Breeding of a high tyrosol‐producing sake yeast by isolation of an ethanol‐resistant mutant from a trp3 mutant

A novel breeding strategy for a high tyrosol‐producing sake yeast was developed by isolating an ethanol‐resistant mutant from a tryptophan auxotrophic mutant of a sake brewery yeast. Since tyrosol has antioxidant, cardioprotective and taste‐sharpening effects, increasing the tyrosol level of alcohol beverages could be beneficial in alcohol production. Since the transporters of aromatic amino acids are degraded by several stresses and mutants defective in the synthesis of aromatic amino acids are sensitive to ethanol, it was hypothesized that the degradation of these transporters should be inhibited in ethanol resistant mutants isolated from the auxotrophic mutants of aromatic amino acids, and that the uptake of aromatic amino acids would be increased in the mutants. Consistent with this hypothesis, sake was brewed with the ethanol‐resistant mutant of a tryptophan auxotrophic mutant and the sake was found to contain a lesser content of tyrosine and a higher content of tyrosol relative to the sake brewed with the parental strains. The taste of the sake brewed with the mutant strain could be discriminated from the sake brewed with the parental strains, probably because of the altered concentrations of tyrosol and certain amino acids and organic acids. The results suggest that combining the isolation of an ethanol‐resistant mutant and an auxotrophic mutant is an effective method to breed a brewing strain with a modified metabolism of these substances. Copyright © 2012 The Institute of Brewing & Distilling     

Control of antioxidant beer activity by the mashing process

Beer is considered to be a good source of antioxidants. The composition and the quantity of the antioxidant compounds depend not only on the qualities of the raw materials, but also on the technology processes. Barley and malt represent the main source of antioxidant compounds in beer and the contribution of the hop antioxidants is lower. The influence of the mashing process on the antioxidant activity and polyphenol concentration is crucial. The antioxidant state of the sweet wort and the hopped wort are dependent on the technology processes and the raw materials used. The spontaneous sorption of polyphenols onto wort dregs and the polymerization of catechin and epicatechin lead to decreasing concentrations of individual polyphenols in the final beer. Two methods, based on electron spin resonance were used to determine antioxidant activity. These were the DPPH (2,2‐diphenyl‐1‐picryl‐hydrazyl) assay and the ‘lag time’ assay using free radical spin‐trapping agent PBN (N‐tert‐butyl‐α‐phenylnitrone). HPLC with CoulArray detection was used to measure the concentration of the individual polyphenols. This study focused on the antioxidant compounds and on the correlation of their concentrations with the values of total antioxidant activity depending on the mashing process. A good correlation was found between the decline in the concentrations of DPPH (expressed as ARA2) and concentrations of catechin and epicatechin (in sweet wort samples R² = 0.970, R² = 0.961, respectively, and in hopped wort samples R² = 0.949, R² = 0.956 respectively). Copyright © 2012 The Institute of Brewing & Distilling     

固定化酵母啤酒连续后发酵工艺

将主发酵进行完毕后的嫩啤酒先离心除去酵母,再经加热处理,冷却后通入装有木片作为固定化酵母载体的固定床反应罐进行连续后酵。通过试验确定工艺条件,并将连续后酵与传统后酵工艺生产的啤酒进行对比。试验结果表明,室温下,固定化16 h为宜,热处理温度为80℃,时间为10 min;设定后发酵温度为10℃,滞留时间为3.1 h,双乙酰还原速度大为提高,缩短了酒龄;经过风味测定和感官品评得出,采用连续后发酵工艺生产的啤酒,品质上无明显缺陷。     

1株浓香型白酒酵母对糟醅的乙醇发酵作用

将1株分离自浓香型白酒糟醅的酵母菌分别接种于装有入窖粮糟和无菌糟醅浸提液中的三角瓶中,发酵后固态糟醅乙醇浓度达到15.0%(V/V,下同),比其空白对照和窖池内正常发酵糟醅分别高8.0%和8.2%;糟醅浸提液中的乙醇浓度也达到了12.3%。经部分生理生化特征检测和26S rDNA D1/D2区系统发育分析,鉴定该菌为伊萨酵母(Issatchenkia sp.),最适生长温度为34℃,在28～40℃下都能生长,能够耐受pH 3.5以下的生长环境。     

