DEHYDROGENASE ACTIVITY FOR HIGHER ALCOHOLS IN CELL-FREE EXTRACTS OF SACCHAROMYCES CEREVISIAE

Alcohol dehydrogenase activities were determined in cell-free extracts of Saccharomyces cerevisiae with fusel oil-alcohols and other higher alcohols (including straight and branch-chain aliphatic alcohols, cinnamyl alcohol and phenethanol) as substrates. A fluorometric measurement of the formation of reduced coenzyme (NADH) was needed because of the necessity for increased sensitivity with the required use of very low concentrations of substrates. For the first time, dehydrogenase activities were measured in cell-free extracts for active-pentanol, n-hexanol and n-heptanol as substrates. Optimal molar concentration of the substrates was found to decrease with increasing carbon number. Activity measurements were made in extracts of yeasts grown under various conditions of oxygen induction and catabolite repression. Dehydrogenase activities for all substrates were higher in extracts of yeast grown aerobically as compared to those grown anaerobically. A comparison of the activities with the fusel oil-alcohols as substrates suggests a plurality of alcohol dehydrogenase activities in the last enzymic step in fusel oil formation.     

THE INFLUENCE OF WORT GLUCOSE LEVEL ON THE FORMATION OF AROMATIC HIGHER ALCOHOLS

Increasing amounts of glucose either in solid form or in solution were added to all-malt worts, and to worts that contained maize as adjunct. Fermentations were then carried out using either ale or lager yeast. The resultant beers were analysed by gas chromatography for the aromatic higher alcohols tryptophol, tyrosol and phenylethanol; the amyl alcohols were also determined as typical representatives of the aliphatic higher alcohols. Increasing concentration of glucose in the wort resulted in either decreasing levels of tyrosol and phenylethanol (ale yeast) or increasing levels (lager yeast). Tryptophol demonstrated a different pattern both with ale and lager yeasts, by increasing in concentration up to a certain maximum, then decreasing.     

SYNTHESIS OF HIGHER ALCOHOLS IN THE GENUS ZYMOMONAS

Several strains of bacteria of the genus Zymomonas were examined with respect to their potential for higher alcohol synthesis. All strains studied were able to produce higher alcohols during growth in a simple medium containing glucose and yeast extract. The higher alcohols produced were mainly n-propanol and iso-amyl alcohol. In contrast to Saccharomyces cerevisiae, only trace amounts of higher alcohols were produced from glucose by resting cells. When amino acids or other precursors were added to the fermentation medium, the resting cells formed higher alcohols. The stimulation of n-propanol synthesis by precursors was the most pronounced. The results obtained indicate that, with minor differences, the mechanisms of higher alcohol synthesis are comparable to these used by yeasts.     

THE FORMATION OF ESTERS AND HIGHER ALCOHOLS DURING BREWERY FERMENTATION; THE EFFECT OF CARBON DIOXIDE PRESSURE

The influence of the size and geometry of brewery fermentation vessels on beer flavour and aroma formation is generally attributed to carbon dioxide pressure. In order to study this pressure effect, brewery batch fermentations were carried out on the laboratory scale with Saccharomyces cerevisiae. The formation rates and yields of esters and fusel alcohols were studied in relation to the growth of metabolically active biomass. The results indicate that the observed reduction in the formation of esters and fusel alcohols with increased carbon dioxide pressure is mainly caused by reduced yeast growth. The overall formation of fusel alcohols is less affected than the formation of esters.     

THE INFLUENCE OF A COLIFORM BACTERIUM ON FERMENTATION BY YEAST

Hopped wort (20°C) was inoculated with brewing yeast alone (10⁷ cells/ml), or with Citrobacter freundii (10⁵ cells/ml) or with both organisms at the concentrations stated. The mixture grew somewhat more quickly than the pure yeast culture, the oxidation-reduction potential and S.G. fell more quickly but the pH less rapidly. The mixed culture produced more ethanol and various organic acids but less volatile carbon. Dimethyl sulphide was produced in the mixed culture but not in the pure yeast culture. It is concluded that C. freundii can have a profound influence on yeast fermentation, consistent with its pure culture characteristics.     

