Autosampler/Sample Concentrator 3100 (Tekmar-Dohrmann, Cincinnati, OH) connected to a GC/MS (HP 6890/HP 5973, Hewlett-Packard Co.) according to the method of Ahn et al. (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 i.d., 1.4 lm nominal), Table 4 TBARS values of irradiated cooked pork patties affected by oleoresin + tocopherol and packaging during refrigerated storage Irradiation Antioxidant a Packaging 0 day 10 day SEM (mg MDA/kg meat) 0 kgy Control Vacuum 1.60ay 2.26ax kgy Control Vacuum 1.57ay 2.33ax kgy Onion + tocopherol A3/V7 b 0.57cy 1.96bx kgy Onion + tocopherol V7/A3 c 0.41cy 1.78bx kgy Rosemary + tocopherol A3/V7 0.36by 1.18cx kgy Rosemary + tocopherol V7/A3 0.30cy 0.99cx 0.02 SEM Mean values with different letters (a c) within a column are significantly different (P < 0.05). a Oleoresin tocopherol combination added at % of meat wt. b Aerobically packaged for 3 days first and then vacuum-packaged for 7 days. c Vacuum-packaged for 7 days first and then aerobically packaged for 3 days. Table 5 Color values of irradiated raw pork patties affected by oleoresin + tocopherol and packaging during refrigerated storage Irradiation Antioxidant a Packaging 0 day 10 day SEM L * value 0 kgy Control Vacuum 58.1a kgy Control Vacuum 54.5aby 57.5x kgy Onion + tocopherol A3/V7 b 56.3ab kgy Onion + tocopherol V7/A3 c 53.4by 59.8x kgy Rosemary + tocopherol A3/V7 57.5a kgy Rosemary + tocopherol V7/A3 55.3aby 59.1x 0.9 SEM a * value 0 kgy Control Vacuum 11.6by 12.9abx kgy Control Vacuum 13.4ay 14.4ax kgy Onion + tocopherol A3/V7 b 11.4b 10.3c kgy Onion + tocopherol V7/A3 c 11.2by 13.4ax kgy Rosemary + tocopherol A3/V7 13.3ax 11.9by kgy Rosemary + tocopherol V7/A3 12.8ab 14.4a 0.5 SEM b * value 0 kgy Control Vacuum 16.1b 15.1d kgy Control Vacuum 14.6cy 16.4dx kgy Onion + tocopherol A3/V7 b 16.7b 16.5d kgy Onion + tocopherol V7/A3 c 13.9cy 20.1bx kgy Rosemary + tocopherol A3/V7 19.0a 18.5c kgy Rosemary + tocopherol V7/A3 16.0by 21.9ax 0.3 SEM Mean values with different letters (a d) within a column are significantly different (P < 0.05). a Oleoresin tocopherol combination added at % of meat wt. b Aerobically packaged for 3 days first and then vacuum-packaged for 7 days. c Vacuum-packaged for 7 days first and then aerobically packaged for 3 days.

5 K.C. Nam et al. / Meat Science 75 (2007) an HP-1 column (52.5 m, 0.25 mm i.d., 0.25 lm nominal), and an HP-Wax column (7.5 m, mm i.d., 0.25 lm 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 at10 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 MS was 70 ev, and the scan range was m/z. Identification of volatiles was achieved by the Wiley library (Hewlett-Packard Co.). The area of each peak was integrated using ChemStationä 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 Statistical analysis The experiment was a completely randomized design with four replications. Data were analyzed by the procedure of generalized linear model using SAS software (SAS Institute, 1995): Student Newman Keuls 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). 3. Results and discussion 3.1. Screening of oleoresin or oleoresin tocopherol combinations To screen two best oleoresins or oleoresin tocopherol combinations in preventing lipid oxidation of irradiated ground pork, the TBARS values of irradiated pork patties added with oleoresins or oleoresin + a-tocopherol combinations were determined during the 10 days of storage under aerobic conditions. The TBARS values between nonirradiated and irradiated raw ground pork were not different, but increased significantly during the 10-day storage under aerobic conditions (Table 1). Rosemary, onion, and dill oleoresins were effective in decreasing TBARS values in irradiated ground raw pork, whereas basil and garlic oleoresins had no antioxidant effects. Rosemary oleoresin had the most potent antioxidant effects among the oleoresins, and all the oleoresins except for garlic oleoresin showed strong antioxidant effects when they were combined with a-tocopherol. Rosemary, rosemary tocopherol, onion tocopherol, and dill tocopherol reduced the TBARS values Table 6 Color values of irradiated cooked pork patties affected by oleoresin + tocopherol and packaging during refrigerated storage Irradiation Antioxidant a Packaging 0 day 10 day SEM L * value 0 kgy Control Vacuum 76.9ab 76.9a kgy Control Vacuum 76.7ab 76.9a kgy Onion + tocopherol A3/V7 b 77.7ax 72.8by kgy Onion + tocopherol V7/A3 c 74.8by 77.9ax kgy Rosemary + tocopherol