Effect of pimaricin on the resistance of Saccharomyces cerevisiae to heat, freezing, and ultraviolet irradiation.

Exposure of washed cells of Saccharomyces cerevisiae C-299 to inhibitory concentrations of pimaricin decreased resistance to lethal temperatures and to freezing and thawing. Varying the pH of the recovery medium had little effect on the decrease in heat resistance, but addition of peptone or yeast extract resulted in a partial recovery of apparent heat resistance. Addition of peptone or calcium ion to the heating menstruum did not affect the reduction in resistance caused by pimaricin. Varying the composition of the recovery medium similarly affected the resistance to freezing the thawing of pimaricin-exposed and unexposed cells. Sensitivity to ultraviolet light was apparently not affected by pimaricin either by preliminary exposure or when irradiated in the presence of pimaricin. It is suggested that pimaricin lowers the heat resistance of S. cerevisiae by depleting essential nutrients of the cells through a disruption of permeability, and that heat-damaged cells cannot resynthesize these nutrients. It is also suggested that spoilage of acid foods by S. cerevisiae may be retarded by a combination of mild heat treatment and the addition of pimaricin.