Comparison of Protective Effects of Several Sugars on Thermal and Freeze Denaturations of Fish Myofibrillar Protein

Abstract

The protective effect of several kinds of sugars on freeze denaturation of carp myofibrillar protein was studied by measuring the rate constant (k_D) for inactivation of its Ca-ATPase.
As the inactivation of Ca-ATPase proceeded in two first order steps, the rate of an early fast step was employed to make a linear relation as a function of sugar concentration (M). The pro-tective effect of sugar on freeze denaturation of myofibrillar protein was estimated from the slope of log k_D versus sugar (M). The protective effect (E) was thus found to become lower in the order of lactitol, glucose, maltitol=sucrose, sorbitol, and maltose. This rank of sugars coincided with that of the same sugars against thermal denaturation of fish myofibrillar protein, which has been previously reported.
It was also found that a relatively lower concentration (0.1-0.3M) of sugar was enough to protect freeze denaturation of myofibriliar protein than that of sugar required to protect thermal denaturation of the same protein.