THERMAL INJURY AND RECOVERY OF Saccharomyces cerevisiae

Abstract

ABSTRACTThis investigation was undertaken to determine the effect of mild heat treatments on the survival, injury and recovery of Succharomyces cerevisiae. Cells of S. cerevisiae strain Y‐25 were grown in yeast extract‐malt extract, harvested, by centrifugation, washed 2X, and suspended in 0.1M phosphate buffer at pH 7.0. Cell suspensions were heated in a water bath at various temperatures and survivors were determined by plating on Plate Count Agar (PCA) and Potato Dextrose Agar (PDA) with or without acidification. The heated suspensions were stored at room temperature (20–22°C) and sampled at various periods to monitor the recovery of injured cells. Using the system described above, heat‐injured cells of S. cerevisiue were not recovered when plated on PCA or PDA immediately after heating. Heat‐injured cells were recovered on the plating media after storage in buffer at room temperature, but 5–7 days were required for maximum recovery. Initially, the rate of recovery on PCA was greater than on PDA; this was not attributable to the differences in pH of the media, but apparently was due to nutritional factor(s). Resting cells of S. cerevisiae did not undergo a comparable recovery when heated and stored in either water or buffer.