THE EFFECT OF PITCHING YEAST AERATION ON THE PRODUCTION OF ACETIC ACID DURING FERMENTATIONS WITH BREWERS' YEAST: AN ENZYMATIC APPROACH

Aeration of pitching yeast signicantly increases the metabolism of acetate. This increase is particularly noticed at an enzymatic level, with special reference to the specific activity of the Fe⁺⁺⁺ linked pyruvate de-carboxylase which has been shown to be involved in the production of acetic acid. At the beginning of fermentations carried out with aerobic and anaerobic pitching yeasts, an increase in acetic acid production is observed, this is followed by reabsorption. Stabilisation in the concentration of acetic acid is observed until the end of fermentation. Initial and final concentrations of acetic acid obtained during fermentations were significantly higher in fermentations carried out with aerobic pitching yeasts than in fermentations carried out with anaerobic pitching yeasts.     

Fast identification of wine related lactic acid bacteria by multiplex PCR

The microflora of must and wine consists of yeasts, acetic acid bacteria and lactic acid bacteria (LAB). The latter group plays an important role for wine quality. The malolactic fermentation carried out by LAB leads to deacidification and stabilisation of wines. Nevertheless, LAB are often associated with wine spoilage. They are mainly responsible for the formation of biogenic amines. Furthermore, some strains produce exopolysaccharide slimes, acetic acid, diacetyl and other off-flavours. In this context a better monitoring of the vinification process is crucial to improve wine quality. Moreover, a lot of biodiversity studies would also profit from a fast and reliable identification method.     

Role of oxygen on acetic acid production by Brettanomyces/Dekkera in winemaking

Since the large occurrence of Brettanomyces yeasts in strict anaerobiosis environments (sparkling wines) has been found without an increase in acetic acid content, we evaluated the influence of the oxygen concentration on acetic acid production. Results showed that the oxygen concentration exerted a strong influence on both growth and acetic acid production by Brettanomyces yeasts in winemaking. Full aerobiosis lead to a large production of acetic acid causing a block of metabolic activity. Semi-aerobiosis resulted in the best condition for alcoholic fermentation (Custers effect) combined with acetic acid production. In anaerobic condition Brettanomyces yeasts did not result in high acetic acid production and a pure, even if slow, alcoholic fermentation occurred. The absence of an increase in acetic acid in wines, does not exclude the active presence of Brettanomyces yeast since the characteristic ‘high acetic producer’ in Brettanomyces yeast is linked to the presence of oxygen. ©1997 SCI     

Inferring the role of microorganisms in water kefir fermentations

Water kefir is a slightly alcoholic, lactic and acetic beverage fermented by yeasts, lactic acid bacteria and acetic acid bacteria that are associated with the polysaccharide of the water kefir grains. In this study, the three main metabolic products of microorganisms were evaluated during a traditional 192‐h water kefir fermentation and also after inoculating the microorganisms in fresh medium or sterilised broth from different fermentation stages. The first process to occur was alcoholic fermentation, carried out in particular by Saccharomyces cerevisiae. After 24 h, lactic and acetic acid accumulation was generated by Lactobacillus hilgardii and Acetobacter tropicalis. By the end of fermentation, ethanol had been almost entirely consumed and oxidised to acetic acid, possibly by a dissimilatory route of Acetobacter species. An original hypothetical diagram is proposed for the carbon flux from sucrose, and the metabolic role of the main yeasts and bacteria is assigned for the distinct stages of water kefir fermentation.     

藏灵菇牦牛酸乳发酵过程中乳酸菌和酵母菌对品质的作用

藏灵菇酸乳是由乳酸菌、酵母菌、醋杆菌和霉菌共同发酵形成的一种发酵乳制品,其品质特征与普通酸乳有显著差异。为研究藏灵菇发酵酸乳中乳酸菌和酵母菌分别发挥的作用,利用放线菌酮和青链霉素分别抑制发酵过程中的酵母菌和乳酸菌,测定并比较正常发酵酸乳、抑制乳酸菌发酵酸乳和抑制酵母菌发酵酸乳的风味、口感和质构等相关指标。实验结果显示抑制酵母菌发酵的酸乳中乙醇含量由1.85g/kg上升为2.77g/kg,VB2含量由168μg/100g下降为157μg/100g,与正常发酵组差异较大;抑制乳酸菌发酵的酸乳中酸度由18°T上升为28°T,氨基酸态氮由65mg/100g下降为53mg/100g,乳酸含量持续2mg/g,乙酸由1mg/g下降为0.7mg/g,VB1含量由20μg/100g下降为18μg/100g,与正常发酵组差异较大。乳酸菌在酸乳发酵过程中,对酸度、氨基酸态氮、质构、乳酸、乙酸与VB1的生成贡献较大;酵母菌对乙醇、VB2的生成贡献较大。     

