Early post-mortem sarcoplasmic proteome of porcine muscle related to lipid oxidation in aged and cooked meat.

In order to identify specific markers of lipid oxidation generated in meat during refrigerated storage and cooking 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 the level of lipid oxidation. This study was performed in Longissimus lumborum pig muscle. Proteome was analysed by 2-D electrophoresis in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and lipid oxidation was estimated by the TBA reactive substances (TBA-RS) measurement. Many markers of lipid oxidation were identified, but no single marker covered the oxidative process in its entirety. The role of five protein groups (albumin, redoxins, annexins, lipid transporters and enzymes of aerobic respiration), from which a link with lipid oxidation can be established, is discussed. This study, which completes a precedent work focused on protein oxidation, clearly demonstrates that a combination of several markers is needed to assess the sensitivity of meat to oxidation during both ageing and cooking.

Early post-mortem sarcoplasmic proteome of porcine muscle related to protein oxidation.

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.

Changed dynamics in myofibrillar protein aggregation as a consequence of heating time and temperature.

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.

Effect of cooking on protein oxidation in n-3 polyunsaturated fatty acids enriched beef. Implication on nutritional quality.

The effect of cooking on protein oxidation was investigated in M. Longissimus thoracis of eight Normand cows fed during a 100 days finishing period with two different diets: a conventional diet (concentrate/straw based diet) and a diet rich in n-3 polyunsaturated fatty acids (PUFAs), obtained by addition to the conventional diet of a mixture of extruded linseed and extruded rapeseed. After 11 days storage, at 4 degrees C under vacuum, meat was cooked by applying jets of steam. Three experimental heating treatments were tested: two with constant surface temperatures of 65 and 96 degrees C during 300s, and one with a continuous increasing surface temperature up to 207 degrees C. Protein oxidation was evaluated by the measurement of carbonyls, aromatic amino acids, and free thiols content. The formation of Schiff bases due to the reaction of proteins with aldehydic products of the lipid oxidation was also evaluated. Cooking resulted in a significant increase of carbonyl groups and Schiff bases as well as a significant degradation of tyrosine and tryptophan. Nevertheless, enrichment of the animal diet in n-3 PUFAs had minor effects on protein oxidation induced by cooking which are unlikely to be of nutritional significance.

Digestion study of proteins from cooked meat using an enzymatic microreactor.

A semi automatic flow procedure with photometric detection was developed for the study of meat protein digestion. This system comprised two independent flow pathways, gathered by two compartments. The gastric compartment was simulated by an ultrafiltration cell fitted with a 10 KDa cut off membrane and the intestinal compartment was simulated by a 1 KDa cut off dialysis membrane. The pathways were filled with solutions simulating digestive conditions. The proposed system was employed in digestion studies of whole protein extracts from raw and cooked (100°C) meat. A mathematical modelling for the determination of the digestive kinetic constants was established. The results show that meat cooking leads to an important decrease of protein digestibility by proteases of the digestive tract.

Use of meat fluorescence emission as a marker of oxidation promoted by cooking.

Accumulation of fluorescent pigments in cooked bovine meat (M. Longissimus thoracis) was studied in relationship with the heating parameters (time and temperature). Muscles were aged at 4°C for 11days under vacuum before cooking. Meat cooking was performed by applying jets of steam. Three different heating treatments were tested: two with constant surface temperatures of 65 and 96°C for 300s, and one with a continuously increasing surface temperature up to 207°C. After extraction in water/dichloromethane/ethanol, fluorescence pigments were distributed between the apolar phase (emission 420-440nm after excitation at 360nm) and the polar phase, where two emission peaks were seen (emission 410-430 and 515nm after excitation at 360nm). Fluorescence in the two phases was little affected by heating at the two constant temperatures while it increased exponentially after 1min of treatment, as the varying temperature reached 141°C. The maximum fluorescence increases, measured in the extreme conditions of cooking (207°C/300s), were of 5000% in the apolar phase and 1700% in the polar phase. Thiobarbituric acid reactive substances (TBARS) and protein carbonyls were measured in parallel. The correlations between these two parameters and the fluorescence emission demonstrated that the interaction between proteins and aldehyde products of lipid peroxidation was mainly involved in the production of fluorescent pigments in cooked meat.