J.I. Gray

Oxidative quality and shelf life of meats

Lipid oxidation is one of the primary mechanisms of quality deterioration in foods and especially in meat products. The changes in quality are manifested by adverse changes in flavor, color, texture and nutritive value, and the possible production of toxic compounds. Lipid oxidation in muscle systems is initiated at the membrane level in the intracellular phospholipid fractions. How this occurs has still not been resolved, although it is generally believed that the presence of transition metals, notably iron, is pivotal in facilitating the generation of species capable of abstracting a proton from an unsaturated fatty acid. This paper provides an overview of how lipid oxidation affects the quality and shelf life of meat and meat products, and how shelf life can be extended through dietary vitamin E supplementation above requirement levels. The formation of cholesterol oxidation products and the possible role of lipids and their oxidation products in the formation of heterocyclic aromatic amines are also discussed.

Effect of dietary administration of oil extracts from rosemary and sage on lipid oxidation in broiler meat

1. Oxidation of meat and membrane from broilers fed on a diet containing 500 mg/kg rosemary and sage extracts was compared to meat and membrane oxidation from broilers receiving a control diet (not enriched with antioxidants) and a diet enriched in alpha-tocopheryl acetate (200 mg/kg). 2. After 9 d of refrigerated storage, thiobarbituric acid reactive substances of white meat from broilers fed on the control and the alpha-tocopheryl acetate-enriched diets were 0.51 and 0.25 mg malonaldehyde/kg meat, respectively. Values for meat from broilers fed on the diets containing the rosemary and sage extracts were in the range 0.30 to 0.35 mg malonaldehyde/kg meat, significantly lower than those from birds fed on the control diet. A similar trend was observed in the dark meat but differences were not significant at 9 d of storage. Similar trends were observed in raw samples stored at -20 degrees C for up to 4 months and in samples cooked at 70 degrees C and kept stored under refrigeration for up to 4 d. 3. The meat from broilers fed on the diet containing spice extracts had smaller concentrations of total cholesterol oxidation products (COPS) than meat from the control group (P < 0.05). Supplemental alpha-tocopheryl acetate reduced the COPS concentrations to a greater extent than did spice extracts (P < 0.05). 4. A similar trend was observed in microsomal fraction isolates, in which the rate of metmyoglobin/hydrogen peroxide-catalysed lipid peroxidation was lower in animals receiving spice extracts than in those fed on the basal diet.

Influence of dietary fat and α-tocopherol supplementation on lipid oxidation in pork.

Sixty-four pigs, approximately 3 weeks old, were fed diets containing 3% beef tallow or 3% soya oil with either a basal (10-50 mg/kg diet) or supplemented (200 mg/kg diet) level of α-tocopheral acetate. In pigs fed the soya oil diet the neutral and polar lipid fractions of muscle tissue and the total lipid fraction of adipose tissue had significantly (P < 0·05) higher C18:2/C18:1 ratios when compared to pigs fed the tallow diet. Muscle from pigs fed the soya oil diet was significantly more susceptible (P < 0·05) to lipid oxidation than muscle from pigs fed the tallow diet. In pigs receiving the α-tocopherol supplemented diet, α-tocopherol levels were approximately 3·3, 2·8 and 2-times higher in plasma, muscle and adipose tissue, respectively, when compared to pigs fed the basal level of α-tocopherol acetate. α-Tocopherol supplementation significantly increased (P < 0·05) the oxidative stability of muscle from pigs fed both the tallow and soya oil diets.

Effects of synthetic antioxidants (BHA, BHT and PG) on the mutagenicity of IQ-like compounds☆

Abstract This study investigated the effects of the phenolic antioxidants (BHA, BHT and PG) on the mutagenicity of IQ, MeIQ and MeIQx by the Ames test. Results demonstrated that MeIQ, IQ and MeIQx were all mutagenic when tested with the Ames test with their potency being in the order listed above. This was true on testing with both TA98 and TA100, both of which required added S-9 for activation. It was clearly demonstrated that BHA and PG significantly inhibited the mutagenicity of IQ, MeIQ and MeIQx. On the other hand, BHT had little effect on the mutagenicity of IQ and MeIQ at low concentrations, but significantly increased their mutagenicity at high concentrations. BHT slightly inhibited the mutagenicity of MeIQx at all concentrations tested.

Effects of oxidised dietary oil and antioxidant supplementation on broiler growth and meat stability

1. Broilers were fed on diets containing oxidised sunflower oil, sunflower oil and sunflower oil supplemented with alpha-tocopherol, butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT). 2. Oxidised oil caused a significant reduction in broiler body and carcase weights, whereas alpha-tocopherol and BHA/BHT supplementation improved growth. 3. Meat samples from these broilers were stored at 4 degrees C and -20 degrees C and their oxidative stability evaluated. Feeding oxidised oil to broilers resulted in meat that underwent rapid oxidative changes during refrigerated and frozen storage. 4. On the other hand, dietary alpha-tocopherol and BHA/BHT supplementation increased alpha-tocopherol and BHA/BHT concentrations in meat and significantly (P less than 0.05) improved the oxidative stability of meat during refrigerated and frozen storage.

