Effects of ascorbic acid and antioxidants on color,lipid oxidation and volatiles of irradiated ground beef

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1 ARTICLE IN PRESS Radiation Physics and Chemistry 71 (2004) Effects of ascorbic acid and antioxidants on color,lipid oxidation and volatiles of irradiated ground beef D.U. Ahn*,K.C. Nam Animal Science Department, Iowa State University, 2276 Kildee, Ames, IA , USA Abstract Beef loins with 3 different aging times after slaughter were ground,added with none,0.1% ascorbic acid,0.01% sesamol+0.01% a-tocopherol,or 0.1% ascorbic acid+0.01% sesamol+0.01% tocopherol. The meats were packaged in oxygen-permeable bags,irradiated at 2.5 kgy,and color,oxidation reduction potential (ORP),lipid oxidation and volatile profiles were determined. Irradiation decreased the redness of ground beef,and visible color of beef changed from a bright red to a green/brown depending on the age of meat. Addition of ascorbic acid prevented color changes in irradiated beef,and the effect of ascorbic acid became greater as the age of meat or storage time after irradiation increased. The ground beef added with ascorbic acid had lower ORP than control,and the low ORP of meat helped maintaining the heme pigments in reduced form. During aerobic storage,s-volatiles disappeared while volatile aldehydes significantly increased in irradiated beef. Addition of ascorbic acid at 0.1% or sesamol+a-tocopherol at each 0.01% level to ground beef prior to irradiation were effective in reducing lipid oxidation and S-volatiles. As storage time increased,however,the antioxidant effect of sesamol+tocopherol in irradiated ground beef was superior to that of ascorbic acid. r 2004 Elsevier Ltd. All rights reserved. Keywords: Irradiated ground beef; Color and volatiles; Ascorbate; Antioxidants 1. Introduction *Corresponding author. Tel.: ; fax: address: duahn@iastate.edu (D.U. Ahn). Ground beef comprises over 40% of beef consumption in the US (AMI,1998),and is the most susceptible form of meat to microbial contamination during processing and handling. Therefore,prevention of pathogens from ground beef is the most demanding. Irradiation is the most effective technology in controlling pathogenic microorganisms in ground beef,but can influence color,lipid oxidation and odor of beef significantly. Meat color is a prime quality parameter that determines the consumer acceptance of meat. Liu et al. (1995) indicated that the loss of value due to discoloration in beef at the retail level in the US could be over 700 million dollars per year. The color changes induced by irradiation are different depending on animal species, muscle type,irradiation dose,and packaging type (Ahn et al.,1998). In general,light meat such as pork loin and poultry breast meat produced pink color,while dark meat such as beef became brown or gray after irradiation (Millar et al.,1995; Nanke et al.,1998; Kim et al.,2002a). The pink color compounds in irradiated light meat was characterized as a carbon monoxide-heme pigment complex (Nam and Ahn, 2002a,b),but the mechanisms and cause of color changes in irradiated beef is not known yet. The major volatile compounds responsible for offodor in irradiated meats are mainly sulfur compounds (Ahn et al.,1999,2000,2001). The volatile sulfur compounds were produced from the radiolytic degradation of the side chains of sulfur-containing amino acids, X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi: /j.radphyschem

