Growth/no growth interfaces of table olive related yeasts for natamycin, citric acid and sodium chloride

The present work uses a logistic/probabilistic model to obtain the growth/no growth interfaces of Saccharomyces cerevisiae, Wickerhamomyces anomalus and Candida boidinii (three yeast species commonly isolated from table olives) as a function of the diverse combinations of natamycin (0–30 mg/L), citric acid (0.00–0.45%) and sodium chloride (3–6%). Mathematical models obtained individually for each yeast species showed that progressive concentrations of citric acid decreased the effect of natamycin, which was only observed below 0.15% citric acid. Sodium chloride concentrations around 5% slightly increased S. cerevisiae and C. boidinii resistance to natamycin, although concentrations above 6% of NaCl always favoured inhibition by this antimycotic. An overall growth/no growth interface, built considering data from the three yeast species, revealed that inhibition in the absence of citric acid and at 4.5% NaCl can be reached using natamycin concentrations between 12 and 30 mg/L for growth probabilities between 0.10 and 0.01, respectively. Results obtained in this survey show that is not advisable to use jointly natamycin and citric acid in table olive packaging because of the observed antagonistic effects between both preservatives, but table olives processed without citric acid could allow the application of the antifungal.

► Cocktails for each yeast species were used instead of only one strain.
► Natamycin alone inhibited yeast growth at very low concentrations.
► The presence of increasing concentrations of citric acid produced a loss of activity in the antimycotic.
► For S. cerevisiae and C. boidinii, salt concentrations between 4 and 5% stimulated yeast growth.
► However, this last behavior was not noticed for W. anomalus.