A3/V7 77.5ax 73.0by kgy Rosemary + tocopherol V7/A3 74.5by 78.4ax 0.3 SEM a * value 0 kgy Control Vacuum 8.2b 8.5a kgy Control Vacuum 10.9ax 8.6ay kgy Onion + tocopherol A3/V7 b 7.9b 7.4bc kgy Onion + tocopherol V7/A3 c 10.9ax 8.0aby kgy Rosemary + tocopherol A3/V7 8.4bx 7.0cy kgy Rosemary + tocopherol V7/A3 11.2ax 8.1aby 0.2 SEM b * value 0 kgy Control Vacuum 22.6a 23.1b kgy Control Vacuum 22.3a 23.0b kgy Onion + tocopherol A3/V7 b 22.5a 22.8b kgy Onion + tocopherol V7/A3 c 21.6aby 23.8abx kgy Rosemary + tocopherol A3/V7 22.4ay 23.8abx kgy Rosemary + tocopherol V7/A3 20.8by 24.3ax 0.3 SEM Mean values with different letters (a c) within a column are significantly different (P < 0.05). a Oleoresin tocopherol combination added at % of meat wt. b Aerobically packaged for 3 days first and then vacuum-packaged for 7 days. c Vacuum-packaged for 7 days first and then aerobically packaged for 3 days.

6 66 K.C. Nam et al. / Meat Science 75 (2007) of irradiated raw ground pork by 80% after 10 days of aerobic storage. The use of oleoresin alone was not much effective in preventing oxidative changes in cooked pork except for rosemary and onion. However, combinations of oleoresin and tocopherol produced strong antioxidant effects in cooked pork (Table 2). Among the oleoresin tocopherol combinations, rosemary tocopherol and onion tocopherol produced the most potent antioxidant effects in irradiated cooked pork loins Oleoresin tocopherol/packaging combinations on lipid oxidation of irradiated pork From the previous screening result, two oleoresin tocopherol combinations (onion + tocopherol and rosemary + tocopherol) that provided the best control for lipid oxidation in irradiated raw and cooked pork were selected, and the effects of oleoresin tocopherol combinations on antioxidant and off-odor reducing effects of irradiated raw and cooked pork with double-packaging were determined. Double-packaging was selected as a packaging method of choice because Nam et al. (2004) reported that double-packaging was better than aerobic- or vacuumpackaging in controlling both lipid oxidation and off-odor of irradiated meat. Irradiated raw pork patties with oleoresin tocopherol/ double-packaging combinations developed significantly lower TBARS than those of irradiated and nonirradiated controls with vacuum-packaging (Table 3). However, the differences were very small and would not have any practical meanings. Nam and Ahn (2003b) reported that the TBARS increase in turkey meat was proportional to the exposure time to aerobic conditions: the TBARS of meat was the highest with aerobic-packaging, lowest with vacuum-packaging, and in the middle with double-packaging. However, the irradiated meat with antioxidants and double-packaging combinations had lower TBARS than nonirradiated vacuum-packaged meat after 10 days of storage. The antioxidant effects of oleoresin tocopherol combinations in irradiated cooked pork were distinct (Tables 2 4). The double-packaging conditions exposed patties to aerobic conditions for 3 days during the 10-day storage period, but the added oleoresin tocopherol combinations Table 7 Tentative identification of volatile compounds produced in irradiated raw pork patties treated by oleoresin tocopherol combination and packaging at 0 day Compound NonIR Irradiated (2.5 kgy) Onion + tocopherol Rosemary + tocopherol Vacuum Vacuum A3/V7 a V7/A3 b A3/V7 a V7/A3 b SEM c (Total ion counts 10 4 ) Acetaldehyde Methanethiol 0c 2136a 233b 2183a 307b 1306ab Pentene 0b 220a 179a 207a 203a 182a 22 Pentane 273c 1110a 666b 658b 719b 633b 65 2-Propanone Carbon disulfide 0c 7177a 572c 1947c 1061c 4019b 619 Ethanol Hexene 0b 285a 261a 266a 219a 195a 37 2-Propanol Hexane 92b 550a 489a 495a 472a 427a 51 2-Butanone 0b 0b 242a 86ab 0b 0b 55 3-Methyl butanal Propanol 0c 197a 47bc 82b 41bc 68bc 19 1-Heptene Heptane Heptene 0b 788a 627a 703a 695a 560a 52 1-Methylthio propane S-Methyl ester d 0c 117c 24238b 28320a 303c 1305c 1180 Dimethyl disulfide 0b 81b 210a 348a 85b 114ab 45 Toluene Octene 0b 3482a 4158a 5470a 2277a 2471a 864 Octane Butanal Methyl propyl disulfide 0b 0b 581ab 1052a 0b 0b 168 Total 10519c 28238b 42769a 53503a 16763bc 19970bc 3738 Different letters (a c) within a row are significantly different (p ); n = 4. a Aerobically packaged for 3 days and then vacuum-packaged for 7 days. b Vacuum-packaged for 7 days and then aerobically packaged for 3 days. c Standard error of the means. d Sulfur methyl ester ethanethioic acid.

