THE INFLUENCE OF MEDIA CONDITIONS ON THE UTILISATION OF MONOSACCHARIDES BY A STRAIN OF SACCHAROMYCES UVARUM (CARLSBERGENSIS)

The utilisation of glucose and fructose by the brewing yeast species Saccharomyces uvarum (carlsbergensis) was investigated. When sucrose was used as the substrate, one of the hydrolysis products, glucose was taken up preferentially over the other hydrolysis product fructose. However, when glucose and fructose were added separately to the media, the uptake profile for each sugar was very similar. Growth promoting media enhanced the differential uptake, whereas non-growth promoting media reduced it. Increase in osmotic pressure of the medium eliminated the preferential uptake of glucose over fructose. The results suggest the presence of a complex uptake system and could be explained by a combination of (1) molecular configuration of the sugars in aqueous solutions, (2) differential phosphorylation effect of glucose and fructose and (3) intracellular accumulation of ethanol in yeast.     

浓香型白酒醅中高产酒精酵母菌的定向筛选及分子鉴定

为了获得适用于酿酒生产的高产酒精酵母菌株,从浓香型白酒醅样品中,经不同浓度乙醇和pH条件下的定向富集和耐受性筛选以及发酵实验,获得3株能在酒精度13%vol、pH3.50的条件下稳定生长且产酒能力较强的酵母菌)XP-3、XP-7和XP-8,其中XP-3的产酒力达87.04%,粮食出酒率可达44.71%,高于一般酿酒酵母.18S rDNA序列分析结果表明,3株酵母菌均与酿酒酵母(Saccharomyces cerevisiae)具有极高的相似性.     

以大豆糖蜜为原料高产乙醇酵母的筛选鉴定及其发酵特性研究

从大豆糖蜜中进行高产乙醇酵母的筛选和鉴定,并对其发酵特性进行研究。从大豆糖蜜中通过菌种的富集分离,TTC平板法初筛,耐乙醇能力及乙醇发酵能力的测定,筛选出一株乙醇产量达9.07%(V/V)的菌株P14。通过个体形态、菌落特征、生理生化及26S rDNA D1/D2区序列分析将菌株P14鉴定为酿酒酵母。研究了大豆糖蜜浓度及添加氮源和无机盐对酿酒酵母P14发酵生产乙醇的影响及酿酒酵母P14对大豆糖蜜中低聚糖的利用,结果表明大豆糖蜜浓度、添加氮源和无机盐对乙醇发酵影响显著,最佳的大豆糖蜜浓度为40%,添加氮源为1.2 g/L的蛋白胨;补加的无机盐为0.4 g/L MgSO4。在此培养基中发酵72 h后,糖蜜中90.10%的葡萄糖,91.23%的蔗糖,92.56%的棉籽糖和96.97%的水苏糖被酵母利用。因此大豆糖蜜中筛选出来的酿酒酵母P14具有较强的利用大豆糖蜜中的大豆低聚糖发酵产生乙醇的能力。     

Fermentative capacity of Kluyveromyces marxianus and Saccharomyces cerevisiae after oxidative stress

Volatile compound production during alcoholic fermentation has been studied in the production of many beverages. Temperature, yeast strain, nutrients and pH have been identified as important factors in the production of volatile compounds. In addition, other factors could influence this production during the fermentation process as well. Oxidative stress could occur during yeast biomass production because oxygen is an essential nutrient that is added to the growth medium. The fermentation parameters and the volatile compound production of one Saccharomyces cerevisiae strain (MC4) and two Kluyveromyces marxianus strains (OFF1 and SLP1) were evaluated in relation to fermentation parameters after oxidative stress induced by hydrogen peroxide or menadione. These yeasts were compared with S. cerevisiae W303–1A and showed significant differences in ethanol production, ethanol yield and maximum ethanol production rate. K. marxianus (OFF1) showed better fermentative capacity after oxidative stress. The higher alcohol production decreased after oxidative stress by >35% after 72 h fermentation time, and the amyl alcohol decreased at a higher level (>60%); however, the isobutanol production increased after oxidative stress between 1.5 and 4 times. The yeasts produced significant concentrations of esters however ethyl lactate, ethyl caprylate and the ethyl caproate were not detected in the control fermentation, while in the stress fermentation they accounted for up to 3 mg/L. These results demonstrate that oxidative stress can play an important role in the final aroma profile; but it is necessary to guarantee adequate yeast growth to obtain the volatile compounds desired. Copyright © 2017 The Institute of Brewing & Distilling     

