高温高浓发酵工业啤酒酵母菌种的构建

Construction of industrial brewing yeast for fermentation under high temperature and high gravity condition

摘要:

高温高浓发酵技术作为一项新兴的啤酒生产技术，它为啤酒生产带来诸多利益的同时，也存在着发酵结束后酵母絮凝性下降、高级醇生成量过高等系列问题。为提高高温高浓发酵条件下酿酒酵母的絮凝性同时降低高级醇的合成能力，首先构建了以酿酒酵母BAT2基因为整合位点过表达FLO5基因的菌株，重组菌株S6-BF的絮凝性达到67.67%，比出发菌株S6提高了29%，而高级醇生成量仅降低5.9%；进一步构建以BAT2基因为整合位点再次过表达FLO5 基因的菌株，与出发菌株S6相比，重组菌株S6-BF2的絮凝性提高了63%，达到85.44%，高级醇生成量下降至159.58 mg/L，降低了9.0%；通过弱化线粒体支链氨基酸转氨酶 (BAT1) 的表达，高级醇的生成量得到进一步的降低，达到142.13 mg/L，比原始菌株S6降低了18.4%，同时重组菌株S6-BF2B1的絮凝性没有受到影响；风味物质的测定结果表明啤酒中醇酯比例较为合理。研究结果对工业啤酒酵母发酵后的沉降分离和提高啤酒风味品质有着重要的意义。

Abstract:

As a new beer fermentation technology, high temperature and high gravity fermentation has brought many benefits to brewery industry, but there are also a series of problems such as the decrease of yeast flocculation ability at the end of fermentation and the high concentration of higher alcohols. To increase yeast flocculation ability and reduce the production of higher alcohols in high temperature and high gravity fermentation of beer, BAT2 was replaced by the FLO5 expression cassette to obtain the mutant strain S6-BF2. Real-time quantitative PCR showed that the relative transcriptional level of FLO5 in S6-BF2 improved 17.8 times compared with that in S6. The flocculation ability of mutant S6-BF2 heightened by 63% compared to that of the original strain S6, and the concentration of higher alcohols decreased from 175.58 mg/L to 159.58 mg/L in high temperature and high gravity fermentation of beer. Moreover, the activity of mitochondrial branched-chain amino acid transferase was repressed, resulting in the production of higher alcohols of 142.13 mg/L, reduced by 18.4% compared to that of the original strain S6, meanwhile, the flocculation ability of mutant S6-BF2B1 kept unchanged compared to the mutant S6-BF2. The determination result of flavor compounds showed that the higher alcohols/ester ratio in beer was reasonable. This research has suggested an effective strategy for enhancing yeast flocculation ability and decreasing production of higher alcohols in high-temperature and high-gravity brewing.