M. Renerre

Lipid and protein oxidation in vitro, and antioxidant potential in meat from Charolais cows finished on pasture or mixed diet

In this work, the effect of finishing diet (pasture- or mixed-diet) on lipid and protein oxidation in beef homogenates was evaluated. Oxidation was chemically induced by ferrous iron and hydrogen peroxide. Lipid and protein oxidation were respectively measured by determining TBA reactive substances (TBA-RS) and protein carbonyl groups (DNPH coupling method). Evaluation of the antioxidant status of meat was also performed by measuring vitamin E concentration and antioxidant enzyme activities: superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase. Pasture-finishing mode of animals significantly protected lipids in meat from oxidation but diet mode did not affect protein oxidation. Concentration of vitamin E was higher in meat from pasture-fed animals. Different diets had opposite effects on SOD and GPx activities, pasture-finishing mode of animals increasing SOD activity but decreasing GPx activity. No significant effect of diet was noted on catalase activity.

Effect of dietary fat and vitamin E on colour stability and on lipid and protein oxidation in Turkey meat during storage

The objectives of the study were to investigate the effects of dietary fat (6% soya oil or rapeseed oil or tallow), together with tocopheryl acetate at either a basal (30 ppm) or a supplemented (400 ppm) level for 16 weeks on lipid and protein oxidation, including myoglobin, during refrigerated storage of turkey muscles. When turkeys were fed tallow in particular, vitamin E supplementation improved the vitamin E status of the muscles. Vitamin E supplementation significantly delayed lipid oxidation measured by TBARS, whatever the dietary fat. TBARS were highest in meat from animals fed soya oil. Vitamin E supplementation had no positive effect on colour stability of meat during refrigerated storage. Feeding soya oil induced significantly higher oxidation of proteins (carbonyl content) than rapeseed oil or tallow and vitamin E supplementation induced a slight decrease in carbonyl content at day 9 of storage for M. sartorius. SH content was significantly higher in vitamin E supplemented M. sartorius and M. pectoralis than in controls.

Chemical oxidation decreases proteolytic susceptibility of skeletal muscle myofibrillar proteins

The objective of this study was to investigate the effect of chemical oxidation on proteolysis susceptibility of myofibrillar proteins. Myofibrils were prepared from pig M. longissimus dorsi and oxidised by a hydroxyl radical generating system. Protein oxidation level was measured by the carbonyl content, free thiol group content and bityrosine formation. Oxidised or non-oxidised myofibrillar proteins were exposed to papain and proteolysis was estimated by fluorescence using fluorescamine. Oxidation of myofibrillar proteins was dependent upon the oxidising agent concentration. Disulfide bridge and bityrosine formation indicated that oxidation by OH° can induce protein polymerization. Electrophoretic study showed that myosin was the protein most sensitive to oxidation. Results showed a direct and quantitative relationship between protein damages by hydroxyl radical and decreased proteolytic susceptibility. Electrophoretic observations suggest that polymerization and aggregation may explain in part decreased susceptibility of myofibrillar proteins to proteolysis.

Antioxidant enzyme activities in beef in relation to oxidation of lipid and myoglobin

Lipid- and oxy-free radical generation has been implicated in oxidative processes which occur during meat maturation but the importance of the antioxidant enzyme (AOE) activity in these processes is not known. It was shown that metmyoglobin (MetMb) % and lipofuscin content were higher in colour-unstable muscles such as psoas major (PM) and diaphragma (D) compared to longissimus lumborum (LL) and tensor fasciae latae (TFL). Although Superoxide dismutase (SOD) activity is higher post mortem in PM and D muscles than in LL and TFL muscles, catalase and glutathione peroxidase (GPx) activities were higher only in D muscle. The higher AOE activity in colour-unstable muscles such as PM and D was not sufficient to prevent increased formation of MetMb and lipofuscin in these muscles compared to LL and TFL muscles.

Effect of diet finishing mode (pasture or mixed diet) on antioxidant status of Charolais bovine meat

The aim of this study was to better understand the effect of diet finishing mode (pasture or mixed diet) on the antioxidant status of bovine meat (M. Longissimus dorsi). Effects of sex (cow, heifer and steer) and age (only in cows) were also studied. Vitamin E content of muscle and activity of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (Cat) and glutathione peroxidase (GPx), were measured. Total antioxidant status was also estimated by measuring Trolox equivalent antioxidant capacity (TEAC) and benzoate hydroxylation. Vitamin E content was higher in meat from pasture-finished animals than from mixed diet-finished animals. Diet had also an important effect on antioxidant enzyme activity. Pasture finishing mode increased SOD activity and decreased GPx activity in muscle. Effect of diet on catalase activity was less pronounced. Total antioxidant status measured by benzoate hydroxylation was higher in the mixed diet-group but no effect of diet was observed on TEAC measurement. Effect of sex was observed on SOD and catalase activity and also in benzoate hydroxylation. Effect of age was only noticed on benzoate hydroxylation.