FERMENTATION PROPERTIES OF BREWING YEAST WITH KILLER CHARACTER

The cytoplasmically-inherited killer character of a laboratory strain of Saccharomyces cerevisiae has been transferred to three different commercially-used brewing yeasts; two ale strains and one lager strain. The ease with which the character can be transferred is very strain dependent. In addition to killer character, mitochondria from the brewing strain have been transferred into the new ‘killer’ brewing strains. Fermentations carried out with the manipulated strains produced beers which were very similar to those produced by the control brewing strains. The beers produced by killer brewing strains containing brewing yeast mitochondria were most like the control beers and could not be distinguished from them in three glass taste tests. In addition to producing good beers the genetically manipulated yeasts killed a range of contaminant yeasts and were themselves immune to the action of Kil-k₁ killer yeasts.     

保健功能性黄酒的生产工艺研究

利用固定化酵母细胞技术对传统黄酒酒母生产经过改造，确定了完整的全发酵特种黄酒生产工艺，该技术产品对人体有一定的保健功能。     

活性干酵母在淀粉质酒精发酵生产中的应用

本文利用市售活性干酵母代替培养酒母,分别进行淀粉质酒精间歇发酵、半连续发酵和连续发酵大型生产,均取得了发酵速度快、出酒率高的好效果。     

MALT FLAVOUR — TRANSFORMATION OF CARBONYL COMPOUNDS BY YEAST DURING FERMENTATION

Laboratory and pilot scale fermentations have been carried out using worts spiked with a range of carbonyl compounds, many of which are derived from malt. Aldehydes and vinyl ketones were chemically reduced during fermentation and could not be detected in the resulting beers; on the other hand certain saturated and non-conjugated unsaturated ketones were only partially reduced. The corresponding saturated alcohols and acetate esters were usually detected as transformation products.     

FLOW CYTOMETRIC MONITORING OF RHODAMINE 123 AND A CYANINE DYE UPTAKE BY YEAST DURING CIDER FERMENTATION

Flow cytometry of rhodamine 123- or cyanine-stained cider yeast shows that the capacity for mitochondrial uptake of these cationic dyes is lost early in the fermentation. Survival of prolonged anaerobiosis (for at least 22 days) at high ethanol concentrations (at least 11% v/v) during cider fermentation does not require the maintenance of a measurable inner mitochondrial transmembrane electrochemical potential. Confocal laser scanning microscopy of yeasts after exposure to either of the cationic dyes confirms the lack of mitochondrial development and inability of the fermentative organisms to take up the fluorophores. Aeration of samples taken from the fermentation vessels restores the ultrastructure and the dye uptake capacity of the yeasts. This indicates that the changes are reversible, and that the organisms have retained their viability.     

CAMBRIDGE PRIZE LECTURE: STUDIES ON YEAST PHYSIOLOGY-IMPACT ON FERMENTATION PERFORMANCE AND PRODUCT QUALITY*

The physiology of brewing yeast is of pivotal importance in securing and maintaining beer quality. Fundamental studies on aspects of yeast physiology are critically evaluated, areas considered include alternative approaches to yeast propagation and methods for strain differentiation. The proposed role of glycogen in fuelling lipid synthesis and other early events in fermentation is discussed, as are methods for measurement of this reserve polysaccharide. As an extension of this work, a new and novel approach to the improved control of fermentation is described. The interaction between yeast physiology and beer flavour is considered. Evidence is presented that the synthesis of higher alcohols and volatile esters contribute to the regulation of intermediary metabolism in yeast during fermentation.     

蜂窝陶瓷固定化酵母细胞啤酒连续后发酵工艺的研究

将蜂窝陶瓷用作酵母细胞固定化的载体，进行啤酒连续后发酵试验研究。应用均匀试验设计法来安排试验．对试验数据进行统计分析及最优化处理，并通过验证试验，获得优化的工艺条件为：发酵温度13～14℃，稀释率0．142h^-1。啤酒主要理化指标的测定和口味品评结果表明：与传统工艺相比，采用蜂窝陶瓷固定化酵母细胞啤酒连续后发酵工艺不会影响啤酒的品质，而后发酵时间可大为缩短。     

THE EFFECT OF LOW CO2 PRESSURES ON THE ABSORPTION OF AMINO ACIDS AND PRODUCTION OF FLAVOUR-ACTIVE VOLATILES BY YEAST

Laboratory fermentation of 51 batches of wort under CO₂ pressures of 0·5 and 1·0 atm have shown that whilst the speed of fermentation was affected only slightly, absorption of amino acids, production of several flavour-active compounds and some yeast features were affected. The CO₂ pressure led to reduced absorption of Group B amino acids although Group A compounds were unaffected; fusel oil and ester concentration was reduced whereas that of the vicinal diketones and acetaldehyde was increased. Yeast crop and cell viability fell with increase in pressure and at 1·0 atm the mean cell volume was increased. The results suggest that CO₂ could have significant effects on yeast and beer quality within the range of concentration which can be expected to occur in unpressurized commercial fermentations.     

