几种面包活性干酵母发酵不加糖面团性能的比较

对市场上的5种面包活性干酵母(ADY)进行了发酵性能测定。结果表明,不同面包酵母对低糖面团与不加糖面团发酵力存在差异,其中ADY1基本无差别,ADY2的差别较小(3.2%),而ADY4(11.9%)、ADY5(9.4%)的差别较大。通过对5种酵母麦芽糖发酵速度和葡萄糖阻遏程度的分析表明,干酵母ADY1、ADY2发酵麦芽糖速度较快,葡萄糖阻遏程度较小;而ADY4、ADY5发酵麦芽糖速度较慢,葡萄糖阻遏程度较高。可见,麦芽糖发酵速度快、葡萄糖阻遏程度小的酵母品种比较适合于不加糖面团的发酵。     

面包酵母无糖面团发酵力与麦芽糖发酵力相关性的探讨

探讨了面包酵母在无糖面团中的起发速度与麦芽糖发酵力之间的关系，包括葡萄糖阻遏作用对麦芽糖发酵力的影响。结果表明，在8株供试的面包酵母菌中，麦芽糖发酵力较强的菌株在无糖面团中的起发速度较快，反之则较慢。验证了麦芽糖发酵力是决定面包酵母快速发酵无糖面团的关键因素。     

高适应性面包酵母菌株的杂交选育

为了改善耐高糖酵母在不同含糖量面团中的发酵力,首先制备了2 4 0株耐高糖酵母单倍体,通过高麦芽糖发酵筛选培养基筛选出了2 8株麦芽糖发酵性能良好的单倍体菌株,通过测定这些单倍体在无糖面团中的发酵力,发现9株单倍体菌株的发酵力优于或等于其亲本,其中4株为a型,5株为α型。通过它们之间的杂交得到2 0 0株杂交株,在无糖、中糖、高糖面团中测定这些杂交株的发酵力,获得4株在不同含糖量(0～30 % )面团中都具有高发酵力的高适应性面包酵母杂交株。研究表明,来自同一亲本单倍体之间的杂交有可能改善面包酵母的某些特征。     

敲除REG1同时过表达SNF1基因对工业面包酵母不加糖面团发酵的影响

研究了蛋白磷酸酶PP1调节亚基编码基因REG1缺失同时蛋白激酶基因SNF1过表达对工业面包酵母麦芽糖代谢和不加糖面团发酵的影响。比较分析REG1缺失同时SNF1过表达转化子BYKPS-R和亲本菌株BY14α、REG1缺失突变株BYK-R的MAL基因m RNA水平、麦芽糖酶和麦芽糖通透酶活力、麦芽糖代谢水平、不加糖面团发酵力,以及基本生长性能,结果表明,敲除REG1同时过表达SNF1能够显著提高麦芽糖代谢相关基因转录和酶活力,有效减弱葡萄糖阻遏,从而使面包酵母的麦芽糖消耗速率(葡萄糖被完全消耗完之前)较BY14α和BYK-R分别提高了18.59%和4.40%,不加糖面团发酵力分别提高了12.51%和3.22%。在REG1基因缺失的基础上,过表达SNF1可以进一步提高面包酵母的麦芽糖代谢和不加糖面团发酵水平,同时不影响面包酵母菌株生长性能,因此转化子BYKPS-R具备潜在的工业应用价值,同时该研究为快速发酵面包酵母菌株的选育奠定基础。     

玫瑰香葡萄酒专用酵母菌株的选育

2-苯乙醇是玫瑰香葡萄酒主要的特征性风味物质。以发酵性能优良的葡萄酒酵母H为出发菌,采用紫外诱变和化学诱变,获得了1株适量高产2-苯乙醇的葡萄酒酵母H9-24。与原始出发菌株比较,2-苯乙醇产量提高了46.0%,高级醇总量降低了30.7%。对H9-24进行了10次传代培养,其2-苯乙醇和高级醇产量稳定,表明该菌株遗传性能稳定。     