响应面法优化酿酒酵母谷胱甘肽的提取条件

利用Box-Benhnken 中心组合设计和响应面法优化乙醇提取酿酒酵母胞内谷胱甘肽的条件。结果表明,谷胱甘肽最佳提取条件为乙醇体积分数43.7%、乙醇添加量7.03mL/0.1g 干酵母粉、抽提时间80min、谷胱甘肽提取率达最大为9.54mg/g。     

YEAST STRAIN AND KINETIC ASPECTS OF THE FORMATION OF FLAVOUR COMPONENTS IN CIDER

An apple juice was fermented at 8°C using twelve strains of Saccharomyces uvarum. Glucose, fructose, malic and L-lactic acids, isobutanol, 2,3 butanediol, isoamyl alcohol, ethyl acetate and titratable acidity were determined and monitored in the course of fermentation. It was observed that yeast strains differed from one another mainly in fermentation rates. When components were determined in ciders of the same remaining fructose concentration, rather than after the same fermentation time, the only significant effect of the yeast strain was on the amounts of glucose and ethanol in sweeter cider (fructose 34 g/litre), or on the amounts of glucose, acetic acid, isobutanol and amyl alcohols in dryer ciders (fructose 17 g/litre). A sensory analysis showed that standard deviations of concentrations of remaining or formed components in ciders fermented by different yeast strains, was sufficient to be detected by the taste panel. Added glucose in this range of concentration (1.5 g/litre) in cider reduced the perception of sourness while the addition of acetic acid (0.3 g/litre) reduced the perception of the scented flavour. Added Isobutnol (6 mg/litre) reduced the perception of sweetness. No significant effect of added isoamyl alcohol (30 mg/litre) could be detected. Chemical determinations were correlated by means of regression equations derived from earlier work with some organoleptic characteristics. No anticipated effect of the yeast strain could be detected on any studied flavour characteristic. It is concluded that in ciders of the same attenuation, the effect if it does exist, of the S.uvarum strain isolated from ciders, must be low.     

Screening of cider yeasts for sparkling cider production (Champenoise method)

A total of 350 colonies isolated from a cider cellar in Asturias (Spain) were identified by rDNA ITS-RFLP restriction analysis. Saccharomyces spp. strains were characterized by mitochondrial DNA (mtDNA) restriction analysis. Fifty-four different Saccharomyces spp. strains were identified and tested to ascertain their capacity to carry out secondary fermentation of sparkling ciders. The screening of yeasts to determine their principal enological characteristics (tolerance to ethanol, production of volatile acidity and hydrogen sulphide) was accomplished by means of rapid, non-expensive assays (plate agar). As a result, 13 (24%) of the 54 initial Saccharomyces spp. yeast strains were eliminated. The technological properties assessed were flocculation capacity, ethanol and sulphite tolerance, and production of major volatiles. Ten Saccharomyces cerevisiae strains were characterized as true flocculants; all of these strains were able to grow in ethanolic medium and in the presence of 200mg/l of sulphite. Applying cluster analysis to the production of amyl alcohols, isobutanol, propanol and 2-phenylethanol, the strains were classified in two natural groups. Two flocculent yeast strains referred to as 3' and 50', representative of the each statistical group, were selected together with two reference strains (Saccharomyces bayanus C6 and S. cerevisiae Levuline CHP) to elaborate four sparkling ciders by the Champenoise method. The analysis of variance (p<0.01) among ciders revealed that glycerol, acetaldehyde, ethyl acetate, methanol, propanol, i-butanol and 2-phenylethanol were significantly influenced by the secondary yeast strain. The results of sensory analysis indicated that all the sparkling ciders were scored as good. No significant differences among sparkling ciders were found for odour attributes and taste intensity.     

