Influence of oxygen addition during growth phase on the biosynthesis of lipids in Saccharomyces cerevisiae (M(3)30-9) in enological fermentations

The fatty acid, phospholipid and sterol composition of one strain of Saccharomyces cerevisiae under different oxygen levels during grape must fermentation was studied. Anaerobiosis partially inhibited yeast growth and resulted in a drop in the unsaturation index of the fatty acids throughout the fermentation, as well as an abnormally low ergosterol/phospholipid ratio. Aeration after 48 h of fermentation in anaerobiosis stimulated growth and increased cellular viability, as well as raised the unsaturation index of fatty acids. Although the ergosterol/phospholipid ratio remained low in the days following the aeration, by the end of the fermentation the value was that considered optimum for the maintenance of membrane functions.     

Malo-ethanolic fermentation in grape must by recombinant strains of Saccharomyces cerevisiae.

Recombinant strains of Saccharomyces cerevisiae with the ability to reduce wine acidity could have a significant influence on the future production of quality wines, especially in cool climate regions. L-Malic acid and L-tartaric acid contribute largely to the acid content of grapes and wine. The wine yeast S. cerevisiae is unable to effectively degrade L-malic acid, whereas the fission yeast Schizosaccharomyces pombe efficiently degrades high concentrations of L-malic acid by means of a malo-ethanolic fermentation. However, strains of Sz. pombe are not suitable for vinification due to the production of undesirable off-flavours. Heterologous expression of the Sz. pombe malate permease (mae1) and malic enzyme (mae2) genes on plasmids in S. cerevisiae resulted in a recombinant strain of S. cerevisiae that efficiently degraded up to 8 g/l L-malic acid in synthetic grape must and 6.75 g/l L-malic acid in Chardonnay grape must. Furthermore, a strain of S. cerevisiae containing the mae1 and mae2 genes integrated in the genome efficiently degraded 5 g/l of L-malic acid in synthetic and Chenin Blanc grape musts. Furthermore, the malo-alcoholic strains produced higher levels of ethanol during fermentation, which is important for the production of distilled beverages.     

The effects of grape must fermentation conditions on volatile alcohols and esters formed by Saccharomyces cerevisiae

Changes in aroma compounds synthesised from grape must during fermentation carried out by Saccharomyces cerevisiae, in semi-aerobic, anaerobic, short aeration conditions and after adding ergosterol and oleic acid to the must were studied. The biosynthesis of these aroma compounds was strongly dependent on the fermentation conditions and on the growth of the yeast. Ethanol, isoamyl alcohols, isobutyl alcohol, phenethyl alcohol and isoamyl, butyl and hexyl acetates were produced in greater concentrations in semiaerobic conditions, mainly during cellular growth. 1-Butanol and 1-pentanol were produced in greater levels in anaerobic conditions, when cellular growth was lower. Ergosterol and oleic acid added to the musts generally increased the levels of the aroma compounds in wine compared to those obtained in anaerobic conditions. © 1997 SCI.     

Inhibition of malolactic fermentation by a peptide produced by Saccharomyces cerevisiae during alcoholic fermentation

The ability of Saccharomyces to inhibit Oenococcus oeni during the alcoholic fermentation by mechanisms other than SO(2) production was investigated. During fermentation in synthetic grape juice, S. cerevisiae strain RUBY.ferm inhibited the malolactic fermentation by O. oeni while strain EC1118 did not despite both strains producing similar amounts of SO(2). The bacterial inhibition exerted by RUBY.ferm was diminished when the wine was treated with proteases but not through the addition of nutrients. Wine fermented by RUBY.ferm was fractionated based on molecular weight and each fraction tested for the ability to inhibit the growth of O. oeni. The fraction containing compounds larger than 3 kDa was the sole inhibitory fraction. The inhibitory fraction was analyzed by SDS PAGE and showed a 5.9 kDa protein band present in wine fermented by RUBY.ferm that was not present in wine fermented by a non-antagonistic yeast, S. cerevisiae strain Saint Georges S101. The ability of the peptide to inhibit O. oeni seemed to be dependent on the presence of SO(2).     

Effect of clarification on the fatty acid composition of grape must and the fermentation kinetics of white wines

 The effect of different static and dynamic clarification treatments on grape must used in the manufacture of white wines was studied. Turbidity, yeast populations in the musts and must lees, fatty acid composition of the must and must lees after each treatment, and the fermentation kinetics using each cleaned must were measured. Fatty acids not previously found in grape must, such as tridecanoic acid and myristoleic acid, were detected. Dynamic clarification prolonged fermentation, and certain long-chain fatty acids helped activate fermentation. Received: 5 October 1998 / Revised version: 8 February 1999     

Release of cell wall polysaccharides from Saccharomyces cerevisiae thermosensitive autolytic mutants during alcoholic fermentation

In order to increase the release of cell wall polysaccharides during alcoholic fermentation, a wine strain of Saccharomyces cerevisiae was subjected to UV mutagenesis to obtain thermosensitive autolytic mutants affected in cell wall integrity. Five mutants and the parental strain were utilized in fermentation trials conducted at 28, 32 and 34 degrees C. Results showed that at all temperatures the mutant strains released into the medium a higher polysaccharide quantity than the parental strain. In particular, at 28 degrees C there was a doubling of these macromolecules. At the end of alcoholic fermentation, all strains showed at 28 degrees C elevated and similar levels of viable cells; at 32 degrees C this parameter remained high for mutant strains ts16 and ts39 and the parental strain; at 34 degrees C all strains underwent a drop in cell viability, which was less intense in the case of strain ts16. As a relationship between cell viability and the quantity of polysaccharides released by the yeast strain was not found, it can be assumed that the mutation led to cells with a less stable wall and thus an easier release of macromolecules into the medium.     