2 150 ARTICLE IN PRESS D.U. Ahn, K.C. Nam / Radiation Physics and Chemistry 71 (2004) methionine and cysteine (Ahn,2002; Ahn and Lee, 2002). Unlike popular belief,ground beef oxidized faster than ground pork or poultry (Nam et al.,2001; Kim et al.,2002a). Despite the intrinsic antioxidant activities in fresh meat,irradiation accelerated lipid oxidation in raw pork and beef patties under aerobic conditions (Ahn et al.,1998; Kim et al.,2002b). Ascorbic acid is a reducing agent,which inhibits myoglobin oxidation and brown color development in nonirradiated beef (Sanchez-Escalante et al.,2001). The combinations of phenolic antioxidants such as gallate, sesamol,and tocopherol,were effective in reducing the oxidative reactions and the production of sulfur volatiles in irradiated pork by scavenging free radicals produced by irradiation (Nam and Ahn,2003). The objective of this study was to determine the effect of ascorbic acid and selected antioxidants on the color and off-odor volatiles of beef with different postmortem aging time before irradiation and storage time after irradiation. 2. Materials and methods 2.1. Sample preparation Beef loins (Longissimus dorsi) with 3 different aging times after slaughter were used. The freshest loins were obtained from 4 animals 2 d after slaughter. One group of the loins purchased 2 week before sample preparation was further aged at 4 C and the other group was purchased 1 d before preparation. For convenience,the three loins were named pre-aged, aged,and longterm-aged,respectively. Each meat block was ground separately through a 3-mm plate. Five treatments were prepared: (1) nonirradiated control,(2) irradiated control,(3) 0.1% (w/w) l-ascorbic acid-added and irradiated,(4) 0.01% sesamol+0.01% a-tocopheroladded and irradiated,and (5) 0.1% ascorbic acid+0.01% sesamol+0.01% tocopherol-added and irradiated. Each additive was added to the ground beef and then mixed for 1 min in a bowl mixer. Ground beef was individually packaged in oxygen-permeable bags (polyethylene),stored at 4 C overnight,and irradiated next day morning Ionizing radiation The aerobically packaged ground beef were irradiated at 2.5 kgy using a Linear Accelerator Facility with 10 MeV energy and 10.2 kw power level. After irradiation,the irradiated and nonirradiated meat samples were immediately returned to a 4 C cold room and stored for 7 d. Color,ORP values,lipid oxidation and volatile profiles of the samples were determined on 1,4,and 7 d of storage Chemical analyses CIE color values were measured on the surface of meat samples using a LabScan colorimeter. Oxidationreduction potential was measured using a ph/ion meter equipped with a platinum electrode. Lipid oxidation was determined using a TBARS method (Ahn et al.,1999). Volatiles of samples were analyzed using a Solatek 72 Multimatrix-Vial Autosampler/Sample Concentrator 3100 connected to a GC/MS according to the method of Ahn et al. (2001). 3. Results and discussion 3.1. Color values Color L value increased as the aging time of beef increased. During storage after irradiation, L values of ground beef also showed an increasing trend as the storage time increased,and the increase in L value was more apparent in meat from long-term-aged beef than other ones. Irradiation did not influence the L values of beef from all stages of aging. Addition of ascorbic acid and/or sesamol+tocopherol had no effect on the L values of irradiated ground beef. Irradiation reduced the redness (a value) of ground beef significantly,but with varying degree depending on aging time (Table 1). Immediately after irradiation,the color of ground beef changed from a bright red to a greenish brown,which would be unattractive beef color for consumers. The color of irradiated beef was totally different from that of irradiated pork or poultry breast,which was pink or red. Nam and Ahn (2002a) reported that the complex of heme pigments with carbon monoxide produced by irradiation was responsible for the increased redness in irradiated turkey breast. The formation of CO-heme complex,however,could not explain the color changes in beef after irradiation because,while the production of carbon monoxide in beef by irradiation was similar to those of light meats (Kim et al.,2002a),the pigment content in beef is >10-fold higher than that in light meats. Thus,the contribution of CO-heme pigment to the color of ground beef was much smaller than that of light meats. Ascorbic acid incorporated to beef at the level of 0.1% (w/w) was very effective in maintaining redness (a values) of irradiated ground beef. Satterlee et al. (1971) reported that the formation of red,mbo 2 -like pigment formed from MbFe 3+ was greatest in a nitrogen atmosphere,slightly inhibited in air and greatly inhibited in an oxygen atmosphere. Oxygen is an effective scavenger of aqueous electrons (e aq ). Therefore,in the absence of oxygen,a reducing environment is established in the irradiated meat,which converts MbFe 3+ to MbFe 2+ (Giddings and Markakis,1972). Addition of

