Potential of yeasts as biocontrol agent of fungal growth on the surface of Ras Cheese

Abstract

The antifungal activity of seven selected yeast strains namely Saccharomyces cerevisiae, Candida sake, Candida tropicalis, Candida utilis, Pichia anomala, Pichia membranifaciens and Pichia guillermondii against five species of fungi (Aspergillus niger, Aspergillus ustus, Aspergillus flavus, Aspergillus fumigates and Penicillium sp.) previously isolated from the surface of commercial Egyptian Ras Cheese were tested using diffusion method on agar plates. The ability of yeasts to produce lipase, caseinas and lactase enzymes were also examined. All the studied yeast strains were applied separately as life cells and as heat-killed cells on the surface of laboratory manufactured Ras Cheese discs before covering with wax to investigate their inhibitory effect on growth of cheese contaminant fungi during storage for six months under ripening conditions.

            The obtained results indicated that all the examined yeast strains showed varied degrees of growth inhibition against all the studied molds cultivated on agar plates. Adherence of life yeast cells on the surface of Ras Cheese discs were more effective in reducing or preventing growth of the contaminant molds than killed yeast cells. Most of the studied yeasts were not able to produce hydrolytic enzymes and the sensory evaluation test of the treated cheese samples showed good acceptability after six months of storage.