Use of antioxidants to reduce lipid oxidation and off-odor volatiles of irradiated pork homogenates and patties

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1 Meat Science 63 (2003) Use of antioxidants to reduce lipid oxidation and off-odor volatiles of irradiated pork homogenates and patties K.C. Nam, D.U. Ahn* Department of Animal Science, Iowa State University, 1221 Kildee, Ames, IA , USA Received 30 October 2001; received in revised form 11 January 2002; accepted 11 January 2002 Abstract Pork homogenates and patties treated with antioxidants (200 mm, final) were irradiated with an electron beam. Lipid oxidation of the pork homogenates and patties were determined at day 0 and 5 and volatile compounds were analyzed soon after irradiation. Ionizing radiation accelerated lipid oxidation and produced S-containing volatiles in pork homogenates and patties. Addition of an antioxidant (sesamol, gallate, Trolox, or a-tocopherol) and their combinations decreased, but carnosine did not affect the production of off-odor volatiles and lipid oxidation of pork homogenates and patties by irradiation. Antioxidant combinations showed distinct beneficial reduction in lipid oxidation of aerobically packaged irradiated pork patties. The effect of antioxidant combinations in reducing sulfur volatiles of irradiated pork patties was clearer under vacuum than aerobic conditions. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Antioxidants; Irradiation; Lipid oxidation; Off-odor volatiles; Pork 1. Introduction Irradiated meats are susceptible to oxidative quality deterioration such as lipid oxidation and off-odor production. The quality of irradiated meat correlates closely with the amounts of radiolytic products (Woods & Pikaev, 1994). Free radicals possess strong chemical reactivity and can react with unsaturated fatty acids or amino acid side chains of protein (McMillin, 1996). As a result, irradiation promotes lipid oxidation and generates characteristic off-odor volatiles in meats. The production of aldehydes and 2-thiobarbituric acid-reactive substances (TBARS) were irradiation dose-dependent, and had strong correlations with off-odor in irradiated pork (Ahn, Jo, Du, Olson, & Nam, 2000). The gas chromatograms of raw irradiated pork suggested that not only lipid oxidation but also other mechanisms, such as radiolytic degradation of proteins, Journal Paper No. J of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA * Corresponding author. Tel.: ; fax: address: duahn@iastate.edu (D.U. Ahn). played an important role in the off-odor production in irradiated meat (Ahn, Nam, Du, & Jo, 2001). Jo and Ahn (2000) reported that S-containing volatiles generated from S-containing amino acids were responsible for most of the characteristic irradiation odor in meat. Antioxidant additives are added to fresh and further processed meats to prevent oxidative rancidity, retard development of off-flavors, and improve color stability (Xiong, Decker, Robe, & Moody, 1993). Certain antioxidants can interrupt free radical chain reactions by scavenging free radicals (Chen & Ahn, 1998) and using specific antioxidants can reduce lipid oxidation and offodor formation by irradiation. Radiolytic changes in meat are accelerated in the presence of oxygen and the activities and mechanisms of selected antioxidants can vary depending upon the composition of food systems. To be effective, antioxidants added in meat must compete with reactive meat components for free radicals generated by irradiation, or inhibit the formation of free radicals induced by prooxidative metals. Therefore, free radical scavengers (gallate, sesamol, and tocopherol), metal chelators (Trolox) and intrinsic antioxidant (carnosine), or their combinations can be used to reduce the production of off-odor volatiles in electron beam-radiated pork /02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S (02)