3 ARTICLE IN PRESS Table 1 CIE color a values of irradiated ground beef treated with different additives during aerobic storage at 4 C Storage Nonir Irradiated D.U. Ahn, K.C. Nam / Radiation Physics and Chemistry 71 (2004) Control Control Ascorbic 1 S+E 2 A+S+E 3 SEM Pre-aged Day ax 17.4 bx 21.3 ay 17.4 by 21.0 a 0.3 Day cy 17.0 ex 24.5 ax 18.6 dx 22.3 b 0.4 Day cy 14.8 ey 25.6 ax 16.6 dy 22.3 b 0.4 SEM Aged Day bx 17.3 cx 22.7 ay 19.4 b 23.2 a 0.3 Day cx 16.9 dx 25.9 ax 18.4 c 23.3 b 0.4 Day dy 15.3 dy 26.1 ax 18.2 c 22.8 b 0.4 SEM Long-term-aged Day ax 17.6 bx 19.0 ay 14.7 cy 17.2 by 0.3 Day ey 12.5 dy 23.0 ax 15.7 cxy 19.7 bx 0.3 Day ey 11.9 dy 23.2 ax 16.2 cx 20.0 bx 0.3 SEM SEM: standard error of the mean. 1 Ascorbic acid 0.1%; 2 Sesamol 100 ppm+a-tocopherol 100 ppm; 3 Ascorbic acid 0.1%+sesamol 100 ppm+a-tocopherol 100 ppm. n ¼ 4: a d Values with different letters within a row are significantly different (Po0:05). x z Values with different letters within a column of the same sample are significantly different (Po0:05). ascorbate further increased the reducing power in beef and increased the red color intensity of ground beef. On the other hand,sesamol + tocopherol had no effect in preventing color changes,and did not show any synergistic effect between ascorbic acid and sesamol + tocopherol in ground beef by irradiation. The a values of pre-aged beef was not changed much during the storage,and the redness was higher in nonirradiated than irradiated beef. Long-term-aged beef,however,showed drastic decreases in a values during storage and nonirradiated ground beef had lower a values than irradiated beef. Therefore,in long-termaged ground beef,the color of irradiated meat looked better than nonirradiated meat during storage. This difference in color between fresh and old meats could be related to the loss of reducing power in old meat ( longterm-aged ). Ascorbic acid increased the a values of irradiated ground beef and the color stabilizing effects of ascorbic acid was more distinct in long-term-aged than in preaged irradiated ground beef. Only the ground beef added with ascorbic acid produced higher a values than the meat with ascorbate+sesamol+tocopherol. Thus, the use of ascorbic acid was more effective in stabilizing irradiated beef color than using it with other antioxidants. However,addition of strong antioxidants along with ascorbic acid would be more beneficial in controlling lipid oxidation in irradiated ground beef during storage. The addition of ascorbic acid with or without sesamol + tocopherol significantly lowered the ORP values of irradiated ground beef regardless of the age of meat. The lowered ORP values by ascorbic acid maintained heme pigments in ferrous status and stabilized the color of irradiated ground beef. With increased storage time after irradiation,orp values of meat increased steadily in all treatments but ascorbic acid-added ground beef still maintained lower values than others over the storage time Lipid oxidation of irradiated beef Irradiation increased TBARS values of pre-aged and aged ground beef but the difference between irradiated and nonirradiated long-term-aged beef was small (Table 2). Both ascorbic acid (0.01%,w/w) and sesamol+a-tocopherol combination (100 ppm each) showed significant antioxidant activities in irradiated ground beef. As the storage time increased overall lipid oxidation increased,and the rate of lipid oxidation was faster in irradiated than nonirradiated beef. The effect of antioxidants in ground beef was more distinct after 7 d of storage than at Day 0. TBARS of irradiated ground beef added with ascorbic acid was 40% lower than that

