Effect of Acids and Sorbate Combinations on the Growth of Four Osmophilic Yeasts.

The effects of hydrochloric, citric, lactic, phosphoric and malic acids in combination with potassium sorbate on the growth of Saccharomyces bailii , Saccharomyces acidifaciens ( Saccharomyces bailii var. osmophilus ), Saccharomyces rouxii and Saccharomyces bisporus were evaluated. Double strength potato dextrose broth supplemented with 58% (wt/vol) sucrose, 14% (wt/vol) glucose, and 0.2% agar acidulated to a pH of 5.0 to a final a of 0.88 to 0.89 was used as the growth medium. In general, at 0.05% potassium sorbate, S. rouxii and S. bisporus were more resistant than S. bailii and S. acidifaciens to the antimycotic agent independent of the acid used to acidulate the growth medium, whereas 0.1% potassium sorbate inhibited the growth of the four yeast strains. At 0.05% potassium sorbate, growth occurred (1 log number yeast cells/ml) for S. acidifaciens in the lactic acid/sorbate combination after 36 h of incubation, whereas a bacteriostatic relationship existed for the other acids employed. Citric acid potentiated the antimicrobial effectiveness of 0.05% potassium sorbate at pH 5.0 against the growth of S. rouxii and S. bisporus by either delaying the lag phase or reducing the growth rate.