Mechanisms by which nitrite inhibits the development of warmed-over flavour (WOF) in cured meat

Abstract The mechanism by which nitrite functions as an antioxidant in cured meat products was studied using ground beef and meat (beef) pigment extracts (MPE). Nitrite, l -ascorbate, sodium tripolyphosphate, ADP and EDTA were reacted with ground beef and MPE, after which the samples were heated and stored at 4°C. Lipid oxidation was assessed by the TBA method. The results suggested that nitrite functions as an antioxidant in three possible ways: (1) by the formation of a strong complex with heme pigments, thereby preventing the release of non-heme iron and its subsequent catalysis of lipid oxidation; (2) by interacting directly with the liberated non-heme iron (Fe2+) from denatured heme pigments and (3) to a lesser extent, by stabilization of the unsaturated lipids within the membranes. Stabilization of the porphyrin ring, preventing release of Fe2+ during the cooking process, appears to be the most important mechanism.

Influence of oxidised dietary oil and antioxidant supplementation on membrane-bound lipid stability in broiler meat.

1. The effects of oxidised oil, dietary alpha-tocopherol and BHA/BHT-supplementation on the fatty acid composition of mitochondrial, microsomal and soluble protein fractions of broiler muscles, and on their lability to metmyoglobin/hydrogen peroxide-catalysed peroxidation were investigated. 2. Oxidised oil in the broiler diets induced rapid oxidation of the membrane-bound lipids and decreased their stability towards metmyoglobin-hydrogen peroxide-catalysed peroxidation. 3. Supplementation of the broiler diets with alpha-tocopherol increased the alpha-tocopherol concentrations in the microsomal and soluble protein fractions of the dark meat as well as the soluble protein fraction of the white meat. This, in turn, stabilised the membrane-bound lipids against metmyoglobin/hydrogen peroxide-initiated peroxidative changes.

Nitrite stabilization of lipids in cured pork

Peroxidation studies indicated that phospholipids, microsomes and mitochondria from cured pork samples are less susceptible to metmyoglobin/hydrogen peroxide-catalyzed peroxidation than their counterparts from nitrite-free pork samples. The reaction of phospholipids and polyunsaturated fatty acid ethyl esters with dinitrogen trioxide increased their stability to peroxidative changes. Phospholipids from cured pork and those lipids reacted with dinitrogen trioxide were capable of nitrosating a secondary amine. These data, together with infrared analyses, indicate that nitrite or dinitrogen trioxide reacts with unsaturated lipids to form nitro-nitroso derivatives, thus stabilizing the lipids toward peroxidation changes. This mechanism can, in part, explain the antioxidant role of nitrite in cured meats.

Some further observations on the TBA test as an index of lipid oxidation in meats

A modified TBA procedure utilizing an aqueous TBA solution to replace the acetic acid TBA reagent was tested with several meat samples. The modification prevented the formation of an interfering absorption peak at approximately 450 nm. The conversion factor for this method was determined to be 6·2. The method was further modified to allow the addition of TBHQ to raw and cooked samples prior to blending and heat distillation. The addition of 0·01% TBHQ (fat basis) significantly (p < 0·05) reduced TBA numbers of fish and chicken breast and raw chicken thigh meat, but did not significantly influence the TBA numbers for beef or cooked chicken thigh meat.

Effect of reduced sodium chloride concentration and tetrasodium pyrophosphate on pH, water-holding capacity and extractable protein of prerigor and postrigor ground beef

The effect of tetrasodium pyrophosphate (TSPP) (0, 0·25, 0·5% w/w) alone or in combination with salt (NaCl) (0, 0·5, 1·0% w/w) on water-holding capacity (WHC), pH, the ratio of absorbance at 250 nm over the absorbance at 260 nm (R-values) and 150m CaCl extractable protein (EP) was studied in prerigor and postrigor sternomandibularis homogenates over time. The 0 h samples were defined as when the NaCl was incorporated with the muscle. R-values verified that 0 h samples were in a prerigor or postrigor state. In prerigor homogenates, increasing phosphate concentration increased the time required to reach ultimate pH. Ultimate pH values of prerigor homogenates containing phosphate were lower (P < 0·05) than homogenates without phosphate and similarly treated postrigor homogenates. After six hours, no differences (P > 0·10) were noted in EP or WHC at different phosphate concentrations when averaged over NaCl concentrations in prerigor homogenates. With increasing phosphate concentration of postrigor homogenates, there was an increase (P < 0·05) in pH and EP at the initial sampling time. However, 0 and 0·25% phosphate WHC values could not be differentiated (P > 0·10). Results of this study indicate no advantages, after six hours post mortem, to using TSPP alone or in combination with NaCl in prerigor meat homogenates at concentrations added in this study.