Effect of finishing mode (pasture- or mixed-diet) on lipid composition, colour stability and lipid oxidation in meat from Charolais cattle

Effects of pasture- or mixed-diet finishing mode on colour and lipid stability were measured in meat from Charolais steers, heifers and cows of different ages after refrigerated storage. Meats from pasture- and mixed-diet finished cattle have more or less significant differences in lipid composition which will influence the colour and lipid stability. The mixed-diet finished cattle have about the same proportions of saturated and monounsaturated lipids as pasture-diet finished animals; on the contrary, cattle fed on grass have higher proportions of n-3 PUFA, and to a less extent, of n-6. Finishing diet had an important effect on lipid stability, meat from pasture-finished animals showing significantly lower TBA-RS level than meat from mixed-diet finished animals. Effect of diet was also significant on myoglobin content with a higher content of haeminic iron in mixed-diet finished animals. Effect of diet on colour stability was slight with a beneficial effect of pasture finishing mode, significant only in heifers, and after a meat storage of six days in air.

Effect of a dietary vitamin E supplementation on colour stability and lipid oxidation of air- and modified atmosphere-packaged beef

The effects of dietary vitamin E supplementation on tissue α-tocopherol level and on the susceptibility of fresh and modified atmosphere-packaged beef on myoglobin and lipid oxidation were investigated. Charolais cattle, aged 32-44 months, were fed diets containing 75 (control, n=8) or 1000 mg (supplemented, n=8) α-tocopheryl acetate/kg feed/day for 111 days prior to slaughter. Following vacuum packaging, M. Longissimus lumborum and M. triceps brachii were aerobically packaged and held under refrigerated display (3°C) for 9 days or packaged under modified atmosphere (MAP; 20% CO(2): 80%O(2)) and held under refrigerated display (8°C) for 13 days under fluorescent light. α-tocopherol concentrations were significantly higher (P<0.05) in meat from the supplemented group than from the basal one. Whatever the measured colour characteristics (a*, R(630)-R(580),% MetMb), the vitamin E supplementation had a positive but non-significant effect on the rate of discoloration. But by visual assessment, essentially with MAP, a significant and positive effect of vitamin E supplementation was noted to lower discoloration (P<0.05). TBARS values were significantly lowered (essentially at the end of storage time for the two packaged modes) after an α-tocopheryl acetate-supplementation.

Influence of vitamin E on lipid and protein oxidation induced by H2O2-activated MetMb in microsomal membranes from turkey muscle

Lipid and protein oxidation generated by metmyoglobin+H(2)O(2) were studied in microsomal membranes of turkey muscles. With a basal diet enriched with 6% soya oil and supplemented with vitamin E (30 ppm for control and 400 ppm for supplemented animals) oxidations were investigated by different methods. Lipid oxidation was estimated by TBARS and lipofuscins measurement and protein oxidation was measured by an estimation of carbonyl groups and free thiols. Supplementation of turkeys with α-tocopheryl acetate increased the vitamin E content of microsomal membranes and had a protective (and significant) effect on lipid oxidation when measured by the two techniques. Vitamin E supplementation significantly protected free thiols from oxidation but had only a small effect (non significant) on carbonyl group formation. No vitamin E dietary supplementation effect was observed on radical formation, as measured by optical and ESR spectroscopy.

Relationships between post-mortem pH changes and some traits of sensory quality in veal

The aim of this study was to evaluate the relationships between the rate and extent of post-mortem pH changes and the colour, the cooking loss and the eating quality of veal. The experiment used 12 calves aged 18 weeks. Variations in ultimate pH were induced by adrenalin administration (0.1-0.4 mg/kg liveweight) to six of the animals. Measurements were made on the Longissimus thoracis muscle. pH and osmotic pressure were measured at 0.5 h, 4 h and 29 h after slaughter. Pigment content, drip loss and cooking loss were measured at 29 h after slaughter, and colour was measured at 2 days and 9 days after slaughter. Cooking loss, tenderness, juiciness and flavour of roasts were assessed at 9 days after slaughter. Correlations between colour traits and pH values were higher with ultimate pH than with pH at 0.5 h or 4 h after slaughter. Lightness, redness and reflectance decreased when the ultimate pH increased. Drip loss was correlated with the rate of pH fall (r = -0.80, P < 0.01 with pH at 4 h), while cooking loss was correlated with ultimate pH (r = -0.94, P < 0.01). Ultimate pH and the sensory quality traits were linearity and positively correlated (r = 0.83) for tenderness, 0.81 for juiciness and 0.71 for flavour, respectively).

Meat quality traits in the emu (Dromaius novaehollandiae) as affected by muscle type and animal age

Meat quality traits were determined in the major muscles of the emu (Dromaius novaehollandiae) at different slaughter ages (6, 10, 14, 17 or ≥20 months). A mean ultimate pH value of 5.5 was reached within around 3 h post mortem, but this value was 6.1 in animals that had suffered a preslaughter stress (transportation and fasting). The collagen and pigment contents varied widely among the muscles. The protein and pigment contents increased with animal age, but this effect was perceptible only between 6 and 14 months. The other chemical constituents were little affected by muscle type or animal age. The intense red colour of emu meat, due to a high pigment content, was very sensitive to oxidation, thus limiting the storage of fresh meat under aerobic conditions to short periods of time. Despite a rapid post-mortem tenderization (≤24 h), the residual myofibrillar strength obtained after extended ageing remained intermediate between those reported for chicken and beef. The tenderness of meat, cooked to 60 °C, differed between muscles and decreased with increasing age, thus reflecting the changes occuring in the concentration and in the heat stability of the intramuscular connective tissue.