酵母提前絮凝的研究进展

介绍了国内外关于酵母提前絮凝的研究进展及导致酵母提前凝的因素和酵母提前絮凝的假说机理,归纳了酵母絮凝的检测方法,提出了预防酵母提前絮凝的措施及酵母提前絮凝的研究方向。     

啤酒酵母提前絮凝的研究进展

酵母提前絮凝是啤酒企业时有发生的现象,因其复杂的影响因素至今对酵母提前絮凝的发生机理及提前絮凝因子的本质没有明确的证实,也因此给整个啤酒酿造产业链造成了极大的困扰。近年来,随着环境污染及各种恶劣天气的出现,导致啤酒酵母提前絮凝发生相对增多,对麦芽企业及啤酒企业造成一定经济和名誉损失。作者综述了啤酒酵母提前絮凝的国内外最新研究进展,包括机理假说、提前絮凝因子的来源、形成机制及控制研究,以期对啤酒产业链提供有效解决酵母提前絮凝的思路和方法。     

利用麦芽PYF值调整酵母絮凝性

麦芽的PYF值对酵母的絮凝性影响较大，PYF值越低，酵母絮凝性越强，发酵过程表现为酵母沉降早，双乙酰还原缓慢，发酵不彻底；麦芽PYF值越高，酵母絮凝性越弱，发酵时酵母沉降慢．酒液中酵母数多，双乙酰还原较快，发酵完全，但酵母回收量少，滤酒困难。在其它条件不变的前提下，可利用麦芽的PYF值对酵母的絮凝性进行适当的调整。     

简单快速测定酵母的絮凝性

介绍一种利用细胞表面疏水性原理快速而简单测定酵母细胞絮凝性的方法(HICF法)。酵母细胞悬浮液注入Sepharose凝胶柱 ,然后加入含有氯化钠的缓冲液 ,疏水细胞吸附于凝胶柱 ,通过测定吸附于凝胶柱的细胞的百分数可反映出酵母细胞的疏水程度[1],以此指示酵母的絮凝性。     

麦芽质量对酵母絮凝性的影响

很多酿酒师认为:在发酵后期,不论是酵母提前絮凝,还是酵母在有可发酵性糖的情况下不降糖,这都与麦芽的质量有关。以前我们已经认识到葡萄糖、阿位拍糖与木聚糖类的复合糖与酵母结合能导致酵母提前絮凝,现在我们又认识到某种蛋白质也能起到同样的作用。这种蛋白质与大麦麦芽的外层组织联系在一起,对大麦进行简单的浸泡就能得到。但它不存在于大麦的表面,而是在浸麦阶段产生的,所以估计它是为了抑制微生物的生长而在浸麦阶段产生的一种抗菌蛋白。利用膜过滤和柱色谱技术能部分提纯这种蛋白。它具有热稳定性,能够忍耐麦汁煮沸的高温。我们不仅研究出这种蛋白是如何导致酵母提前絮凝,而且证实了它为什么会抑制降糖。因此,如果了解这种蛋白在制麦过程中的变化,我们就可以将其含量及其对发酵的影响降到最低。     

絮凝性酵母IFFI 1792在酒精连续发酵中的应用

絮凝性酵母菌株IFFI 1792被用于酒精连续发酵的研究。连续发酵试验在单级和串联的气升式内循环生物反应器中进行,实现了高细胞浓度高强度酒精连续发酵。试验研究了各种因素对酒精连续发酵的影响,发现溶解氧浓度在一定范围内对高效发酵有利。在单级气升式生物反应器中,生产强度可达30乙醇/L·h;临界生产强度在菌体浓度为80g/L时达到24.5g乙醇/L. h。在两级串联反应器中,生产强度在达到23.5g乙醇/L·h,对应于最终酒糟浓度7.22％(V/V)。连续发酵试验进行到40天,未见发酵活力下降。由试验结果归纳建立了一个非结构的无生长因素的发酵动力学模型,用于连续酒精发酵过程的理论分析。     

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。     

高产酒精絮凝酵母SY-130菌株的选育

以絮凝性强的葡萄汁酵母SN-154和高产酒精酵母菌种NHY4-36做亲本，通过原生质体融合技术，获得一支发酵速度快、高产酒精且絮凝性强的酵母菌株SY-130，以玉米淀粉为原料，32℃发酵60—68h，可产酒精17．5—18．5％(v／v)，耐酒精度可达20％以上，酵母絮凝性能良好。     

麦芽PYF因子活力评价及其与酵母絮凝联系研究

通过考察标准培养基下动态培养下面絮凝啤酒酵母的生长进程、酵母悬浮液初始浓度和用量、缓冲液pH、体系水质、PYF因子提取方式等多因素对测定结果的影响,确立了麦芽PYF因子活力测定体系的最佳参数。麦芽PYF因子加和性及其与酵母絮凝性能关系的进一步分析结果表明:PYF因子具有很好的加和性,对酵母絮凝起促进作用。     

