Modelling of Yeast in Suspension During Malt Fermentation Assays

Premature yeast flocculation (PYF) is a poorly understood condition leading to attenuation of fermentation and poor alcohol yields. The yeast in suspension in fermenting worts prepared from either normal or premature flocculating malts was continually measured during the small 15 mL fermentation test recently developed in the Dalhousie laboratories. A simple inexpensive monitoring system was constructed from a laser level, photometric cell and data logger. This system allowed non‐destructive data collection of absorbance data (over 700 data points per fermentation) at ?650 nm. A non‐linear modeling technique was applied to the data, and yielded two best‐fitting logistic models. The model parameters were quantitatively compared to determine if statistical differences between PYF and normal wort were apparent. A student's t test of the logistic parameters indicated a significant difference (p > 0.025) between control and PYF worts for the increase in absorbance at the beginning of the fermentation. A significant difference (p > 0.0001) in the inflection time of absorbance down‐curve between the control and PYF wort was also noted.     

Evaluation of a Brazilian Fuel Alcohol Yeast Strain for Scotch Whisky Fermentations

Traditionally, distilling companies in Scotland have employed a very limited number of yeast strains in the production of alcohol for Scotch whiskies. Recent changes such as the decline in availability of brewers' yeast as a secondary yeast strain and the availability of yeast in different formats (e.g., dried and cream yeast as alternatives to compressed yeast) have promoted interest in alternative Scotch whisky distilling yeasts. In previous work, we investigated different strains of yeasts, specifically Brazilian yeasts which had been isolated from and used in fuel alcohol distilleries. One of the Brazilian yeasts (CAT 1) showed a comparable fermentation performance and superior stress tolerance compared with a standard commercial Scotch whisky distilling yeast (M Type). The Brazilian CAT 1 yeast isolate was further assessed in laboratory scale fermentations and subsequent new make spirit was subjected to sensory analyses. The spirits produced using the Brazilian strain had acceptable flavour profiles and exhibited no sensory characteristics that were atypical of Scotch whisky new make spirit. This study highlights the potential of exploiting yeast biodiversity in traditional Scotch whisky distillery fermentation processes.     

低温条件下干鲜面包酵母发酵特性的研究

用量筒面团直观法分析比较了马利牌干酵母及发发牌鲜酵母在低温（３～５℃）条件下的发酵力，耐盐性及耐糖性，并确定了低温发酵过程中，两种酵母的适宜用量及适宜发酵时间。研究结果表明，马利牌干酵母及发发牌鲜酵母都具有一定的耐低温性     

Optimised Acidification Power Test of Yeast Vitality and its Use in Brewing Practice

The optimised acidification power test (APT) of brewer's yeast quality includes storing the yeast slurry at 2°C under beer (AP remains constant for up to 6 days), a 15 min sample equilibration to room temperature, decantation, and washing by triple centrifugation in deionised water. The final yeast pellet keeps its AP for up to 6 h at room temperature under water and thus the APT does not need to be performed immediately after yeast collection. The correct AP value (maximum acidification produced by given yeast) is determined at 25 ± 0.1°C in a 15 mL sample containing ≥5% glucose and ≥1.5 g yeast wet weight. The cell concentration is conveniently measured as absorbance (A₆₆₀). Cell flocculation and/or sedimentation that can distort APT results can be prevented by stirring the sample at ≥200 rpm. The AP of yeast of different generations used to pitch brewery fermentations in cylindroconical tanks had a very low correlation with the wort half‐attenuation time (T_1/2) due to large scatter, while each yeast generation separately showed a clear T_1/2‐AP relationship. The lowest AP of yeast cropped from cylindroconical tanks was displayed by the first cropped fraction. Post‐cropping cooling had no effect on AP. Variations in pitching yeast vitality and their effect on the outcome of a brewery fermentation can be masked by variations in pitching rate, wort composition, ambient conditions in the cylindroconical tanks and other factors.     

Dry Yeast Strain For Use in Fermentation of Alicante Wines: Selection and DNA Patterns

We previously reported a study on the microbial flora of Alicante wines at different stages of vinification. On the basis of those data, we selected a Saccharomyces cerevisiae strain which is capable of producing high quality wine in pilot fermentation experiments with musts. The strain was characterized using several DNA fingerprinting techniques. These results open the way to use the strain as a dry yeast in order to perform controlled fermentations.     

