Ethyl carbamate formation regulated by Saccharomyces cerevisiae ZJU in the processing of Chinese yellow rice wine

Ethyl carbamate (EC) is a probable carcinogen existing in most fermented foods. Throughout traditional fermentation processes, the Chinese fermentation starter plays an important role, but it contains varieties of microorganisms which make inhibiting EC efficiently become a challenge. Therefore, the traditional fermentation starter is substituted with a single yeast strain (Saccharomyces cerevisiae ZJU) to regulate EC catabolism. In this work, S. cerevisiae ZJU can reduce EC formation and the data of EC concentration show that there is 85.6% reduction of EC at most using S. cerevisiae ZJU instead of the traditional fermentation starter. Extracellular urea and citrulline were the leading precursors of EC. The content of amino acids and volatile flavour compounds in the experimental group has no significant influence compared to the natural fermentation. The findings in this work suggest that EC can be regulated by means of the fermentation starters variation.     

YDL080C和LEU2基因敲除对工业黄酒酵母异戊醇生成量的影响

通过敲除生成途径中关键酶的编码基因,对异戊醇在工业黄酒酵母N85中的生成进行了研究。采用融合PCR技术,分别构建类丙酮酸脱羧酶基因（YDL080C）缺失组件\     

不同种类可同化氮素对黄酒酵母产高级醇能力的影响

为研究不同种类可同化氮素对黄酒酵母产高级醇的影响,通过添加不同种类可同化氮素进行2株黄酒酵母的发酵实验,使用GC-MS对发酵液中高级醇进行测定,比较发酵结束时高级醇含量变化。结果表明:RWBL Y1739 LZH异戊醇合成能力较强,RWBL Y1615 ZC β-苯乙醇合成能力较强;可同化氮素的添加对酵母生长、乙醇产生有着重要影响;对于酵母RWBL Y1739 LZH和RWBL Y1615 ZC,无机氮素降低高级醇的效果最好(29.97%~63.15%),氯化铵降低高级醇的幅度最大(62.60%,63.15%),添加特定的氨基酸能加强酵母Ehrlich途径,产生更多高级醇。     

基于PCR方法敲除黄酒酵母精氨酸酶基因的工程菌构建

用一种高效快速的免克隆方法-长侧翼同源PCR（LFH-PCR）,构建基因敲除组件,然后通过化学转化方法把敲除组件转入黄酒酵母细胞中,利用同源重组机制精确敲除精氨酸酶基因（CAR1）,构建了黄酒酵母工程菌株。结果表明,敲除CAR1基因的工程菌与出发菌株相比,酒液中尿素的含量降低了72%,氨基甲酸乙酯含量降低了38%,并且该菌株的遗传稳定性好,发酵性能与出发菌株基本一致。      

Effect of γ‐aminobutyric acid supplementation on the composition of Chinese rice wine

This study investigated the effect of γ‐aminobutyric acid (GABA) supplementation on the composition of Chinese rice wine. GABA was added at 188.5 and 377 mg/L at the beginning of primary fermentation or post‐fermentation. Addition of GABA during primary fermentation had no impact on alcohol and total acid formation or the utilisation of sugar. However, total free amino acids, total essential amino acids and GABA in rice wine supplemented with GABA were significantly lower than the control rice wine without supplementation. Alcohol formation, total acid, sugar content and total essential amino acids were similar compared with the control. However, the GABA post‐supplementation was significantly higher, suggesting that GABA supplementation post‐fermentation process could enhance the GABA content in rice wine. © 2018 The Institute of Brewing & Distilling     

Effect of ‘wheat Qu’ on the fermentation processes and volatile flavour‐active compounds of Chinese rice wine (Huangjiu)

Wheat Qu is a unique saccharifying agent used for Chinese rice wine brewing. In recent years, the impact of wheat Qu on Chinese rice wine flavour has attracted great interest. In this study, Chinese rice wine fermentations were conducted with different saccharifying agents (wheat Qu and mixed commercial enzymes) to study the effect of wheat Qu on the fermentation process and aroma characteristics of Chinese rice wine. Our results showed that wheat Qu not only acted as a saccharifying agent, but also increased yeast activity and the formation of aroma compounds. A higher yeast growth and fermentation rate, in addition to a lower yeast death rate, were observed when wheat Qu was used as a saccharifying agent. Global analysis of the aromatic profiles revealed that the use of wheat Qu greatly promoted the formation of the aroma compounds during a Chinese rice wine fermentation. The concentrations of the volatile phenolic compounds and higher alcohols were higher in the Chinese rice wine samples fermented with wheat Qu. It was concluded that the role of wheat Qu cannot simply be replaced by commercial enzymes and that the Chinese rice wine aromatic profiles can be modulated depending on the amount of wheat Qu used in the fermentation. Copyright © 2013 The Institute of Brewing & Distilling