The isolation and identification of microbes from a fermented tea beverage, Haipao, and their interactions during Haipao fermentation

Samples of Haipao from three cities of Taiwan were analyzed for their microbial population. Two species of acetic acid bacteria and three species of yeast were isolated from tea fungus Haipao using appropriate isolation media. The isolated bacteria were identified asAcetobacter acetiandAcetobacter pasteurianus, based on their biochemical properties, and compared with those of the type strains of the genusAcetobacter. The yeasts wereSaccharomyces cerevisiae, Zygosaccharomyces bailii, andBrettanomyces bruxellensisaccording to conventional phenotypic characterization combined with the Yeast Identification Program. The brew broth analyzed by high−performance liquid chromatography (HPLC) was shown to contain glycerol, acetic acid and ethanol. The symbiosis phenomenon between the yeast andAcetobacterwas studied. It was found that the autoclaved yeast cells and ethanol produced by yeasts were helpful forAcetobacterto grow or produce acetic acid. The acetic acid produced byAcetobactercould stimulate the yeast to produce ethanol. The ethanol and acetic acid produced by yeasts andAcetobactermight prevent the competition from other micro-organisms.     

Formation of α-ketoglutaric acid by wine yeasts and its oenological significance

α-Ketoglutaric acid was measured enzymically in wines made in the laboratory from three grape varieties by pure cultures of 12 wine yeasts of the genus Saccharomyces. The results were confirmed with the same juices and 4 yeasts on pilot-plant scale in replicated 30 gallon lots. Mean values for the 12 yeasts ranged from 9 to 117 ppm (overall mean 53). In any one juice the yeasts differed by at least 10-fold in the amounts produced, and certain yeasts produced consistently high or low yields in all juices. The amounts of α-ketoglutaric acid produced depended somewhat on the grape juices used, even though these had comparable pH values, and a significant yeast-juice interaction occurred. The amount of α-ketoglutaric acid formed during fermentation at 15° was 60 per cent of that formed at 25°, and over twice as much was formed at pH 4.2 as at pH 3.0, using four yeast strains. Formation of α-ketoglutaric and pyruvic acids were not significantly correlated. The α-ketoglutaric acid content of 18 white table wines made under comparable conditions on pilot-plant scale from different grape varieties using the same yeast strain ranged from 38 to 152 ppm (mean 90). The significance of the results is discussed, particularly in relation to the binding of sulphur dioxide in wine, and recommendations are given on how to make wines which are low in α-ketoglutaric acid. Formation of α-ketoglutaric acid by three yeasts in a chemically defined medium was lower with increased amounts of nitrogen as ammonium sulphate and higher in the presence of L-glutamic acid, both being used separately as sole nitrogen sources. These findings are discussed in relation to the rǒle of α-ketoglutaric acid in nitrogen metabolism of yeasts.     

啤酒中乙酸的影响因素及控制方法

测定了两种不同浓度淡爽型啤酒中乙酸阈值结果,比较了不同菌株产生乙酸的差异性。用浅蓝菌素成功筛选出低产乙酸啤酒酵母,对其发酵性能做了系统评价,并探讨了低产乙酸的初步机理,系统跟踪了大生产发酵中乙酸的产生量及波动情况,用支持向量机建立了大生产啤酒发酵过程中乙酸的产生模型。     

Acetic Acid, Formic Acid, and Potassium Sorbate as Preservatives for Short Term Storage of Bovine Hides

Total numbers of aerobic microorganisms, Gram negative bacteria, Clostridium perfringens, coagulase positive staphylococci, and yeasts and molds were monitored during storage of segments of bovine hides. The preservatives tested were acetic acid, formic acid, and potassium sorbate. Potassium sorbate at any concentration tested did not control adequately any group of microorganisms monitored. Acetic and formic acids at all concentrations tested, significantly inhibited growth of all groups of microorganisms. At the highest concentration tested (0.67M) not only did the formic acid inhibit growth of microogramisms, but it had a lethal effect on all groups monitored except yeasts and molds. Formic acid was a better preservative than acetic acid. Neither formic nor acetic acid inhibited growth of yeasts and molds to the same extent as the other groups monitored.     