2 2 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) 1 8 The effect of antioxidants on controlling oxidative reactions in meat has been well documented. However, the information on added antioxidant effects on lipid oxidation and off-odor volatiles in irradiated meats is lacking. In addition selected antioxidants may differ in reducing lipid oxidation and S-containing volatiles in irradiated meats depending upon the type and combinations of antioxidants and packaging method used. Therefore, the objective of this study was to determine the effect of selected antioxidants and their combinations on lipid oxidation and production of off-odor volatiles in irradiated pork homogenates and patties with aerobic or vacuum packaging. 2. Materials and methods 2.1. Antioxidants Gallic acid (3,4,5-trihydroxybenzoic acid), sesamol (3,4- methylenedioxyphenol), and l-carnosine (b-alanyl-l-histidine) were purchased from Sigma Chemical Company (St. Louis, MO), and a-tocopherol (vitamin E) and Trolox (6- hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) were obtained from Aldrich Chemical Co. (Milwaukee, WI). The antioxidants were selected on the basis of their antioxidant functions and solubility to water and lipids Preparation of pork homogenates and patties Pork loins were purchased from four local stores. Loins from each store were combined and separately ground twice through a 3-mm plate and used as a replication. The ground meat (50 g) was homogenized with deionized water (200 ml) using a laboratory blender (Waring Commercial, New Hartford, CT) for 1 min at high speed. Each antioxidant (gallic acid, tocopherol, Trolox, sesamol or carnosine) was added in meat homogenate to make a final concentration of 200 mm. To determine the synergistic effects of selected antioxidants, several antioxidant combinations were prepared. Either 100 or 66.7 mm of each antioxidant was added depending upon 2 or 3 antioxidant combinations to make equal final total concentration of antioxidants of 200 mm in all treatments. Three of the most effective antioxidants or antioxidant combinations in reducing off-odor production and TBARS in meat homogenates were selected for the study with pork patties. The effects of selected antioxidant on lipid oxidation and off-odor volatiles of pork patties were determined. To prepare antioxidant-treated pork patties, the three different antioxidant combinations that produced the least amount of off-odor volatiles from the previous pork homogenate study were used. Ground pork and antioxidants combination (final 200mM) were mixed for 3 min in a bowl mixer (Model KSM90; KitchenAid Inc., St. Joseph, MI) to ensure uniform distribution of the added antioxidants. Pork patties (100 g) were prepared and half of the patties from each treatment were aerobically packaged by individually placing in polyethylene oxygen-permeable bags (1015 cm, 2 MIL-Associated Bag Company, Milwaukee, WI) and the other half were vacuum-packaged in high oxygen-barrier bags (nylon/ polyethylene, 9.3 ml O 2 /m 2 /24 h at 0 C; Koch, Kansas City, MO). Four replications were performed for both pork homogenate and patty studies Ionizing radiation and storage Antioxidant-treated pork homogenates and patties were electron beam-irradiated at 0 or 4.5 kgy using a linear accelerator (Circe IIIR; Thomson CSF Linac, Saint-Aubin, France) with 10 MeV of energy, 10 kw of power level, and kgy/min of average dose rate. The max/min ratio was approximately 1.16 for 4.5 kgy. Alanine dosimeters were attached to the top and bottom surfaces of a sample, and read using a 104 Electron Paramagnetic Resonance Instrument (Bruker Instruments Inc., Billerica, MA) to check the absorbed dose. The irradiated samples were stored at 4 C. The TBARS of the samples were determined at day 0 and 5, and volatiles were analyzed soon after irradiation Thiobarbituric acid-reactive substances (TBARS) Lipid oxidation was determined by the TBARS method (Ahn, Olson, Jo, Chen, Wu, & Lee, 1998). Sample (5 g) was placed in a 50-ml test tube and homogenized with 15 ml of deionized distilled water (DDW) using a Brinkman