CALORIMETRIC DETERMINATION OF INHIBITION OF ICE CRYSTAL-GROWTH BY ANTIFREEZE PROTEIN IN HYDROXYETHYL STARCH SOLUTIONS

Differential scanning calorimetry and cryomicroscopy were used to investigate the effects of type I antifreeze protein (AFP) from winter flounder on 58% solutions of hydroxyethyl starch. The glass, devitrification, and melt transitions noted during rewarming were unaffected by 100 mug/ml AFP. Isothermal annealing experiments were undertaken to detect the effects of AFP-induced inhibition of ice crystal growth using calorimetry. A premelt endothermic peak was detected during warming after the annealing procedure. Increasing the duration or the temperature of the annealing for the temperature range from -28 and -18-degrees-C resulted in a gradual increase in the enthalpy of the premelt endotherm. This transition was unaffected by 100 mug/ml AFP. Annealing between -18 and -10-degrees-C resulted in a gradual decrease in the premelt peak enthalpy. This process was inhibited by 100 mug/ml AFP. Cryomicroscopic examination of the samples revealed that AFP inhibited ice recrystallization during isothermal annealing at -10-degrees-C. Annealing at lower temperatures resulted in minimal ice recrystallization and no visible effect of AFP. Thus, for 100 mug/ml AFP to have a detectable influence on thermal events in the calorimeter, conditions must be used that result in significant ice growth without AFP and visible inhibition of this process by AFP.