A New Theory of Tenderness in Meat, Based on Gap Filaments

Tenderness is a quality of meat highly regarded by the consumer, who may have a very clear idea of how he rates it. For the meat scientist, interested in putting a number on it, it poses problems. Tenderness, or more often toughness, is ideally measured by selected human jaws. Fortunately for experimental convenience and precision, mechanical shear values correlate fairly well with panel scores, although there is some doubt as to what shearing devices actually measure, and whetherthe various models now in use measure the same thing. In spite of this, shear force remains the preferred measure of toughness in research. It is a more complex parameter than tensile strength along the fibre. The relationship between the two is not entirely agreed (for a discussion see Locker et al., 1977). An interesting visual demonstration of stretching around the blunt shearing wedge of the MlRlNZ tenderometer (MacFarlane and Marer, 1966) was provided by Davey and Winger (1980, their Fig. 16). Considering all the evidence, it seems reasonable to conclude that tensile strength is the dominant factor in shear force. We have given a great deal of attention to tensile properties in recent work, since these are more amenable to structural interpretation, and, used properly, can distinguish the contributions of various components. But understanding what is being measured by such parameters still has complications. Firstly, muscle is a composite of contractile machinery enveloped in connective tissue. Knowledge of the former has advanced enormously under the stimulus of the sliding filament theory of muscular contraction, and with the advent of sophisticated techniques in molecular biology. Collagen chemistry has flourished to a comparable degree, although the organization of the protein into connective tissue, particularly at the macro-end of the scale, has been an area of neglect. This essay will concentrate on the myofibrillar component. It is of course what I know best, but it is also the eminently controllable factor, capable of being grossly modified for better or for worse by post mortem treatment. Early research on tenderness over-emphasized connective tissue, of necessity, because new doors had yet to open. Recognition of the role of stateof contraction swung theemphasis probably too far in the direction of the myofibril. Interest in connective tissue revived somewhat with the important concept of the perimysium as a