Effect of Sugar Transport Inactivation in Saccharomyces cerevisiae on Sluggish and Stuck Enological Fermentations

Sluggish and stuck (i.e., very delayed or incomplete) fermentations have been often observed in wine making. Some of them appeared to be associated with insufficient levels of yeast nutrients such as assimilable nitrogen. In these conditions, sugar transport catabolite inactivation, which is triggered by the protein synthesis arrest, may account in part for the inhibition of fermentation. Moreover, this mechanism of inhibition may explain the failure of added ammoniacal nitrogen to nitrogen-limited musts to restore or elevate rate of fermentation after the early yeast growth phase.     

Yeast Diversity and Persistence in Botrytis-Affected Wine Fermentations

Culture-dependent and -independent methods were used to examine the yeast diversity present in botrytis-affected (“botrytized”) wine fermentations carried out at high (~30°C) and ambient (~20°C) temperatures. Fermentations at both temperatures possessed similar populations of Saccharomyces, Hanseniaspora, Pichia, Metschnikowia, Kluyveromyces, and Candida species. However, higher populations of non-Saccharomyces yeasts persisted in ambient-temperature fermentations, with Candida and, to a lesser extent, Kluyveromyces species remaining long after the fermentation was dominated by Saccharomyces. In general, denaturing gradient gel electrophoresis profiles of yeast ribosomal DNA or rRNA amplified from the fermentation samples correlated well with the plating data. The direct molecular methods also revealed a Hanseniaspora osmophila population not identified in the plating analysis. rRNA analysis also indicated a large population (>10⁶ cells per ml) of a nonculturable Candida strain in the high-temperature fermentation. Monoculture analysis of the Candida isolate indicated an extreme fructophilic phenotype and correlated with an increased glucose/fructose ratio in fermentations containing higher populations of Candida. Analysis of wine fermentation microbial ecology by using both culture-dependent and -independent methods reveals the complexity of yeast interactions enriched during spontaneous fermentations.     

Molecular Monitoring of Wine Fermentations Conducted by Active Dry Yeast Strains

A simple and rapid method of yeast strain characterization based on mitochondrial DNA restriction analysis was applied to the control of wine fermentations conducted by active dry yeast strains. This molecular approach allows us to understand several important aspects of this process, such as the role of the active dry yeast strain and that of the natural Saccharomyces cerevisiae flora during vinification. In this paper, we demonstrate that the inoculated strain is really responsible for the fermentation but does not suppress significant development of natural strains during the first stages. During this early period, natural strains could have important effects on wine flavor.     

WL营养琼脂对葡萄酒相关酵母的鉴定效果验证

利用WL营养琼脂对采自葡萄园和葡萄汁发酵过程中的35株酵母菌进行了分类鉴定,同时进行了5.8S-ITS和26S rDNA D1/D2区的扩增与测序。结果表明利用WL营养琼脂的鉴定结果与测序结果基本符合。WL营养琼脂是一种较为有效的葡萄酒相关酵母菌的分类鉴定培养基。     

Effect of Dietary Yeast Chromium and l-Carnitine on Lipid Metabolism of Sheep

A 56-day feeding experiment was conducted to investigate the effects of yeast chromium (Cr, 300 μg/kg diet) and/or l-carnitine (100 mg/kg diet) on lipid metabolism and their interaction in sheep. After a 14-day adaptation period, 32 3-month-old sheep were randomly divided into four groups of eight. All sheep were fed with basal diets according to the American feeding standard of the National Research Council. At the end of the experiment, yeast Cr and/or l-carnitine supplementation significantly decreased abdominal fat mass and abdominal fat percentage, suggesting an improved mutton quality. Compared with the control group, the ratio of glucose to insulin was significantly increased, due to unchanged glucose levels and reduced insulin levels in yeast Cr and/or l-carnitine supplement groups, indicating high insulin sensitivity and well-controlled serum glucose levels. In addition, yeast chromium and/or l-carnitine induced significant decreases in serum triglyceride levels and serum total cholesterol levels, while increasing serum free fatty acid levels and high-density lipoproteincholesterol levels. The findings show that adding a yeast Cr and/or l-carnitine supplement may give better control of glucose and lipid variables.     

Effect of Selenium on Lipid and Amino Acid Metabolism in Yeast Cells

Biological Trace Element Research - This article discusses the effect of selenium in aqueous solutions on aspects of lipid and amino acid metabolism in the cell biomass of Saccharomyces cerevisiae...     

Correction to: Effect of Selenium on Lipid and Amino Acid Metabolism in Yeast Cells

Biological Trace Element Research - The authors forgot to include the following information in Materials and Methods.     

