D.J. Buckley

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.

Effects of fat level and maltodextrin on the functional properties of frankfurters formulated with 5, 12 and 30% fat.

The effects of fat level (5, 12 and 30%) and maltodextrin on emulsion stability, cook loss, colour, texture and sensory characteristics of frankfurters were investigated. Three fat levels (5, 12 and 30%) were formulated containing added maltodextrin. For each fat level a control was prepared without added maltodextrin giving a total of 6 treatments (3×2 factorial design). Reducing the fat from 30 to 5% increased cook loss and decreased emulsion stability. Panellists detected an increase in juiciness and a decrease in overall texture, overall acceptability when the fat level was reduced from 30 to 5%. Instron texture profile analysis showed a decrease in hardness, chewiness and gumminess and an increase in springiness with decreasing fat level. Maltodextrin addition caused a significant decrease in cook loss of the frankfurters but also decreased the emulsion stability. An interactive effect (P<0.05) occurred between fat level and maltodextrin resulting in no significant difference in hardness, gumminess and chewiness values when maltodextrin was present in the reduced-fat (5 and 12%) frankfurters. Saltiness, overall flavour intensity, overall texture and overall acceptability were unaltered (P>0.05) by maltodextrin. The results indicate that maltodextrin can be used as a suitable fat replacer since it offset some of the changes brought about by fat reduction, decreasing cook loss and maintaining a number of textural and sensory characteristics of the frankfurters.

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 salt level and high hydrostatic pressure processing on frankfurters formulated with 1.5 and 2.5% salt.

The effects of salt level and high pressure processing on cook loss, emulsion stability, colour, textural and sensory characteristics of frankfurters were investigated. Two salt levels (1.5 and 2.5%) and two pressure treatments (150 and 300 MPa) were examined. For each batch a control was set up which was non-pressure treated. Cook loss values were significantly decreased in 150 MPa products at the 2.5% salt level compared to controls. Significantly lower cook losses were recorded at the lower salt level after the application of 150 MPa pressure. The stability of the meat emulsions was significantly increased at the lower salt level, especially after 150 MPa pressure. Sensory analysis results for overall flavour acceptability after pressure application of 150 MPa and 300 MPa were similar to control products and panellists preferred products formulated at 1.5% salt after pressure treatment (150 MPa). Hardness, cohesiveness, gumminess and chewiness were also improved after pressure treatment. The results demonstrate that high pressure technology is a viable process that partially compensates for the reduction of salt levels in frankfurters.

The role of endogenous proteases in the tenderisation of fast glycolysing muscle.

The activities of lysosomal cathepsins and the calpain-calpastatin system were measured to determine their involvement in the more rapid tenderisation of fast glycolysing muscle. The rate of pH fall of M. longissimus dorsi (LD) of Hereford cross Friesian heifers (n = 52, Experiment 1; n = 36, Experiment 2) was measured. Muscles were selected according to their rate of glycolysis; slow and fast (n = 16, Experiment 1; n = 10, Experiment 2). Fast glycolysing muscles were rated more tender in sensory analysis and had a lower shear force than slow glycolysing muscles. Slow glycolysing muscles had shorter sarcomere lengths. Low pH conditions in fast glycolysing muscle correlated with the enhanced release of cathepsins B and L from lysosomes. Calpain I activity was higher and calpastatin activity was lower in fast glycolysing muscle early post mortem. SDS-PAGE electrophoresis patterns showed increased proteolysis, such as the earlier appearance of the 30 kDa fragment in fast glycolysing muscle. Transmission Electron Microscopy (TEM) results showed a greater degree of ultrastructural breakdown early post mortem in fast glycolysing muscle. The results suggest that the increase in tenderness in muscles that undergo fast glycolysis early post mortem may be caused by proteolysis by released lysosomal cathepsins and calpain I uninhibited by calpastatin.

The relationship between early post-mortem pH and the tenderisation of beef muscles

The rate of early post-mortem pH fall in bovine muscle was studied to determine its influence on the rate and extent of the tenderisation process. The pH of M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles of Hereford cross Friesian heifers (n = 127) was taken up to 24 h post mortem. Twenty-four LD and 24 SM muscles were selected according to their rate of pH fall; slow (n = 8), intermediate (n = 8) and fast (n = 8) and were sampled at 2, 7 and 14 days post mortem for sensory, mechanical, physicochemical and biochemical analysis. Fast glycolysing LD muscles were rated more tender in sensory analysis and texture assessment whereas slow glycolysing muscles were considered significantly tougher (p < 0.001). Fast glycolysing LD had a significantly lower shear force (p < 0.001) at each stage of ageing. Slow glycolysing LD and SM had the highest shear force values. No significant difference was found in intramuscular fat or moisture content between the groups. Slow glycolysing LD muscles had shorter sarcomere lengths at 2 days post mortem. SDS-PAGE electrophoresis patterns showed increased proteolysis, such as the earlier appearance of the 30 kDa fragment, which is believed to be a good indicator of tenderness, in fast glycolysing muscle. These results suggest that the rate of post-mortem pH fall plays an important role in proteolysis and tenderisation.