The effect of microbial arabinoxylanases on premature yeast flocculation

The use of barley malt infected with microorganisms can induce premature yeast flocculation (PYF) during fermentation. To understand this further, it is necessary to determine the role of microbial enzymes influencing PYF. In this study, the induction of PYF by two arabinoxylanases from Bacillus subtilis (A and B) and one from Aspergillus brasiliensis (F) was investigated. The results showed that all three arabinoxylanases could induce premature yeast flocculation. Husk from PYF negative (PYF-) malt pre-treated with arabinoxylanases could induce severe PYF. An increase in enzyme activity resulted in an increase in of PYF. Bound ferulic acid – an important component inducing PYF – increased significantly in the 40% (v/v) ethanol precipitate of wort. However, the ratio of ferulic acid/arabinoxylan in the 40% ethanol precipitate decreased with an increase in arabinoxylanase F, but increased with arabinoxylanases A and B. The addition of the three arabinoxylanases at the beginning of the PYF- mashing process showed that the arabinoxylanases A and B could induce PYF with greater intensity than arabinoxylanase F. It can be inferred that the bacterial arabinoxylanases produced more PYF factors than from Aspergillus brasiliensis. The results of this study may provide new insights for further research and focus on the role of bacteria in PYF. © 2020 The Institute of Brewing & Distilling     

Premature yeast flocculation factors from barley malt present in both malt husk and the non‐husk part

In the present study, small‐scale fermentations of seven malts from different maltsters in China were used to monitor their premature yeast flocculation (PYF) potential. Husk exchange was applied between PYF negative malt (PYF‐) and PYF positive malt (PYF+) to investigate the PYF factors potentially present in the husk. The results showed that PYF factors were present in both malt husk and the non‐husk part. The two factors showed various ratios among different PYF+ malts, and either of them could induce PYF if it reached the threshold. Moreover, the major antimicrobial substances damaging the yeast cells were in the non‐husk part. Copyright © 2014 The Institute of Brewing & Distilling     

Isolation and partial purification of mannose-specific agglutinin from brewer's yeast involved in flocculation

Yeast cell-agglutinating activity, designated agglutinin (possible lectin), was isolated from cell walls of both non-flocculent and flocculent brewer's yeast cells. Agglutinin-mediated aggregation of yeast cells in a manner similar to flocculation with respect to specific mannose-sensitivity, pH-dependence and calcium-dependence. Agglutinating activity was found to be heat-stable and protease-insensitive. Furthermore, addition of agglutinin to flocculent cells strongly stimulated the flocculation ability of the cells, whereas addition to non-flocculent cells rendered these cells weakly flocculent. Agglutinin was found to be released from flocculent cells during the course of a flocculation assay, but not from non-flocculent cells. Presence of mannose during the assay inhibited release of agglutinin. Our results suggest that (i) mannose-specific agglutinin is continuously synthesized during growth of brewer's yeast cells, (ii) agglutinin is present in cell walls of non-flocculent cells but is unable to bind its ligand on other cells, and (iii) the ability of yeast cells to flocculate in a flocculation assay depends, among other factors, on release of agglutinin from the cells. A 10-kDa polypeptide might represent one form of agglutinin.     

林芝青稞酒曲酵母菌的分离鉴定及性能测定

以西藏林芝八一镇采购青稞酒曲为样品,对酒曲中的产酸、产酒精酵母菌进行分离、鉴定及性能测定。结果表明,菌株Y1、Y7为脲酶阴性菌,使MRS培养基变黄,能利用多种氮源和碳源;菌株Y8、Y10为脲酶阳性菌,能发酵多种糖类。根据个体形态、菌落特征、生理生化特征,初步鉴定菌株Y1、Y7为产酸酵母菌,菌株Y8、Y10为产酒精酵母。进行了不同条件对酵母菌产酸和产酒精能力的影响实验及耐受性实验,并分析产酸酵母菌和产酒精酵母菌的发酵性能。其中,菌株Y1、Y7的产酸量分别为145.06 μg/mL、128.59 μg/mL,菌株Y8、Y10酒精度分别为2.84%vol、2.31%vol。     

Nitrogen starvation induces expression of Lg‐FLO1 and flocculation in bottom‐fermenting yeast

When exponentially growing cells of bottom‐fermenting yeast were starved for nitrogen or were grown on proline (a non‐preferred nitrogen source), flocculation was induced. This flocculation was not induced by starvation for either carbon or amino acids. Expression of Lg‐FLO1, which is required for flocculation of bottom‐fermenting yeast, was also found to be induced by starvation for nitrogen. This suggests that the flocculation of bottom‐fermenting yeast is under the control of a nitrogen catabolite repression (NCR)‐like mechanism. Copyright © 2012 John Wiley & Sons, Ltd.     

