High and low rigor temperature effects on sheep meat tenderness and ageing

Immediately after electrical stimulation, the paired in. longissimus thoracis et lumborum (LT) of 40 sheep were boned out and wrapped tightly with a polyethylene cling film. One of the paired LT's was chilled in 15degreesC air to reach a rigor mortis (rigor) temperature of 18degreesC and the other side was placed in a water bath at 35degreesC and achieved rigor at this temperature. Wrapping reduced rigor shortening and mimicked meat left on the carcass. After rigor, the meat was aged at 15degreesC for 0.8, 26 and 72 h and then frozen. The frozen meat was cooked to 75degreesC in an 85degreesC water bath and shear force values obtained from a 1 x 1 cm cross-section. The shear force values of meat for 18 and 35degreesC rigor were similar at zero ageing, but as ageing progressed, the 18 rigor meat aged faster and became more tender than meat that went into rigor at 35 C (P<0.001). The mean sarcomere length values of meat samples for IS and 35degreesC rigor at each ageing time were significantly different (P<0.001). the samples at 35degreesC being shorter. When the short sarcomere length values and corresponding shear force values were removed for further data analysis, the shear force values for the 35degreesC rigor were still significantly greater. Thus the toughness of 35degreesC meat was not a consequence of muscle shortening and appears to be due to both a faster rate of tenderisation and the meat tenderising to a greater extent at the lower temperature. The cook loss at 35degreesC rigor (30.5%) was greater than that at 18degreesC rigor (28.4%) (P<0.01) and the colour Hunter L values were higher at 35degreesC (P<0.01) compared with 18degreesC, but there were no significant differences in a or h values. (C) 2002 Elsevier Science Ltd. All rights reserved.