Inhibition of the growth and ochratoxin A production by Aspergillus carbonarius and Aspergillus ochraceus in vitro and in vivo through antagonistic yeasts

Aspergillus carbonarius (AC) and Aspergillus ochraceus (AO) are the major ochratoxin A (OTA)-producing fungi isolated from grapes. Seventy-three yeast strains from 10 species were tested for their capabilities in inhibiting the growth and OTA production by AC and AO in agar medium and grape berries using a co-culture method for in vitro and in vivo experiments, respectively. Results showed that five yeast strains, namely, Candida zemplinina M3, Saccharomyces cerevisiae M114 and C297, Pichia kluyveri M117, and Metschnikowia aff. fructicola M179, significantly inhibited AC and AO in agar medium and grape berries. OTA production in grape berries also significantly decreased. The inhibition efficacy varied with the yeast used. Comparatively, M114 showed the highest reduction of decay incidence of 80% and 40% caused by AC and AO, respectively. The spore germination of AC was inhibited when co-cultured with M114 in liquid cultivation but not when co-cultured in yeast-free supernatant. However, the yeast-free supernatant obtained from 3 d of co-culture of AC and M114 inhibited the germination of fungal spores. The population of M114 in grape berries inoculated with AC was higher than that of the control, particularly at 72 h (28.35 times higher). The volatile compounds produced by M114 had no effect on AC growth. In summary, five strains of yeast that can inhibit growth and OTA production by AC and AO were obtained. Results demonstrated the intrinsic mechanism of the inhibition effect, which was possibly attributed to the competition for space and nutrients of fungi and yeasts or the production of antifungal metabolite(s) by yeast in the co-culture.