CHANGES IN CYTOCHROME LEVELS DURING THE STORAGE OF BAKER'S YEAST AT DIFFERENT TEMPERATURES

The content of cytochromes determined per g fresh yeast was found to stay constant during nearly 3 months' storage of baker's yeast at 5°C. When stored at 24°C and 35°C the content of cytochromes apparently increased during the first 14 and 4 days of storage, respectively, and then decreased continuously.     

ESTERASES OF BAKER'S YEAST. II. SUBSTRATE SPECIFICITIES TOWARDS ESTERS FORMED DURING SUGAR FERMENTATIONS

Ethyl esters of fatty acids (C₂–C₁₂), isoamyl acetate and 2-phenethyl acetate were studied as substrates for yeast esterases and compared with the synthetic substrates, p-nitrophenyl esters and β-naphthyl esters. Intact yeast, the 55% and 55–75% ammonium sulphate precipitate of centrifuged yeast homogenate, and partly purified esterases were used for the determination of the hydrolysation activity towards the esters. The results showed that the yeast esterases prefer to hydrolyse the ethyl esters with acyl chain length of C₅ to C₁₂. The acetate esters, ethyl acetate, isoamyl acetate and 2-phenethyl acetate are only very slowly hydrolysed or remain unaffected. The substrate specificity of different esterases varies and can be used for their characterisation. Investigating pH optimum curves using intact yeast and a crude esterase preparation and different substrates confirmed the earlier result that there are esterases on both sides of the plasma membrane. The specificity of intracellular and periplasmically located esterases is, however, different.     

Comparison of Genetic and Enological Characteristics of New and Existing S. cerevisiae Strains for Chardonnay Wine Fermentations

Wine makers are currently looking for ways to enhance the flavor and develop complexity in their wines by applying new enological tools, utilizing novel yeasts or mixed strain cultures. This research characterized the genetic fingerprints and killer phenotypes of two Burgundian yeast isolates (C2, C6). Chardonnay must was fermented, and the Burgundian yeast strains were assessed for their enological characteristics (ethanol, acetic acid, glycerol and sulfur dioxide production, foam formation, ethanol tolerance) in individual and mixed cultures and compared to six commercial wine strains. Their unique genetic fingerprints and killer positive phenotypes confirmed that the Burgundian strains would predominate in individual culture or would be able to grow simultaneously in mixed culture. Analyses of variance and principal component analysis were used to compare the enological characteristics of the individual and mixed strains. The individual and mixed strain fermentations of C2 and C6, were more similar to one another compared to the commercial strains, yet enologically equivalent. As such, the novel Burgundian yeast strains offer wine makers a new tool for customizing the characteristics and enhancing complexity of the wines, while ensuring that their enological characteristics are consistent with commercial requirements.     

RESERVE CARBOHYDRATE METABOLISM AND CELL SURVIVAL IN AEROBICALLY STARVING BAKER'S YEAST

Changes in the level of reserve carbohydrates, cell number, viability and medium pH values were observed in aerobically starving baker's yeast. The starvation was carried out at 35°C in the physiological saline solution using two different initial pH values (4·4 or 5·5) of the medium. In addition, the formation of ethanol and acetate as well as actual and endogenous respirations were measured at a pH of 4·4. The results revealed that the initial pH value of the medium affected the pattern of glycogen and trehalose degradation and consequently, also caused the loss of viability and cell lysis. Changes in the quantity of metabolic products and respiration activity are discussed in connection with the metabolism of the starving cells and the effect of environmental conditions.     

烟台贵人香葡萄自然发酵醪中本土酿酒酵母的选育及酿造特性研究

自葡萄原料生产地选育优良酿造特性的本土酵母是开发地方特色葡萄酒品种的重要措施。本研究以烟台地区贵人香葡萄自然发酵醪为材料,筛选酿酒酵母并对其发酵特点和耐受能力进行测定,进而选育本土酿酒酵母用于霞多丽干白和赤霞珠干红葡萄酒的酿造试验。采用孟加拉红选择性培养基筛选本土酵母菌,并经WL鉴定培养基和5.8S ITS序列鉴定获得12株酿酒酵母。通过测定发酵后残糖量和酒精度及耐受能力(酒精度、SO2、酸、高糖),选育4株酵母用于酿造霞多丽干白葡萄酒,对酒样指标、主要挥发物和香气组分分析,显示菌株YGF2、YGF5和YGF10的酿造特性和发酵指标较好,并用于酿造赤霞珠干红葡萄酒。结果表明菌株YGF2酿造的葡萄酒质量较好,香气浓郁,部分指标优于商品酿酒酵母,具备生产区域特色葡萄酒的潜力。     

YEAST ESTERASES AND AROMA ESTERS IN ALCOHOLIC BEVERAGES

It has been shown that the proportion of fatty acid ethyl esters retained by the yeast cell increases with increasing acyl chain length as the ester becomes more lipid soluble. The distribution of esters depends on the yeast strain and on the fermentation temperature; larger amounts of esters were found to transfer from the cells into the medium at higher temperature. It was shown that esterase activity is located both inside and outside the yeast cell plasma membrane. Intact yeast was capable of hydrolysing the ethyl esters of caproic, caprylic and capric acid. Acetate esters, were hydrolysed only very slowly or not at all. The hydrolytic activity of baker's yeast was studied with ethyl caprylate as substrate. The hydrolysis was very fast at the beginning. The equilibrium attained depended not only on the concentration of ester and alcohol but also on the pH, a higher amount of ester remaining in solutions of lower pH. It was also shown that the esterases possess appreciable ester synthesizing ability and an equilibrium was attained by incubating yeast with caprylic acid and ethanol. The experiments described show that the ester level in an alcoholic beverage, such as beer, is not dependent solely on the ester concentration formed during fermentation: in the presence of yeast the level can be shifted in either direction by changing temperature, pH or alcohol concentration — or the amount and type of yeast.     

