Thierry Astruc

Effect of Meat Cooking on Physicochemical State and in Vitro Digestibility of Myofibrillar Proteins

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.

Proteinaceous determinants of surface colonization in bacteria: bacterial adhesion and biofilm formation from a protein secretion perspective

Bacterial colonization of biotic or abiotic surfaces results from two quite distinct physiological processes, namely bacterial adhesion and biofilm formation. Broadly speaking, a biofilm is defined as the sessile development of microbial cells. Biofilm formation arises following bacterial adhesion but not all single bacterial cells adhering reversibly or irreversibly engage inexorably into a sessile mode of growth. Among molecular determinants promoting bacterial colonization, surface proteins are the most functionally diverse active components. To be present on the bacterial cell surface, though, a protein must be secreted in the first place. Considering the close association of secreted proteins with their cognate secretion systems, the secretome (which refers both to the secretion systems and their protein substrates) is a key concept to apprehend the protein secretion and related physiological functions. The protein secretion systems are here considered in light of the differences in the cell-envelope architecture between diderm-LPS (archetypal Gram-negative), monoderm (archetypal Gram-positive) and diderm-mycolate (archetypal acid-fast) bacteria. Besides, their cognate secreted proteins engaged in the bacterial colonization process are regarded from single protein to supramolecular protein structure as well as the non-classical protein secretion. This state-of-the-art on the complement of the secretome (the secretion systems and their cognate effectors) involved in the surface colonization process in diderm-LPS and monoderm bacteria paves the way for future research directions in the field.

Antioxidant Supplementation Restores Defective Leucine Stimulation of Protein Synthesis in Skeletal Muscle from Old Rats

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.

Effects of high-intensity high-frequency ultrasound on ageing rate, ultrastructure and some physico-chemical properties of beef

High-intensity and high-frequency ultrasound was tested for its ability to accelerate meat ageing and increase beef tenderness. Samples (≈50g) of semimembranosus muscles from 8 cull cows were assigned to ultrasonic treatment (2.6MHz; 10W/cm(2); 2 ×15s) either pre-rigor (day 0, pH 6.2) or post-rigor (day 1, pH 5.4). When applied pre-rigor, ultrasound induced a slight delay in rigor mortis onset, a stretching (12-15%) of the sarcomeres (p<0.05), an ultrastructural alteration in the Z-line region and an immediate increase (around 30%) in the release of calcium in the cytosol (p<0.05). However, no conclusive effect on meat ageing rate was observed. Post-rigor ultrasonic treatment did not induce any structural modification but slightly improved the ageing index after 6 days (p<0.05). However, no improvement in the final (day 14) ageing index was observed compared to the controls. As ultrasound had also no effect on the thermal stability of collagen, at both postmortem times, no improvement in meat tenderness can be expected under the conditions used.

Tenderization of beef by lactic acid injected at different times post mortem

The potential to tenderize beef muscles by the injection of lactic acid (0.5 M, 10% w/w) was studied using the pectoralis profundus muscle from cull cows. The injection was performed either 1 h (pre rigor) or 24 h (post rigor) post mortem, and the meat was stored for 2 or 14 days post mortem. Both treatments caused a rapid pH drop to around 5.0 within 4 h of injection. Other effects were: (1) an accelerated release of lysosomal enzymes into the cytosol; (2) a greater degradation of myosin heavy chains; (3) ultrastructural alterations of the myofibrils which included a general weakening or rupture in the M-lines and, to a lesser extent, in the I-bands; (4) a decreased heat stability of perimysial collagen indicated by a lower insoluble collagen content, lower differential scanning calorimetry transition temperature, and lower transition temperatures in isometric tension tests on muscle strips. The lactic acid injections improved significantly the textural traits of the meat (shear value, tensile strength, sensory scores) at 2 days post mortem with little further improvement when storage was extended to 14 days post mortem. Changes in texture were of similar amplitude at both post mortem injection times. The tenderization mechanisms of lactic acid injection are discussed.

Bacterial adhesion to animal tissues: protein determinants for recognition of extracellular matrix components

The extracellular matrix (ECM) is present within all animal tissues and organs. Actually, it surrounds the eukaryotic cells composing the four basic tissue types, i.e. epithelial, muscle, nerve and connective. ECM does not solely refer to connective tissue but composes all tissues where its composition, structure and organization vary from one tissue to another. Constituted of the four main fibrous proteins, i.e. collagen, fibronectin, laminin and elastin, ECM components form a highly structured and functional network via specific interactions. From the basement membrane to interstitial matrix, further heterogeneity exists in the organization of the ECM in various tissues and organs also depending on their physiological state. Back to a molecular level, bacterial proteins represent the most significant part of the microbial surface components recognizing adhesive matrix molecules (MSCRAMM). These cell surface proteins are secreted and localized differently in monoderm and diderm–LPS bacteria. While one collagen‐binding domain (CBD) and different fibronectin‐binding domains (FBD1 to 8) have been registered in databases, much remains to be learned on specific binding to other ECM proteins via single or supramolecular protein structures. Besides theinteraction of bacterial proteins with individual ECM components, this review aims at stressing the importance of fully considering the ECM at supramolecular, cellular, tissue and organ levels. This conceptual view should not be overlooked to rigorously comprehend the physiology of bacterial interaction from commensal to pathogenic species.