Effect of Increased Yeast Alcohol Acetyltransferase Activity on Flavor Profiles of Wine and Distillates

The distinctive flavor of wine, brandy, and other grape-derived alcoholic beverages is affected by many compounds, including esters produced during alcoholic fermentation. The characteristic fruity odors of the fermentation bouquet are primarily due to a mixture of hexyl acetate, ethyl caproate (apple-like aroma), iso-amyl acetate (banana-like aroma), ethyl caprylate (apple-like aroma), and 2-phenylethyl acetate (fruity, flowery flavor with a honey note). The objective of this study was to investigate the feasibility of improving the aroma of wine and distillates by overexpressing one of the endogenous yeast genes that controls acetate ester production during fermentation. The synthesis of acetate esters by the wine yeast Saccharomyces cerevisiae during fermentation is ascribed to at least three acetyltransferase activities, namely, alcohol acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT. To investigate the effect of increased AAT activity on the sensory quality of Chenin blanc wines and distillates from Colombar base wines, we have overexpressed the alcohol acetyltransferase gene (ATF1) of S. cerevisiae. The ATF1 gene, located on chromosome XV, was cloned from a widely used commercial wine yeast strain of S. cerevisiae, VIN13, and placed under the control of the constitutive yeast phosphoglycerate kinase gene (PGK1) promoter and terminator. Chromoblot analysis confirmed the integration of the modified copy of ATF1 into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression of ATF1 at high levels in these yeast transformants. The levels of ethyl acetate, iso-amyl acetate, and 2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature, cultivar, and yeast strain used. The concentrations of ethyl caprate, ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect on the solvent or chemical aroma (associated with ethyl acetate and iso-amyl acetate) and the herbaceous and heads-associated aromas of the final distillate and the solvent or chemical and fruity or flowery characters of the Chenin blanc wines. This study establishes the concept that the overexpression of acetyltransferase genes such as ATF1 could profoundly affect the flavor profiles of wines and distillates deficient in aroma, thereby paving the way for the production of products maintaining a fruitier character for longer periods after bottling.     

Occurrence of Killer Yeasts in Spontaneous Wine Fermentations from the Tuscany Region of Italy

The occurrence of killer yeasts in an area of Tuscany (central Italy) was studied. Killer yeasts were found in 88% of spontaneous wine fermentations from 18 wineries. The incidence of killers varied with respect to fermentation stage and vintage period, increasing from the first vintage to successive ones and from the commencement to the end of fermentation. At the end of fermentation, the proportion of killer strains relative to total yeast population was below 25% in 15 cases, above 75% in 6 cases, from 25 to 50% in 5 cases, and from 50 to 75% in 3 cases. Karyotype analysis also showed a mixed killer population in the fermentations in which the killers dominated.     

Metabolic Flux Analysis during the Exponential Growth Phase of Saccharomyces cerevisiae in Wine Fermentations

As a consequence of the increase in global average temperature, grapes with the adequate phenolic and aromatic maturity tend to be overripe by the time of harvest, resulting in increased sugar concentrations and imbalanced C/N ratios in fermenting musts. This fact sets obvious additional hurdles in the challenge of obtaining wines with reduced alcohols levels, a new trend in consumer demands. It would therefore be interesting to understand Saccharomyces cerevisiae physiology during the fermentation of must with these altered characteristics. The present study aims to determine the distribution of metabolic fluxes during the yeast exponential growth phase, when both carbon and nitrogen sources are in excess, using continuous cultures. Two different sugar concentrations were studied under two different winemaking temperature conditions. Although consumption and production rates for key metabolites were severely affected by the different experimental conditions studied, the general distribution of fluxes in central carbon metabolism was basically conserved in all cases. It was also observed that temperature and sugar concentration exerted a higher effect on the pentose phosphate pathway and glycerol formation than on glycolysis and ethanol production. Additionally, nitrogen uptake, both quantitatively and qualitatively, was strongly influenced by environmental conditions. This work provides the most complete stoichiometric model used for Metabolic Flux Analysis of S. cerevisiae in wine fermentations employed so far, including the synthesis and release of relevant aroma compounds and could be used in the design of optimal nitrogen supplementation of wine fermentations.     

