选育抗老化啤酒酵母提高啤酒风味稳定性的研究

Improvement of Beer Flavor Stability by Screening Anti-staling Brewers' Yeast

对一株啤酒酵母青②进行紫外线诱变 ,在蛋氨酸浓度为 15g L的耐性平板上筛选获得一株A2 7菌株。为使A2 7菌株的蛋氨酸耐性特征稳定遗传 ,在 11℃、稀释率为 0 0 35h- 1 的条件下对A2 7菌株进行高浓度蛋氨酸 (2 0g L)连续驯养 ,然后分离得到一株MI4 菌。在锥形瓶中连续发酵 5代后 ,与A2 7菌株相比 ,MI4 菌株发酵液中GSH浓度高4 4 % ,TBA值低 2 4 % ,主酵液RSV值高 77% ,且遗传稳定性明显提高 :连续传代 5次后 ,MI4 菌株胞内GSH含量基本不变 ,而A2 7菌则下降了 2 2 %。在相同的糖化和发酵工艺条件下 ,对优选株MI4 和出发株啤酒酵母青②进行 1m3发酵罐中试。与出发株青②相比 ,两者的总高级醇与酯量几乎不变 ,常规指标没有显著差别 ,品尝风味也基本一致。但MI4 菌株发酵液中GSH浓度提高了 30 % ,TBA值降低了 19% ,成品啤酒的RSV值则提高了 92 % ,表明优选株MI4是一株具有抗老化能力的优良啤酒酵母 。

In order to improve the flavor stability of beer, a brewers' yeast mutant, A 27, was selected for methionine (15 g/L) resistance after UV mutagenesis. Compared with the parent strain ②, the glutathione concentration in the main fermentation broth of strain A 27 increased by 20%, the carbonyl compound content (TBA value) decreased by 14%, and the flavor resistance staling value (RSV value) increased by 37%. To obtain a genetically-stable mutant, the culture of strain A 27 was domesticated by continuously feeding a medium supplemented with high concentration of methionine (20 g/L) at a dilution rate of 0.035 h -1 at 11℃, which lead to the identification of M I 4. Compared with strain A 27, the glutathione content of strain M I 4 increased by 44%, the TBA value decreased by 24% and the RSV value increased by 77%. To compare the genetic stability, strains M I 4 and A 27 were inoculated into flasks and transfered continuously 5 times. The intracellular glutathione content of strains M I 4 kept constant while that of strain A 27 decreased by 22%. Pilot-scale experiments were carried out in a 1 m 3 fermentor, using the same mashing and fermentation conditions. Comparing strain M I 4 with the original parent strain ②, the concentration of total long-chain alcohol and ester was at a similar level. Furthermore, no significant difference in routine fermentation parameters was found. Most important, flavor test of beer demonstrated that typical Tsingtao beer flavor was kept after the mutagenesis and domestication, while the glutathione content in the finished beer of strain M I 4 increased by 30%, the TBA value decreased by 19% and the RSV value increased by 92%. All above results demonstrate that strain M I 4 is an excellent anti-staling brewers' yeast, and therefore has great potential for improvement of the flavor stability of Tsingtao beer.