Softening Mechanism of Vacuum-cooked Squid Muscle

Abstract

A soft-type cooked squid muscle (mantle of Todarodes pacificus) was prepared by vacuum cooking, and its sensory and rheological properties and changes in muscle proteins were investigated to determine the softening mechanism. The soft-type sample was prepared by heating for one hour at 60°C and was compared with the sample prepared by heating for one hour at 80°C. The intramuscular collagen of both samples was assumed to be solubilized since the outer skin comprising the third and forth layers disappeared. The rupture stress of the former sample measured by breaking both perpendicular and parallel to the muscle fibers encircling the mantle was smaller than that of the latter sample and the difference of the values between the samples was remarkably large for the breaking parallel to the muscle fibers. SDS-PAGE analysis demonstrated that heating of squid muscle induced irreversible liberation of actin from myofibrils. Such reactions proceeded more prominently at 60°C than at 80°C with most of the liberated actin being soluble even after two hours of cooking at 60°C. All results suggested that the extensive liberation and solubilization of actin from myofibrils induced by a lower temperature heating as well as the solubilization of intramuscular collagen was responsible for softening of the vacuum-cooked squid muscle.