Introducing a New Breed of Wine Yeast: Interspecific Hybridisation between a Commercial Saccharomyces cerevisiae Wine Yeast and Saccharomyces mikatae

Interspecific hybrids are commonplace in agriculture and horticulture; bread wheat and grapefruit are but two examples. The benefits derived from interspecific hybridisation include the potential of generating advantageous transgressive phenotypes. This paper describes the generation of a new breed of wine yeast by interspecific hybridisation between a commercial Saccharomyces cerevisiae wine yeast strain and Saccharomyces mikatae, a species hitherto not associated with industrial fermentation environs. While commercially available wine yeast strains provide consistent and reliable fermentations, wines produced using single inocula are thought to lack the sensory complexity and rounded palate structure obtained from spontaneous fermentations. In contrast, interspecific yeast hybrids have the potential to deliver increased complexity to wine sensory properties and alternative wine styles through the formation of novel, and wider ranging, yeast volatile fermentation metabolite profiles, whilst maintaining the robustness of the wine yeast parent. Screening of newly generated hybrids from a cross between a S. cerevisiae wine yeast and S. mikatae (closely-related but ecologically distant members of the Saccharomyces sensu stricto clade), has identified progeny with robust fermentation properties and winemaking potential. Chemical analysis showed that, relative to the S. cerevisiae wine yeast parent, hybrids produced wines with different concentrations of volatile metabolites that are known to contribute to wine flavour and aroma, including flavour compounds associated with non-Saccharomyces species. The new S. cerevisiae x S. mikatae hybrids have the potential to produce complex wines akin to products of spontaneous fermentation while giving winemakers the safeguard of an inoculated ferment.     

红葡萄酒对大鼠肝脏抗氧化酶和脂质过氧化的影响

选用雄性SD大鼠,分别灌胃红葡萄酒、酒精及水。实验90 d中每隔30 d处死一批动物,测定大鼠肝脏匀浆组织中的超氧化物歧化酶(Superoxide dismutase SOD)、过氧化氢酶(Catalase CAT)、谷胱甘肽过氧化物酶(Glutathione peroxidase GSH-Px)活性和脂质过氧化产物丙二醛(Malondialdehyde MDA)含量变化。观察摄入红葡萄酒后大鼠肝脏抗氧化酶活性变化及对肝脏脂质过氧化的影响。结果表明,红葡萄酒能提高SOD活性,且SOD活性与灌胃时间、剂量有一定关系;长期红葡萄酒和酒精摄入可诱导CAT活性增强,加剧肝脏的脂质过氧化(LPO)作用;红葡萄酒组、酒精组0.63、1.25 g/kg剂量GSH-Px活性均明显升高(P<0.05),酒精组1.88 g/kg剂量有极显著性差异(P<0.01);试验初期,红葡萄酒大剂量显著降低肝脏中MDA的含量。试验中期,红葡萄酒中大剂量显著降低MDA含量。试验末期,红葡萄酒大剂量和酒精中大剂量显著升高肝脏中MDA含量。     

Effect of Lipid Particle Biogenesis on the Subcellular Distribution of Squalene in the Yeast Saccharomyces cerevisiae

Squalene belongs to the group of isoprenoids and is a precursor for the synthesis of sterols, steroids, and ubiquinons. In the yeast Saccharomyces cerevisiae, the amount of squalene can be increased by variation of growth conditions or by genetic manipulation. In this report, we show that a hem1Δ mutant accumulated a large amount of squalene, which was stored almost exclusively in cytoplasmic lipid particles/droplets. Interestingly, a strain bearing a hem1Δ deletion in a dga1Δlro1Δare1Δare2Δ quadruple mutant background (QMhem1Δ), which is devoid of the classical storage lipids, triacylglycerols and steryl esters, and lacks lipid particles, accumulated squalene at similar amounts as the hem1Δ mutant in a wild type background. In QMhem1Δ, however, increased amounts of squalene were found in cellular membranes, especially in microsomes. The fact that QMhem1Δ did not form lipid particles indicated that accumulation of squalene solely was not sufficient to initiate proliferation of lipid particles. Most importantly, these results also demonstrated that (i) squalene was not lipotoxic under the conditions tested, and (ii) organelle membranes in yeast can accommodate relatively large quantities of this non-polar lipid without compromising cellular functions. In summary, localization of squalene as described here can be regarded as an unconventional example of non-polar lipid storage in cellular membranes.     

Beneficial Effect of Corncob Acid Hydrolysate on the Lipid Production by Oleaginous Yeast Trichosporon dermatis

In this work, corncob acid hydrolysate and its simulated medium whose sugar composition was the same as the corncob acid hydrolysate were used as fermentation substrate for lipid production by oleaginous yeast Trichosporon dermatis. On the corncob acid hydrolysate, after 7 days of fermentation, the biomass, lipid content, lipid yield, and lipid coefficient of T. dermatis were 17.3 g/L, 40.2%, 7.0 g/L, and 16.5%, respectively. Interestingly, during the lipid fermentation on the corncob acid hydrolysate, glucose, xylose, arabinose, and even acetic acid could be well utilized as carbon sources by T. dermatis. Surprisingly, the lipid yield (7.0 g/L) of T. dermatis on the corncob acid hydrolysate was much higher than that (3.8 g/L) on the simulated medium, in spite of the fact that the lipid coefficient (17.4%) on the simulated medium was a little higher. This phenomenon further showed that lignocellulosic acid hydrolysate was a suitable substrate for lipid fermentation by T. dermatis. This work would help the comprehensive utilization of lignocellulosic biomass for lipid production.     

