Effect of Protective Agents on the Viability of Geotrichum candidum during Freeze-Drying and Storage

The effect of 3 cryoprotective agents (trehalose, sucrose, and maltose) on the survival of concentrated cultures of Geotrichum candidum was studied. Initially, the effect of the carbohydrates at 9% and 23% concentrations or combined with skim milk (16%) was compared to the control (skim milk alone) immediately after freeze-drying. Two freeze-drying shelf temperatures, 25 degrees C and 35 degrees C, were investigated. Afterwards, the survival of G. candidum freeze-dried with carbohydrates at 23% concentration (alone or combined with skim milk 16%) was studied during 12 wk of storage at 4 degrees C, in the darkness, under vacuum, and at 0% relative humidity. The glass transition temperature (T(g)) of the dehydrated protective agents was measured by differential scanning calorimetry. The results showed that the survival after freeze-drying was proportional to the concentration of the protective agents, with skim milk alone giving poor survival of G. candidum. However, when skim milk was combined with disaccharides, a clear improvement was noted. No general tendency of shelf temperature on the survival of G. candidum was noted immediately after freeze-drying. However, changes in the viability were observed during storage. Glass transition temperature (T(g)) of protective agents linked to their moisture may contribute to predict the stability of lyophilized G. candidum during freeze-drying and storage.