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EFFECT OF POSTRIGOR SARCOMERE LENGTH ON MECHANICAL AND STRUCTURAL CHARACTERISTICS OF RAW AND HEAT‐DENATURED SINGLE PORCINE MUSCLE FIBRES

Light microscopy during tensile tests was used to examine the effect ofpostrigor sarcomere length (SL) on mechanical and structural characteristics of raw and heat-denatured (I h at 80C) muscle fibres of porcine longissimus lumborum and the structural deformation mechanisms of such fibres inducing mechanical differences. The effect of the collagenous network associated with single cold-shortened muscle fibres on maximum stress was analysed. Muscle bundles developed rigor at 2C (cold-shortened = CS), at 22C (control = C), and at 22C after being streteched (S) and were frozen (-26C) 12 h postmortem. Diameter, length, and SL of the unextended muscles fibres were measured. Force and displacement were recorded during fibre extension until fracture. CS, C, and S muscle fibres had different SL's in both the raw and heat-denatured state. Maximum stress values of raw CS, C and S muscle fibres were not different. The shape of the stress-strain relationship of heat-denatured CS muscle fibres was sigmoid and not r-shaped. Heat-denatured CS muscle fibres showed a five- and threefold increase in maximum stress and maximum strain, respectively, in comparison with control. CS muscle fibres showed less concerted breaking of myofibrils during fibre extension. The maximum stresses for intact and longitudinally split heat-denatured CS muscle fibres were similar, indicating that the structural mechanisms causing the heat-denatured CS muscle fibres are not related to an intact collagenous network. It is concluded that the maximum stress of heat-denatured muscle fibres or porcine longissimus lumborum varies with postrigor sarcomere length much more than the shear strength of whole meat. This indicates that slippage between muscle fibres may ameliorate postrigor sarcomere length-related effects on maximum stress of muscle bundles.