Yeast flocculation: a dynamic equilibrium

The steady state in yeast flocculation is a dynamic equilibrium between flocculated and dispersed yeast cells. The free cell concentration is directly proportional to the total cell concentration and may be expressed as an equilibrium constant. Increased agitation decreases floc size and equilibrium constant whilst increasing floc-surface area and free-cell concentration. Values of equilibrium constant are influenced by agitation in a complex relationship probably involving the floc-surface area and floc momentum. Inhibition of flocculation by mannose and low pH is reversible and becomes greater with increased agitation. Both these inhibitions appear consistent with a weakening of flocculent bond strength by these inhibitors.     

Yeast flocculation: quantification

Yeast flocculation is an orthokinetic process dependent upon mechanical agitation for all quantitative measurements. From several methods which were assessed, orbital shaking was selected as being the most practical as well as producing the most meaningful results. Quantitative measurements of flocculation were made in terms of minimum agitation threshold, initial rate, extent of flocculation at equilibrium and flocculated particle size at equilibrium. All these parameters were strain dependent. Critical cell density functions were formed if agitation was limiting regardless of how the agitation was imposed, and are unlikely to be related to bond strength.     

Yeast flocculation: Calcium specificity

Expression of flocculation in yeast requires the presence of multi-charged cations. Calcium ions fulfil this role over a broad pH range. At near neutral pH, magnesium and a variety of transition elements can induce flocculation. Calcium-induced flocculation was competitively inhibited by excess sodium ions whereas magnesium-induced flocculation was not competitively inhibited. Potassium and lithium ions caused similar inhibition but to a lesser extent. ⁴⁵Ca effux from yeast cells was greatly increased by the external presence of buffer and cations. Inhibition of flocculation by chelating agents, EDTA or EGTA, was overcome by excess calcium ions. Flocculation could not be induced, under these conditions, by excess magnesium or transition-element salts. It was concluded that yeast flocculation has a direct specific requirement for calcium ions. Other ions cause flocculation indirectly by effecting calcium ion leakage from cells, which is then able to initiate flocculation. Low calcium concentrations were susceptible to competitive inhibition by sodium ions present in most acidic buffers. In addition, citrate ions inhibited flocculation, probably by sequestration of leaked calcium. Flocculation by salts, other than calcium, was thus restricted to a neutral or high pH range.     

Yeast flocculation: kinetics and collision theory

Flocculent yeast cells have an absolute requirement for mechanical energy input in order for flocculation to occur. Flocculation is arrested by cessation of energy input. The initial rate of flocculation increases as the square of the cell concentration. There is a minimum shaking speed to initiate flocculation and thereafter the initial rate of flocculation increases exponentially with the shaking speed. The minimum shaking speed for flocculation to occur increases with pH value. Activation energy for flocculation, derived from Arrhenius-like plots, varies with pH value. We propose that activation energy is required to overcome mutual repulsion between charged yeast cells and allow flocculent bonds to be formed.     

Yeast flocculation: Flo1 and NewFlo phenotypes and receptor structure.

Flocculation characteristics of 42 flocculent strains of Saccharomyces cerevisiae were examined. Two entirely distinct 'lectin-like' mechanisms of flocculation were distinguished by sugar, salt, and low pH inhibitions, protease sensitivity, and selective expression of flocculation. One group, termed Flo1 phenotype, was inhibited by mannopyranoses and contained all strains bearing known genes affecting flocculation. The other group, termed NewFlo phenotype, contained the majority of brewery ale stains and was inhibited by manno- and glucopyranoses. Detailed sugar-inhibition work revealed the probable receptor identity of both Flo1 and NewFlo flocculation, as being non-reducing termini of alpha-(1-3)-linked mannan side branches, two or three mannopyranose residues in length.     

用于准确评价酵母絮凝性能的新方法研究

建立了1种快速、灵敏分析特定酵母絮凝性能的新方法。通过考察酵母悬浮液初始浓度、缓冲液pH值、各组分用量比例、体系水质等多因素对酵母絮凝性能的影响规律,优化确立了该测定体系的最佳参数:pH3.90的缓冲液2.7 mL和0.8 mL初始浓度0.3 g/mL的酵母悬浮液,体系适宜水质选择经离子交换处理后的纯净水。该方法操作简便,测定结果准确可靠。     

Yeast flocculation: reconciliation of physiological and genetic viewpoints.

