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.
The objective of this study was to investigate the effect of chemical oxidation on myofibrillar protein digestibility. Myofibrils were prepared from pig M. longissimus dorsi and oxidized by a hydroxyl radical generating system. Oxidative modifications of proteins were assessed by the carbonyl content, surface hydrophobicity, electrophoresis, and immunoblotting. Oxidized or nonoxidized myofibrillar proteins were then exposed to proteases of the digestive tract (pepsin, trypsin, and alpha-chymotrypsin). Results showed a direct and quantitative relationship between protein damages by hydroxyl radical and loss of protein digestibility.
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.
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.
The aim of this work was to compare the oxidative processes occurring in
myofibrillar proteins
during meat maturation and after an in vitro exposure to
different enzymic and nonenzymic oxidative
systems. Myofibrils were prepared from bovine Longissimus lumborum
and Diaphragma pedialis
at day 1 and day 10 post-mortem. Myofibrillar protein oxidation
was measured by the carbonyl
content, with the 2,4-dinitrophenylhydrazine (DNPH) method, and by
(thiol group) SH content with
the 2,2‘-dithiobis(5-nitropyridine) (DTNP) method.
Polymerization and/or fragmentation of oxidized
proteins were estimated by SDS-PAGE and Western blot analysis using a
polyclonal antibody to
myosin. Oxidation of myofibrillar proteins is dependent upon the
different metal-catalyzed oxidation
(MCO) systems. The increase in carbonyl content and also the
decrease in SH content of myofibrillar
proteins, after maturation of 10 days, were similar to those obtained
after a 1 h incubation of
myofibrillar proteins in the presence of several MCO systems.
Electrophoretic studies showed that
myosin was the protein the most sensitive to oxidation, and to a lesser
extent, troponin T. Myosin-oxidative products were also detected by Western blot
analysis.
Keywords: Beef; myofibrillar proteins; protein oxidation; carbonyl content;
SH-content; metal-ion
catalyzed oxidation system; SDS−PAGE; Western blotting
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.
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