The effects of lipids on the alcoholic fermentation of molasses using Saccharomyces cerevisiae

The addition of appropriate lipids to the fermentation medium offers a considerable advantage to ethanol production on a large scale and in addition in stirred fermentations, lipids can equally act as effective anti-foam.     

富含谷氨酸酿酒酵母的筛选及发酵培养基优化

从农家自酿葡萄酒中筛选出一株富含谷氨酸酿酒酵母菌（Saccharomyces cerevisiae）F-5,其26S rDNA核苷酸序列与S. cerevisiae TY12的26S rDNA核苷酸序列同源性为100%。以胞内谷氨酸含量为目标,采用响应面法对其发酵培养基进行了优化,建立糖蜜、工业蛋白胨和KH2PO4的二次回归模型,确定培养基最佳配方为：糖蜜（含30%蔗糖）100 mL/L、酵母浸粉10 g/L、工业蛋白胨20 g/L、MgSO4·7H2O 1 g/L、KH2PO4 0.5 g/L、FeSO4·7H2O 2 g/L。在此优化培养基中发酵培养24 h,胞内游离谷氨酸达到了3.29%,比优化前提高了87.8%。     

酿酒酵母对萝卜泡菜发酵过程的影响

以樱桃萝卜为原料,设置4个试验组,分别为乳酸菌接种发酵组、乳酸菌与酵母菌混合接种发酵组、酵母菌接种发酵组和自然发酵组。对各试验组发酵过程中pH值、总酸、亚硝酸盐、色度、硬度、感官品质、乳酸菌数量、酵母菌数量及大肠菌群数量进行研究。实验结果表明:在樱桃萝卜发酵过程中,接种酿酒酵母能够阻止发酵后期pH进一步下降,降低总酸生成量,抑制泡菜过度酸化,使泡菜保持较高的脆度,并且产生浓郁的酯香风味;酿酒酵母的加入不改变亚硝酸盐消长规律,也不影响接种乳酸菌对大肠菌群的抑制效果;但在发酵后期,加入酿酒酵母的试验组,其乳酸菌的生长受到一定程度的抑制,因此酿酒酵母的使用量还需进一步研究。     

酿酒酵母QY-1发酵过程中有机酸及游离氨基酸变化分析

该研究对酿酒酵母（Saccharomyces cerevisiae）QY-1发酵过程中的OD600 nm值、pH值、葡萄糖消耗量、乙醇生成量、有机酸及游离氨基酸种类及生成量进行监控和分析。结果表明,随着发酵时间的延长,发酵液的pH值与OD600 nm值呈负向耦合;乙醇的生成量与葡萄糖消耗量呈负向耦合,发酵36 h时,乙醇含量最高,为（26.87±2.76） g/L;有机酸含量呈现先升高后稳定的趋势,最高达（3.242±0.213） g/L,其中乙酸含量最高;游离氨基酸含量呈现先升高后降低的趋势,最高达（5.57±0.08） mg/L,其中谷氨酸含量最高。S. cerevisiae QY-1具有较强的产酸和氨基酸能力。     

Saccharomyces cerevisiae cell fatty acid composition and release during fermentation without aeration and in absence of exogenous lipids.

Medium-chain fatty-acids (MCFA) are among the main aroma compounds of fermented beverages. High concentrations of MCFA have been found in sluggish and stuck fermentations. It has been suggested that they arrest cell growth, as they may be toxic, but the causes of sluggish and stuck fermentations are still unclear. The aim of this work was to see whether the production of MCFA is related to fatty acid synthesis in the absence of exogenous lipids and aeration, and whether their increase can be regarded as a consequence, instead of the cause, of sluggish and stuck fermentations. Two possibilities were considered: (i) MCFA are produced to replace unsaturated fatty acids (UFA) for cell membrane fluidity when the lack of oxygen makes desaturation of saturated fatty acids (SFA) impossible; or (ii) MCFA are produced following the release of medium-chain acyl-CoA from the fatty acid synthetase complex (FAS) due to the accumulation of SFA, and their hydrolysis to recycle CoA-SH. In the first hypothesis, MCFA should be active in cell metabolism and be found in cell structures; in the second, MCFA should be a discard and prevalently found outside the cell. We carried out a Saccharomyces cerevisiae fermentation experiment in a synthetic, lipid-free medium without aeration. We measured the fatty acid composition of yeast cells and the amounts of MCFA and their ethyl esters in the medium throughout the fermentation. Cell growth and the oxygen content of the medium were also monitored. We found that MCFA are not immobilized in cell structures, but mainly released into the medium. Cell growth is arrested because fatty acid biosynthesis is prevented by the lack of oxygen. The higher MCFA concentrations found in sluggish and stuck fermentations can be thus regarded as an effect, and not the cause, of this arrest. Some suggestions for the prevention of these events are proposed.     