INTRODUCTION OF FLOCCULATION INTO AN INDUSTRIAL YEAST STRAIN BY TRANSFER OF A SINGLE CHROMOSOME

The transfer of chromosomes from a laboratory strain FLO5 to a wine strain using cytoduction yielded flocculent clones. The fermentation performance of such clones was closely correlated with the quantity of genetic material transferred. The fermentation properties of clones receiving only a single chromosome I were very similar to those of the original strain. The transferred chromosome I was more stable when it replaced the original chromosome than when it remained as an additional element.     

毛细管气相色谱法测定糯米酒中的甲醇、乙酸乙酯和杂醇油

建立了一种用毛细管气相色谱法测定糯米酒中甲醇、乙酸乙酯和杂醇油的方法，并对色谱条件进行了优化。样品加标回收率在90．7％～98，8％之间，相关系数在0,9954以上，相对标准偏差0．89％-2，53％。该方法简便、快速、准确、结果令人满意。     

INDUCTION OF PREMATURE YEAST FLOCCULATION BY A POLYSACCHARIDE FRACTION ISOLATED FROM MALT HUSK

A husk polysaccharide component from a malt causing premature yeast flocculation was isolated and characterized, and its effect on the fermentation pattern of Saccharomyces cerevisiae 2036 established. A particular malt husk extract, obtained using a mild aqueous extraction procedure, induced premature flocculation when added to fermentations in normal wort. In sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of the malt husk extract, 4 protein bands (42,600; 17,500; 15,100 and 13,100 daltons) and a high molecular weight polysaccharide were identified. These components were separated by gel chromatography and their effect on the fermentation pattern established. Only the polysaccharide fraction induced premature flocculation. Sugar analysis of this fraction indicated the presence of arabinose, galactose, glucose, mannose, xylose, rhamnose and an acidic sugar component. The polysaccharide fraction showed haemoagglutination activity, which was not inhibited by any of 11 simple sugars tested.     

SUGAR UTILIZATION BY A BREWING YEAST IN RELATION TO THE GROWTH AND MAINTENANCE PHASES OF METABOLISM

In batch fermentations, carried out using a range of conditions, the specific rate of sugar utilization is shown to decline throughout. When yeast mass is increasing, the yield coefficient relating carbohydrate utilization to mass production remains approximately constant and the declining specific fermentation rate parallels declining specific growth rate. When mass production ceases, maintenance of the yeast population requires only a low rate of sugar utilization. Attenuation associated with maintenance phase activity is relatively insignificant compared with that associated with growth.     

THE INFLUENCE OF FILM YEAST ACTIVITY ON THE AROMA VOLATILES OF FLOR SHERRIES—A STUDY OF VOLATILES ISOLATED BY HEADSPACE SAMPLING

Headspace analyses of Australian flor sherries showed the aroma-significant components were ethyl esters of n-hexanoic, n-octanoic, n-decanoic acids as well as n-hexanol. After varying periods of flor film growth, changes in the composition of aroma substances occurred. A decrease in concentrations of ethyl n-octanoate and ethyl n-decanoate was accompanied by an increase in the concentrations of 2-phenethyl alcohol and diethyl succinate whilst the concentration of n-hexanol was unaffected.     

THE EFFECT OF OSMOTIC PRESSURE ON THE PRODUCTION AND EXCRETION OF ETHANOL AND GLYCEROL BY A BREWING YEAST STRAIN*

When the cells of a lager brewing yeast Saccharomyces uvarum (carlsbergensis) were grown in minimal media containing sucrose and a non-metabolized sugar sorbitol, significant levels of intracellular ethanol were obtained. Intracellular ethanol concentration decreased as the osmotic pressure of the medium was lowered and the proportion of extracellular ethanol increased. A reduction in cell viability occurred when there were high levels of intracellular ethanol. The total amount of glycerol produced increased with increased osmotic pressure, but glycerol diffused out of the cells faster than ethanol.