Genetic parameters of meat technological quality traits in a grand-parental commercial line of turkey

Genetic parameters for meat quality traits and their relationships with body weight and breast development were estimated for a total of 420 male turkeys using REML. The birds were slaughtered in a commercial plant and the traits measured included pH at 20 min (pH20) and 24 h post-mortem (pHu) and colour of the breast and thigh meat. The heritabilities of the rate and the extent of the pH fall in the breast muscle were estimated at h2 = 0.21 ± 0.04 and h2 = 0.16 ± 0.04, respectively. Heritabilities ranging from 0.10 to 0.32 were obtained for the colour indicators in the breast muscle. A marked negative genetic correlation (rg= -0.80 ± 0.10) was found between pH20 and lightness (L*) of breast meat, both traits corresponding to PSE indicators. The pH20 in the thigh muscle had a moderate heritability (h2 = 0.20 ± 0.07) and was partially genetically related to pH20 in the breast muscle (rg= 0.45 ± 0.17). Body weight and breast yield were positively correlated with both initial and ultimate pH and negatively with the lightness of breast meat.

How Muscle Structure and Composition Influence Meat and Flesh Quality.

Skeletal muscle consists of several tissues, such as muscle fibers and connective and adipose tissues. This review aims to describe the features of these various muscle components and their relationships with the technological, nutritional, and sensory properties of meat/flesh from different livestock and fish species. Thus, the contractile and metabolic types, size and number of muscle fibers, the content, composition and distribution of the connective tissue, and the content and lipid composition of intramuscular fat play a role in the determination of meat/flesh appearance, color, tenderness, juiciness, flavor, and technological value. Interestingly, the biochemical and structural characteristics of muscle fibers, intramuscular connective tissue, and intramuscular fat appear to play independent role, which suggests that the properties of these various muscle components can be independently modulated by genetics or environmental factors to achieve production efficiency and improve meat/flesh quality.

Effects of the rate of muscle post mortem pH fall on the technological quality of turkey meat

1. This experiment evaluated the influence of the rate of post mortem pH fall on the processing ability of turkey meat. 2. Four hundred and twenty male turkeys from a selected pure line (grand-parental female line, BUT Ltd) were slaughtered at 16 weeks of age in a commercial plant and pH was measured in the Pectoralis superficialis (PS) and Ilio tibialis (IT) muscles, at 20 min post mortem . Three groups of PS muscle differing in pH 20 and two groups of IT muscle differing in pH 20 were constituted and processed as cured-cooked white meat and turkey ham, respectively. 3. The technological yield was lower in the groups showing the lowest pH 20 (97.4% at pH 20 5.90 vs 98.6 and 98.3% at pH 20 6.24 and 6.55, respectively, for white meat and 97.2% (pH 20 6.28) vs 98.3% (pH 20 6.56) for turkey hams). The groups showing the lowest pH 20 also showed higher drip loss in commercially packed products. 4. Acceptability tests of processed products were carried out in the commercial plant. Texture and taste of white meat were better in the highest pH group but the overall impression was similar in the lowest and the highest pH groups (mean scores of 4.2 and 4.1, respectively), due to better colour in the former (mean scores of 4.4 for the lowest pH 20 group vs 4.0 and 3.9 for the medium and highest pH 20 groups, respectively). 5. For turkey hams, the meat processed from the highest pH group got the best score for all items.

Curcumin treatment prevents increased proteasome and apoptosome activities in rat skeletal muscle during reloading and improves subsequent recovery.

Immobilization is characterized by activation of the ubiquitin (Ub)-proteasome-dependent proteolytic system (UPS) and of the mitochondrial apoptotic pathway. Increased oxidative stress and inflammatory response occur in immobilized skeletal muscles. Curcumin exhibits antioxidant and anti-inflammatory properties, blocked proteasome activation in intact animals, and may favor skeletal muscle regeneration. We therefore measured the effects of curcumin on immobilization-induced muscle atrophy and subsequent recovery. Rats were subjected to hindlimb immobilization for 8 days (I8) and allowed to recover for 10 days (R10). Fifty percent of the rats were injected daily with either curcumin or vehicle. Proteolytic and apoptotic pathways were studied in gastrocnemius muscles. Curcumin treatment prevented the enhanced proteasome chymotrypsin-like activity and the trend toward increased caspase-9-associated apoptosome activity at I8 in immobilized muscles. By contrast, the increase of these two activities was blunted by curcumin at R10. Curcumin did not reduce muscle atrophy at I8 but improved muscle recovery at R10 and the cross-sectional area of muscle fibers of immobilized muscles. Curcumin reduced the increased protein levels of Smac/DIABLO induced by immobilization and enhanced the elevation of X-linked inhibitory apoptotic protein levels at R10. Ub-conjugate levels and caspase-3 activity increased at I8 and were normalized at R10 without being affected by curcumin treatment. Altogether, the data show that curcumin treatment improved recovery during reloading. The effect of curcumin during the atrophic phase on proteasome activities may facilitate the initiation of muscle recovery after reloading. These data also suggest that this compound may favor the initial steps of muscle regeneration.