Muscle foods:: Water, structure and functionality

Main constituents of skeletal muscle are water, protein, fat, carbohydrate and other soluble compounds. The amount of water is usually found in the range 70-80%. Part of this water is found in free form while the rest is bound to proteins, especially myofibrillar proteins, through charged and polar groups. The amount of immobilised water depends on the available space within the myofibrillar structure and, in fact, the volume of myofibrils is decisive to the water-binding capacity of the muscle. Some variations exist between muscles due to the types of muscle fibres, degree of fibre contraction and pre-rigor pH. The water retention will also depend on the ultimate pH reached after rigor mortis and this will have a strong influence on the activity of muscle enzymes involved in proteolysis and lipolysis during ageing and further processing. Variations may be also expected between animal or fish species and age at slaughter. It is of primary importance to understand metabolic processes in post-mortem muscle as they will directly influence water-binding and thus, the relative amount of drip loss.