7 K.C. Nam et al. / Meat Science 75 (2007) were effective in preventing oxidative changes in irradiated cooked pork. Rosemary tocopherol combination was more effective than onion tocopherol in reducing the TBARS of irradiated cooked pork. However, the sequence of double-packaging method (A3/V7 vs V3/A7) did not affect the TBARS values of irradiated cooked pork significantly. Nam and Ahn (2003a) showed similar results with turkey meat: the antioxidant effect was more distinct in cooked meat than raw meat. Therefore, the problem of lipid oxidation in double-packaged irradiated cooked pork could be prevented by the addition of rosemary tocopherol combination Oleoresin tocopherol/packaging combinations on color of irradiated pork Irradiation changed the color of raw pork patties redder, as indicated by the increased a * values in Table 5. Nam and Ahn (2002a) 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. Lee and Ahn (2004) reported that asparagine, glyceraldehydes, and phospholipids were the major sources of irradiation-dependent CO production from meat components. The amounts of CO produced from these sources were large enough to react with most of the heme pigments present in light meats, and the production of CO was via the radiolytic degradation and was closely related to the chemical structure of molecules. The mechanism of color changes in irradiated turkey breast can be similarly applied to that of irradiated pork loin because the contents of heme pigments in those muscles are relatively low. Onion tocopherol combination was effective in reducing a * -values of irradiated raw pork patties but rosemary tocopherol was not because of the characteristic red color of rosemary oleoresin. The increased red color in the control pork by irradiation was maintained during the storage under vacuum conditions, but A3/V7 doublepackaging mode reduced a * -values after 10 days of storage. The color of cooked pork was also changed to red by irradiation as in irradiated raw pork, but the red color was not stable as in irradiated raw meat (Table 6). It can be considered that the aerobic conditions during irradiation and early storage periods were helpful in minimizing the formation of carbon monoxide-myoglobin complex. Nam et al. (2004) reported that the packaging conditions during irradiation process were important in determining color changes in pork loin. Table 8 Tentative identification of volatile compounds produced in irradiated raw pork patties treated by oleoresin tocopherol combination and packaging at 10 days Compound NonIR Irradiated (2.5 kgy) Onion + tocopherol Rosemary + tocopherol Vacuum Vacuum A3/V7 a V7/A3 b A3/V7 a V7/A3 b SEM c (Total ion counts 10 4 ) Acetaldehyde 1575c 2728b 3734a 3081b 691d 472d 202 Methanethiol 0b 590a 0b 0b 0b 0b 19 1-Pentene 0b 184a 198a 174a 141a 136a 16 Pentane 306c 1122a 665b 685b 695b 592b 84 2-Propanone Carbon disulfide 0c 9829a 549c 1930bc 938c 2828b 484 Ethanol Hexene 0c 206a 225a 181ab 146ab 120b 19 2-Propanol Hexane 80b 470a 444a 419a 388a 344a 65 2-Butanone 356b 577a 403b 463ab 367b 336b 37 Benzene 0b 258a 21b 51b 0b 25b 17 1-Heptene 0c 491a 276b 300b 263b 228b 25 Heptane 0c 762a 683ab 679ab 621ab 541b 41 Pentanal 113a 125a 0b 0b 0b 0b 7 1-Methylthio propane 0b 0b 25740a 23390a 150b 115b 1221 Dimethyl disulfide 0b 149a 0b 0b 0b 0b 10 Toluene 0c 262a 159b 146b 146b 129b 17 1-Octene 0c 125a 114a 81b 65b 55b 9 Octane 155b 504a 400a 267b 242b 152b 35 1-butanal 477a 159ab 138ab 132ab 0b 0b 86 Methyl propyl disulfide 0b 0b 356a 183ab 0b 0b 61 Total 11698c 26396b 40540a 40155a 11359c 11699c 2014 Different letters (a c) within a row are significantly different (p ); n = 4. a Aerobically packaged for 3 days and then vacuum-packaged for 7 days. b Vacuum-packaged for 7 days and then aerobically packaged for 3 days. c Standard error of the means.

