Tensile Properties of Beef Semitendinosus Muscle as Affected by Heating Rate and End Point Temperature

Tenderness of meat is one of its most important attributes of quality. The purpose of this study was to study the effect of heating rate (comparable to oven roasting at 93° and 149°C) and end point temperature (50°, 60° and 70°C) on tensile properties of muscle fibers and connective tissue of beef semitendinosus muscle. Cores of meat were heated in tubes in a water bath programmed to produce the desired rate of heating. Samples were evaluated by Warner-Bratzler shears and by lnstron measurements of breaking strength and work of rupture. Tensile measurements with fibers parallel to the stress were interpreted as reflecting the heat effects on the muscle fibers, whereas measurements with fibers perpendicular to the stress were considered representative of the heat effects on the connective tissue. Slow rate of heating resulted in lower (P \u3c 0.01) shear values than heating at the fast rate. Shear values decreased significantly (P \u3c 0.01) between 50° and 60°C and reached a minimum at 67°C. Although shears were lower at 70° than 60°C the decrease was not significant. Muscle fibers (fibers oriented parallel) were more resistant (P \u3c 0.001) to shearing than the connective tissue (fibers oriented perpendicularly). Breaking strength and work of rupture were not significantly affected by rate of heating. A significant interaction (P \u3c 0.001) between endpoint temperature and fiber direction was illustrated by polynomial curves. Fibers oriented parallel to the stress deceased significantly (P \u3c 0.01) in breaking strength and work of rupture from 50° to 60°C and from 60° to 70°C. Minimum breaking strength and work of rupture were obtained at 67°C; thereafter as internal temperature increased breaking strength and work of rupture started to increase. A nonsignificant decrease in breaking strength and work of rupture occurred with increasing internal temperature when fibers were oriented perpendicularly to the stress. Major changes in tensile strength occurred in the muscle fibers rather than in the connective tissue. Instron measurements in this study give no explanation for the reported increase in tenderness of meat heated at slow rates. Further work might be directed toward studying the changes in the muscle fibers which resulted in the decreased tensile strength that occurred during the early stages of heating