Polytron (Type PT 10/35; Brinkman Instrument Inc., Westbury, NY) for 15 s at high speed. A meat homogenate (1 ml) was transferred to a disposable test tube (13100 mm), and butylated hydroxytoluene (7.2% in ethanol, v/v, 50 ml) and thiobarbituric acid/ trichloroacetic acid (20 mm TBA/15% TCA, w/v, 2 ml) solutions were added. The mixture was vortexed and then incubated in a 90 C water bath for 15 min to develop color. After cooling for 10 min in cold water, the sample was vortexed and centrifuged at 3000g for 15 min at 5 C. The absorbance of the resulting upper layer was read at 531 nm against a blank prepared with 1 ml DDW and 2 ml TBA/TCA solution. The amounts of TBARS were expressed as mg of malonedialdehyde (MDA) per kg meat or per 4 l meat homogenate (equivalent to 1 kg of meat) Volatile compounds analysis A purge-and-trap apparatus (Precept II and Purge & Trap Concentrator 3000; Tekmar-Dohrmann, Cincinnati, OH) connected to a gas chromatograph/mass spectrometer (GC/MS; Hewlett-Packard Co., Wilmington,

3 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) DE) was used to analyze volatiles produced (Ahn et al., 2001). Minced meat sample (3 g) or meat homogenate (3 ml) was placed in a 40-ml sample vial, and the vials were flushed with helium (40 psi) for 5 s. The maximum waiting time of a sample in a refrigerated (4 C) holding tray was less than 4 h to minimize oxidative changes before analysis. The meat sample was purged with helium (40 ml/min) for 12 min at 40 C. Volatiles were trapped using a Tenax column (Tekmar-Dohrmann) and desorbed for 2 min at 225 C, focused in a cryofocusing module ( 90 C) and then thermally desorbed into a column for 30 s at 225 C. An HP-624 column (7.5 m 0.25 mm i.d., 1.4 mm nominal), an HP-1 column (52.5 m0.25 mm i.d., 0.25 mm nominal; Hewlett-Packard Co.) and an HP-Wax column (7.5 m0.25 mm i.d., 0.25 mm nominal) were connected using zero deadvolume column connectors (J&W Scientific, Folsom, CA). Ramped oven temperature was used to improve volatile separation. The initial oven temperature of 0 C was held for 2.50 min. After that, the oven temperature was increased to 15 C at 2.5 C/min, increased to 45 C at 5 C/min, increased to 110 Cat20 C/min, increased to 210 Cat10 C/min, and then was held for 2.5 min at 210 C. Constant column pressure at 20.5 psi was maintained. The ionization potential of the mass-selective detector (Model 5973; Hewlett-Packard Co.) was 70 ev, and the scan range was m/z. Identification of volatiles was achieved by comparing mass spectral data of samples with those of the Wiley Library (Hewlett-Packard Co.). Standards, when available, were used to confirm the identification by the mass-selective detector. The area of each peak was integrated using the ChemStation TM (Hewlett-Packard Co.), and the peak area (total ion counts10 4 ) was reported as an indicator of volatiles generated from the sample Statistical analysis This experiment was designed to determine the antioxidant effects on lipid oxidation and volatile profiles of the nonirradiated and irradiated samples. Analysis of variance was conducted using the generalized linear model procedure of the SAS software (SAS Institute, 1995); Student Newman Keul s multiple range tests were used to compare the mean values. Mean values and standard error of the means (SEM) were reported (P<0.05). 3. Results and discussion 3.1. Lipid oxidation Irradiation and antioxidants affected the TBARS values of pork homogenates during storage (Table 1). Irradiated pork homogenates had higher TBARS than nonirradiated in all antioxidant treatments. The added antioxidant effect to reduce TBARS was found in irradiated pork homogenates, but not in nonirradiated. Most antioxidants but carnosine at 200 mm levels decreased the TBARS of irradiated pork homogenates. The antioxidant effects in meat homogenates were more notable after 5 days of storage. Sesamol and Trolox were superior to other antioxidants and reduced TBARS of irradiated pork homogenate by 72% of control at