Philippe Gatellier

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.

Effect of Meat Cooking on Physicochemical State and in Vitro Digestibility of Myofibrillar Proteins

The effect of meat cooking was measured on myofibrillar proteins from bovine M. Rectus abdominis. The heating treatment involved two temperatures (100 degrees C during 5, 15, 30, and 45 min and 270 degrees C during 1 min). Protein oxidation induced by cooking was evaluated by the level of carbonyl and free thiol groups. Structural modifications of proteins were assessed by the measurement of their surface hydrophobicity and by their aggregation state. With the aim of evaluating the impact of heat treatment on the digestive process, myofibrillar proteins were then exposed to proteases of the digestive tract (pepsin, trypsin, and alpha-chymotrypsin) in conditions of pH and temperature that simulate stomach and duodenal digestion. Meat cooking affected myofibrillar protein susceptibility to proteases, with increased or decreased rates, depending on the nature of the protease and the time/temperature parameters. Results showed a direct and quantitative relationship between protein carbonylation (p<0.01) and aggregation (p<0.05) induced by cooking and proteolytic susceptibility to pepsin. However, no such correlations have been observed with trypsin and alpha-chymotrypsin.

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.

Technical note: A simplified procedure for myofibril hydrophobicity determination.

A simple and reliable method for the determination of surface hydrophobicity of nonsolubilized myofibrils (from pig M. longissimus dorsi) was developed and validated. This method is based on the interaction of the hydrophobic chromophore bromophenol blue (BPB) with myofibrillar proteins and the separation of free and bound BPB by centrifugation. The titration of bound BPB is performed by absorption spectroscopy, and the amount of bound BPB is considered as an index of protein hydrophobicity. Heating, which is known to increase protein hydrophobicity, was performed in order to validate this method. Fixation of BPB to myofibrils increased with heating time and temperature, strongly suggesting that it may be closely related to protein hydrophobicity.

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.

Cooking temperature is a key determinant of in vitro meat protein digestion rate: investigation of underlying mechanisms.

The present study aimed to evaluate the digestion rate and nutritional quality of pig muscle proteins in relation to different meat processes (aging, mincing, and cooking). Under our experimental conditions, aging and mincing had little impact on protein digestion. Heat treatments had different temperature-dependent effects on the meat protein digestion rate and degradation potential. At 70 °C, the proteins underwent denaturation that enhanced the speed of pepsin digestion by increasing enzyme accessibility to protein cleavage sites. Above 100 °C, oxidation-related protein aggregation slowed pepsin digestion but improved meat protein overall digestibility. The digestion parameters defined here open new insights on the dynamics governing the in vitro digestion of meat protein. However, the effect of cooking temperature on protein digestion observed in vitro needs to be confirmed in vivo.

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.