酒醅来源酵母菌合成异戊醇能力与途径解析

【背景】异戊醇是酵母菌在白酒发酵过程中通过氨基酸合成代谢途径和氨基酸分解代谢途径合成的主要高级醇，其含量影响白酒饮用的舒适度。【目的】分析和比较分离自浓香型白酒酒醅中的酵母菌合成异戊醇的能力，揭示酵母菌合成异戊醇的途径。【方法】从酒醅中分离具有异戊醇合成能力的酵母菌株，比较不同生长时期酵母菌合成异戊醇的能力，通过前体物代谢分析它们合成异戊醇的途径。【结果】分离自酒醅的5株酵母的异戊醇合成能力从强到弱依次为Naumovozyma castellii JP3-1、Saccharomyces cerevisiae JP3、Pichia fermentans JP22、Pichia kudriavzevii JP1和Naumovozyma dairenensis CBS421。这些酵母合成异戊醇的时期主要在对数生长期，N. castellii JP3-1、P. fermentans JP22和N. dairenensis CBS421在稳定生长期也合成异戊醇。S. cerevisiae JP3、N. castellii JP3-1和N. dairenensis CBS421在整个生长时期主要通过Harris途径合成异戊醇；P. kudriavzevii JP1在整个时期主要通过Ehrlich途径合成异戊醇；P. fermentans JP22在对数生长期通过Harris途径和Ehrlich途径合成异戊醇的能力接近，在稳定生长期主要通过Harris途径合成异戊醇。【结论】本研究揭示了酒醅来源5个属种酵母合成异戊醇的途径、能力与其生长时期的关系，研究结果可为解析浓香型白酒发酵过程异戊醇合成、积累机制及实施白酒发酵过程异戊醇合成的精准调控提供理论依据。

Synthesis ability and pathways of isoamyl alcohol in yeasts from fermented grains

Background] Isoamyl alcohol is the main higher alcohol synthesized by yeast via the catabolic Ehrlich pathway or by anabolic amino acid metabolism during Chinese spirit fermentation, and the content of isoamyl alcohol influences the drinkability of Chinese spirit. Objective] To analyze and compare the ability of yeasts isolated from fermented grains to synthesize isoamyl alcohol and reveal the synthetic pathways of isoamyl alcohol in the yeasts.Methods] Isoamyl alcohol-synthesizing yeast strains were isolated from fermented grains of strong-aroma Chinese spirit, and their capability of synthesizing isoamyl alcohol at different growth phases was compared. Moreover, the synthetic pathways of isoamyl alcohol in these strains were detected based on the metabolism of its precursors. Results] The capability of synthesizing isoamyl alcohol by the five yeast strains isolated from the fermented grains was in the order of Naumovozyma castellii JP3-1>Saccharomyces cerevisiae JP3>Pichia fermentans JP22>P. kudriavzevii JP1>Naumovozyma dairenensis CBS421. Overall, isoamyl alcohol was synthesized mainly at the logarithmic phase, and it was also synthesized at the stationary phase of N. castellii JP3-1, P. fermentans JP22, and N. dairenensis CBS421. In addition, it was synthesized via the Harris pathway in the whole growth periods of S. cerevisiae JP3, N. castellii JP3-1, and N. dairenensis CBS421 and via the Ehrlich pathway in the whole growth period of P. kudriavzevii JP1. At the logarithmic phase, the isoamyl alcohol-synthesizing ability of P. fermentans JP22 through Harris pathway was identical to that through the Ehrlich pathway. However, P. fermentans JP22 at the stationary phase mainly synthesized isoamyl alcohol via the Harris pathway. Conclusion] This study revealed the relationship of the synthesis ability and pathways of isoamyl alcohol in five yeast strains isolated from fermented grains with their growth phase. The result lays a theoretical basis for analyzing the mechanism of isoamyl alcohol synthesis and accumulation in the fermentation process of strong-aroma Chinese spirit and the precisely regulating isoamyl alcohol synthesis during the fermentation of strong-aroma Chinese spirit.