day 5. The effects of antioxidants in nonirradiated pork homogenates could not be found even at day 5. TBARS values of pork homogenates treated with antioxidant combinations (Table 2) also showed similar trends as in individual antioxidant treatments (Table 1). However, it is impossible to compare the TBARS values from the two studies (Tables 1 and 2) directly because we used meat samples having different storage history at different times. Although the effects of antioxidant combinations were significant in irradiated pork homogenates, the difference among antioxidant combinations was minimal at day 0. The effects of antioxidant combinations, however, were distinct after 5 days of storage. The sesamol plus tocopherol, or Trolox plus tocopherol was more effective than other combinations in inhibiting lipid oxidation. These 2-antioxidant combinations reduced TBARS of irradiated pork homogenates by 47% of the control at 5 days storage. The combination of sesamol plus g-tocopherol was efficient in inhibiting hydroperoxide formation in oils (Yoshida & Takagi, 1999). The effects of 3-antioxidant combinations were not different from those of 2-antioxidant combinations. Irradiation, antioxidants, and packaging methods influenced the TBARS values of pork patties during storage (Table 3). Pork patties were susceptible to lipid oxidation, especially when irradiated and stored in the presence of oxygen. Antioxidant combinations decreased TBARS in both nonirradiated and irradiated pork patties under aerobic conditions, but there were little differences among antioxidant combinations at day 0. Vacuum-packaged patties did not develop lipid oxidation at day 0 regardless of irradiation and antioxidant treatments, but the effects of irradiation and antioxidant combination were evident at day 5. When irradiated and stored for 5 days, the effects of antioxidant combinations on oxidative changes in pork patties were more distinct in aerobically packaged than vacuum-packaged pork, but the differences among antioxidant combinations were still minimal. Chen, Jo, Lee, and Ahn (1999) also reported that phenolic antioxidants were effective in reducing lipid oxidation in aerobically packaged irradiated pork patties. All treated antioxidant combinations reduced TBARS of aerobically and vacuumpackaged irradiated pork patties by about 50 and 20% of the control value at day 5, respectively. Therefore, the use of antioxidant combinations was more effective in reducing oxidative changes in aerobically packaged than vacuum-packaged irradiated pork patties.

4 4 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) 1 8 Table 1 TBARS values of nonirradiated and irradiated pork homogenates treated with different antioxidants during storage at 4 C a Antioxidant b Day 0 (mg MDA/4 l meat homogenate) Day 5 (mg MDA/4 l meat homogenate) Non Irradiated c SEM Non Irradiated SEM Control 0.12by 0.99ax y 1.52ax 0.01 Gallate 0.12by 0.64bx c 0.07 Tocopherol 0.12by 0.73bx y 0.94bx 0.01 Trolox 0.12by 0.58bx y 0.42dx 0.01 Sesamol 0.13by 0.58bx y 0.42dx 0.01 Carnosine 0.20ay 1.07ax y 1.50ax 0.01 SEM a Mean values with different letters within a column are significantly different (P< 0.05), n=4. Mean values with different letters within a row with same storage are significantly different (P<0.05). b 200 mm of antioxidant concentration. c Irradiated at 4.5 kgy. Table 2 TBARS values of nonirradiated and irradiated pork homogenates treated with different antioxidant combinations during storage at 4 C a Antioxidant b Day 0 (mg MDA/4 l meat homogenate) Day 5 (mg MDA/4 l meat homogenate) Non Irradiated c SEM Non Irradiated SEM Control 0.37by 0.79ax y 0.89ax 0.01 S d +G e 0.36by 0.64bx y 0.61bx 0.01 G+T f 0.44ay 0.70bx y 0.59bcx 0.01 S+T 0.36by 0.65bx y 0.56bcx 0.01 S+E g 0.37by 0.65bx y 0.47dx 0.01 T+E 0.38ay 0.63bx y 0.48dx 0.01 S+E+T 0.36by 0.66bx y 0.53cdx 0.01 S+E+G 0.40aby 0.63bx y 0.53cdx 0.01 SEM a Mean values with different letters within a column are significantly different (P<0.05), n=4. Mean