Influence of yeast strain on ochratoxin A content during fermentation of white and red must

The aim of this work was to examine whether the yeast strains, responsible for alcoholic fermentation, have an influence on the concentration of ochratoxin A (OTA) in wine. Before the fermentation, OTA was added to musts up to a concentration of about 2 microg/l. OTA content was determined in white and red wines resulting from respective musts and in methanolic extract of the yeast lees (MEL). Data showed a significant reduction of OTA at the end of alcoholic fermentation. However, depending on the yeast strain involved in the fermentation, there was a difference in the content of OTA in the wines. The percentage of OTA removal during the fermentation was between 46.83% and 52.16% in white wine and between 53.21% and 70.13% in red wine. The absence of degradation products suggested an adsorption mechanism. OTA concentration in MEL resulting from red must fermentation was higher than in white. A significant amount of OTA was not recovered either from wine or from MEL.     

Influence of assimilable nitrogen on volatile acidity production by Saccharomyces cerevisiae during high sugar fermentation

We analyzed the variability of volatile acidity and glycerol production by Saccharomyces cerevisiae on a large sample of high sugar musts. The production of volatile acidity was inversely correlated with the maximum cell population and the assimilable nitrogen concentration. The higher the nitrogen concentration, the less volatile acidity was produced. An approach to minimize volatile acidity production during high sugar fermentations by adjustment of assimilable nitrogen in musts was investigated in terms of both quantity and addition time. It was found that the optimal nitrogen concentration in the must is 190 mgN.l(-1). The best moment for nitrogen addition was at the beginning of fermentation. Addition at the end of the growth phase had less effect on volatile acidity reduction. We suggest that by stimulating cell growth, nitrogen addition provides NADH in the redox-equilibrating process, which in turn reduces volatile acidity formation.     

Influence of decantation of viura must on the cation content. Evolution during wine fermentation and stabilization

Must has many metallic cations which greatly affect wine fermentation, stability and quality. In this study we investigated the influence of clarification of viura must by static sedimentation studying the concentration of four macroelements (potassium, calcium, magnesium and sodium) and of four oligoelements (iron, copper, zinc and manganese). This treatment eliminated potassium (11%), calcium (25%), and a greater proportion of iron (46%). The evolution of cations during fermentation was similar in the clarified sample and in the control. Both young and stablised wines had similar concentrations of these elements.     

Evolution of the population of Saccharomyces cerevisiae from grape to wine in a spontaneous fermentation

To determine the grape or winery origin of the Saccharomyces cerevisiae involved in spontaneous fermentation, musts were collected at different stages of wine-making process and fermented. First, grapes were collected in two different vineyards and crushed at the laboratory. Second, musts were collected after crushing and clarification in the cellar. Third, musts collected in the cellar were sterilized and inoculated with tartar deposit collected in the vats. The fourth fermentation was in the cellar. For the two vineyards, two hundred of S. cerevisiae clones were isolated for each of the four fermentations, driving to a library of 1600 clones. All the library was analysed by inter-delta PCR with a basic set of primers and about 20% of the library was further analysed by inter-delta PCR with an improved set of primers. Six, and more than 30 different PCR patterns were obtained from basic- and improved-PCR analysis, respectively. The amounts of each family were analysed at the different stages of wine making. Our study demonstrates that the two vineyards present different S. cerevisiae populations. Moreover the S. cerevisiae strains involved in spontaneous fermentation in the cellar originate partly from the vineyard and partly from the winery, in amounts varying with the must.     

Influence of vacuum filtration on the fatty acids content and its evolution during vinification of garnacha must

Abstract

Unsaturated fatty acids and sterols are necessary substances for yeast development and can be eliminated by clarification of must. In this work the influence of vacuum filtration clarification on Garnacha must with respect to fatty acids concentration and its evolution during fermentation was studied. Vacuum filtration of the must, eliminated unsaturated (95%) and saturated (91%) fatty acids. Elimination was complete in the case of linolenic, arachidic and behenic acids. During the first half of fermentation the fatty acids were consumed in the control must (48%) whereas they were excreted in the filtered must. During the second half of fermentation and during aging in bottle, their concentrations decreased in both samples.     

Effect of the nitrogen source on the fatty acid composition of Saccharomyces cerevisiae

The source and content of nitrogen in the medium are very important in the development of alcoholic fermentations since they both affect the growth of Saccharomyces cerevisiae. Furthermore, the composition of the growth medium and the environmental conditions are known to affect the cell membrane fatty acid composition. The aim of this work was to study how the nitrogen source affects the membrane fatty acid composition. A mixture of amino acids and ammonia delayed the yeast growth when a high content of yeast assimilable nitrogen was present in the media. Cells grown in the mixed nitrogen source had a lower content of total fatty acids with a higher unsaturation degree than cells grown on sole ammonia.