Kinetics analysis of the reactions responsible for myoglobin chemical state in meat using an advanced reaction-diffusion model.

Here we developed an advanced reaction-diffusion model to predict the evolution of the myoglobin state in beef meat using numerous reactions with rate constants of different orders of magnitude. The initial scheme included 44 reactions from the literature. Sensitivity analysis proved that this initial scheme was equivalent to a simple 22-reaction scheme. Results calculated with this scheme were compared against the spatial distributions of oxymyoglobin (MbO2), metmyoglobin (MMb) and deoxymyoglobin (DMb) measured in meat cuts stored at 20°C under air-permeable packaging. We found global agreement between measured and calculated distributions when adequate rate constant values were used, particularly for the formation of MbO2 from DMb. The model was used to calculate evolutions in MbO2 and MMb distributions under different situations (modified-atmosphere packaging, Fenton chemistry with or without water-soluble antioxidants, increased mitochondrial oxygen consumption). Results were used to discuss the underlying kinetics reaction mechanisms and the performances and limits of the model.

Review: divergent selection for residual feed intake in the growing pig.

This review summarizes the results from the INRA (Institut National de la Recherche Agronomique) divergent selection experiment on residual feed intake (RFI) in growing Large White pigs during nine generations of selection. It discusses the remaining challenges and perspectives for the improvement of feed efficiency in growing pigs. The impacts on growing pigs raised under standard conditions and in alternative situations such as heat stress, inflammatory challenges or lactation have been studied. After nine generations of selection, the divergent selection for RFI led to highly significant (P<0.001) line differences for RFI (-165 g/day in the low RFI (LRFI) line compared with high RFI line) and daily feed intake (-270 g/day). Low responses were observed on growth rate (-12.8 g/day, P<0.05) and body composition (+0.9 mm backfat thickness, P=0.57; -2.64% lean meat content, P<0.001) with a marked response on feed conversion ratio (-0.32 kg feed/kg gain, P<0.001). Reduced ultimate pH and increased lightness of the meat (P<0.001) were observed in LRFI pigs with minor impact on the sensory quality of the meat. These changes in meat quality were associated with changes of the muscular energy metabolism. Reduced maintenance energy requirements (-10% after five generations of selection) and activity (-21% of time standing after six generations of selection) of LRFI pigs greatly contributed to the gain in energy efficiency. However, the impact of selection for RFI on the protein metabolism of the pig remains unclear. Digestibility of energy and nutrients was not affected by selection, neither for pigs fed conventional diets nor for pigs fed high-fibre diets. A significant improvement of digestive efficiency could likely be achieved by selecting pigs on fibre diets. No convincing genetic or blood biomarker has been identified for explaining the differences in RFI, suggesting that pigs have various ways to achieve an efficient use of feed. No deleterious impact of the selection on the sow reproduction performance was observed. The resource allocation theory states that low RFI may reduce the ability to cope with stressors, via the reduction of a buffer compartment dedicated to responses to stress. None of the experiments focussed on the response of pigs to stress or challenges could confirm this theory. Understanding the relationships between RFI and responses to stress and energy demanding processes, as such immunity and lactation, remains a major challenge for a better understanding of the underlying biological mechanisms of the trait and to reconcile the experimental results with the resource allocation theory.

Application to proteomics to understand and modify meat quality.

The use of proteomics in the field of meat science has gained in robustness and accuracy. This is consistent with the genomic and bioinformatic tools. Its application to sensorial and technological meat quality traits is discussed as well as the emergence of sanitary and nutritional issue which will grow in a next future.

Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 1. Microscopic analysis of muscles.

