Transcriptional Analysis of Mixed-Culture Fermentation of Lachancea thermotolerans and Saccharomyces cerevisiae for Natural Fruity Sour Beer

Abstract

Increasingly high interest in yeast–yeast interactions in mixed-culture fermentation is seen along with beer consumers’ demands driving both market growth and requests for biotechnological solutions that can provide better sensory characteristics. In this study, Lachancea thermotolerans and Saccharomyces cerevisiae with a cell population ratio of 10:1 were inoculated for sour beer fermentation while the process conditions within the brewing industry remained unchanged. With L. thermotolerans producing lactic acid (1.5–1.8 g/L) and bringing down the pH to 3.3–3.4 whilst adding no foreign flavors herein, this study revealed a new natural, fruity sour beer with a soft, sour taste. In this study, the double-yeast mixed-culture fermentation produced more flavor substances than a single-culture process, and plenty of isobutyl acetate and isoamyl acetate enhanced the fruit aroma and balanced the sour beer with a refreshing taste. While playing a positive role in improving the beer’s quality, the double-yeast mixed-culture fermentation developed in this study helps to offer an alternative mass production solution for producing sour beer with the processes better controlled and the fermentation time reduced. The stress responses of the L. thermotolerans during the fermentation were revealed by integrating RNA sequencing (RNA-Seq) and metabolite data. Given that the metabolic flux distribution of the S. cerevisiae during the fermentation differed from that of the non-Saccharomyces yeasts, transcriptional analysis of non-Saccharomyces yeast and S. cerevisiae could be suitable in helping to develop strategies to modulate the transcriptional responses of specific genes that are associated with the aroma compounds released by S. cerevisiae and non-Saccharomyces yeasts. In the case of some non-Saccharomyces yeast species/strains, the diversion of alcoholic fermentation and the formation of a great number of secondary compounds may, in part, account for the low ethanol yield.