Undesirable flavor caused by excessive higher alcohols restrains the development of the wheat beer industry. To clarify the regulation mechanism of the metabolism of higher alcohols in wheat beer brewing by the top-fermenting yeast Saccharomyces cerevisiae S17, the effect of temperature on the fermentation performance and transcriptional levels of relevant genes was investigated. The strain S17 produced 297.85 mg/L of higher alcohols at 20 °C, and the production did not increase at 25 °C, reaching about 297.43 mg/L. Metabolite analysis and transcriptome sequencing showed that the metabolic pathways of branched-chain amino acids, pyruvate, phenylalanine, and proline were the decisive factors that affected the formation of higher alcohols. Fourteen most promising genes were selected to evaluate the effects of single-gene deletions on the synthesis of higher alcohols. The total production of higher alcohols by the mutants Δtir1 and Δgap1 was reduced by 23.5 and 19.66% compared with the parent strain S17, respectively. The results confirmed that TIR1 and GAP1 are crucial regulatory genes in the metabolism of higher alcohols in the top-fermenting yeast. This study provides valuable knowledge on the metabolic pathways of higher alcohols and new strategies for reducing the amounts of higher alcohols in wheat beer.
Keywords: Higher alcohol; Saccharomyces cerevisiae; Temperature; Top-fermenting; Transcriptome; Wheat beer.