浓香型白酒生产中耐酒精酵母菌的选育研究

以宋河酒厂窖泥、酒糟、酒厂废水为样品,从中分离出100株菌株,经初筛、复筛和酒精发酵试验,最终获得1株耐酒精度为18%vol酵母菌,编号为A16。通过单因素实验确定最佳发酵条件为:发酵温度30℃、p H值4.5、碳源为葡萄糖、氮源为复合氮源(酵母膏和蛋白胨的比例为2∶1)、无机盐为Mg SO4·7H2O、接种量为10%、转速100 r/min、装液量为150 m L/250 m L;通过正交试验确定培养基最佳配比为:葡萄糖25%,酵母膏2%,蛋白胨1%,Mg SO4·7H2O 1%,(NH4)2SO41%,KH2PO41%,菌株A16的酒精得率70%。     

使用挤压膨化原料时酒精发酵中酿酒酵母的变化规律探讨

通过试验选取挤压膨化工艺参数组合为 :挤压机模孔直径Φ =1 1mm ,套筒温度T =1 70℃ ,脱胚玉米含水量W =1 3 % ,螺杆转速 1 60r/min。在此参数下获得的物料 ,与未膨化样品对比 ,酿酒酵母在膨化物料中酵母数最高值可由 1 68× 1 0 8/mL升至 2 67× 1 0 8/mL。酵母增代时间可由 1 6 0 3h缩短至 1 3 3 6h。添加营养盐尿素和KH2 PO4 后此种效果更加明显 ,这种处理有可能使发酵时间缩短。     

响应面法优化萌发藜麦芽乳发酵工艺

以萌发藜麦芽为原料,研究发酵条件对藜麦芽发酵乳酸度和活菌数的影响。选用植物乳杆菌和干酪乳杆菌2种混合菌进行发酵,通过单因素试验、响应面优化试验探究菌种比例、接种量和发酵时间对发酵的影响。结果表明,萌发藜麦芽乳混合菌发酵最佳工艺条件为植物乳杆菌和干酪乳杆菌比例2.5∶1、接种量3%、发酵时间10.3 h,得到的萌发藜麦芽发酵乳酸度为85.32°T,活菌数为9.21(lg(CFU/m L)),与预测值吻合,表明萌发藜麦芽的匀浆发酵培养基适合乳酸菌生长。     

酵母抽提物中呈味核苷酸含量偏低的原因探讨(Ⅱ) 啤酒酵母自溶过程核酸的降解规律研究

本论文通过详细测定酵母自溶过程中蛋白质、核酸以及各种核苷酸在产物中的变化量，研究pH、外加5’-磷酸二酯酶(麦芽根核酸酶)、外加蛋白酶等对酵母自溶的影响，从而探讨外加5’-磷酸二酯酶不能显著提高酵母自溶产物中呈味核苷酸含量的原因。研究结果显示：在自溶过程直接添加麦芽根核酸酶只能略提高酵母抽提物中呈味核苷酸的含量，但提高程度不明显；在pH8自溶的产物中5’-核苷酸和3’-核苷酸的量均显著低于在pH5自溶的产物中的量。酵母在pH8～8．5条件下自溶时，外加蛋白酶可以显著提高酵母自溶物产物中可溶性固形物含量、可溶性蛋白质和核苷酸的含量，显著降低核酸含量，产物中的5’-核苷酸含量显著比3’-核苷酸含量高。上述结果说明了酵母在外加麦芽根核酸酶条件下自溶时，核酸未能迅速降解并生成大量的呈味核苷酸的原因之一是由于酵母细胞壁的存在阻碍了细胞器中核酸的溶出，致使外加的5’-磷酸二酯酶不能很好与核酸底物接触，从而不能有效提高呈味核苷酸的产量。     

基于竞争性等位基因特异性PCR技术的麦芽品种纯度定性和定量检测

利用测序技术筛选和确认4?个可以区分7?种大麦麦芽的单核苷酸多态性（single nucleotide polymorphisms,SNP）位点,并建立区分图谱。同时,利用竞争性等位基因特异性聚合酶链式反应检测技术对预混样品进行定量测试,其检测的结果与真实性之间相对误差小于3%。该技术的建立对大麦麦芽纯度检测提供方法,对大麦麦芽SNP指纹数据库的完善提供了数据支持。     

Barley and Malt Proteins and Proteinases: II. The Purification and Characterisation of Five Malt Endoproteases,Using the Highly Degradable Barley Protein Fraction (HDBPF) Substrate