Yeast flocculation results from surface expression of specific proteins (lectins). Two flocculation phenotypes were suggested by physiological and biochemical tests, whereas genetic data suggested a larger number of mechanisms of flocculation. After reviewing the biochemistry, physiology and genetics of flocculation, a new hypothesis combining the data available from these different sources, is proposed. Flocculation results when lectins present on flocculent cell walls bind to sugar residues of neighbouring cell walls. These sugar receptors are intrinsic to the mannan comprising cell walls of Saccharomyces cerevisiae. Two lectin phenotypes were revealed by sugar inhibition studies. The gluco- and mannospecific NewFlo phenotype is not, as yet, found in genetically defined strains. Mannospecific flocculation (Flo1 phenotype) is found in strains containing the genes FLO1, FLO5 and FLO8. This phenotype is also found following mutation of the TUP1 or CYC8 loci, in previously non-flocculent strains. It is therefore proposed that the structural gene for mannospecific flocculation is common or possibly ubiquitous in non-flocculent strains and in consequence, FLO1, FLO5 and FLO8 are probably regulatory genes, exerting positive control over the structural gene. Flocculation expression requires lectin secretion to the cell surface. Many of the observed 'suppressions' of flocculation may be due to mutations of the secretory process, involved in transporting structural proteins to the cell wall. The possible involvement of killer L double-stranded RNA with flocculation is suggested, given the lectin properties of viral coat proteins and an association between L double-stranded RNA and the Flo1 phenotype.     

利用酵母营养盐提高酵母活性的研究

酵母营养盐能为酵母提供所需的生长素和微量矿物质元素,使酵母形体均匀,健壮,不易衰老,提高酵母活性,提高啤酒中双乙酰还原能力,缩短发酵周期10－15％,营养盐的添加较适于凝集性酵母菌种,添加量在20－40mg/L之间。     

胞内pH法评价酵母活性的研究

酵母细胞内pH与酵母生长和发酵状况密切相关，用胞内质子的释放能力可以衡量酵母细胞的生理状态。为了测定质子在酵母生理条件下的释放能力．在较低pH下，利用荧光法来测量胞内pH，简称ICP法。通过发酵试验证明，ICP法对于准确地评估啤酒生产过程中酵母细胞活性的细微区别，是非常有效的。     

一步法制备高果糖浆工程及产酶菌体营养价值研究

利用克鲁维酵母菊粉酶酶解菊粉制作高果糖浆 ,优选的酶解条件是 :菊糖浓度15.0 % ,酶作用剂量 2 2U/g ,50℃下作用 6～ 36h ,底物水解率 >95%。水解产物中果糖占95%以上 ,葡萄糖占 5%以下 ,不含其它糖。产酶酵母所含营养物质非常丰富。真蛋白含量4 3.10 % ,赖氨酸、蛋氨酸、胱氨酸、色氨酸分别是 3.0 2、0 .58、0 .4 4、0 .52mg/kg ,维生素B1和B2含量分别是 5.53和 6 0 .70mg/kg ,重要微量元素铜、锌、铁、锰的含量分别是 19、110、170和 15mg/kg。在本研究设计工艺下 ,高果糖浆和高值兼用酵母生产可以一举两得。     

白酒酵母的pH种群研究

采用微生物学的相关技术原理和方法 ,研究白酒发酵系统中 ,酵母菌的 pH种群及生态特性。探讨白酒发酵过程中 ,发酵环境的 pH变化与白酒酵母pH种群的生态学关系 ,以及酵母菌的 pH种群变化对白酒发酵的影响     

Yeast flocculation: Lectin synthesis and activation

Yeast flocculation involves binding of surface lectins to carbohydrate receptors on neighbouring cell walls. Brewing strains of Saccharomyces cerevisiae normally become flocculent in the stationary phase of growth. This paper presents evidence that lectins are synthesized in exponential phase, inserted into the cell wall, and activated later at the time of flocculation onset. Cycloheximide failed to prevent flocculation unless it was added in early growth; with later additions progressively larger degrees of flocculation occurred. Flocculation onset was delayed by cycloheximide but was otherwise cycloheximide insensitive. Preflocculent cells could be artificially activated to full flocculation by heat. Artificial activation of samples from growing yeast cultures confirmed the progressive synthesis of lectins throughout exponential growth. Pronase E treatment of whole cells prior to heating prevented any activation of flocculation. It was concluded that lectins were synthesized continuously from an early stage of growth and rapidly inserted into the cell wall (accessible by pronase E), where they remained inactive for up to 14 h, before being activated at flocculation onset by an as-yet unknown mechanism. It was found that lectin synthesis and activation occurred in all brewing strains tested.     

