Evaluation of the potential of the yeast Pichia guilliermondii as a biocontrol agent against Aspergillus flavus and fungi of stored soya beans

The ability of Pichia guilliermondii to inhibit growth of grain microflora was studied using naturally contaminated soya beans and sterilized soya beans artificially inoculated with Aspergillus flavus . When A. flavus (at a spore concentration of 10 2 spores ml −1 ) and P. guilliermondii (at concentrations of 10 7 or 10 9 cells ml −1 ) were applied simultaneously to sterilized soya beans, fungal proliferation, as measured by colony-forming-units counts, was markedly inhibited during 16 d of storage. Application of yeast cells 3 d prior to fungal inoculation resulted in decreased inhibitory activity. The inhibitory effect of the yeast was compared with that of propionic acid using naturally infested soya beans at two levels of moisture content (11 and 16%). At both levels the yeast prevented fungal proliferation on the grain for a limited period but propionic acid showed better fungistatic activity. Of the two methods of yeast application tested — spraying or dipping — dipping provided a longer inhibitory period. However, the yeast treatment did not prevent the increase in the level of free fatty acids (an indicator of the incipient grain deterioration) at the later stages of the storage period.