High gravity primary continuous beer fermentation using flocculent yeast biomass

The current work assessed a new immobilized cell reactor system throughout a long‐term (54 days) continuous primary fermentation of lager‐type wort of high specific gravity. The experiment was performed in a 4 L airlift bioreactor and immobilization of biomass was attained solely by flocculation. Despite the constant liquid agitation and washout of biomass, up to 53 g dry wt/L of yeast remained immobilized in the system. Two types of beer were produced without interrupting the reactor, based on two types of wort: a Pilsener type with high specific gravity of 15.6 ± 0.3°P; and a dark lager wort with specific gravity of 14.4 ± 0.03°P. Even during the inlet of high gravity wort, the desired attenuation was achieved without the need for either recirculation or an auxiliary second stage bioreactor. The specific saccharide consumption rate was kept around 7.9 ± 0.4 g/L/h and ethanol productivity oscillated at 3.36 ± 0.2 g/L/h for nearly a month. During this period the volumetric productivity of the current bioreactor reached 1.6 L beer/L/day. The green beers produced from the Pilsener and dark lager worts met the standards of regular finished primary beer fermentation. The productivity of diacetyl through the entire experiment could be correlated to the free amino nitrogen consumption rate. Copyright © 2014 The Institute of Brewing & Distilling     

Distribution of the flocculation protein,Flop, at the cell surface during yeast growth: The availability of Flop determines the flocculation level

The yeast FLO genes encode cell surface proteins which are expected to play a major role in the control of flocculation. We have assessed the availability of the Flo proteins at the cell surface during the growth of two flocculent strains, ABXL-1D (FLO1) and STX347-1D (FLO5) using immunological approaches, enzyme-linked immunosorbent assays and immunofluorescence. Our data show that they are not permanently present at the cell surface but that their amount increases during growth. With both strains the flocculation level is tightly correlated to the amount of Flop antigen detected, suggesting that it is the availability of the Flo proteins at the cell surface which determines the flocculation level. Our data are consistent with the idea that the Flo proteins correspond to the flocculation lectins. The differences of flocculation pattern among strains could originate from variations in the regulation of the expression of the FLO genes. Monitoring of the distribution of the Flo proteins during cellular development revealed that they are incorporated essentially in the cell wall of growing buds. Incorporation of the Flo proteins in the cell wall displays a highly polarized aspect, at the bud tip and at the mother–daughter neck junction, which can persist in mature cells. Such a localization could be relevant to constraints of the cell wall incorporation of the mannoproteins. Depending on the regulation of Flop expression and on the incorporation of the proteins in the cell wall, a yeast population can be highly heterogeneous in Flo protein equipment. © 1998 John Wiley & Sons, Ltd.     

酵母超前絮凝因子检测方法的优化研究

酵母在啤酒酿造过程中可能会发生超前絮凝现象.文中对麦芽中存在的超前絮凝因子的麦汁检测法进行研究,发现引起检测结果不稳定的几个重要的干扰因素,对其加以优化改善,经发酵测试对比后,验证了新方法的检测结果更加真实可信.同时对如何降低PYF因子的含景进行了初步研究.     

The role of ferulic acid and arabinoxylan in inducing premature yeast flocculation

Premature yeast flocculation (PYF) is a universal phenomenon and has caused serious problems in the brewing industry. For brewing quality control, it is of great value to investigate the PYF factors that induce this destructive phenomenon. In the present study, two barley malts (PYF+ and PYF?), made from the same barley cultivar by one maltster in China, were selected for PYF factor investigations. The results showed that considerably higher amounts of the bound ferulic acid (FA), rather than arabinoxylan (AX), existed in the PYF+ wort compared with the PYF? wort. To better understand the role of these polysaccharides in PYF+ and PYF? wort, they were fractional precipitated with graded ethanol concentrations. The AX and FA contents in each fraction, as well as the molecular weight profiles and monosaccharide composition, were determined. Furthermore, the PYF?inducing activities of each fraction were measured using a small‐scale fermentation. It was found that the 40% ethanol‐precipitated fraction of both the PYF+ and PYF? wort, and the 60% fraction from the PYF+ wort, could induce the severe PYF phenomenon when added to the PYF? wort. These fractions were proposed to contain PYF factors of suitable molecular weight and a sufficient amount of the polysaccharides. In addition, it was found that the bound FA in arabinoxylan behaved as an important PYF factor in barley malt. The results of this work may contribute to the further study of the PYF mechanism. Copyright © 2015 The Institute of Brewing & Distilling