Mannitol and erythritol reduce the ethanol yield during Chinese Baijiu production

Chinese Baijiu is prepared using multiple microbial strains and complex metabolites by simultaneous saccharification and fermentation (SSF). Yeasts are challenged by various endogenous and exogenous factors, detrimentally affecting the ethanol yield. It is imperative to identify and control inhibitory factors. In the present study, microbial taxa and metabolites during Baijiu fermentation were evaluated to identify inhibitors of ethanol production. We found that filamentous fungi and Bacillus, contributing to saccharification, were negatively related to the ethanol content (Spearman's |rho| 0.5, P < 0.05). To explore how they affect ethanol production, ten filamentous fungi and three Bacillus strains were isolated. In addition to glucose and maltose, polyols were simultaneously generated by filamentous fungi and Bacillus via the hydrolysis of starch, among which mannitol and erythritol had the highest contents of up to 41.56 +/- 2.01 g/kg and 16.16 +/- 1.13 g/kg, respectively. The presence of mannitol and erythritol inhibited ethanol production by the functional yeasts Saccharomyces cerevisiae and Pichia kudriavzevii. The presence of 10.0 g/L mannitol significantly (P < 0.01) decreased the ethanol yield of S. cerevisiae by 12.67% (from 39.34 +/- 0.02% to 32.71 +/- 0.49%). These results revealed that polyols may inhibit the production of Baijiu and other fermented foods, suggesting that the origin and influence of polyols should be a focus of future research.