盐法提取啤酒废酵母RNA的研究

采用正交设计试验法对盐法提取啤酒废酵母RNA工艺过程中的酵母浓度、NaCl浓度、抽提温度和抽提时间等因素进行了研究。用方差分析处理，实验结果表明：酵母浓度8％，NaCl 6％，抽提温度95℃，抽提时间6h是提取啤酒废酵母RNA的适宜条件，并将其用于啤酒厂废酵母泥的RNA提取试验，得率为3．23％。     

添加酵母营养素 提高酵母活性

阐述了啤酒酵母细胞生命活动所需的营养物质和环境因素,酵母营养素的成分及生物功能,论述了营养素物质在酵母细胞代谢过程所起的作用,以及营养素在实验室和生产实践应用中的效果。     

阳离子石油树脂施胶剂在纸袋纸中的应用

用新型阳离子石油树脂中性施胶剂,替代松香施胶剂在纸袋纸生产线上应用。分析了该施胶剂的施胶效果,以及影响施胶度的各种因素探讨使用该施胶剂后,生产上出现的异常情况和应对措施;评价使用纸袋纸生产使用中性施胶剂的可行性和经济效益。     

Yeast flocculation: Flocculation onset and receptor availability

Flocculent strains of brewing yeast grow and ferment as single cells and flocculate in the stationary phase of growth. The switch from single-celled yeast growth to multi-celled aggregation, flocculation onset, is of critical importance to the brewing industry. Yeast flocculation involves adhesion of surface-lectins on flocculent cells to carbohydrate receptors on neighbouring cell-walls. The presence of carbohydrate receptors, outer-chain mannan side-branches, was monitored throughout growth of flocculent and non-flocculent strains of Saccharomyces cerevisiae, with particular attention to the growth phases where flocculation is normally developed. Receptors were probed by coflocculation with flocculent strains and by aggregation with concanavalin A, a lectin shown to use the same receptors as flocculation. While considerable variation was found in coflocculation and concanavalin A aggregation between strains, little or no change in receptor availability was found throughout the growth of all yeast strains. Yeast cells could easily be coflocculated at any growth stage. It was concluded that receptor availability is not involved in the process of flocculation onset.     

A Novel Bread Making Process Using Salt-Stressed Baker's Yeast

ABSTRACT:  By adjusting the mixing order of ingredients in traditional formula, an innovative bread making process was developed. The effect of salt-stressed Baker's yeast on bread dough of different sugar levels was investigated. Baker's yeast was stressed in 7% salt solution then mixed into dough, which was then evaluated for fermentation time, dough fermentation producing gas, dough expansion, bread specific volumes, and sensory and physical properties. The results of this study indicated that salt-stressed Baker's yeast shortened fermentation time in 16% and 24% sugar dough. Forty minutes of salt stress produced significant amount of gas and increased bread specific volumes. The bread was softer and significantly improved sensory properties for aroma, taste, and overall acceptability were obtained.     

葡萄酒酵母和酵母营养物对蜂蜜酒发酵的影响

实验研究了 3株葡萄酒酵母 (Saccharomycescerevisiae)D2 4、C19和CHP在蜂蜜酒发酵过程中的特性 ,初步探讨了蜂蜜酒的发酵工艺流程 ,对成品酒进行了理化指标和感官特征的分析 ,确定了酿造蜂蜜酒的优选葡萄酒酵母菌株为C19,并以C19发酵蜂蜜酒作为对照 ,在发酵过程中分别进行添加两种酵母营养物Helper和酵母浸膏的处理 ,观察各处理的发酵过程变化 ,并分析成酒的品质 ,实验结果表明 :以Helper为酵母营养物且添加浓度为 10g/hL时 ,提高了蜂蜜酒的发酵速度 ,使蜂蜜酒获得了最佳的感观品质。     

谈啤酒酵母的管理

介绍了啤酒生产过程中酵母从实验室培养、现场培养到大生产回收使用的过程中管理要点。     

富铁、富锌麦汁对啤酒酵母代谢副产物的影响

于13.4P麦汁中分别添加不同含量的FeSO4·7H2O和ZnSO4·7H2O,接入富铁、富锌酵母进行常规啤酒发酵,同时以空白麦芽汁发酵作为对照;在整个发酵过程中,跟踪检测酵母生长情况、pH、外观糖度、双乙酰、高级醇变化、后酵结束各理化指标,发现添加FeSO4·7H2O离子浓度为1.3516×10-6的麦汁经富铁酵母发酵14d后,双乙酰含量为0.067mg/L,高级醇含量为56.2mg/L,酒精度为4.615,真正发酵度达67.6%;添加ZnSO4·7H2O,离子浓度为1.6638×10-6的麦汁经富锌酵母发酵14d后,双乙酰含量为0.049mg/L,高级醇含量为59.1mg/L,酒精度为4.670,真正发酵度为67.3%,啤酒风味基本不变,缩短了发酵周期,提高了产品质量。