Modelling of Continuous Corn Starch Hydrolysate Fermentations in Immobilised Cell Reactors

Corn starch hydrolysate has been fermented by two different strains of Saccharomyces cerevisiae and Saccharomyces oviformis, either in batch or in continuous modes, using both suspended-cell and en-trapped-cell systems, provided with different porous supports, namely a commercial synthetic sponge, crushed almond skins and alginate beads. The present results demonstrate that starch hydrolysate is an excellent substrate for alcohol fermentation, whether out of the presence of growth factors for the yeast or in absence of inhibiting substances. A semi-empirical kinetic model, previously proposed for comparing the results of continuous fermentations of various substrates in different reactors, is now successfully extended to the study of different porous supports for cell entrapment in a fixed-bed column. The best results in terms of ethanol productivity (7.8 g^p/1h, referred to the whole reactor volume) are obtained entrapping the yeast cells within the spongy matrix.     

Fermentative stress adaptation of hybrids within the Saccharomyces sensu stricto complex

Along the fermentation process yeasts are affected by a succession of stress conditions that affect their viability and fermentation efficiency. Among the stress conditions the most relevant are high sugar concentration and low pH in musts, temperature and, as fermentation progresses, ethanol accumulation. Nowadays, due to the demanding nature of modern winemaking practices and sophisticated wine markets, there is an ever-growing search for particular wine yeast strains possessing a wide range of optimized, improved or novel enological characteristics. Traditionally, the species S. cerevisiae and S. bayanus within the Saccharomyces sensu stricto species are considered some of the most important yeast species involved in fermentation processes. However, in the last years, hybrid strains between the species S. cerevisiae, S. bayanus and S. kudriavzevii have been described as yeasts conducting the alcoholic fermentations and some of them are commercially available. Our results indicate that yeasts in the Saccharomyces sensu stricto complex were not affected by low pH or high glucose content in the media; however temperature and ethanol concentration variables appreciably affected their growth. The strains pertaining to S. cerevisiae were able to tolerate high temperature stress, whereas strains within S. bayanus and S. kudriavzevii were better adapted to growth at lower temperatures. Regarding to alcohol tolerance, S. cerevisiae is tolerating alcohol better than S. bayanus or S. kudriavzevii. Surprisingly, the natural hybrids between these species have adapted to growth under ethanol and temperature stress by inheriting competitive traits from one or another parental species. These results open new perspectives in the construction of new hybrid strains with biotechnological interest, as the characteristics of the parents may result in interesting combinations in the hybrids.     

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）     

不同基质浓度对酒精发酵的影响

研究了 1株酿酒酵母在清液发酵过程中不同基质浓度对发酵的影响。研究发现 ,在初糖质量分数 >15 %时 ,该酵母的生长开始受到抑制 ;在初糖质量分数为 3 5 %时 ,可达最大发酵酒精体积分数 16 5 %。将平均对基质菌体得率与初糖浓度进行关联 ,描述了基质与菌体生长之间的关系 ;而在葡萄糖质量分数≤ 15 %时 ,产物浓度与初糖浓度之间存在线性关系。     

高浓度发酵中酵母菌性能调控及优化

高浓度发酵能有效提高乙醇发酵的经济效益,但反应过程中高浓度基质和产物对酵母菌性能抑制作用是限制最终乙醇产率的关键因素。文中通过分析比较了不同基质及产物浓度下的发酵中基质浓度、菌体浓度、乙醇产量的变化规律,确定酵母菌对抑制物的耐受浓度。并对比内源和外源乙醇对于发酵初始12 h酵母菌平均比增长速率和平均乙醇发酵速率的影响,揭示内外源乙醇抑制作用的差异。结果表明,在实验浓度范围内,该酵母菌株发酵基质最大投加浓度为160 g/L,所产乙醇最大浓度为55 g/L;产物乙醇是发酵过程中的首要抑制因素,菌体对发酵初始时所添加乙醇的耐受浓度为70 g/L,内源乙醇对酵母菌的抑制作用大于外源乙醇。     