Three porcine muscles (Longissimus thoracis, Semitendinosus, Masseter), known to have large differences in biochemical and histological traits, were fully characterized and the link between muscle structure and quality evaluated. The oxidative Masseter had more pigment, higher content of metmyoglobin, haem iron, protein and collagen, and was redder with higher fibre numbers, fibre circularity, pH and water holding capacity than the glycolytic Longissimus. Fibre type distribution showed predominance of type IIB in Longissimus and Semitendinosus white, type I in Semitendinosus red and IIA in Masseter. Type I fibres were larger than type IIB and IIA in Semitendinosus and Masseter, respectively, but not in the Longissimus, indicating that fibre size is muscle dependent. Muscle redness was positively correlated with type I fibre traits, haem iron and metmyoglobin, and negatively associated with type II fibre characteristics, non-haem iron and oxymyoglobin. Expressible juice had positive correlation with fibre size and negative with fibre number and connective tissue.

Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 2. Composition of muscles.

The composition of three porcine muscles (Longissimus thoracis: LT, Semitendinosus: ST, Masseter: MS) was characterized and its link with muscle quality was evaluated. The LT muscle had a higher content of tyrosine, tryptophan, and carbohydrates and a lower content of vitamin E and haem iron than the MS muscle, while the ST had similar composition to MS but a lower content of haem iron. Large differences between muscles were observed in relative amounts of most of the major fatty acids. The LT muscle had higher saturated fatty acids (SFA) and n-6:n-3 fatty acid ratio, and lower polyunsaturated fatty acids (PUFA), PUFA:SFA ratio, unsaturation index and average fatty acid chain length than the ST and MS muscles. Muscle pH, redness and chroma were positively correlated with vitamin E and unsaturated lipids and negatively correlated with tyrosine, tryptophan, carbohydrates and saturated lipids, whereas muscle lightness and expressible juice showed similar correlations but an opposite sign with these variables.

Kinetics of protein physicochemical changes induced by heating in meat using mimetic models: (2) effects of fibre type, peroxides and antioxidants.

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 ß-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.

Kinetics of protein physicochemical changes induced by heating in meat using mimetic models: (1) relative effects of heat and oxidants.

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.

Effect of heat treatment on protein oxidation in pig meat.

We investigated the oxidative mechanisms and identified the target protein induced by heat treatment. The study was carried out on M. longissimus thoracis from Galia and Redone pigs. Post mortem metabolic parameters and drip loss were determined. Heat treatment was performed at 100 °C for 10 and 30 min. Physicochemical state of the protein, TBA-RS and Schiff bases were assessed. Protein aggregates were evaluated and the protein target of oxidation studied. Muscles from Galia had higher residual glycogen and drip loss. Heat treatment increased surface hydrophobicity, carbonyl, protein aggregate and Schiff bases and TBA-RS whatever the treatment time. Immunoblotting revealed oxidized myosin, oxidized actin and high molecular weight proteins after 30 min cooking. Oxidation products were significantly correlated with drip loss, suggesting a possible reduced ability of oxidized proteins to retain water. Moreover, residual glycogen was positively correlated with oxidized myosin, suggesting a possible role of glycogen as a glucose donor.

Higher drip loss is associated with protein oxidation.

The study aimed to investigate the mechanisms underlying drip loss in meat other than those related to post mortem energy metabolism. The study was carried out on M. longissimus thoracis assessing carcass and meat quality traits plus metabolic parameters and drip loss. Based on the data obtained, three drip loss groups were established: low, medium and high. Heat treatments were performed at 100°C for 30 min. Physicochemical protein modifications were assessed before and after cooking. IMF and L* were higher in the high drip loss group, whereas b* was higher in the medium drip loss group. Residual glycogen, glucose and glycolytic potential were higher in LT muscle from the high drip loss group. Before cooking, protein surface hydrophobicity and carbonyl levels were similar in the three groups. However, after cooking, carbonyl, oxidized actin and oxidized aggregates were higher in the high drip loss group, suggesting that protein oxidation may affect the water holding capacity of meat.

Effect of frozen storage duration and cooking on physical and oxidative changes in M. Gastrocnemius pars interna and M. Iliofiburalis of Rhea americana.