values with different letters within a row with same storage are significantly different (P<0.05). b 100 mm for each of 2-antioxidants or 66.7 mm for each of 3-antioxidants. c Irradiated at 4.5 kgy. d Sesamol. e Gallate. f Trolox. g Tocopherol Volatile compounds Irradiation and antioxidants affected the volatiles of pork homogenates qualitatively as well as quantitatively (Table 4). In nonirradiated pork homogenates, antioxidant or antioxidants combination showed little effect on the production of volatiles because only a few volatiles were detected. On the other hand, irradiation produced many new volatiles, mostly aldehydes (propanal, 2- methylpropanal, 3-methylbutanal, 2-methylbutanal, pentanal, and hexanal) and S-containing compounds (methanethiol, dimethyl sulfide, and dimethyl disulfide). Irradiated pork homogenates treated with antioxidants produced less aldehydes and S-containing volatiles than the control. Ahn et al. (2000) reported that dimethyl disulfide was a major sulfur compound responsible for the irradiation off-odor. Gallate, tocopherol, and sesamol were effective in reducing the off-odor volatiles produced by irradiation, but sesamol was the most effective among them. Sesamol reduced the amounts of dimethyl disulfide and total volatiles by 48 and 43% of the control values, respectively. Sesamol was effective in reducing the generation of volatiles in irradiated pork during the 7 days of storage (Chen et al. 1999). Despite the fact that carnosine is known as an antioxidant in meats (Chan & Decker, 1993; Lee, Hendricks & Cornforth, 1999), it did not show any antioxidant or volatiles-reducing activities in irradiated pork homogenates. The small antioxidant effect of carnosine is possibly because the added amount of carnosine (200 mm) was so small. Carnosine concentrations in beef, pork, chicken and fish range from mm (Plowman & Close, 1988). Therefore, carnosine would not be economical as an antioxidant in reducing lipid oxidation or off-odor production in irradiated meat.

5 Table 3 TBARS values of nonirradiated and irradiated pork patties treated with different antioxidant combinations during storage at 4 C a Antioxidant b Day 0 (mg MDA/kg meat) Day 5 (mg MDA/kg meat) Non Irradiated c SEM Non Irradiated SEM Aerobic packaging Control 0.33a 0.32a ay 0.74ax 0.06 S d +G e 0.20b 0.27ab by 0.37bx 0.02 S+T f 0.18b 0.26ab by 0.37bx 0.02 S+E g 0.19b 0.22b by 0.35bx 0.02 SEM Vacuum-packaging Control ay 0.42ax 0.02 S+G by 0.34bx 0.02 S+T 0.16y 0.21x by 0.34bx 0.02 S+E by 0.35bx 0.02 SEM a Mean values with different letters within a column with same packaging are significantly different (P<0.05), n=4. Mean values with different letters within a row with same storage are significantly different (P<0.05). b 100 mm for each of 2-antioxidants. c Irradiated at 4.5 kgy. d Sesamol. e Gallate. f Trolox. g Tocopherol. K.C. Nam, D.U. Ahn / Meat Science 63 (2003) Table 4 Volatile compounds of nonirradiated and irradiated pork homogenates treated with different antioxidant (200 mm) a Volatiles Total ion counts 10 4 Control Gallate Tocopherol Trolox Sesamol Carnosine SEM Nonirradiated Acetaldehyde Pentane Propanone Carbon disulfide 3632bc 4795abc 2758c 6412a 5244ab 5986ab 601 Hexane 326a 96b 0c 66b 65b 135b 32 Total volatiles 4083ab 4910ab 3071b 6503a 5328ab 6190a 486 Irradiated at 4.5 kgy 2-Methyl-1-propene Acetaldehyde 1091a 48b 0b 0b 400ab 217b 183 Methanethiol Pentane Propanal 131a 0b 0b 61ab 29b 31b 28 Dimethyl sulfide 599a 268c 0d 361b 323b 617a 24 Carbon disulfide 1267b 1780b 2995a 2504a 1877b 1603b Methylpropanal 876a 0b 371ab 0b 0b 232ab 95 Hexane 347d 329d 387c 404c 428b 496a 6 3-Methylbutanal 2083a 1336b 2055a 1510ab 1180b 1609ab Methylbutanal 1171a 836a 0b 1079a 937a 1061a 94 Heptane 475b 429c 0e 499a 209d 472b 4 Pentanal Dimethyl disulfide 3774a 2330b 2316b 3275ab 1965c 3998a 377 Octane 816ab 518b 670ab 572ab 440b 930a 90 Hexanal Total volatiles a Mean values with different letters within a row are significantly different (P<0.05), n=4.