4 152 ARTICLE IN PRESS D.U. Ahn, K.C. Nam / Radiation Physics and Chemistry 71 (2004) Table 2 TBARS values of irradiated ground beef treated with different additives during aerobic storage at 4 C Storage Nonir Irradiated Control Control Ascorbic 1 S+E 2 A+S+E 3 SEM Pre-aged Day bz 0.58 az 0.28 cy 0.20 c 0.23 c 0.03 Day by 0.96 ay 0.29 cy 0.17 d 0.23 cd 0.02 Day bx 1.90 ax 0.39 cx 0.18 c 0.27 c 0.08 SEM Aged Day by 1.27 az 0.44 cy 0.35 c 0.33 c 0.05 Day by 1.79 ay 0.57 cy 0.36 d 0.41 cd 0.05 Day bx 2.81 ax 0.76 cx 0.31 c 0.37 c 0.14 SEM Long-term-aged Day ay 4.40 ay 1.15 by 0.81 bz 0.81 bz 0.11 Day ay 4.54 ay 1.42 by 0.93 by 0.92 by 0.30 Day ax 7.23 ax 2.85 bx 1.06 cx 1.07 cx 0.17 SEM SEM: standard error of the mean. 1 Ascorbic acid 0.1%; 2 Sesamol 100 ppm+a-tocopherol 100 ppm; 3 Ascorbic acid 0.1%+sesamol 100 ppm+a-tocopherol 100 ppm. n ¼ 4: a c Values with different letters within a row are significantly different (Po0:05). x z Values with different letters within a column of the meat are significantly different (Po0:05). of irradiated control,but sesamol+tocopherol had stronger antioxidant effect than ascorbic acid. The incorporation of ascorbic acid prevented color changes while sesamol+a-tocopherol showed a very strong antioxidant effect in irradiated beef during storage. This suggested that the combined use of these additives could prevent color changes and lipid oxidation in long-termaged irradiated ground beef during storage Volatiles of irradiated beef Irradiation increased the amounts of sulfur compounds (Fig. 1). The S-volatiles newly generated or greatly increased by irradiation were ethanethioic acid S- methyl ester,dimethyl disulfide,and dimethyl trisulfide. Ahn et al. (2000) reported that S-containing volatiles were highly dependent upon irradiation dose and the off-odor in irradiated pork was produced by the compounding effects of volatiles from lipid oxidation and radiolytic degradation of various amino acid side chains. Both ascorbic acid and sesamol+tocopherol lowered the amounts of dimethyl disulfide in irradiated ground beef. Aging time of beef was an important factor influencing volatile production by irradiation. Irradiation of long-term-aged ground beef produced greater amounts of total and S-volatiles than pre-aged and aged beef. This could be related to more severe structural disintegration in long-term-aged than preaged and aged beef,and the structural damage should have made the meat susceptible to the attacks of free radicals produced by irradiation. When irradiated ground beef were stored for 7 d under aerobic conditions,the profiles of volatile compounds were totally different from those at day 1. Almost all volatile compounds produced in ground beef after 7-d storage under aerobic conditions were lipid oxidation-related products such as hydrocarbons and volatile carbonyl compounds. Ketones such as 2- propanone,2-butanone,and 2,3-butadione were the predominant compounds in ground beef after 7-d storage,irrespective of irradiation. Hexanal,a good indicator of lipid oxidation,was the most predominant aldehyde compound and was significantly detected at even pre-aged beef at day 7. As aging time before irradiation increased,many more volatile aldehydes (propanal,pentanal,hexanal,and heptanal) were found and their amounts also increased. As storage time after irradiation increased,considerable amounts of ethanol were produced in aged and long-term-aged nonirradiated beef,which could be attributed to microbial growth. The S-volatiles predominant immediately after irradiation were not found in irradiated ground beef after 7 d of aerobic storage. Although aerobic packaging was very effective in eliminating the S-volatiles produced

