Changes in Tenderness and Collagen of Beef Semitendinosus Muscle Heated at Two Rates

Tenderness, an important quality attribute of meat, is affected by many factors, including rate of heating. The purpose of this investigation was to study the changes occurring in beef semitendinosus muscle and intramuscular connective tissue heated at rates comparable to oven roasting at 93 and 149°C. The sequence of changes occurring during heating was followed by evaluating samples heated to four end points, 40, 50, 60, and 70°C. Cores of meat and isolated connective tissue samples in buffer were heated in a water bath programmed to produce the desired rate of heating. As internal temperature increased Warner Bratzler shear values of cores decreased (P\u3c 0.001). Slow heating produced more (P\u3c 0.05) tender cores than faster heating. Shear values were negatively related (P\u3c 0.05) to percent connective tissue solubilized during heating. More (P\u3c 0.01) connective tissue was solubilized in slowly heated cores and solubilization increased (P\u3c 0.001) with internal temperature. Enzyme activity was exhibited in cores heated to all end points but decreased (P\u3c 0.01) from 60 to 70°C. Small amounts of activity were found in the drip lost during heating. Activity in the drip decreased (P\u3c 0.05) with heating, more slowly (P\u3c 0.05) at the slow rate than at the fast rate of heating. It is postulated that enzyme activity could affect the difference in tenderness between the slow and the fast heated cores. Isolated connective tissue heated in buffer was solubilized to a greater (P\u3c 0.001) extent when heated at the slow rate than at the fast rate. Solubilization increased (P\u3c 0.001) as end point temperature increased. Peptides in samples heated to 70°C were estimated to be longer (P\u3c 0.05) than those heated to lower temperatures. Solubility of the heated connective tissue in guanidine hydrochloride decreased (P\u3c 0.001) with heating and to a greater (P\u3c 0.05) extent in the slowly heated samples. From the results of this study it would appear that solubilization of connective tissue is not the only factor affecting the increased tenderness of slowly heated meat. General proteolytic activity may play a role in this increased tenderness. Further investigation of the residual connective tissue and the effects of the two heating rates on myofibrillar proteins is needed to explain the differing effects of slow and fat rates of penetration