Studies of Dehydration of Cellular Water in the Freeze-Drying of Microorganisms, with Special Reference to Changes in Cell Viability

Investigation of the removal of cellular water, previously unexamined in freezedrying of microorganisms, and of its direct effect upon cell survival during the drying process have been made using some newly devised technical means. A thin layer of a highly concentrated cell suspension of Escherichia coli in deionized water was frozen in a specially designed ampoule and dried at different temperatures. After drying, the weight of the residual moisture content of the cells was measured and cell survival was determined by viable count following rehydration. The results thus obtained demonstrated that cell survival was reduced as the residual moisture content decreased in the final drying stage. The mechanism of cell injuries resulting from dehydration is discussed with reference to the cellular water and particularly to the unfrozen water, as reported in our previous paper.