6 6 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) 1 8 Synergistic effects by antioxidant combinations in reducing the production of off-odor volatiles by irradiation were found in pork homogenates (Table 5). Antioxidant combinations decreased the amounts of aldehydes and S-compounds in irradiated pork homogenates. But the synergistic effects of 3-antioxidant combinations were not higher than those of 2-antioxidant combinations. Among the antioxidant combinations, sesamol plus gallate, sesamol plus Trolox, and sesamol plus tocopherol were the most effective in reducing aldehydes and S-compounds in irradiated pork homogenates. Sesamol plus Trolox treatments had the lowest amount of dimethyl disulfide, which was about 50% of the control. Sesamol plus tocopherol was the most effective in reducing carbon disulfide, 3-methylbutanal, and total volatiles production. The amount of carbon disulfide, a main volatile compound in nonirradiated pork homogenates, decreased dramatically after irradiation. The result suggested that carbon disulfide could be a precursor or an intermediate of S-compounds responsible for off-odor in irradiated pork homogenates. Antioxidant and packaging affected the volatiles of nonirradiated pork patties (Table 6). All antioxidant combinations added to pork patties reduced the amounts of volatiles by about 40% of the control. Pork patties with added sesamol plus gallate, or sesamol plus Trolox had lower total volatiles than sesamol plus tocopherol in aerobically packaged pork, but there was little difference in S- volatiles that affect irradiation offodor the most. Much greater amounts of volatiles were found in vacuum-packaged than aerobically packaged pork patties. All antioxidant combinations decreased the production of 2-propanone and carbon disulfide in pork patties. The differences among antioxidant combinations, however, were not significant. Irradiation not only increased the amounts of volatiles found in nonirradiated pork patties but also produced a few volatiles not found in nonirradiated pork (Table 7). Acetaldehyde, pentane, 2-propanone, carbon disulfide, and dimethyl disulfide were the major volatiles produced in irradiated pork patties. The amounts of these volatiles were much higher in vacuum-packaged than aerobically packaged pork patties. The result shows that S-compounds produced by irradiation volatilized rapidly under aerobic packaging conditions. The addition of antioxidant combinations decreased the Table 5 Volatile compounds of irradiated and nonirradiated pork homogenates treated with different antioxidant combination (final 200 mm) a Volatiles Total ion counts10 4 Control S b +G c G+T d S+T S+E e T+E S+E+T S+E+G SEM Nonirradiated Acetaldehyde Pentane Propanone Carbon disulfide 3632b 7780a 7297a 7361a 7708a 4596ab 3679b 3622b 372 Hexane Total volatiles 4083b 7958a 7849a 8129a 7929a 4972b 3799b 3875b 695 Irradiated at 4.5 kgy 2-Methyl-1-propene Butane Acetaldehyde 1091a 30b 90b 49b 155b 45b 105b 108b 193 Methanethiol 578a 209a 149ab 43ab 0b 0b 0b 0b 54 Pentane Propanal Dimethyl sulfide 599a 596a 511a 605a 390b 576a 576a 593a 32 Carbon disulfide 1267b 2175ab 2346a 2755a 2606a 2590a 2117ab 2806a Methylpropanal 876a 204b 754a 436ab 222b 149b 323ab 420ab 80 Hexane 347ab 435ab 411ab 426ab 307b 434ab 478a 481a 33 3-Methylbutanal 2083a 1241b 1303b 1229b 924c 1621b 1261b 1598b Methylbutanal 1176a 903b 857b 522c 0d 660bc 0d 621bc 72 Heptane 475a 298c 444ab 428ab 0d 0d 420ab 351c 26 Pentanal 184a 0b 45b 17b 0b 0b 0b 0b 31 Dimethyl disulfide 3774a 2168b 2238b 1862b 2124b 2394b 2258b 2052b 297 Octane Hexanal Total volatiles a Mean values with different letters within a row are significantly different (P<0.05), n=4. b Sesamol. c Gallate. d Trolox. e Tocopherol.

