Freezing of Water in the Presence of the Ice Nucleation Active Bacterium,<i>Erwinia ananas</i>, and Its Application for Efficient Freeze-drying of Foods

Abstract

Factors affecting the development of the ice nucléation (IN) activity of Erwinia ananas IN-10 were examined, using the degree of supercooling (DS) as a parameter. An aqueous suspension of the bacterial cells or the outer membrane fraction showed two particular DS values, i.e., near 0°C and 3°C. The development of the DS of 0°C required two conditions: a high cell (or membrane) concentration and the presence of a water/glass interface in the system. Sugars inhibited the development of this type of supercooling. The IN activity was stable in the pH range of 5 to 10. On the basis of these data, a possible mechanism for the IN activity development was proposed. The application of the IN activity of the cells to the freeze-drying of high salt containing foods was attempted. It led to a shortening of their freezing times and efficient formation of powdered products.