Thermal treatment of yeast cells in a strawberry product enumeration procedure

Abstract

The purpose of this work was to set up an enumeration procedure to quantify the heat resistance of yeasts in food products in order to establish pasteurization schedules. The heat resistance of Saccharomyces cerevisiae was studied in a fruit-based product. Experiments were carried out to evaluate the number of viable cells after heat treatment at temperatures between 60 and 65°C. Among different enumeration methods the surface-spread method was selected to enumerate viable cells. The study shows that the plates should be incubated long enough for 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.