THERMAL-TREATMENT OF YEAST-CELLS IN A STRAWBERRY PRODUCT ENUMERATION PROCEDURE

The purpose of this work was to set up an enumeration procedure to qua ntify the heat resistance of yeasts in food products in order to estab lish pasteurization schedules. The heat resistance of Saccharomyces ce revisiae was studied in a fruit-based product. Experiments were carrie d out to evaluate the number of viable cells after heat treatment at t emperatures between 60 and 65 degrees C. Among different enumeration m ethods the surface-spread method was selected to enumerate viable cell s. The study showed that the plates should be incubated long enough fo r all injured cells to recover. The degree of cell injury may be such that the recovery only occurs after 10 days of incubation. Experiments showed that after a mild heat treatment in the selected fruit product , the number of resistant cells varied neither with the composition of the plating medium nor with the incubation temperature.