8 68 K.C. Nam et al. / Meat Science 75 (2007) Oleoresin tocopherol/packaging combinations on volatiles of irradiated pork Irradiation increased the amounts of many volatile compounds or newly generated a few volatiles not found in nonirradiated raw pork: almost 3 times higher amounts of volatiles were found in irradiated raw pork compared with the nonirradiated meats (Table 7). Newly generated compounds by irradiation were mainly sulfur-containing compounds such as methanethiol, carbon disulfide, and dimethyl disulfide. Ahn, Jo, and Olson (2000) reported that sulfur volatiles 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. Added oleoresin tocopherol combinations for the purpose of preventing lipid oxidation had little effects on the production of sulfur-volatiles by irradiation. The onion tocopherol combination added new sulfur volatile compounds such as sulfur methyl ester ethanethioic acid and methyl propyl disulfide not found in other irradiated pork, indicating that these compounds were derived from onion. Sulfur compounds such as methanethiol, carbon disulfide, dimethyl disulfide, and dimethyl trisulfide are responsible for irradiation off-odor (Ahn et al., 2000; Patterson & Stevenson, 1995), but some other sulfur compounds such as 2-pentylthiophene are important for freshly cooked meat flavor (Tang, Jin, Ho, & Chang, 1983). The contribution of sulfur compounds to irradiation off-odor, however, has not been studied. The amount of sulfur volatiles in irradiated pork loin was highly dependent upon packaging conditions. More amounts of methanethiol and carbon disulfide were found in vacuum-packaged meat. The effects of packaging conditions on the sulfur volatiles were clearer after 10 days of storage (Table 8). Double-packaged irradiated pork patties (exposed to aerobic conditions for 3 days during the 10 days of storage) had no methanethiol and dimethyl disulfide and lower amount of carbon disulfide than the vacuum-packaged control. Both double-packaging modes Table 9 Tentative identification of volatile compounds produced in irradiated cooked pork patties treated by oleoresin tocopherol combination and packaging at 0 day Compound NonIR Irradiated (2.5 kgy) Onion + tocopherol Rosemary + tocopherol Vacuum Vacuum A3/V7 a V7/A3 b A3/V7 a V7/A3 b SEM c (Total ion counts 10 4 ) Acetaldehyde Pentene 0b 559a 440a 370a 403a 376a 51 Pentane 18855b 26869a 2846c 2713c 4067c 3823c 1151 Propanal 3144b 4571a 3196b 2085c 1334d 903d Propanone Carbon disulfide Methyl propanal Ethanol a Hexene 0b 590a 615a 572a 697a 463a 49 2-Propanol 375b 752a 661a 428b 920a 912a 66 Hexane 1578a 1516a 1222ab 1267ab 1352ab 962b 110 Butanal 546b 1039a 320c 245c 390bc 270c 51 2-Butanone 609c 1122ab 1449a 1248a 1142ab 803bc 91 3-Methyl butanal 1100a 1037ab 1264a 1030ab 1121ab 939b 68 2-Methyl butanal 959a 648b 902a 744ab 733ab 629b 45 Benzene 0b 212a 186a 221a 200a 213a 19 1-Heptene 144b 1392a 1323a 1182a 1392a 842a 124 Heptane 1153b 3411a 2180b 1895b 2209b 1292b 253 Pentanal 9293b 13879a 1900c 1556c 2739c 1589c Methylthio propane 0b 0b 13449a 12761a 196b 101b 337 Dimethyl disulfide Toluene 0c 732b 918a 678b 952a 654b 55 1-Octene 0c 556a 482a 396ab 557a 324b 41 Octane 1832b 2728a 1580bc 1255bc 1875b 1073c Butanal Hexanal 57081b 82731a 8607c 7047c 8712c 6588c 214 Heptanal 228b 748a 100b 30b 69b 112b 49 Methyl propyl disulfide 0b 0b 396a 295a 0b 0b 37 Total b a 93799bc 72424c 83642bc 65799c 7528 Different letters (a c) within a row are significantly different (p ); n = 4. a Aerobically packaged for 3 days and then vacuum-packaged for 7 days. b Vacuum-packaged for 7 days and then aerobically packaged for 3 days. c Standard error of the means.