7 Table 6 Volatile compounds of nonirradiated pork patties treated with different antioxidant combination (final 200 mm) and packaging condition a Volatiles Total ion counts 10 4 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) Aerobic packaging Vacuum-packaging Control S b +G c S+T d S+E e SEM Control S+G S+T S+E SEM 2-Methylbutane 34b 31b 43a 38ab 2 295a 94bc 193ab 20c 13 Pentane 606a 341b 262b 310b a 1082b 681b 732b 176 Ethanol 1458ab 902b 794b 2056a Propanone a 1852b 2966b 473c 380 Dimethyl sulfide 119c 251a 175b 190b Carbon disulfide a 620b 365b 344b 69 1-Hexene a 0b 0b 0b 4 Hexane Hexene Butanone 71a 0b 0b 0b 15 79a 0b 63a 0b 11 3-Methylbutanal 94a 50b 73a 0c Heptane a 158b 147b 132b 22 2-Pentanone 126a 46b 0c 0c Total volatiles 3793a 2830b 2461b 4223a a 5778bc 6723b 4296c 540 a Mean values with different letters within a row are significantly different (P<0.05), n=4. b Sesamol. c Gallate. d Trolox. e Tocopherol. Table 7 Volatiles of irradiated (4.5 kgy) pork patties treated with different antioxidant combination (final 200 mm) and packaging condition a Volatiles Total ion counts 10 4 Aerobic packaging Vacuum packaging Control S b +G c S+T d S+E e SEM Control S+G S+T S+E SEM 2-Methylpropane 199b 201b 191b 310a b 291b 349b 1096a 52 2-Methyl-1-propene 641b 767b 1183a 1286a b 2030a 2086a 2382a 122 Butane 860b 843b 1199ab 1421a Acetaldehyde 520a 0b 103b 395a a 455b 372b 492b Butene b 1512a 1443a 1463a Methyl-2-butene Methylbutane ab 112b 129b 425a 30 1-Pentene Pentane 3467a 1422b 1341b 994b a 1174b 1107b 1185b 99 Ethanol Propanone 5379a 1954b 1004b 2889b a 2035b 2028b 3848a 423 Dimethyl sulfide 1007a 511b 608b 899a a 1937b 2244b 3653a 336 Carbon disulfide a 1100b 1188b 1009b Hexene b 197c 400a 374ab 26 Hexane a 491ab 272b 758a 84 2-Hexene ab 55b 37b 188a 34 2-Butanone Heptane b 261b 273b 878a 54 Dimethyl disulfide 1056a 246b 78b 183b a 917b 1513b 4668a 375 Total volatiles 15024a 7939c 7478c 11053b a 14699b 16015b 24804a 1410 a Mean values with different letters within a row are significantly different (P< 0.05), n=4. b Sesamol. c Gallate. d Trolox. e Tocopherol.