EFFECT OF INCORPORATING ADDITIONAL OLEIC ACID INTO THE PLASMA MEMBRANE OF BAKER'S YEAST ON THE PERMEATION OF PYRUVIC ACID

Addition of Tween 80 to the growth medium of baker's yeast (Saccharomyces cerevisiae) under anaerobic conditions resulted in an increased content of 9-cis-octadecenoic acid (oleic acid) in a membrane preparation consisting mainly of plasma membrane. There was no significant effect on the pyruvate decarboxylation capacity of disintegrated cells, but that of intact cells was significantly enhanced, presumably because of an oleate-induced increase in the permeability of the plasma membrane to pyruvate.     

高产SOD酵母菌的诱变选育及发酵条件研究

用紫外线诱变酿酒酵母B094原生质体,得到1株SOD含量较高的菌株BUV094,其SOD含量为720U／g湿菌体。用正交试验及单因了条件试验对该突变株进行培养基组成及发酵条件的研究,结果表明：其最佳培养基组成为葡萄糖2％,蛋白胨1％,酵母膏1％,7Be麦芽汁9％（V／V）,CuSO475mmol／ml,ZnSO425mmol／ml;最佳培养条件为：初始pH5．5,摇瓶装量为75ml／500ml三角瓶,接种量为15％,培养时间24h。在此条件下,该菌细胞生物量为5．39g／100ml,SOD含量为1024U/g湿菌体,SOD产量为5520U／100ml,SOD产量较出发菌株提高103％。     

橘皮果醋的研制

采用液体发酵法酿制橘皮果醋,经水解、酒精发酵及醋酸发酵等工序。试验结果表明:酶解后橘皮汁的还原糖含量可达3.8g/100mL,用大米糖浆补糖至7.8g/100mL;经酒精发酵60h,酒精度达5.0°;再经醋酸发酵80h,酸度达3.15g/100mL。产品澄清透明,有柑橘特有的清香,酸味浓郁,醇香不涩。     

METABOLIC RESPONSES OF BAKER'S YEAST TO GLUCOSE ADDITION DURING AEROBIC STARVATION

The kinetics and extent of glucose uptake, ethanol and acetate production, glucose-induced medium acidification and endogenous respiration were studied in baker's yeast starved aerobically for 0, 28, 54 and 96 h in saline (9 g litre^?1 NaCI) at 35°C. Except for the last interval, prolonged starvation brought about an overall increase in most parameters; the transient increase in endogenous respiration observed after glucose addition was lowered with proceeding starvation. A 96 h starvation brought about a change in the kinetics of ethanol production, sharp increase in acetate production and a strong reduction of both the extent and the rate of glucose-induced acidification and of endogenous metabolism.     

一株非酿酒酵母分离鉴定及多菌种混菌发酵对葡萄酒香气的影响研究

实验从红茶菌液中分离得到一株性质优良的非酿酒酵母H8(克鲁斯假丝酵母Candida crusei),并与全美梅氏酵母、葡萄有孢汉生酵母按1：1：1比例混合,经过46 h培养,与酿酒酵母顺序接种发酵赤霞珠红葡萄酒,通过测定挥发香气物质以及感官品评,与法国酿酒活酵母(RX)在单菌种条件下发酵比较,结果表明:混菌发酵与单菌发酵的理化检测指标差异不明显,挥发性物质的组成及其含量差别较大,其中混菌发酵的酒样中共有挥发性物质29种,其中酯类物质17种,醇类物质3种,酸类物质3种,烯烃类物质2种,酮类物质1种,其他物质3种;而单菌发酵的酒样中有23种挥发性物质,其中酯类物质16种,醇类物质3种,酸类物质2种,烯烃类物质1种,酮类物质1种。结论:混菌发酵中含量较多且单菌种没有的物质如苯乙醇、薄荷醇、柠檬烯、十一醛、肉豆蔻醛等均具有丰富复杂的特征相香气,对葡萄酒香气有一定积极的贡献,有利于改善目前市场上葡萄酒同质化的问题。     

酿酒活性干酵母在酒精生产中的应用

酿酒活性干酵母应用于酿酒行业和超级酿酒酵母应用于酒精浓醪发酵,不仅是我国酿酒工业的技术革命,而且极大地推动了酒精行业的技术快速发展。目前,酿酒活性干酵母广泛应用于酿酒工业和酒精的浓醪发酵以及燃料酒精工业。针对酒精生产原料的变化,酒精生产工艺的不同,酿酒活性干酵母的适应性和发酵浓度将会提高;酵母对温度、渗透压以及对产物、底物的抑制的敏感度将降低;酒精生产工艺的控制要求将进一步提高,对酿酒活性干酵母对酵母质量的要求也将更高。（孙悟）