Resistance of Yeast Species to Benzoic and Sorbic Acids and to Sulfur Dioxide

Abstract

Effects of sorbic and benzoic acids and SO2 on the growth and survival of 12 strains of yeasts, differing widely in their preservative resistance, were studied. Exponential phase cultures not adapted to preservative were tested under anaerobic conditions at pH 3.5. In general, species tolerant of one preservative were also tolerant of the others, but significant differences in the relative effectiveness of the preservatives were found in some species. Maximum tolerated levels of benzoic acid ranged from 0.5 mM for Hansenula anomala to 4 mM for Zygosaccharomyces bailii. The range in tolerance to SO2 was 0.05 mM free SO2 for Klockera apiculata to 2.8 mM for Z. bailii. The principal effect of sorbic and benzoic acids was to reduce cell yield. At higher concentrations, growth rates and lag times were affected. Benzoic acid generally inhibited growth less than sorbic acid, but had a greater effect on lag time and so had a similar overall degree of effectiveness. Cultures treated with SO2 characteristically showed long lag times of up to 600 h. Reductions in growth rate and final yield were often not apparent, mainly because SO2 became bound by metabolic products.