Five barley‐malt endoproteases have been purified using the highly degradable barley protein fraction (HDBPF) as the substrate for activity detection and measurement. The five purified endoproteases were identified as the most active and, hence, we believe the most important proteolytic enzymes during barley germination and malting. This was demonstrated by showing that the component of HDBPF, degraded in test tubes during the reaction to determine their activity, cannot be recovered from malt by extraction, indicating that this component has been degraded during germination and malting. These endoproteases differ in their specificities, pH and temperature optima, thermostability and ionic‐cationic behaviour. The gel filtration chromatographic‐profiles of the peptide products of these enzymes versus parallel profiles of beer peptides exhibit very close similarities.     

发泡酒酿造用贫氮酵母性质的研究

研究了贫氮酵母在发酵过程中麦汁各组成成分的利用情况及其生理特性，研究发现，贫氮酵母在贫氮麦汁中能利用少部分的脯氨酸和相当部分的麦芽三糖，发酵后的啤酒中总含氮量符合淡爽啤酒的要求；它是一株中等凝聚性的酵母，具有一定的实际应用价值。     

谷胱甘肽(GSH)高产酵母菌株的初筛及营养条件优化

对实验室保藏的14株不同种属的酵母菌株的谷胱甘肽(GSH)产量进行了比较,发现其中log酵母菌株的GSH产量最高,达127.785 mg/L.对其营养条件进行了研究,发现其最佳碳源为葡萄糖;硝酸盐会抑制其生长,而有机氮源对其生长有利;考虑到磷和钾对酵母细胞生长及发酵代谢的作用,选择KH2PO4为培养基中的基本成分.采用正交试验对培养基的基本成分进行优化,在最佳培养条件下log酵母的GSH产量有较大幅度的提高,达到148.547 mg/L.     

酿造蓝莓果酒的酵母菌筛选和发酵特性研究

以从蓝莓自然发酵物中分离得到的酵母作为出发菌,经过三级筛选,得到了1株适宜蓝莓果酒发酵的菌株,命名为CNBG002,并研究了该菌株在麦芽汁中的生长特性。该酵母的最适生长温度为26℃,最适生长p H值为2.5~4.5。该菌耐酒精能力较高,可达到15%vol,耐SO2能力可达150 mg/L,是一株优良的蓝莓果酒酿造酵母。     

酵母生产过程中芽孢杆菌污染的溯源——核糖体DNA扩增片段限制性内切酶分析

采用基于16S rDNA序列多样性的ARDRA技术(限制性酶切片段分析法)对活性干酵母生产过程的嗜热芽孢杆菌污染进行分型和溯源。通过对从酵母工厂各个生产环节中的取样和成品中分离得到的23株芽孢杆菌进行ARDRA分型,检测出有:枯草芽孢杆菌、地衣芽孢杆菌、巨大芽孢杆菌和蜡样芽孢杆菌,结果经细菌生理生化鉴定验证。溯源分析生产过程的芽孢杆菌污染可能是来自糖蜜高温灭菌过程未杀灭的嗜热芽孢。基于核酸检测的分子生物学ARDRA技术的优点是快速、专一性强和灵敏度高,适于应对工业生产中出现的污染事件。     

A New Germinative Classification Model of Barley for Prediction of Malt Quality Amplified by a Near Infrared Transmission Spectroscopy Calibration for Vigour “On Line” Both Implemented by Multivariate Data Analysis

A new germinative two‐dimensional classification plot fully compatible to the current EBC analyses (EBC methods 3.5–3.7) is proposed for malting barley based on separate estimates for “vigour” (24 h germination) as abscissa with limits at 70% and 30% and for “viability” (72 h germination) as ordinate with limits at 98% and 92%. Early detection of germination by image analysis was improved by utilising the auto fluorescence of the root cap. The seven hierarchical germinative classes visualise the quality differences in a consistent way, ordering classes according to falling extract % and increasing wort β‐glucan (mg/L). It was surprising to discover that significant barley Near Infrared Transmission (NIT) spectroscopy based Partial Least Squares Regression prediction models for “vigour” and “viability” were obtained after removing the PLSR outliers. The majority of these were found to be low in vigour. It was concluded after experimental validation that the physical‐chemical structure of the seed, reflected by the correlation of the barley NIT spectral fingerprints to germination speed, is connected to the availability of substrate for germ growth. This is another aspect of the speed of malt modification. An automated combination instrument for measuring physical‐chemical and seed germination parameters is suggested for quality control and to establish an on‐line NIT calibration network for integrated germinative and malting quality classification.     

