Heating-induced changes in meat proteins were investigated using models made of aqueous suspensions of myofibrils according to muscle fibre types and cellular compounds (oxidants and antioxidants). These changes were evaluated by measurements of carbonyl groups and protein surface hydrophobicity. Model results were compared to trial results obtained on pork meat (M. Longissimus dorsi) heated under the same conditions (45 and 75°C, from 5 to 120 min). Myofibrillar proteins from α-white fibres were more sensitive to oxidation and thermal denaturation than those from β-red fibres. At 45°C, there were negligible differences due to peroxide or antioxidant types. At 75°C, organic peroxides (ROOH) were less oxidative than hydrogen peroxide (H2O2), and antioxidant enzymes were less efficient than vitamin E and carnosine at protecting proteins against oxidation. Protein oxidation observed in meat is lower than in the mimetic models and the increase in hydrophobicity remained limited in meat.

Optimizing the nutritional quality of cooked meat needs a better understanding of the mechanisms responsible for protein changes induced by heating. The relative contributions of chemical and thermal effects on protein physicochemical changes were studied using meat models. Two models were tested: a basic model made of an aqueous suspension of myofibrillar proteins, and a complex model, in which oxidants were added in physiological concentrations. Various heating time-temperature combinations were applied to both models in the ranges 45-90 °C and 5-120 min. Protein oxidation was evaluated by carbonyl and free thiol contents. Conformational changes of proteins were assessed by measurements of surface hydrophobicity and aggregation. Carbonyl formation was weakly affected by the thermal process alone but exacerbated by oxidants. A synergistic effect of oxidants and heat treatments on protein oxidation was noted. Changes in protein hydrophobicity and aggregation were dominated by the thermal process.

Oxidative deterioration or modifications of proteins which appear during meat storage and processes can result in the impairment of technological, sensorial and nutritional qualities. Improving the quality involves a better understanding of the biochemical mechanisms responsible for protein oxidation in meat. For that purpose, an analysis was conducted to investigate the relationships between the early post-mortem sarcoplasmic proteome, which contains the majority of enzymes involved in the oxidative process, and protein oxidation generated during meat storage and cooking. This study was performed in Longissimus lumborum pig muscle. In order to have sufficient variability in the proteome and in the meat oxidation level, five groups of 10 animals issued from two different breeds and raised in three different rearing systems were analysed. Protein oxidation was estimated by the measurement of carbonyl groups after 1 and 4days of refrigerated storage, and after 100°C experimental cooking of the 4days aged meat. Significant correlations (p<0.05) were observed between the level of carbonyl groups and the intensities of 104 spots of the 2D electrophoresis, out of which 52 were clearly identified. The possible involvement of some proteins in the muscle oxidative stress leading to protein oxidation is discussed.

The effect of meat cooking on protein aggregation was measured in pig M. Longissimus dorsi. Muscles were aged 4 days in air and then cooked at 100 °C for 10 or 30 min. Meat was ground in a KCl solution and the whole extract was delipidated with a mixture of butanol and di-isopropyl ether in a 40:60 v/v ratio. Protein aggregation induced by cooking was evaluated with a laser granulometer, which enabled reliable and reproducible characterisation of particle size distributions, and particle shape distributions using automated imaging techniques. Cooking significantly decreased the level of big particles, while the number of small particles remained stable. Cooking also affected the form and size of the particles. In order to better understand the mechanisms implicated in the aggregation process the level of protein oxidation and the protein surface hydrophobicity were evaluated in parallel with the granulometry measurements. Significant correlations were observed between the granulometry parameters and some of the protein oxidation indices. The protein surface hydrophobicity was also correlated with the granulometry parameters demonstrating the impact of thermal denaturation on the aggregation process.

The kinetics of protein aggregation induced by cooking were investigated in pig M. Longissimus dorsi. The 4 day aged muscles were cooked either in water or under dry heat conditions for 30 min. Four temperatures from 50 to 100 degrees C were tested for the "in water" cooking mode and an additional temperature of 140 degrees C was tested in the dry condition. Raw and cooked meat specimens were ground in a KCl solution. After delipidation of the meat extract, protein aggregation was evaluated with a laser granulometer (Sysmex FPIA-3000) which enabled reliable and reproducible characterization of particle number, size, and shape distribution using automated imaging techniques. The cooking mode (dry/"in water") did not affect the granulometry measurements. But, increasing cooking time and temperature affected the number, the size, and the shape of particles. An important decrease in particle number was observed during cooking in parallel with a reduction in particle size and a change in circularity. From these data a model with intermediary fibrillar aggregates and final amorphous aggregates was proposed.