Influence of dietary fat and vitamin E supplementation on α-tocopherol levels and fatty acid profiles in chicken muscle membranal fractions and on susceptibility to lipid peroxidation

Broiler chickens were fed a basal feed supplemented with 10% tallow or olive oil and varying levels of vitamin E (20 and 200 mg vitamin E/kg feed). The concentration of α-tocopherol in the membranes of breast and thigh muscles was significantly influenced by the α-tocopherol level in the feed (p < 0.001). Deposition of vitamin E was not influenced by the type of oil in the feed, except in the mitochondrial fraction of breast where the vitamin E concentration was higher in those fed olive oil than in those fed tallow (p < 0.05). Dietary oil influenced the fatty acid composition of the muscle membranal fractions (p < 0.001). The oxidative stability of the membranal fractions tended to increase with increasing concentrations of α-tocopherol in the membranal fractions. In conclusion, the supplementation of vitamin E appeared to enhance the stability of muscle to oxidation. Thus, incorporation of α-tocopherol into the membranes via dietary manipulation helped in stabilizing the membrane-bound lipids.

COMPARISON OF EFFECTS OF DIETARY OLIVE OIL, TALLOW AND VITAMIN E ON THE QUALITY OF BROILER MEAT AND MEAT PRODUCTS

1. The effect of dietary fat and vitamin E supplementation on quality attributes (drip loss, oxidative stability, sensory quality) in chicken meat and meat products was investigated. Broiler chicks were fed on diets containing tallow (60 g/kg) or olive oil (60 g/kg) at a basal (30 mg/kg diet) or supplemental (200 mg/kg diet) concentration of alpha-tocopheryl acetate for 8 weeks. The alpha-tocopherol content and fatty acid composition of breast and thigh meat was determined. Drip loss was determined in breast fillets. Lipid oxidation (thiobarbituric acid-reacting substances/TBARS) and sensory quality (warmed-over flavour development/WOF) were assessed in minced thigh meat during storage. 2. Dietary olive oil increased the ratio of monounsaturated to saturated fatty acids (MUFA/SFA) in the diets. In breast and thigh, this resulted in approximately a two-fold increase in the MUFA/SFA ratio. Supplemental alpha-tocopherol increased the alpha-tocopherol content of muscles. 3. Dietary fat not influence drip loss in thawed breast fillets during refrigerated storage, but supplemental alpha-tocopherol reduced drip loss. 4. TBARS and WOF development in minced thigh meat patties were also reduced by supplemental alpha-tocopherol following frozen storage, or cooking and refrigerated storage. Storage stability was not adversely affected by dietary fat. 5. Overall, the results showed that increasing the monounsaturated profile of chicken meat lipids did not adversely affect quality characteristics. Dietary alpha-tocopherol supplementation was a more important factor in the determination of broiler meat quality.

Non-destructive prediction of selected quality attributes of beef by near-infrared reflectance spectroscopy between 750 and 1098 nm

Heifers (n = 70) were slaughtered and hung conventionally in an industrial meat plant. Near infrared (NIR) spectroscopy was studied for its ability to predict selected meat quality attributes, i.e. Warner-Bratzler shear force (WBSF), sensory tenderness, texture, flavour and acceptability. Freshly cut steaks (2.5 cm thick) were taken from the longissimus dorsi (LD) muscle at 1, 2, 7 and 14 days post mortem for NIR analysis. Other samples (also 2.5 cm thick) were taken at 2, 7 and 14 days post mortem, vacuum-packaged in plastic bags and stored at -20 °C for WBSF measurement and sensory analysis. Heifers were slaughtered in two groups; between slaughterings, replacement of the spectrophotometer lamp and lamp assembly was necessitated by a bulb failure. Using principal component regression (PCR), correlation coefficients of 0.82 and 0.73 were obtained for the prediction of WBSF in sample sets 1 and 2, respectively. On merging both sample sets, this value was lowered slightly (r = 0.61). Correlation coefficients obtained for the prediction of tenderness, texture, flavour and acceptability were 0.67, 0.53, 0.51 and 0.46 respectively (set 1); 0.72, 0.71, 0.45 and 0.67 (set 2); 0.53, 0.54, 0.24 and 0.42 (combined sets).

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.