5 ARTICLE IN PRESS D.U. Ahn, K.C. Nam / Radiation Physics and Chemistry 71 (2004) Total ion counts 2.E+08 a Sulfur-volatiles 1.E+08 b c 5.E+07 d 0.E the heme pigments of beef red. The S-volatiles produced by irradiation had characteristic odor,but the intensity of irradiation off-odor in ground beef diminished over storage period because S-volatiles disappeared during aerobic storage. As storage time increased, long-termaged irradiated ground beef developed severe lipid oxidation unless antioxidant was added. Sesamol+tocopherol was highly effective in reducing lipid oxidation, and ascorbic acid stabilized color of irradiated beef. Therefore,the combined use of ascorbic acid and sesamol+tocopherol was recommended to control overall quality changes in irradiated ground beef during storage. Total ion counts 3.E+07 2.E+07 1.E+07 0.E+00 by irradiation,the amounts of volatile aldehydes in irradiated ground beef significantly increased during storage unless antioxidant additives were added. Addition of antioxidant was very effective in inhibiting not only a few hydrocarbons but volatile aldehydes also in irradiated beef at day 7. Especially,volatile aldehydes were not detected in ground beef incorporated with sesamol+tocopherol,while ascorbic acid produced some aldehydes. Therefore,when irradiated beef is aerobically stored,the generation of lipid oxidation products is of more concern than S-volatiles. 4. Conclusion Aldehydes Storage time (d) Fig. 1. Changes of the amounts of sulfur-volatiles and aldehydes of aged ground beef treated with different additives during the aerobic storage at 4 C. (K) Nonirradiated control; (J) irradiated control; ( ) irradiated ascorbic acidadded; (&) Irradiated sesamol+tocopherol-added; (~) irradiated ascorbic acid+sesamol+tocopherol-added. (a d) Different letters within a storage time shows that the means are significantly different (Po0:05). n ¼ 4: As in nonirradiated beef,addition of ascorbic acid at 0.1% (w/w) to ground beef prior to irradiation stabilized the color of ground beef during aerobic storage. The color stabilizing effect of ascorbic acid was derived from the reducing power of ascorbic acid,which maintained a b c a b c d References Ahn,D.U.,2002. Production of volatiles from amino acid homopolymers by irradiation. J. Food Sci. 67 (7), Ahn,D.U.,Lee,E.J.,2002. Production of off-odor volatiles from liposome-containing amino acid homopolymers by irradiation. J. Food Sci. 67 (7), Ahn,D.U.,Olson,D.G.,Jo,C.,Chen,X.,Wu,C.,Lee,J.I., Effect of muscle type,packaging and irradiation on lipid oxidation,volatile production and color in raw pork patties. Meat Sci. 47 (1), Ahn,D.U.,Jo,C.,Olson,D.G.,1999. Headspace oxygen in sample vials affects volatiles production of meat during the automated purge-and-trap/gc analyses. J. Agric. Food Chem. 47 (7), 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 Sci. 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 Sci. 57 (4), AMI (American Meat Institute),1998. Meat and Poultry facts. American Meat Institute,Washington,DC. Giddings,G.G.,Markakis,P.,1972. Characterization of the red pigments produced from ferrimyoglobin by ionizing radiation. J. Food Sci. 37, Kim,Y.H.,Nam,K.C.,Ahn,D.U.,2002a. Color,oxidationreduction potential and gas production of irradiated meat from different animal species. J. Food Sci. 67 (5), Kim,Y.H.,Nam,K.C.,Ahn,D.U.,2002b. Volatile profiles, lipid oxidation and sensory characteristics of irradiated meat from different animal species. Meat Sci. 61 (3), Liu,Q.,Lanari,M.C.,Schaefer,D.M.,1995. A review of dietary vitamin E supplementation for improvement of beef quality. J. Anim. Sci. 73 (10), Millar,S.J.,Moss,B.W.,MacDougall,D.B.,Stevenson,M.H., The effect of ionizing radiation on the CIE Lab color co-ordinates of chicken breast meat as measured by different instruments. Int. J. Food Sci. Technol. 30 (6),

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