酒醅中酵母的分离及其生理生长特性的研究

通过对酒醅中酵母菌的分离和对其生理、生化特性进行系统的研究,了解酒醅中主要有机酸己酸、丁酸、乙酸、乳酸对酒醅中酵母菌生长发酵影响情况,掌握酒醅中的有机酸影响浓香型大曲酒发酵的规律,进一步提高酿酒生产技术水平。     

Microbial evolution during storage of seasoned olives prepared with organic acids with potassium sorbate, sodium benzoate, and ozone used as preservatives

The effect of potassium sorbate, sodium benzoate, and ozone in combination with citric, lactic, and acetic acids on the microbial population of seasoned table olives of the olive 'Alore?a' cultivar was studied in both fresh (FF) and stored fruits (SF). The inactivation/growth curves were modeled and the biological parameters estimated, with yeast used as the target microorganism. Regardless of the acid added, potassium sorbate showed a general inactivation effect on yeasts in the products prepared from both FF and SE Sodium benzoate had a rapid inactivation effect with FF, but with SF, it was effective only in the presence of acetic acid. A strain of Issatchenkia occidentalis was found that was resistant to the combination of this preservative with citric or lactic acids. In FF, ozone showed an initial marked inhibition against yeasts, but later, yeasts were again able to grow. In SF, ozone was a strong inactivating agent when it replaced any of the traditional preservatives. Lactic acid bacteria were always absent in products prepared from FF, and apparently were not affected by the different preservative agents in those prepared from SF. The behavior of yeasts and lactic acid bacteria populations in commercial products were similar to those found in experimental treatments.     

含乙酸玉米芯水解液中四株油脂酵母联产多糖与油脂的研究

为了研究木质纤维素水解液中高浓度乙酸的存在对油脂酵母发酵的影响,本研究以4株油脂酵母(皮状丝孢酵母、浅白隐球酵母、Trichosporon dermatis与Trichosporon coremiiforme)为研究对象,在玉米芯水解液中添加高浓度乙酸(15 g/L)作为发酵底物,研究发酵的底物代谢与产物积累规律。结果表明:发酵培养基中的糖与乙酸几乎可被皮状丝孢酵母与T.dermatis完全代谢;而T.coremiiforme与浅白隐球酵母对糖与有机酸的代谢效果不佳。皮状丝孢酵母与T.dermatis在高效降低高底物浓度培养基的COD的同时,可在胞外合成一定浓度的多糖产品。四株油脂酵母的油脂脂肪酸组成以C16、C18系列为主,其中油酸(C18:1)比例最高;除合成微生物油脂外,它们还能在胞内大量积累多糖类物质以及少量的蛋白质与灰分。本文可为油脂酵母利用廉价原料联产酵母多糖与微生物油脂这两种高附加值食品提供参考。     

Effects of buffer and temperature on formation of furan, acetic acid and formic acid from carbohydrate model systems

Effects of temperature, pH and phosphate buffer on volatiles formed by heating model solutions of fructose, glucose, sucrose, lactose or starch were investigated by selected ion flow tube-mass spectrometry (SIFT-MS). Among the carbohydrates studied, the monosaccharide reducing sugars fructose and glucose were more reactive than macro molecular starch, lactose and sucrose, which are not reducing sugars. Furan was formed from fructose heated at 120, 100 and 80 °C at pH 5-7 in phosphate buffer and at 100 °C in unbuffered solution. Glucose did not yield furan in unbuffered solution at 100 °C but glucose did yield furan in phosphate buffer solution at a similar pH. Furan formation increased as temperature and pH increased. As temperature, pH value, and buffer components changed, furan formation may occur by different reactive pathways. Both of the buffer components, NaH₂PO₄ and citric acid, enhanced the formation of thermal degradation products from fructose. The enhancing effect of NaH₂PO₄ was stronger than citric acid. Formic and acetic acids were concomitantly formed with furan. More formic acid was produced from fructose than glucose, and more acetic acid was produced from glucose than fructose.     

