Effects of Electrical Stimulation and Conditioning Periods upon Pre-Rigor Beef Samples Cooked with a Microwave Oven ¹

Thirty beef carcasses were used to evaluate the effects of electrical stimulation and conditioning periods and microwave cooking upon sensory and shear properties of pre-rigor semitendinosus muscle samples. The intact muscle was removed from the right side within 45 min post-exsanguination and was electrically (ES) stimulated [100 impulses (1 s on and 1 s off, A.C., 110V, <5 amps)], while the remaining paired muscle served as the control (NS). After electrical stimulation, the muscle was cross-sectioned into three portions. A 2.54-cm thick sample was removed from the central portions of the ES and NS muscles and cooked immediately in a microwave oven to an internal temperature of 66°C. The remaining two similar sized portions were conditioned at 13°C for 2 h or 4 h before cooking. Three cores (1.27 cm) were removed from each sample parallel to the muscle fiber, and all cores were sheared twice. Samples from the conditioning periods were frozen, thawed, reheated and evaluated for palatability traits by a 10-member trained panel. Results indicate higher sensory panel ratings (P<.05) for tenderness, connective tissue and flavor intensity and lower shear force (WBS and Instron) values and longer sarcomeres from ES. With the conditioning periods used, microwave cooking was too rapid for pre-rigor muscle, as exemplified by the high shear values (6.4 and 7.8 kg/1.27 cm for ES and NS, respectively) which indicates a very tough sample of meat. Cooking yield was highest for muscle samples cooked immediately after slaughter. Roasts conditioned for 4 h before cooking had higher (P<.05) juiciness and flavor intensity scores than roasts held for 2 h, regardless of stimulation treatments.