8 8 K.C. Nam, D.U. Ahn / Meat Science 63 (2003) 1 8 production of these volatiles as well as total volatiles in pork patties. In aerobically packaged pork patties, most antioxidant combinations were effective in reducing the amounts of S-compounds such as carbon disulfide and dimethyl disulfide, which contribute the characteristic off-odor of irradiated meats. However, no significant differences on the production of carbon disulfide and dimethyl disulfide among the antioxidant combinations were found in aerobically packaged pork patties. Higher amounts of volatiles were found in vacuum-packaged pork patties than aerobically packaged patties. The addition of sesamol plus gallate (final 200 mm) to vacuum-packaged irradiated pork patties reduced acetaldehyde, carbon disulfide, dimethyl sulfide, dimethyl disulfide, and total volatiles by 59, 53, 58, 81, and 43% of the control, respectively. 4. Conclusion The addition of antioxidant combinations using sesamol, gallate, and a-tocopherol to a final concentration of 200 mm was effective in reducing lipid oxidation and off-odor volatiles in irradiated pork patties. Antioxidant combinations reduced the S-containing volatiles, which are the main off-odor compounds in irradiated, vacuum-packaged pork patties. Treatments containing a combination of antioxidants also controlled lipid oxidation in aerobically packaged irradiated pork patties. Therefore, modification of the packaging method with addition of antioxidants will be a key to solve the off-odor problems in the storage of irradiated pork patties. Acknowledgements This project, No. 3706, was funded by National Pork Producers Council, on behalf of the Iowa pork Producers Association. References Ahn, D. U., Jo, C., Du, M., Olson, D. G., & Nam, K. C. (2000). Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions. Meat Science, 56(2), Ahn, D. U., Nam, K. C., Du, M., & Jo, C. (2001). Volatile production in irradiated normal, pale soft exudative (PSE), and dark firm dry (DFD) pork under different packaging and storage conditions. Meat Science, 57(4), Ahn, D. U., Olson, D. G., Jo, C., Chen, X., Wu, C., & Lee, J. I. (1998). Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production, and color in raw pork patties. Meat Science, 47(1), Chan, K. M., & Decker, E. A. (1993). Extraction and activity of the natural antioxidant, carnosine, from beef muscle. Journal of Food Science, 58(1), 1 5. Chen, X., & Ahn, D. U. (1998). Antioxidant activities of six natural phenolics against lipid oxidation induced by Fe 2+ or ultraviolet light. Journal of American Oil Chemists Society, 75(12), Chen, X., Jo, C., Lee, J. I., & Ahn, D. U. (1999). Lipid oxidation, volatiles, and color changes of irradiated pork patties as affected by antioxidants. Journal of Food Science, 64(1), Jo, C., & Ahn, D. U. (2000). Production volatile compounds from irradiated oil emulsions containing amino acids or proteins. Journal of Food Science, 65(4), Lee, B. J., Hendricks, D. G., & Cornforth, D. P. (1999). A comparison of carnosine and ascorbic acid on color and lipid stability in a ground beef patties model system. Meat Science, 51(3), McMillin, K. W. (1996). Initiation of oxidative processes in muscle foods. Reciprocal Meat Conferences Proceedings, 49, Plowman, J. E., & Close, E. A. (1988). An evaluation of a method to differentiate the species of origin of meats on the basis of the contents of anserine, balenine and carnosine in skeletal muscle. Journal of the Science of Food and Agriculture, 45(1), SAS Institute Inc. (1995). SAS/STAT User s Guide. Cary, NC: SAS Institute Inc. Woods, R. J., & Pikaev, A. K. (1994). Interaction of radiation with matter.. In R. J. Woods, & A. K. Pikaev (Eds.), Applied radiation chemistry: radiation processing (pp ). New York: John Wiley. Xiong, Y. L., Decker, E. A., Robe, G. H., & Moody, W. G. (1993). Gelation of crude myofibrillar protein isolated from beef heart under antioxidant conditions. Journal of Food Science, 58(6), Yoshida, H., & Takagi, S. (1999). Antioxidative effects of sesamol and tocopherols at various concentrations in oils during microwave heating. Journal of the Science of Food and Agriculture, 79(2),