复合诱变选育木聚糖酶高产菌株

目的：米曲霉高产木聚糖酶菌株的诱变筛选。方法：以米曲霉FSl为出发菌株,采用紫外线＋氯化锂复合诱变,筛选出一株高产木聚糖酶菌株FSl－41,并对该突变株的遗传稳定性初步研究。结果：紫外线的最佳照射时间为210s,氯化锂的最佳浓度为0．8％,筛选出来的突变株FSl－41产酶水平可达4992．51U．mL－1,比出发菌株提高了22．49％,突变株经5代连续培养,产酶性能稳定。     

耐冻性面包酵母菌种的选育及其特性的研究

通过对实验室保藏和市售的面包酵母进行耐冻性测定 ,以存活率为主要指标 ,选育出 1支耐冻性良好的菌株 (FTY 5 ) ,在 -2 0℃条件下冷冻保存 5 6d ,存活率达 90 %以上。并且通过冷冻贮藏、耐糖性、产气性和生长曲线测定等实验对该菌株的特性进行了研究 ,在此基础之上采用正交实验确定了糖蜜培养基的配方和培养条件。     

高产食用蛋白质产朊假丝酵母菌的选育及发酵条件优化

通过对产朊假丝酵母菌的紫外诱变,筛选蛋白质含量较高的可食用菌株。结果表明：在15W紫外线(30cm)处,照射120s,致死率为89%,得到蛋白质含量为33% 的诱变菌株,比诱变前的22.9% 提高了37.12%。对此菌种进行稳定性测试(传代10 次并进行蛋白质测定),性质稳定;对诱变后的发酵条件：碳源、氮源、培养温度和溶氧量(培养箱转速)进行优化,最终得到采用葡萄糖为碳源、硫酸铵和酵母浸膏粉的混合物为氮源、培养温度为32℃、转速为160r/min 时培养出的蛋白质含量及菌体生物量都在较高水平,蛋白质含量为37%。     

低温快速发酵酵母菌的选育

经紧外线诱变处理,从法国酵母中筛选到一株在较低温度(20℃)下快速发酵的面包酵母U.V-45。在相同测定条件下,U.V-45比目前市售活性最高的美国酵母发酵力高29～40%;比出发苗株高24～28%。研究中还采用了原生质体融合育种方法,但未得到优于U.V—45的生产菌株。     

STUDIES IN CONTINUOUS FERMENTATION I. EFFECTS OF YEAST CONCENTRATION

Saccharomyces cerevisiae (NCYC 1026) was grown in synthetic medium, brewer's wort and media intermediate in composition, using both open and closed systems of continuous culture. The level of nitrogen source in the synthetic medium severely restricted growth in the open system but with similar flow-rates in the closed system much higher yeast populations were maintained. The levels of the ethanol and fusel alcohols in the spent media were not, however, commensurate with the difference in cell numbers but the total fusel alcohol production at higher yeast concentrations was about five times as great and that of ethanol was two-fold. With wort or an intermediate medium, the level of assimilable nitrogen was greater and in the closed system some of the nitrogen, particularly proline, was not utilized. Proline uptake was stimulated by increasing the level of carbohydrate in the medium or by increasing aeration so that more carbohydrate was diverted into metabolic pathways associated with growth rather than fermentation.     

CONTINUOUS FERMENTATION IN RELATION TO YEAST METABOLISM

In homogeneous systems for the continuous fermentation of wort by Saccharomyces cerevsiae fluctuations often occur in the ability of cells to remove and ferment sugars even under steady-state conditions. In partially closed systems of this type where high concentrations of yeast are accumulated and growth is suppressed, such fluctuations are magnified. The results of these fluctuations are demonstrated and the causes and results of a simultaneous decline in the rate of removal and fermentation of maltose are discussed. Such undesirable effects are largely eliminated by the use of a system which incorporates at least two stages and a continuous fermentor of such a design has operated with a high degree of stability at dilution rates as high as 0·4 h^?1.     

FUNDAMENTALS OF IMMOBILISED YEAST CELLS FOR CONTINUOUS BEER FERMENTATION: A REVIEW

Recent fundamental research conducted on immobilised cells with a focus on continuous primary beer fermentation is presented in this review. The knowledge of whole-cell immobilisation, continuous fermentation, yeast biochemistry associated with beer flavour production, and bioreactor engineering design is required to apply immobilised yeast cells for industrial scale beer production. Understanding how immobilisation and continuous bioreactor operation affect yeast cell metabolism and viability will provide the groundwork for optimising beer quality. The latest studies on immobilised cell carriers, viability, vitality, mass transfer characteristics and bioreactor design indicate that an industrial scale immobilised cell system for primary beer fermentation may soon be a reality in the modern brewery .     

