Recrystallization behavior of ice crystals in sucrose solution in the presence of AFP Type I

Recrystallization rate of ice crystals in 33% sucrose solutions, a model frozen dessert, was measured in the presence of antifreeze protein Type I (AFP type I) at -10°C, which is relevant to practical storage or distribution temperature of frozen dessert. The concentrations of AFP type I were set to 0.01, 0.1, and 1g/ml, respectively. Ice crystals during recrystallization process were observed by using a light microscope equipped with cold stage as follows. 2l sample solution enclosed between two coverslips was placed on the sample stage and cooled to -30°C at 90°C /min. After 10min, sample temperature was elevated to -10°C and recrystallization of ice crystals was observed for about 15 hours. Using the ice crystal images obtained by microscopic digital camera, number-averaged ice crystal size was evaluated by the technique of image analysis. Based on the theory of Ostwalds ripening, recrystallization rate of ice crystals was obtained by analysis of time course of the number-averaged ice crystals size, and effect of addition of AFP type I upon recrystallization rate was evaluated quantitatively. The recrystallization rate of the sample containing 1 g/ml AFP type I was about 13% of that of sample without AFP. However, no significant reduction of recrystallization rate was observed for the samples containing 0.1g/ml or 0.01g/ml AFP type I. These results suggest the followings; first, 1 g/ml AFP type I has strong suppression effect on recrystallization of ice crystals in frozen sucrose at one of practical storage or distribution conditions. Secondly, less than 0.1g/ml AFP type I is no longer effective for suppressing recrystallization of ice crystals.