上面发酵小麦啤酒酵母发酵性能的比较研究

采用3株上面发酵酵母在相同条件下酿造了同等浓度(11°Bx)的小麦啤酒,在此过程中对各种酵母在扩培期的悬浮细胞数、酵母的凝聚性、外观糖度的变化、双乙酰的还原以及高级醇和酯类物质的形成进行了跟踪检测比较,并测定了啤酒的各种理化指标。结合它们所酿制啤酒的感官品评,得出了它们各自的优良特性。     

活性干酵母在酱油中的应用

酵母菌在酱油及酱类生产中能产生特殊的香味,是酱香的重要来源;在酱油生产中添加酱油活性干酵母,能使酱油中的乙醇和总酯的含量等指标明显提高,酱油品质显著改善;酱油活性干酵母作为一种活性干菌体使用、存储也非常方便.     

酵母培养物对3种肠道有益菌体外增殖的影响

该文研究了酵母培养物对双歧杆菌、嗜酸乳杆菌和植物乳杆菌体外增殖的影响。结果显示由发酵培养基制备的酵母培养物具有较好地促进肠道有益菌体外增殖的效果,且添加1%酵母培养物能极显著促进嗜酸乳杆菌和植物乳杆菌体外增殖,但对双歧杆菌的影响不显著;添加5%或10%酵母培养物均能极显著促进3种肠道有益菌体外增殖。通过有益菌生长动力学曲线可以看出添加酵母培养物可以缩短延滞期,延长对数期,且生物量有大幅度提高。     

Formation of styrene dependent on fermentation management during wheat beer production

Styrene is formed by the thermal decarboxylation of cinnamic acid during wort boiling or by enzymatic decarboxylation during fermentation. The enzymatic reactions proceed in parallel to the decarboxylation of ferulic- and p-cumaric acid to 4-vinylguaiacol and 4-vinylphenol by the same decarboxylase enzyme. However, the formation of styrene occurs much faster and all available cinnamic acid in wort was converted completely within a few hours. Moreover, the comparison of various manufacturing parameters shows that a higher fermentation temperature of 25 °C compared to 16 °C and an open fermentation management lead to a rapid decrease of styrene. This allows minimising the content of styrene in beer while maintaining the typical wheat beer flavours.     

Natural occurrence of citrinin in widely consumed traditional Chinese food red yeast rice, medicinal plants and their related products

Natural occurrence of citrinin in traditional Chinese food red yeast rice, medicinal plants and their related products has been investigated for the first time. Samples were extracted by methanol/water, cleaned-up with an immunoaffinity column (IAC) and quantified by HPLC-FLD. The mean recoveries, spiking with citrinin at levels ranging from 25 to 200 μg/kg, were 73.4-92.5%, and the coefficients of variations (CVs) were 1.4-7.9%. The limit of detection (LOD) was 0.8 μg/kg. Out of a total of 109 widely consumed samples analysed, citrinin was detected in 31 samples (28%) ranging from 16.6 to 5253 μg/kg, all of them derived from 59 red yeast rice and related products. None of the remaining 50 medicinal plants samples was found to contain citrinin. The positive samples were further confirmed using LC-ESI-MS/MS.     

Breeding of lager yeast with Saccharomyces cerevisiae improves stress resistance and fermentation performance

Lager beer brewing relies on strains collectively known as Saccharomyces carlsbergensis, which are hybrids between S. cerevisiae and S. eubayanus‐like strains. Lager yeasts are particularly adapted to low‐temperature fermentations. Selection of new yeast strains for improved traits or fermentation performance is laborious, due to the allotetraploid nature of lager yeasts. Initially, we have generated new F1 hybrids by classical genetics, using spore clones of lager yeast and S. cerevisiae and complementation of auxotrophies of the single strains upon mating. These hybrids were improved on several parameters, including growth at elevated temperature and resistance against high osmolarity or high ethanol concentrations. Due to the uncertainty of chromosomal make‐up of lager yeast spore clones, we introduced molecular markers to analyse mating‐type composition by PCR. Based on these results, new hybrids between a lager and an ale yeast strain were isolated by micromanipulation. These hybrids were not subject to genetic modification. We generated and verified 13 hybrid strains. All of these hybrid strains showed improved stress resistance as seen in the ale parent, including improved survival at the end of fermentation. Importantly, some of the strains showed improved fermentation rates using 18°Plato at 18–25°C. Uniparental mitochondrial DNA inheritance was observed mostly from the S. cerevisiae parent. Copyright © 2012 John Wiley & Sons, Ltd.