Mechanical properties of meat.

Determination of meat mechanical properties is still usually performed under empirical conditions, using tests which have been developed many years ago. This paper discusses the limitations of these methods. It also reviews recently developed research which has been focused on a more analytical approach to mechanical tests performed in closely controlled conditions. The objectives of these investigations are on the one hand to obtain specific properties of the myofibre and connective tissue structures involved in meat toughness and on the other hand to understand the fracture mechanisms involved in the perception of texture. Due to the anisotropic and composite nature of meat, attention has been focused on the influence of the direction and amplitude of strains to be used for the characterisation of myofibres and connective tissue, respectively. These strain conditions are linked to the contraction and stretching state of each of these structures. Indeed, whatever the type of deformation (shear, compression or tension), myofibre resistance can be determined under low strain conditions as long as collagen fibres in the connective tissue remain in a more crimped state than myofibres, i.e. in raw or slightly cooked meat of normal sarcomere length. On the contrary, determination of connective tissue resistance has, up to now, only been obtained using large strain tests. Contraction of collagen fibres induced by cooking makes the separate analysis of meat structures more difficult, but this can partially be overcome by applying mechanical tests in different strain directions. However, the role of the spatial distribution of connective network on the mechanical properties of meat still remains largely unknown. Image analysis and ultrasonic methods, currently developed to study this problem, are briefly presented.