Ethyl carbamate (EC), a multisite carcinogenic compound, is naturally produced from urea and ethanol in alcoholic beverages. In order to reduce the content of EC in wine, the accumulation of arginine in Saccharomyces cerevisiae was regulated by genetic modifying genes involved in arginine transport and synthesis pathways to reduce the production of urea. Knockout of genes encoding arginine permease (Can1p) and amino acid permease (Gap1p) on the cell membrane as well as argininosuccinate synthase (Arg1) respectively resulted in a maximum reduction of 66.88% (9.40µg/L) in EC, while overexpressing the gene encoding amino acid transporter (Vba2) reduced EC by 52.94% (24.13µg/L). Simultaneously overexpressing Vba2 and deleting Arg1 showed the lowest EC production with a decrease of 68% (7.72µg/L). The yield of total higher alcohols of the mutants all decreased compared with that of the original strain. Comprehensive consideration of flavor compound contents and sensory evaluation results indicated that mutant YG21 obtained by deleting two allele coding Gap1p performed best in must fermentation of Cabernet Sauvignon with the EC content low to 9.40μg/L and the contents of total higher alcohols and esters of 245.61mg/L and 41.71mg/L respectively. This study has provided an effective strategy for reducing the EC in wine.

Non-Saccharomyces cerevisiae can effectively improve the wine quality by co-fermentation with Saccharomyces cerevisiae. In this study, the effects of Pichia kluyveri DG2 on the flavor characteristics of wine when co-culturing with S. cerevisiae MT were systematically researched. Compared to the fermentation by S. cerevisiae alone, P. kluyveri slowed down the fermentation process slightly but increased the productions of glycerol and esters (8.5% and 142%). Additionally, yield of total higher alcohols reduced in the co-fermentation. The sensory characteristics of the wine obtained by co-fermentation were improved obviously. Transcriptome analysis further showed that 512 genes were differentially expressed in S. cerevisiae in the co-fermentation, of which 318 genes were up-regulated including genes participating in the biosynthesis of flavor compounds in wine and 194 genes were down-regulated including the ones involved in glycolytic and amino acid metabolic pathways. These results indicated that P. kluyveri was a very promising non-S. cerevisiae for co-fermentation to regulate flavor and improve quality of wine.

Regulation of Aroma and Color Characters in ‘Cabernet Sauvignon’ Wines through ‘Coupage’ Technique LING Meng-qi, ZOU Wen-wen, WU Guang-feng, YANG Wei-ming, DUAN Chang-qing, SHI Ying (1.Center for Viticulture & Enology, College of Food Science and Nutritional Engineering, China Agricultural University, Key Laboratory of Viticulture and Enology, Ministry of Agriculture and Rural Affairs, Beijing 100083, China) (2.Chateau ZhihuiYuanshi Co. Ltd., Yinchuan 750026, China) Abstract: To avoid deficiencies in monovarietal wines and improve flavor quality by blending different wines with different proportion through the technique of wine blending after fermentation (‘coupage’), Cabernet Sauvignon wine was regarded as base wine and blended with Cabernet Franc, Marselan, and Petit Verdot wines with proportion of 10%, 20%, 30%, respectively. Gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography triple quadrupole mass spectrometry (HPLC-QqQ-MS/MS) were used to detect flavor compounds, namely, volatile aroma compounds and phenolic compounds. Quantitative descriptive analysis (QDA) and CIELAB model were conducted to evaluate the difference of wine sensory quality. The results showed it was not an efficient way to increase fruity aroma by merely blending wines with high level of esters. Only Cabernet Franc wine with proportion above 20% increased the concentration of acetates in blending wine samples after 6-month bottle aging (p<0.05). Marselan wine with proportion over 10% could promote flower attribute and reduce herbal notes by increasing concentration isoprenoids, and lower the yellow hue at the same time. Petit Verdot wine with proportion of 30% had great contribution to the improvement of phenolic composition, especially by increasing the concentration of flavanols (1.43 times), flavonols (1.27 times) and phenolic acids (4.68 times), which was beneficial for color stabilization. Therefore, it is practicable to regulate aroma and color