康普茶感官品质及其相关化学组分研究进展

康普茶是以茶糖水为主要发酵基质，经酵母菌、醋酸菌以及乳酸菌等微生物共同发酵而成的一种功能性饮品。近年来，随着人们健康意识的提升，具有保健功效的康普茶受到国内外的广泛关注。本文通过对康普茶的化学组成，主要包括有机酸、茶多酚和芳香类物质，以及感官品质，包括其外观、香气和滋味进行总结，探讨了不同发酵条件对其化学组分及感官品质的影响，并对两者的相互关系进行了初步的分析和阐述，以期深入系统地了解康普茶的感官特性及其生化成因，为康普茶的产品稳定、品质提升及品种创新提供理论依据。     

ORGANIC ACID METABOLISM OF YEASTS DURING FERMENTATION OF ALCOHOLIC BEVERAGES—A REVIEW

The acids of alcoholic beverages are largely those present in the raw materials but the concentrations of some may be changed by yeast action during fermentation. In addition a number of other acids are formed by the yeasts often as by-products of main metabolic pathways. The inter-relationships of organic acid and amino-acid metabolism, yeast growth and formation of fusel alcohols are discussed.     

藏灵菇中醋酸菌和酵母菌的分离及初步鉴定

结合藏灵菇扫描电镜结果,从藏灵菇叶中分离出1株醋酸菌和4株酵母菌依据其彤态、培养特征和部分生理牛化研究,初步鉴定醋酸菌为巴氏醋杆菌（Acetobacter pasteurianus）,4株酵母菌分别为酒香酵母属（Brettanomyces）、类酵母属（Saccharomycodes）和酵母属（Saccharomycs）的菌株。     

FORMATION OF HIGHER ALCOHOLS BY VARIOUS YEASTS

The formation of higher alcohols by various yeasts has been studied as a function of the nitrogen level of the medium. Two types of substrate were used. In one ammonium sulphate was the sole nitrogen source and in the other a complex amino acid mixture simulating that present in brewery wort was used. In the former medium, the patterns exhibited by the yeasts were all very much alike, indicating that the formation of higher alcohols through the biosynthetic activities of yeasts is always basically similar. In the medium containing a complex mixture of amino acids, where the higher alcohols can be formed partly or entirely from the exogenous amino acids through Ehrlich's mechanism, widely different patterns were observed, indicating that the utilization of exogenous amino acids as a source of nitrogen and the extent of regulation of biosynthetic pathways vary with species and strain. All the brewery strains seem to be rather similar and no distinct differences between top and bottom fermentation strains could be observed.     

SYNTHESIS OF AROMA COMPOUNDS BY WORT ENTEROBACTERIA DURING THE FIRST STAGE OF LAMBIC FERMENTATION

Lambic is a special type of Belgian beer obtained by a spontaneous fermentation. The fermentation is initiated by a growth of enterobacteria and non-maltose fermenting yeasts. These organisms die off after one to two months. To gain a clear insight in the relations between the enterobacteria and the aroma compounds formed in wort during this first period, several bacterial isolates were studied with respect to their metabolites formed in a synthetic medium and in two different lambic worts, using aerobic or semi-anaerobic conditions. The results showed that enterobacteria, especially Enterobacter species, are responsible for the production of 2, 3-butanediol, acetic, lactic and succinic acid and lower amounts of ethyl acetate and higher alcohols which are the main aroma compounds found in 1 to 2 months old lambic. Ethanol production is mainly due to yeast activity. The results are in agreement with previous determinations of entero-bacterial species present in first phase lambic¹⁸ .     

Influence of aerobic and anaerobic conditions and yeasts on the reaction between (+)-catechin and glyoxylic acid

The reaction between (+)-catechin and glyoxylic acid in wine model solutions was studied under aerobic and anaerobic conditions in the presence and absence of yeasts with a view to determine their contributions to browning of white wine. Under aerobic conditions, the presence of yeasts reduced the production of colored products, the formation rate of which was similar to that observed under anaerobic conditions and in the absence of yeasts. These results reveal that yeasts and intermediate reaction products compete for oxygen. In the absence of oxygen, the production of colored compounds was even smaller in presence of yeasts, as a result of their ability to retain browning products as they form. Because the absence of oxygen not inhibited the formation of intermediate products resulting from oxidation reactions, an alternative oxidation pathway are proposed acting the glyoxylic acid as oxidant. In the usual concentrations of catechin in white wines, the studied reaction of (+)-catechin-glyoxylic acid can contribute significantly to the alteration of the wine color.