Alcohol-mediated haemolysis in yeast

Although yeast are generally non-haemolytic, we have found that addition of alcohol vapour confers haemolytic properties on many strains of yeast and other fungi. We have called this phenomenon 'microbial alcohol-conferred haemolysis' (MACH). MACH is species- and strain-specific: whereas all six Candida tropicalis strains tested were haemolytic in the presence of ethanol, none among 10 C. glabrata strains tested exhibited this phenomenon. Among 27 C. albicans strains and 11 Saccharomyces cerevisiae strains tested, ethanol-mediated haemolysis was observed in 11 and 4 strains, respectively. Haemolysis is also dependent on the alcohol moiety: n-butanol and n-pentanol could also confer haemolysis, whereas methanol and 2-propanol did not. Haemolysis was found to be dependent on initial oxidation of the alcohol. Reduced haemolysis was observed in specific alcohol dehydrogenase mutants of both Aspergillus nidulans and S. cerevisiae. MACH was not observed during anaerobic growth, and was reduced in the presence of pararosaniline, an aldehyde scavenger. Results suggest that initial oxidation of the alcohol to the corresponding aldehyde is an essential step in the observed phenomenon.     

Impact of ammonium additions on volatile acidity, ethanol, and aromatic compound production by different Saccharomyces cerevisiae strains during fermentation in controlled synthetic media

Variations in ethanol, volatile acidity, and aromatic compounds produced by different Saccharomyces cerevisiae strains were studied in controlled synthetic medium (CSM). Different amounts of assimilable nitrogen (in the form of ammonium sulfate) were added at two fermentation stages (i.e. the beginning of fermentation and the halfway point). There were significant differences in the amount of ethanol produced when ammonia was added to the CSM, although this depended on the yeast strain used. When assimilable nitrogen was added, ethanol production either increased (with Fermicru AR2 and Stellevin NT116 yeast strains) or decreased (with LW LVCB CT1+ yeast strain). The degree of variation also depended on the time that the ammonia was added, with differences of up to 0.7% (v/v). Adding ammonium to the CSM always resulted in lower volatile acidity in the fermentation product. Different yeast strains ( P < 0.0001) and varying amounts of ammonium produced significant differences. Maximum impact – up to 70% less volatile acidity – was obtained using the Stellevin NT116 yeast strain and adding 280 mgN/L ammonium at the halfway point in fermentation. Acetoin production increased at higher concentrations of added ammonium, most markedly when it was added halfway through fermentation. The total amount of esters increased when 140 mgN/L was added to all three yeasts strains tested, irrespective of the fermentation stage. Smaller amounts of higher alcohols were produced following larger ammonium additions, especially at the beginning of fermentation.     

冰酒中的毕赤属和汉逊属酵母菌的筛选及其在葡萄酒酿造中的应用

从冰葡萄酒自然发酵过程中分离、鉴定出10株毕赤属(Pichia)和汉逊属(Hanseniaspora)酵母,对其耐受性(酒精、糖、酸、SO2)进行研究,筛选得到4株耐受性能优良的酵母菌株,编号为"HO"和"HU"(Hanseniaspora属)、"PO"和"PK"(Pichia属).再将此4个酵母菌株与商业酿酒酵母(S...     

不同酿酒酵母对柑橘果酒香气成分的影响

研究不同来源酿酒酵母对柑橘果酒香气成分的影响,以锦橙表皮和柑橘园土壤为酵母的来源,经培养、分离、纯化、初筛和复筛得到适于柑橘果酒酿造的酵母菌株。确定其最适生长温度、pH 值及对乙醇和SO2 的耐受性,并用GC-MS 分析其对柑橘果酒香气的影响。结果显示：筛选得到3 株酵母菌L3、L5、L9,其最适生长温度为28～30℃,最适pH 值在3.5 左右,其中L3 耐低温和高温的能力最强,L9 乙醇耐受力最强,L5 对SO2 的耐受能力最强。3 株酵母所酿柑橘果酒的香气成分有特异性差异,庚酸乙酯、萜品油烯等13 种物质为L3 酵母菌所酿柑橘果酒独有;月桂醇、乙酸异丁酯等8 种物质仅见于L5 酵母菌所酿柑橘果酒中;正辛醇、5- 甲基呋喃醛等4 种物质只在L9 酵母菌所酿柑橘果酒中存在。     