INDUCTIVE EFFECTS OF OXYGEN ON YEAST FERMENTATION IN GLUCOSE- AND MALTOSE-MEDIA

The findings presented demonstrate that both growth yield and fermentation activity of yeast cells cultured in maltose-media are highly affected by pretreatment of the pitching yeast or by oxygen induction in the medium and by the presence of ergosterol and Tween 80. Variable responses to oxygen are reported from three different strains of brewer's yeast (Saccharomyces carlsbergensis). Yeast growth and fermentation were significantly reduced in media containing glucose above a certain threshold value. Previous reports concerning glucose repression are discussed. It is suggested that sucrose has a repressive effect similar to that of glucose. When nitrogen is a limiting factor, the fermentation velocity in the presence of maltose is reduced.     

NEW SYSTEMS OF CONTINUOUS FERMENTATION BY YEAST

Two new types of apparatus for carrying out yeast fermentation continuously have made possible study of certain scientific aspects of continuous fermentation. The first is open in that it permits free escape of yeast and the second is a homogeneous system in which the extent of retention of the yeast can be adjusted to a wide range of predetermined levels. The course of fermentation in, and the quality of the products from, the two systems show that the first fermenter reproduces the sequential changes which occur during a batch fermentation and produces beers which are very similar to those fermented under conventional conditions. The second system has revealed adverse effects resulting from an excessive degree of yeast retention and these suggest the advisability of ensuring a measured rate of yeast growth.     

耐高渗酵母的分离、筛选及鉴定

建立了从含糖量高的花粉、未经加工的蜂蜜、水果、发酵物等样品中分离耐高渗酵母的简单方法，共分离得到1株极耐高渗酵母，并通过生理生化实验及形态学观察对其进行了鉴定，确定其为酿酒酵母属的酿酒酵母。     

德国啤酒酵母和国内啤酒酵母发酵性能的研究

酵母菌种是啤酒酿造的关键，不同的菌种可用来酿造不同类型的啤酒。本试验对德国酵母和国内酵母的发酵性能进行了对比研究，总结出了二者之间的差异。     

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.     

FORMATION AND REMOVAL OF ACETOIN DURING YEAST FERMENTATION

The main yeast fermentation process can be characterized by two separate phases, the acetoin-producing phase (phase I) and the acetoin-reducing phase (phase II). The time at which yeast changes from production to removal is here designated as the ‘point of metabolic change’. The rise and fall in acetoin concentration was affected by composition of the wort, inoculum size, yeast strain, presence of traces of oxygen and addition of ergosterol, whereas temperature seemed to be of somewhat less importance. A high and positive correlation between the maximum level of acetoin and the concentration of ethanol measured at the ‘point of metabolic change’ has been demonstrated. The appearance of the ‘point of metabolic change’ is discussed in light of the level of acetoin in finished beer. The absolute threshold for acetoin was determined as 17 ppm.     

METHIONINE AND SULPHATE AS COMPETING AND COMPLEMENTARY SOURCES OF SULPHUR FOR YEAST DURING FERMENTATION

Study of the uptake of sulphate and methionine by an ale yeast from a range of media showed that utilisation of sulphate was fairly strictly controlled but assimilation of methionine was not. Cells never took up more than about 0.3 mMol sulphate per litre whilst methionine, up to an initial concentration of 10 mMol per litre, was completely absorbed. Sulphate-grown cells had low intracellular pools of amino acids and methinonine was never detected. Methionine-grown cells contained methionine in both cytosol and vacuole and the concentration of several other amino acids also increased in such a way to suggest that methionine catabolism was occurring. With mixed sulphur sources methionine prevented uptake of sulphate when the concentration of sulphate was high but not when it was low suggesting the presence of two sulphate transporters with different control properties. Sulphate did not influence uptake of methionine. Addition of other amino acids to the medium did reduce the rate and extent of methionine uptake but not the intracellular pool sizes. Pilot plant studies suggested that SO₂ production in a brewery is more likely to be a reflection of the overall nutritive status of the wort rather than be connected to the initial methionine concentration .