This study was conducted to evaluate the effect of frozen storage time (30, 60, 90 or 180 days) and cooking (100 °C, 30 min) on the physical characteristics and oxidative stability of M. Gastrocnemius pars interna (GN) and M. Iliofiburalis (IF) of rhea americana. Physical parameters measured included thawing and cooking loss, colour parameters (L*a*b*), while oxidation was assessed by determining the TBA-RS, carbonyl and aromatic amino acid content. Prolonged frozen storage of rhea meat decreased lightness (L*), yellowness (b*), and increased the discoloration parameter hue angle and redness a*. During storage, muscle IF was more prone to lipid and myoglobin oxidation than muscle GN. Cooking loss declined with the increase of storage time and was higher in GN than in IF muscle. With cooking, TBA-RS, carbonyl content, and aromatic amino acids (phenylalanine, tyrosine, and tryptophan) were highly affected, but the extent of oxidation ranged according to muscle and duration of frozen storage.

Comparison of meat and carcass quality in organically reared and conventionally reared pasture-fed lambs.

The 'Organic' product label guarantees a production process that avoids the use of synthetic fertilisers, pesticides and hormones and minimises recourse to pharmaceuticals or veterinary drugs; however, the product's quality remains an issue that needs to be addressed in response to consumer demand. Consequently, this study was conducted to compare the sensory and nutritional qualities of meat and carcasses from pasture-fed lambs reared organically (O) or conventionally (C). Mean lamb growth profile was kept similar between the two treatments to avoid confounding effects with lamb age or weight at slaughter. The experiment was conducted over 3 years (2005 to 2007) with 12 O and 12 C lambs each year. The O and C treatments differed in the level of on-pasture mineral N fertilisation inducing a higher proportion of white clover in the organic pasture than the conventional pasture. Lambs were slaughtered when they attained a fat class of 2 to 3, and carcass and meat quality were evaluated. Lambs were slaughtered at an average weight and age of 35.3 kg and 156 days in the O treatment, respectively, and 35.2 kg and 155 days in the C treatment, respectively. Sensory evaluation indicated that loin chops from the O treatment had a higher level of abnormal fat odour compared with the C treatment. Carcasses from the O treatment had a softer subcutaneous fat one among 3 years (2007) compared to the C treatment. These results are probably due to a higher proportion of white clover in the diet. Organically reared lambs did offer the slight advantage of muscle fatty acid containing a higher level of stearic acid, which may have positive effects in the prevention of cardiovascular disease in humans. This may be the result of a higher rumen bio-hydrogenation of C18:3n-3 due to differences in the botanical composition between the O and the C pasture. Production system had no effect on the colour characteristics of the meat and subcutaneous fat, except lightness of subcutaneous dorsal fat, which was slightly higher in the O lambs. There were no differences between O and C lambs in terms of colour stability and lipid oxidation of the meat during the 6-day refrigerated storage under gas-permeable film.

Colour, lipid and protein stability of Rhea americana meat during air- and vacuum-packaged storage: influence of muscle on oxidative processes.

Physicochemical characteristics and oxidative stability during storage were determined in Gastrocnemius pars interna (GN) and Iliofiburalis (IF) muscles of Rhea americana. Glycolytic potential (GP) and pH decline of muscles were measured within the first 24 h post mortem. Colour, lipid and protein stability were determined during storage of meat, i.e. 5 days under air-packaging at 4°C, or 28 days under vacuum-packaging at 4°C. In parallel, anti-oxidant status of muscles was estimated by measuring α-tocopherol content and anti-oxidant enzyme activities (superoxide dismutase and catalase), while pro-oxidant status was evaluated by determining haeminic iron and long chain fatty acids (especially polyunsaturated fatty acids). The ultimate pH was similar in both muscles, but the GP value was significantly higher in IF than in GN muscle. Haeminic iron and alpha-tocopherol content differed between muscles, with 30% more haeminic iron (p<0.05) and 134% more alpha-tocopherol (p<0.001) in IF than GN muscle. The IF muscle presented higher lipid content and lower PUFA/SFA ratio (polyunsaturated fatty acids/saturated fatty acids) than GN muscle. With storage under air-packaging, lipid and protein oxidation of rhea muscles increased up to 275% and 30%, respectively. This increase was more rapidly and marked in IF muscle. The IF also showed high level of metmyoglobin accumulation after 3 days of storage (47%) and was rejected by 1 consumer out of 2 in sensorial analysis. Under vacuum-packaging, both muscles showed a high stability of colour and no oxidation of lipids and proteins.

