RESUMO

Extracellular matrix (ECM) structures within skeletal muscle play an important, but under-appreciated, role in muscle development, function and adaptation. Each individual muscle is surrounded by epimysial connective tissue and within the muscle there are two distinct extracellular matrix (ECM) structures, the perimysium and endomysium. Together, these three ECM structures make up the intramuscular connective tissue (IMCT). There are large variations in the amount and composition of IMCT between functionally different muscles. Although IMCT acts as a scaffold for muscle fiber development and growth and acts as a carrier for blood vessels and nerves to the muscle cells, the variability in IMCT between different muscles points to a role in the variations in active and passive mechanical properties of muscles. Some traditional measures of the contribution of endomysial IMCT to passive muscle elasticity relied upon tensile measurements on single fiber preparations. These types of measurements may now be thought to be missing the important point that endomysial IMCT networks within a muscle fascicle coordinate forces and displacements between adjacent muscle cells by shear and that active contractile forces can be transmitted by this route (myofascial force transmission). The amount and geometry of the perimysial ECM network separating muscle fascicles varies more between different muscle than does the amount of endomysium. While there is some evidence for myofascial force transmission between fascicles via the perimysium, the variations in this ECM network appears to be linked to the amount of shear displacements between fascicles that must necessarily occur when the whole muscle contracts and changes shape. Fast growth of muscle by fiber hypertrophy is not always associated with a high turnover of ECM components, but slower rates of growth and muscle wasting may be associated with IMCT remodeling. A hypothesis arising from this observation is that the level of cell signaling via shear between integrin and dystroglycan linkages on the surface of the muscle cells and the overlying endomysium may be the controlling factor for IMCT turnover, although this idea is yet to be tested.

RESUMO

El aluminio puede ser consumido por personas a través de la contaminación de alimentos y el agua. Los metales pesa­dos en alimentos de origen animal son un riesgo potencial para la salud de los consumidores. En algunos países, es una práctica habitual que las comidas cocinadas listas para el consumo se presenten y mantengan calientes en bandejas de aluminio en tiendas minoristas, como locales de comida rápida y supermercados. No hay información disponible sobre el desprendimiento de metal en este tipo de recipiente de conservación de alimentos. El objetivo de este estudio fue determinar la concentración de aluminio en la carne y en los líquidos de cocción almacenados en bandejas de aluminio descartables. El diseño del estudio incluyó carne bovina cocida almacenada sola, en una salsa acuosa de hierbas a pH 7, y en una salsa acuosa cítrica (a base de limón) a pH 4, para simular condiciones encontradas en la práctica minorista. El Comité Mixto FAO / OMS de Expertos en Aditivos Alimentarios estableció una ingesta semanal tolerable provisional de 2 mg Al kg-1 de peso corporal. Una sola porción de 250 g de carne en salsa ácida almace­nada en una bandeja de aluminio calentada durante 1, 2, 4 u 8 horas contribuiría con 0,9%, 3,4%, 6,9% y 19,8% respectivamente de acuerdo al límite tolerable. Aunque la carne se mantiene caliente durante largos períodos en bandejas de aluminio descartable, el contenido de aluminio no se acerca a los límites actualmente recomendados. Este estudio proporciona datos que sugieren que puede ser prudente limitar el consumo de este tipo de comidas a base de carne con salsas ácidas almacenadas calientes por tiem­pos extendidos en contenedores de aluminio.

Aluminium can be consumed by people through contamination of foods and in water. Heavy metals in foods of animal origin are a potential risk to the health of consumers. It is common practice in some countries that ready-to-eat cooked meals are often presented and maintained hot in aluminium trays in retail outlets such as fast food take-out stores and supermarkets. There are not available information about the detachment of metal in this kind of container food preservation. The objective of this study was to determine the concentration of aluminium in meat and cooking liquids stored in disposable aluminium trays. The design of the study included cooked beef meat stored either alone, or in an aqueous sauce of herbs at pH 7, or in a citric (base of lemon) aqueous sauce at pH 4, to simulate a range of conditions found in retail practice. The Joint FAO/WHO Expert Committee on Food Additives established a provisional tolerable weekly intake of 2 mg Al kg body weight-1. A single 250 g portion of meat in acid sauce stored in a heated aluminium tray for 1, 2, 4, or 8 hours would contribute 0.9%, 3.4%, 6.9% or 19.8% towards this tolerable limit, respectively. Although the aluminium content in meat held warm for long periods in aluminium foil trays does not approach the consumption limits currently recommended, this study provides data that suggest that is may be prudent to limit consumption of ready-to eat meat-based meals with acid sauces stored warm in aluminium containers for extended times.

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RESUMO

Long-time low-temperature (LTLT) cooking of meat is known to produce a tender product. The current work tested the hypothesis that LTLT cooking for periods of up to 24 h at 60 °C reduces the contribution of intramuscular connective tissue to cooked meat toughness. Tensile tests on perimysium excised after cooking showed that its strength diminished with cooking time, although not as markedly as the Warner-Bratzler peak force measure of toughness. A gradually increasing susceptibility to trypsin digestion with increasing heating time demonstrated that there was a slow and gradual increase in the proportion of denatured collagen in the perimysium. Differential scanning calorimetry on perimysium excised after cooking showed an endothermic peak representing the denaturation of the collagen not already denatured on cooking. With increasing cooking time, the energy per milligram of collagen necessary to denature this remaining fraction increased. These results support the hypothesis that there is both an easily destabilized and more resistant fractions of the collagen in intramuscular connective tissue.

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RESUMO

Matrix metalloproteinases (MMPs) are a group of enzymes that degrade extracellular matrix components but are also important signaling molecules that regulate many biological processes including muscle, adipose and connective tissue development. Most recently it has been discovered that MMPs act as intracellular signaling molecules inducing gene expression and altering related proteins in the nucleus. Several single nucleotide polymorphisms of MMPs and their inhibitors are known to exist and most of the research on MMPs to date has focused on their activity in relation to human health and disease. Nevertheless there is a growing body of evidence identifying important roles of MMPs as regulators of myogenesis, fibrogenesis and adipogenesis. The aim of this review is to highlight the currently known functions of the MMPs that have a direct bearing on the deposition of meat components and their relationship with meat quality. Some central pathways by which these enzymes can affect the tenderness, the amount and type of fatty acids are highlighted.

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