Characterization of bacteria and yeasts isolated from traditional fermentation starter (Fen-Daqu) through a 1H NMR-based metabolomics approach.

Daqu is a traditional fermentation starter for the production of baijiu and vinegar. It is an important saccharifying and fermenting agent associated with alcoholic fermentation and also a determining factor for the flavour development of these products. Bacterial and yeast isolates from a traditional fermentation starter (Fen-Daqu) were examined for their amylolytic activity, ethanol tolerance and metabolite production during sorghum-based laboratory-scale alcoholic fermentation. The selected strains (Bacillus licheniformis, Pediococcus pentosaceus, Lactobacillus plantarum, Pichia kudriavzevii, Wickerhamomyces anomalus, Saccharomyces cerevisiae, and Saccharomycopsis fibuligera) were blended in different combinations, omitting one particular strain in each mixture. 1H nuclear magnetic resonance (NMR) spectroscopy coupled with multivariate statistical analysis was used to investigate the influence of the selected strains on the metabolic changes observed under the different laboratory-controlled fermentation conditions. Principal component analysis showed differences in the metabolites produced by different mixtures of pure cultures. S. cerevisiae was found to be superior to other species with respect to ethanol production. S. fibuligera and B. licheniformis converted starch or polysaccharides to soluble sugars. Lactic acid bacteria had high amylolytic and proteolytic activities, thereby contributing to increased saccharification and protein degradation. W. anomalus was found to have a positive effect on the flavour of the Daqu-derived product. This study highlights the specific functions of S. cerevisiae, S. fibuligera, B. licheniformis, W. anomalus and lactic acid bacteria in the production of light-flavour baijiu (fen-jiu). Our results show that all investigated species deliver an important contribution to the functionality of the fermentation starter Daqu.