固定化酵母直接发酵甜菜汁生产燃料乙醇的研究

为了简化发酵工艺、缩短发酵时间、提高发酵效率,采用聚乙烯醇凝胶作为包埋剂进行酵母固定形成固定化酵母产品,并将其直接发酵甜菜汁进行燃料乙醇生产技术研究,结果表明,固定化后的酿酒酵母接种量为15％时,甜菜发酵液中酒精含量最高,达到9.41％vol,其他接种量都有所降低.利用固定化酵母进行甜菜酒精发酵比对照组酒精平均值提高了2.86％.连续9批次发酵且期间不进行灭菌处理,产酒稳定.因此,利用固定化酵母直接发酵甜菜汁生产燃料乙醇是可行的.     

己酸菌对高产酯酿酒酵母酒精发酵及酯醇代谢的影响

将己酸菌与高产酯酿酒酵母在高粱汁培养基中进行混合发酵,研究己酸菌对高产酯酿酒酵母酒精发酵及酯醇代谢的影响。结果表明,己酸菌菌悬液对高产酯酿酒酵母的生长及代谢没有直接影响;己酸菌的代谢产物对高产酯酿酒酵母的发酵速度及酒精产量有所促进,在培养基己酸浓度为220mg/L时,酒精产量提高了6.63%;在己酸浓度为45~220mg/L时,高产酯酿酒酵母的乙酸酯类和主要高级醇受到的抑制作用逐渐增强,乙酸乙酯最多降低65.32%,乙酸异丁酯最多降低91.32%,乙酸异戊酯最多降低82.14%,高级醇最多降低71.14%;在己酸浓度为220mg/L时,与己酸浓度为0mg/L时对比,高产酯酿酒酵母共有1032个基因转录水平上调,有1037个基因转录水平下调,这些转录水平变化的基因主要涉及到高产酯酿酒酵母的氮代谢、糖酵解、苯丙氨酸代谢、碳代谢等多条代谢途径。     

THE EFFECTS OF INCREASED MAGNESIUM AND CALCIUM CONCENTRATIONS ON YEAST FERMENTATION PERFORMANCE IN HIGH GRAVITY WORTS*

The response of e number of Saccharomyces cerevisiae (ale) and Saccharomyces uvarum (caris-bargenaia) (lager) strains to altered starting levels of magnesium and calcium in 12°P (1048 original gravity) or 20°P (1080 original gravity) wort were investigated. In general, the same trends were observed in all 6 strains, however the extent of the response to adjusted levels of magnesium and calcium were found to be strain dependent. The results indicate that an increased ratio of magnesium to calcium causes an increase in the initial fermentation rate, the rate and yield of ethanol produced and an increase in vitality at the end of fermentation, in all strains employed. Upon increasing the calcium to magnesium ratio it was found that the initial fermentation rate was decreased, resulting in an increased attenuation time in the case of the lager strains. It was also noted that increasing the calcium to magnesium ratio led to a decreased ethanol production, maltotriose uptake, and in the case of the lager strains, maltose uptake was also adversely affected under these conditions. Altering the calcium and magnesium levels had no effect on the viability of the yeast or on glycogen levels .     

STRAIN SPECIFIC RESPONSE OF BREWER'S YEAST STRAINS TO ZINC CONCENTRATIONS IN CONVENTIONAL AND HIGH GRAVITY WORTS*

The effect of zinc on a variety of yeast strains is extensively documented in the literature. However, due to the varied experimental protocols employed in each study there is little opportunity to directly compare the strain specificity of this ion. In the present study, the response of six yeast strains (three Saccharomyces cerevisiae (ale type) and three S.cerevisiae (lager type)) to altered zinc concentrations, in both high (1080 OG) and conventional (1048 OG) gravity worts, was investigated. Varying the initial wort zinc concentration in both gravities had an effect on the ethanol production, rate of fermentation, cell number and sugar uptake of all six strains studied. The extent of the response was found to be dependent upon the zinc concentration, the strain employed and wort gravity employed.