Comparison of proteolysis in native, heat-treated and aged proteins from turkey meat.

1. The present study compared the ability of native, heat-treated and aged turkey breast muscle proteins to undergo proteolysis by digestive tract proteases. 2. Domestic turkey toms were slaughtered under laboratory conditions. Breast muscles were excised immediately post mortem; one was placed under conditions to develop exudative meat by maintaining the muscle at 40 degrees C for at least 30 min and the other was refrigerated under commercial conditions. 3. Meat was collected and stored for 7 d at 4 degrees C. Breast samples removed at d 0 and d 7 were frozen and stored at -80 degrees C until used for determination of solubility, protein surface hydrophobicity and protein oxidation through carbonyl content. Measurements of pepsin and trypsin/chymotrypsin activities were performed in vitro on myofibrillar proteins. 4. Storage increased carbonyl content in control samples while the oxidation increase was not significant in heat-treated myofibrillar protein. Hydrophobicity was not affected by storage time or treatment or protein solubility. 5. Storage significantly increased trypsin + chymotrypsin activity only in the control group. The activities of pepsin and trypsin + chymotrypsin were negatively correlated with protein surface 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 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.

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.

Lipid and protein oxidation in microsomal fraction from turkeys: influence of dietary fat and vitamin E supplementation.

The objectives of this study were to investigate the effects of dietary fats (6% soya oil or rapeseed oil or tallow) and α-tocopheryl acetate supplementation (30 ppm for control and 200 ppm for supplemented animals), on lipid and protein oxidation, induced by Fe(3+)/ascorbate, of microsomal fraction in turkey muscles (M. pectoralis major and M. sartorius). Supplementation of turkeys with α-tocopheryl acetate increased the vitamin E content of microsomal membranes. Vitamin E supplementation strongly decreased lipid oxidation in membranal fractions when animals were fed rapeseed oil or tallow; this effect was less pronounced in animals fed soya oil. Vitamin E supplementation induced a slight decrease in protein carbonyl content, especially in animals fed soya oil. Level of protein free thiols was considerably enhanced in diet enriched with soya oil. Vitamin E supplementation had a stabilizing effect on glucose-6-phosphatase activity of microsomes when oxidized by Fe(3+)/ascorbate. No muscle effect was detected on the level of lipid and protein oxidation in membranal fractions even if M. sartorius is known to be more oxidative than M. pectoralis major.

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 dietary fat and vitamin E supplementation on free radical production and on lipid and protein oxidation in turkey muscle extracts.

The objectives of this study were to investigate the effects of dietary fat (6% soy oil or rapeseed oil or tallow) and alpha-tocopheryl acetate supplementation at two levels (30 or 200 ppm) on radical production, measured by ESR spectroscopy, and on lipid and protein oxidation in turkey muscle extracts oxidized by an enzymic system (NADPH, ADP, FeSO(4)/cytochrome P450 reductase). Two muscles were tested: pectoralis major (glycolytic) and sartorius (oxidative) muscles. Radical production measured by ESR was higher in pectoralis major muscle than in sartorius muscle, whereas lipid and protein oxidation was more important in sartorius muscle, showing the importance of the pro-/antioxidant ratio in oxidative processes in muscular cells and of the measurement methodology to appreciate the free radical production. Dietary fat had no effect on the level of ESR signals, whereas feeding of animals with soy oil induced higher oxidation of lipids. Protein oxidation was less sensitive to the nature of the dietary fat than lipid oxidation. Vitamin E supplementation significantly decreased radical production, as measured by ESR spectroscopy. Vitamin E also decreased lipid and protein oxidation, but the effect of vitamin E on protein oxidation was less pronounced than on lipid oxidation.