以发酵度较高的非絮凝性的啤酒酵母菌株X6和发酵度较低、絮凝性较强的啤酒酵母菌株N1为亲本进行原生质体融合。用亚硝酸诱变原养型的菌株X6,经筛选得到一株需酪素水解物的营养缺陷型菌株X6~20。采用正交试验法分别优化菌株X6~20和N1的原生质体形成和再生的条件。用X6~20菌株的原生质体作为受体和热灭活的N1菌株原生质体作为供体进行融合。融合株经三角瓶发酵筛选,得到一株较优良的融合株GR5。该融合株的絮凝性较强(本斯值为2.7),以12°Bx麦芽汁为培养基,用500 L的发酵罐在12℃下发酵,发酵至第8 d菌株GR5的发酵度为69.2%,发酵液中的双乙酰含量为0.0498 mg/L、乙醛含量为6.34 mg/L,总高级醇含量为74.4mg/L。融合株GR5具有双亲的优点,发酵的啤酒风味较好,是一株具有工业应用前景的啤酒酿造酵母菌株。Saccharomyces cerevisiae X_6 and N_1 strains were used as the parent strains for protoplast fusion.The strain X_6 was a non-flocculence strain with higher fermentation degree and the strain N_1 was a strain with lower fermentation(degree) and stronger flocculence.The auxotrophic mutant X_(6～20) required casein hydrolysate was derived from the(prototrophic) strain X_6 by treatment of nitrous acid(HNO_2) and nutritional identification.The formation and regeneration conditions of strain X_(6～20) and N_1 protoplast were optimized by orthogonal test method.The protoplast fusants were(constructed) with auxotrophic mutant X_(6～20) protoplasts for receptors and heat-inactivated strain N_1 protoplasts for(suppliers).The fusants obtained were fermented and selected.As a result a fine fusant strain GR_5 was obtained.The flocculence of fusant strain GR_5 was stronger with 2.7 mL of burns value.The content of diacetyl,acetaldehyde,total higher(alcohols) in the(fermented) liquid were 0.0498 mg/L,6.34 mg/L,74.4 mg/L,respectively,and the fermentation degree was(69.2 %) in 500 L fermentor using 12°Bx wort as the medimum at 12℃ for 8 days.The sensory evaluation of the beer produced by the fusant strain GR_5 was nice.The results showed that the fusant strain GR_5 with the fine properties from its parent strains and well(applied) prospect in the beer brewing
