Abstract: In order to investigate the changes in the growth state of different yeast species in a mixed culture and the factors affecting their interaction, the effects of initial glucose concentration, pH, and ethanol concentration on the growth of Saccharomyces cerevisiae (Sc) and Pichia fabianii (Pf) when cultured together were investigated, and the differences in the fatty acid composition of both yeasts were also determined by gas chromatography-mass spectrometry (GC-MS). The results showed that Pf had an obvious inhibitory effect on the growth of Sc during their co-culture under normal conditions. At relatively low sugar concentration and low pH, the growth of Sc was more restrained. At an initial glucose concentration of 2%, the Pf/Sc ratio（the ratio of colony numbers) was 28, and the value was 37 at pH 3.5. With increasing concentration of exogenous ethanol, the growth of Pf was more restrained than that of Sc, and Sc became dominant, suggesting it to be more resistant to ethanol than Pf. The Pf/Sc ratio was 0.5 under 12% ethanol stress. The fatty acid composition of Sc mainly consisted of palmitic acid and palmitoleic acid while that of Pf mainly consisted of oleic acid, linoleic acid and linolenic acid. In the mixed culture, the fatty acid composition was dominated by C18 fatty acids, and the linoleic acid and linolenic acid produced by Pf could inhibit the growth of Sc. These results could provide a basis for further research on the interaction of different yeasts in the mixed culture at the transcriptome level and the quality control of fermented products.

Key words: mixed culture, initial glucose concentration, pH, ethanol, fatty acid