EXTENSIBILITY, STRENGTH AND TENDERNESS OF BEEF COOKED TO VARIOUS DEGREES

The response to loading of strips of ox sternomandibularis muscle varies greatly with degree of cooking. In raw or lightly cooked strips a yield point is reached where the myofibrils fail. Within this range, the yield point is independent of degree of cooking, and at 1.4 kg/cm2 is well below the tension which can be developed in the pre-rigor muscle (2.3 kg/cm2). On cooking, the yield point vanishes between 10 and 40 min at 70.degree. C and the strips behave more elastically. This degree of heating coincides with the sharpest change in shrinkage and other properties. By using strips in which the myofibrillar component was destroyed by alkali, and others in which collagen was destroyed by long cooking, an attempt was made to separate the contributions of these components. Between 60-80.degree. C, a fall in connective tissue strength is matched by a rise in myofibrillar strength, maintaining a constant overall value of .apprx. 5 kg/cm2. Both components become more extensible and stretch in unison, until they fail together. After cooking at 100.degree. C, only the myofibrillar component survives (.apprx. 3 kg/cm2). Shear force values are generally in line with these results, but show a dip on cooking at 60.degree. C, due to accelerated aging. Gap filaments may determine the tensile strength of the raw or cooked myofibril.