Antifungal activity of yeasts and lactic acid bacteria isolated from cocoa bean fermentation processes

A collection of more than 400 yeasts and 200 lactic acid bacteria (LAB) was created by a four-year experimentation, in Ivory Coast and Cameroon, on spontaneous cocoa bean fermentation processes. The antifungal activity of the strains was assessed towards six fungi isolated from both fermented and dried cocoa beans, belonging to Aspergillus and Penicillium genera. It has been generally accepted that fungi are not beneficial to cocoa bean and chocolate quality. Their presence during fermentation, drying and storage has been linked to flavor defects and health risk due to the production of mycotoxins. Thus, the aim of this study was to select, from the collection, yeast and LAB strains limiting fungal growth, to be used in application of biological control of fungi during cocoa production. An initial screening was carried out by using the overlay method where the plates, overlaid with malt extract soft agar inoculated with fungal spore suspension, were examined for zone of inhibition around LAB and yeasts streaks. Then, the most active strains were used in direct inhibition method on pulp medium simulating the cocoa bean substrate. The nature of their antifungal strenght (organic acid and/or proteins as bacteriocins) was also evaluated. The most promising candidates as biological agents to be used in bio protection field trials, belonged to the species Lactobacillus fermentum, Lactobacillus plantarum and Saccharomyces cerevisiae.