THE EFFECT OF CRYOPROTECTANTS ON THE SURVIVAL RATE OF SACCHAROMYES CEREVISIAE IN A FREEZE-DRIED GELATIN MATRIX

This study was carried out to determine the effect of cryoprotectants on the survival rate of yeast. The yeast entrapped in gelatin matrix which is mixed with saccharose, hydroxyethylstarch, trehalose, lactose, caboxymethyl cellulose, κ-carrageenan as cryoprotectants was frozen at -40 °C, -30 °C, and -18°C in one-dimensional heat transfer system (Neumann's Model), respectively. After freeze drying gelatin matrix was cut horizontally into every 5 mm thickness from the bottom and measured their pore sizes. The freezing temperature (-40°C, -30°C, and -18°C) during freezing process affected the freezing rate. At freezing temperature, the partial freezing rate in the matrix was depending on this distance. The higher the sample distances from the bottom, the lower the partial freezing rate. It was found that the concentration of cryoprotectants influenced on the freezing rate. Besides, the different survival rate of yeast was depending on the cryoprotectants and freezing rate. The highest survival rate was obtained from the matrix with saccharose and trehalose. The ice dendrite size formed in matrix during freezing process at -18°C, -30 °C and -40 °C showed a direct relationship with freezing rate and concentration. In the matrix, the maximum primary ice dendrite size was 215.88 μm at 1% and minimum primary ice dendrite size was 145.6 μm at 5% from the experiment at -18°C.