Competitive yeast action against Aspergillus carbonarius growth and ochratoxin A production

The aim of the present study was to investigate the interaction between 67 different yeast isolates and 3 wild isolates of Aspergillus carbonarius originated from Greek vineyards and characterized by high ochratoxigenic potential. The selected fungi were used either as single cultures or combined in a mixed culture. Yeasts and fungi were grown as mono-cultures and co-cultures in solid (MEA, CYA) and liquid (CY broth) media, grape berries and sterilized grape juice. Fungal growth was monitored by means of colony area measurements. The model of Baranyi and Roberts was further fitted to growth data to provide estimates of the colony area growth rate (cm(2)/day). Moreover, OTA analysis was undertaken for CY broth and agar as well as for grape berries and juice, on the 8th and 15th days of incubation at 25 degrees C. A significant reduction in fungal growth rate, final colony size and toxin production was observed in both liquid and solid media by the different yeast species assayed. The most competitive strains belonged to Saccharomyces, Pichia, Metschnikowia, Dekkera and Rhodotorula genera. Similar results were obtained from inoculated grape berries and grape juice. Specifically, Saccharomyces cerevisiae Y-33 resulted in a decrease in fungal colony area of > 90% and 93% after 3 and 4 days of co-culture, respectively. Similar results were obtained for OTA, where toxin concentration of the highest producer (A. carbonarius F-3) was reduced from 14,983 and 31,565 ng/mL at 8 and 15 days, respectively, to 5 ng/mL and below detection limit (1 ng/g) when co-cultured with S. cerevisiae Y-33. The results of this study could provide a pool of yeast species that must be further investigated for potential application as biological control agents at pre- and post-harvest level in wine and grape juice processing.