Inhibition of spoilage yeasts in cheese by killer yeast Williopsis saturnus var. saturnus

Williopsis saturnus var. saturnus is a known killer toxin-producing yeast. The effects of this yeast as a biopreservative against spoilage yeasts (galactose fermenting) were investigated in cheeses made under laboratory conditions. At an inoculation level of ∼ 106 CFU/g of cheese, this killer yeast inhibited growth of lactose non-fermenting but galactose-fermenting yeast Saccharomyces cerevisiae VL1 inoculated at ∼ 103 CFU/g; it also inhibited growth of lactose-fermenting and galactose-fermenting yeast Kluvyveromyces marxianus ATCC8640 inoculated at ∼ 103–104 CFU/g in the cheeses manufactured with galactose-producing starter culture Streptococcus thermophilus. In contrast, the two spoilage yeasts grew to ∼ 106 CFU/g from the initial cell count of ∼ 103 CFU/g without the killer yeast. This study indicated that W. saturnus var. saturnus could be an effective biopreservative for cheese spoilage control.