USE OF INDIRECT CONDUCTIMETRY FOR PREDICTING GROWTH OF FOOD SPOILAGE YEASTS UNDER VARIOUS ENVIRONMENTAL-CONDITIONS

Four variables (temperature, a(w), pH and potassium sorbate concentration) at three levels were studied to determine their effects on the growth of six yeasts (Candida glabrata, Candida parapsilosis, Debaryomyces hansenii, Pichia membranaefaciens, Saccharomyces cerevisiae and Zygosaccharomyces bailii) isolated from spoiled food products. The detection time (DT) and the maximum change in conductance (MRC) were measured by indirect conductimetry using a Malthus instrument. Temperature, a(w) and potassium sorbate concentration were the most important variables individually and in combination that affected yeast growth. Shelf life of fruit juice at a(w) less-than-or-equal-to 0.96, pH less-than-or-equal-to 3.8 and containing less-than-or-equal-to 0.03% potassium sorbate, when stored at less-than-or-equal-to 10-degrees-C, would be predicted to be greatly extended. Z. bailii was the most resistant of the yeasts in terms of ability to tolerate stress conditions and is proposed as a test species to develop a predictive model for spoilage.