通用型酵母菌实时荧光PCR检测方法的建立

为建立一种快速检测鉴定食品中酵母污染菌实时荧光PCR法,根据酵母基因序列设计出通用型探针和引物,建立了运用实时荧光PCR法检测酵母的反应体系和反应条件,进而对该方法进行特异性验证,灵敏度分析及稳定性评价,并应用于产品样本的检测。特异性试验表明,酵母菌检测结果均为阳性,而细菌、霉菌均为阴性,荧光PCR检测结果的特异性为100%。灵敏度试验表明,酵母菌检出限在760 cfu/m L。稳定性试验表明,酵母菌组内实验CV在0.62~0.81%之间波动,而组间实验在0.43~0.77%之间波动。通过样品增菌检测发现在培养12 h后能检出阳性。本研究所建立的实时荧光PCR法特异性好、灵敏度高、稳定性好,具有快速、简便的特点,为快速检测食品中酵母污染提供新的方法和途径,具有很好的研究价值和应用前景。     

芝麻香型白酒酿造功能霉菌及其与酵母的相互作用

通过对5株来自不同酿造环境的霉菌的生长速度、产酶、产酸以及产孢子能力的比较,筛选出具有生长迅速、产孢子和产酸较少以及较高的产酶能力的Aspergillus oryzae(XJ10)。将此菌株应用于芝麻香型白酒生产中,优化了霉菌与酵母的相互作用。固定酵母用曲量,霉菌麸曲用量从31 kg提高至125 kg,当霉菌麸曲用量为125 kg时,出酒率达到最高,为27.9%,同时,所产白酒的香气和口味品评分值最高。     

Mode of action of yeast culture (YEA-SACC 1026) for stimulation of rumen fermentation in buffalo calves

The effect of daily supplementation of 5 g Saccharomyces cerevisiae yeast culture (YC, YEA-SACC 1026), 30 g NaHCO₃, supernatant from 5 g YC (YCS), 5 g autoclaved YC (YCH) or 5 g γ-irradiated YC (YCR) to the diet of buffalo calves on rumen microbial populations and fermentation pattern was examined. Addition of 30 g NaHCO₃ increased the rumen pH to the level observed with YC group. The pH and the concentrations of total, total viable and cellulolytic bacteria and total volatile fatty acids (VFA) were significantly higher while that of lactic acid, hexose-unit oligosaccharides and NH₃-N were significantly lower in the rumen fluid of YC compared with the control group. The effect of NaHCO₃ was 39·5 and 59·5% in decreasing the concentrations of lactic acid and hexose-unit oligosaccharides, 48·1, 47·2 and 45·5% in increasing the numbers of total, total viable and cellulolytic bacteria, 50·0 and 58·1% in increasing the concentrations of total VFA and protein and 51·3% in decreasing the concentration of NH₃-N of YC. The corresponding values for YCR addition in the diet were 38·6, 45·7, 48·5, 44·4, 51·5, 39·1, 48·1 and 46·5%. The effect of YCS and YCH was only marginal, but conspicuous up to 2 h after feeding, in changing the above rumen variables when compared with the YC group. The results indicated that contribution of increase in pH in changing the rumen variables was approximately 50% of YC and almost all the stimulatory activity was associated with live yeast cells. Autoclaving of YC destroyed almost all and γ-irradiation of YC retained about 50% of stimulatory activity of YC. The effect of YC on rumen fermentation, which was maximum up to 2 to 4 h after feeding, decreased with time. © 1998 SCI.     

Effect of the Malting Barley Variety (Hordeum vulgare L) on Fermentability1

The influence of the malting barley genotype on the apparent attenuation limit (AAL) was investigated. The AAL level correlated closely with the maltose concentration in the wort but was not affected by other fermentable sugars or by the total carbohydrate content. The chemical composition, modification, amylolytic enzyme activities and several starch properties of selected malts were studied in detail. Variations in the maltose concentration could almost solely be traced back to genotype‐dependent disparities of β‐amylase thermostability. These differences are due to interallelic polymorphisms of the β‐amylase gene and are easily detected by PCR. Hence, PCR primers offer remarkable prospects for breeding barley on the basis of a marker‐assisted selection (MAS).