9 K.C. Nam et al. / Meat Science 75 (2007) Table 10 Tentative identification of volatile compounds produced in irradiated cooked pork patties treated by oleoresin tocopherol combination and packaging at 10 day Compound NonIR Irradiated (2.5 kgy) Onion + tocopherol Rosemary + tocopherol Vacuum Vacuum A3/V7 a V7/A3 b A3/V7 a V7/A3 b SEM c (Total ion counts 10 4 ) Acetaldehyde 11938b 15455b 29120ab 27829ab 23276a 20055ab Pentene 0b 385a 357a 332a 357a 389a 97 Pentane Propanal 31234a 32816a 22498b 18418b 8673c 6492d Propanone Methyl propanal Ethanol 5085a 2138c 3377bc 5135ab 5728a 4828ab Hexene 0b 545a 479a 475a 408a 485a 49 2-Propanol Hexane Butanal 889b 752bc 904b 623c 1177a 945b 64 2-Butanone 844b 889b 1341a 1157ab 1280ab 1105ab 97 3-Methyl butanal 1001b 1087b 1459a 1164ab 1337ab 1013b 86 2-Methyl butanal 999a 715b 956a 759ab 789ab 659b 54 Benzene 0b 241a 170a 170a 180a 202a 16 1-Heptene 101b 1310a 1142a 964a 982a 1206a 125 Heptane 1107b 3465a 3485a 2307ab 2885a 3488a 412 Pentanal 15466a 14982a 10315bc 7314c 10426bc 7895c Methylthio propane 0b 0b 8187a 7724a 0b 0b 295 Dimethyl disulfide 0b 919a 0b 0b 74b 0b 102 Toluene 0b 574a 693a 601a 732a 690a 52 1-Octene 0c 399b 522ab 459ab 564ab 597a 43 Octane Butanal 0c 0c 272b 375a 0c 0c 31 Hexanal 99435a a 70892b 71978b 46658c 16659d 7259 Heptanal Methyl propyl disulfide 0c 0c 293b 316a 0c 0c 11 Total d c bc bc a 83972b Different letters (a d) within a row are significantly different (P ); n = 4. a Aerobically packaged for 3 days and then vacuum-packaged for 7 days. b Vacuum-packaged for 7 days and then aerobically packaged for 3 days. c Standard error of the means. were very effective in eliminating sulfur volatiles, but A3/ V7 double-packaging showed less carbon disulfide than V7/A3 mode, indicating that considerable amounts of sulfur compounds were evaporated under aerobic conditions during irradiation. Onion oleoresin-added pork patties had still considerable amounts of 1-methylthio propane after 10 days of storage. The profile of volatile compounds in irradiated cooked pork was more complex than that in irradiated raw meat because more lipid oxidation products (hydrocarbons, aldheydes) were generated (Table 9). Hexanal was the most predominant aldehyde in irradiated cooked pork but the amount was reduced to about 10% of the control by the oleoresin tocopherol combinations after 10 days of storage. This indicated that oleoresin tocopherol combinations were effective in controlling hexanal content in cooked pork (Table 10). Rosemary tocopherol combination was more effective than onion tocopherol in reducing hexanal production as in TBARS (Table 3). Little dimethyl disulfide was detected in double-packaged irradiated pork patties at Day 10 (Table 10), indicating that regardless of double-packaging modes, exposing meats for 3 days in aerobic conditions was effective in removing sulfur volatiles responsible for irradiation offodor. The onion-added pork patties, however, still had other sulfur volatiles (1-methylthio propane, methyl propyl disulfide) derive from onion. 4. Conclusion Rosemary and onion showed antioxidant effects in both raw and cooked irradiated pork loins. When these oleoresins were used in combination with a-tocopherol, the antioxidant activity was more distinct in irradiated cooked pork. Rosemary oleoresin tocopherol ( % of meat wt.) had stronger antioxidant effect than onion tocopherol, but none of the oleoresin tocopherol combinations showed any effects on the production of sulfur volatiles responsible for the characteristic irradiation off-odor. Double-packaging methods, exposing the irradiated meats to aerobic conditions for 3 days and then keeping them under vacuum conditions for the remaining 7 days of storage, effectively

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