Aging is characterized by a progressive loss of muscle mass that could be partly explained by a defect in the anabolic effect of food intake. We previously reported that this defect resulted from a decrease in the protein synthesis response to leucine in muscles from old rats. Because aging is associated with changes in oxidative status, we hypothesized that reactive oxygen species-induced oxidative damage may be involved in the impairment of the anabolic effect of leucine with age. The present study assessed the effect of antioxidant supplementation on leucine-regulated protein metabolism in muscles from adult and old rats. Four groups of 8- and 20-mo-old male rats were supplemented or not for 7 wk with an antioxidant mixture containing rutin, vitamin E, vitamin A, zinc, and selenium. At the end of supplementation, muscle protein metabolism was examined in vitro using epitrochlearis muscles incubated with increasing leucine concentrations. In old rats, the ability of leucine to stimulate muscle protein synthesis was significantly decreased compared with adults. This defect was reversed when old rats were supplemented with antioxidants. It was not related to increased oxidative damage to 70-kDa ribosomal protein S6 kinase that is involved in amino acid signaling. These effects could be mediated through a reduction in the inflammatory state, which decreased with antioxidant supplementation. Antioxidant supplementation could benefit muscle protein metabolism during aging, but further studies are needed to determine the mechanism involved and to establish if it could be a useful nutritional tool to slow down sarcopenia with longer supplementation.

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Since temperature and water activity are among the most important parameters that affect the Maillard reaction, the glycation sites in pure, native bovine ␤-lactoglobulin were determined after a mild heat treatment (60 ЊC) in an aqueous solution and after a treatment under a restricted water environment (50 ЊC, 65% relative humidity). In both systems, the results obtained underlined the structural heterogeneity of ␤-lactoglobulin (␤-LG) glycoforms with respect to the number of lactose residues linked per protein molecule and to the binding sites involved. Subsequently, the effect of the glycation conditions on both the association behaviour and the conformational changes of the glycated ␤-LG were characterised by proteolytic susceptibility, binding of the fluorescent probe 8anilino-1-naphtalene-sulfonic acid, SDS-PAGE and size exclusion chromatography. The results showed that dry-way glycation did not significantly alter the native-like behaviour of the protein while the treatment in solution led to important structural changes. These changes resulted in a specific denatured ␤-LG monomer, which covalently associated via the free thiol group. The homodimers thus formed and the expanded monomers underwent subsequent aggregation to form high molecular weight species, via non-covalent interactions. The use of monoclonal antibodies with defined epitopes, raised against native ␤-LG, confirmed that the protein conformation was much more modified when glycation was performed in a solution while the structural changes induced during dryway treatment were limited to the AB loop region of the protein.

SummaryA sandwich ELISA (enzyme-linked immunosorbent assay) of the two-site type has been successfully developed for the detection of cows' milk in goats' or ewes' milk. The assay uses two monoclonal antibodies (MAb) raised in mice against cows' β-lactoglobulin (β-lg). These MAb recognize different epitopes of the β-lg, which are sufficiently distinct to allow simultaneous binding of the corresponding antibodies. One of the MAb recognizes a species-specific epitope of the bovine β-lg and was adsorbed to a plastic microtitration plate (capture antibody). The second MAb was labelled with peroxidase and used to detect the captured cows' β-lg. Factors affecting assay performance were investigated. The optimized assay is highly specific, reproducible (intra- and inter-assay CV were 8 and 13% respectively) and sensitive: as little as 5 ng β-lg/ml or 1 part cows' milk per 100000 parts goats' or ewes' milk can be detected. The technique is robust, cheap, rapid, reliable and suitable for high sample throughput, semi-automation and screening surveys. The MAb used guarantee the high specificity of the assay and indefinite reagent supply of constant quality once approved by collaborative national or international trials.

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.