Effect of zinc formulations, sodium chloride, and hydroxytyrosol on the growth/no-growth boundaries of table olive related yeasts

• A logistic model for yeasts as a function of Zn, NaCl, and hydroxytyrosol contents was built.
• The model was obtained in synthetic media using two zinc salts formulations.
• ZnCl2 showed greater inhibitory effects than ZnSO4.
• No interaction between Zn and NaCl was observed.
• A slight antagonistic effect between Zn and high hydroxytyrosol content was noticed.

This study uses a mathematical approach to assessing the inhibitory effect of Zn2 + (0–10 mM, obtained from ZnCl2 and ZnSO4) in presence of NaCl (0–8%) and hydroxytyrosol (0–2588 mg/L), on a yeast cocktail formed by species Pichia galeiformis, Pichia kudriavzevii, Pichia manshurica and Candida thaimueangensis obtained from spoilt green olive packages. The logistic/probabilistic models were built in laboratory medium using a total of 1980 responses (1188 for NaCl and 792 for hydroxytyrosol). ZnCl2 showed significantly higher inhibitory effect than ZnSO4 in the presence of both NaCl (p < 0.033) and hydroxytyrosol (p < 0.009). NaCl did not interfere the effect of Zn2 + while hydroxytyrosol, at high levels, had a slight antagonistic effect. According to models, Zn2 + inhibits (p = 0.01) the yeast cocktail in the range 4.5–5.0 mM for ZnCl2, or 8.5–9.5 mM for ZnSO4. Therefore, this work confirms the fungicidal activity of zinc compounds (mainly ZnCl2) in synthetic medium, and also shows that the loss of zinc effectiveness in real green Spanish-style olive packaging is not due to the presence of NaCl or hydroxytyrosol, two of the most abundant chemical compounds in the product.