Modeling the inhibitory effects of zinc chloride on table olive related yeasts

This survey examines the inhibitory effects of ZnCl2 on 22 yeast strains of the genera Saccharomyces, Wickerhamomyces, Debaryomyces, Issatchenkia, Candida, Pichia, Kluyveromyces and Torulaspora, all of them isolated from diverse table olive processing. The yeasts were first incubated in a laboratory medium supplemented with different ZnCl2 concentrations (0–250 mg/L) and monitored by means of optical density measurements for 100 h in an automated spectrophotometer at 30 °C. Fractional areas were used to estimate the non-inhibitory concentrations, which ranged from 22 mg/L (Debaryomyces etchellsii TOMC Y24) to 178 mg/L (Candida diddensiae TOMC Y1), and minimum inhibitory concentration, which oscillated from 84 mg/L (Wickerhamomyces anomalus TOMC Y11) to 238 mg/L (C. diddensiae TOMC Y1), of the assayed strains to ZnCl2. Time to kill curves were then obtained by spread plating at three ZnCl2 concentrations (250, 500 and 1000 mg/L) above the highest minimum inhibitory concentration obtained. Data showed that, in some cases, the growth was only ceased, but a clear reduction in the initial number of viable cells (well fitted by means of the Weibull’s equation) was always noticed at the highest ZnCl2 concentration. The results obtained in this work open new alternatives to the use of ZnCl2 as a yeast preservative agent in fermented vegetable (olives, cucumber, capers, etc.) which may be spoiled by these microorganisms.