光镊拉曼光谱分析酿酒活性干酵母的活化与生长

应用光镊拉曼光谱新技术(LTRS)对酿酒活性干酵母复水活化与生长进行动态观察, 探索从分子光谱角度窥视胞内糖类、核酸、蛋白等生物大分子的变化过程, 及葡萄糖消耗和乙醇生成的动态过程。结果显示, 酿酒活性干酵母复水活化后, 第6小时和9小时, 即酵母对数生长中期及乙醇产生前期, 是调控酵母细胞生理变化的2个重要的时间点。核酸类物质在细胞活化后迅速增加, RNA在第6小时达到最大值; 而蛋白质和脂类物质从第6小时开始快速增加, 在第9小时达 到最大值, 而后呈下降趋势; 胞内乙醇则是在9 h开始出现, 在9     

Effect of Simultaneous Inoculation with Yeast and Bacteria on Fermentation Kinetics and Key Wine Parameters of Cool-Climate Chardonnay

Inoculating grape musts with wine yeast and lactic acid bacteria (LAB) concurrently in order to induce simultaneous alcoholic fermentation (AF) and malolactic fermentation (MLF) can be an efficient alternative to overcome potential inhibition of LAB in wines because of high ethanol concentrations and reduced nutrient content. In this study, the simultaneous inoculation of yeast and LAB into must was compared with a traditional vinification protocol, where MLF was induced after completion of AF. For this, two suitable commercial yeast-bacterium combinations were tested in cool-climate Chardonnay must. The time courses of glucose and fructose, acetaldehyde, several organic acids, and nitrogenous compounds were measured along with the final values of other key wine parameters. Sensory evaluation was done after 12 months of storage. The current study could not confirm a negative impact of simultaneous AF/MLF on fermentation success and kinetics or on final wine parameters. While acetic acid concentrations were slightly increased in wines after simultaneous AF/MLF, the differences were of neither practical nor legal significance. No statistically significant differences were found with regard to the final values of pH or total acidity and the concentrations of ethanol, acetaldehyde, glycerol, citric and lactic acids, and the nitrogen compounds arginine, ammonia, urea, citrulline, and ornithine. Sensory evaluation by a semiexpert panel confirmed the similarity of the wines. However, simultaneous inoculation led to considerable reductions in overall fermentation durations. Furthermore, differences of physiological and microbiological relevance were found. Specifically, we report the vinification of “super-dry” wines devoid of glucose and fructose after simultaneous inoculation of yeast and bacteria.     

Sugar and Alcohol Stabilization of Yeast in Sweet Wine

Secondary fermentation of sweet wine was prevented by the Delle stabilization procedure. For this procedure, advantage is taken of the inhibitory effects of high concentrations of sugar as well as of alcohol. Thus, relatively small amounts of wine spirits were added to fermenting musts to obtain stability, as compared to the conventional procedure in which larger amounts of alcohol are added and the inhibitory effect of alcohol only is considered. The Delle value is a function of the concentrations in the wine, after spirits addition, of alcohol and sugar. Delle values which gave stable wine were dependent on time of alcohol addition, on strain of wine yeast, and on composition of wine spirits. Fractional addition of spirits, concentration of SO(2), and clarity of must had little effect on the Delle value. Sensory comparison of wines especially prepared for tasting by the Delle procedure and by the conventional procedure showed the wines made by the Delle procedure to be superior in quality. Under proper storage conditions, the Delle wines were shown to be microbiologically stable and resistant to wine spoilage organisms.     

The Effect of Nisin and Monensin on Ruminal Fermentations In Vitro

When mixed ruminal bacteria and alfalfa were incubated in vitro, monensin and nisin both inhibited methane production so long as the concentrations were greater than 1 μM. Monensin- and nisin-dependent methane depressions caused a decrease in the acetate to propionate ratio (4.5 to 3.0). Total volatile fatty acid production was decreased by both monensin and nisin addition at concentrations greater than 2 μM. Starch-digesting ruminal bacteria were initially inhibited by monensin and nisin, but this effect disappeared after two to four transfers. Nisin always inhibited cellulolytic bacteria, but the nisin-dependent inhibition of cellulose digestion was no greater than the inhibition caused by monensin. Monensin and nisin also inhibited amino acid degradation, and nisin was more effective than monensin in controlling the growth of Clostridium aminophilum, an obligate amino acid-fermenting ruminal bacterium that can tolerate low concentrations of monensin. Because nisin was as potent as monensin, bacteriocins such as nisin may have potential as feed additives. Received: 2 December 1996 / Accepted: 10 February 1997