Effects of aging and heat treatment on whole yeast cells and yeast cell walls and on adsorption of ochratoxin A in a wine model system

A wine model was evaluated to determine the influence of aging on the ability of whole yeast cells (WY) and yeast cell walls (YCW) to remove ochratoxin A (OTA). Aging and autolysis were monitored for 214 h in the model wine. The original concentration of OTA in the model wine was 10 microg/liter, and WY and YCW were added at a final concentration of 1 g/liter. YCW mannoproteins were involved in the removal of OTA from the model wine through adsorption mechanisms. Aging affected the capacity of WY to remove OTA, but YCW removal capacity remained constant during aging. A previous heat treatment (85 degrees C for 10 min) of WY and YCW increased their removal capacity and increased the efficiency of the decontamination process.     

Effects of pH and temperature on metmyoglobin solubility in a model system

From a series of experiments heating metmyoglobin solutions at pH 5.0 through 7.0, the effects of temperature and pH on the thermal stability of metmyoglobin were investigated. The percent metmyoglobin denatured at temperatures from 25 to 80 °C was determined. pHs lower than 6.5 caused metmyoglobin denaturation at various temperatures from 25 to 80 °C, but it was particularly apparent when pH was < 5.6. Thermal stability of metmyoglobin increased as pH increased. Metmyoglobin denaturation occurred at 55 °C at pH 5, however, denaturation did not occur until 60 °C at pHs from 5.3 to 7.0. A slower heating rate (0.9 °C/min) resulted in more metmyoglobin thermal denaturation than a faster heating rate (1.3 °C/min) when the temperature was above 55 to 60 °C. The denaturation caused by low pH alone was reversible, while that caused by high temperature was not. Techniques which increase muscle pH, such as the injection of sodium bicarbonate, could effectively improve the color condition of PSE meat.     

Structural and ultrastructural changes in yeast cells during autolysis in a model wine system and in sparkling wines

This study shows the changes that occur during the autolysis of yeast in a model wine medium and in a sparkling wine after 12 months of aging, using Nomarsky Light Microscopy and Low Temperature Scanning Electron Microscopy (LTSEM). The size of the yeasts after 24 h of autolysis in a model medium is much smaller than when they are in the growth stage. With LTSEM. a large number of folds can be observed on the surface of the yeast and practically empty cells. Greater morphological changes, both structural and ultrastructural, can be observed in the yeast after 12 months of aging in wine than in the yeast after 24 h of induced autolysis. However, less of the cytoplasmic content of the yeast that has undergone autolysis in the wine was solubilized than that of the yeast after 24 h of autolysis in the model wine system. These findings indicate that autolysis of yeast in wine is a long-lasting process, which continues for at least 12 months.     

3种杀真菌剂对葡萄酒酿酒酵母生长及发酵性能的影响

在模拟葡萄汁体系中添加不同浓度的常用杀真菌农药嘧霉胺、美铵和金科克,研究它们对酿酒酵母生长及发酵性能的影响.结果发现,3种农药对酵母Saccharomyces cerevisiae AWRI的生长及发酵性能影响不明显,只是在一定程度上影响酵母的发酵速率,但是不影响试验酵母对还原糖的利用率,残糖量都与对照相当.并且3种不同浓度的农药均在一定程度上减少了酵母的酒精生成量.其中10mg/L金科克对酒精生成量的影响效果显著,其他则在统计学上没有显著差异.     

低温对葡萄酒香气成分和酵母代谢的影响

适当的低温胁迫使酵母的代谢受到不同机制的调控而做出相应的反应,产生不同含量的代谢产物,进而影响葡萄酒的品质。低温发酵有利于提高葡萄酒的香气和感官特性,主要是乙酸酯和乙基酯类的增加,高级醇和挥发酸含量的降低。该文从葡萄酒香气成分、相关代谢及基因表达的角度,分析低温对葡萄酒品质的影响,并结合适合低温发酵的非酿酒酵母,为低温发酵葡萄酒提供理论依据。     

Influence of temperature and pH on Saccharomyces bayanus var. uvarum growth; impact of a wine yeast interspecific hybridization on these parameters

The species Saccharomyces bayanus var. uvarum possesses interesting enological characteristics but produces high concentration of volatile fermentative compounds not desirable in Sauvignon blanc wines. Interspecific hybrids between Saccharomyces cerevisiae and S. bayanus var. uvarum were made in order to join the main parental advantages. Two hybrids were selected on the basis of their fermentation characteristics and their karyotypes, i.e. they have a different mitochondrial DNA. In order to produce these hybrids as active dry yeast to be used as starter in wine-making, their optimal environmental conditions for growth, i.e. temperature and pH, were determined as the objective of our work. Using a two-level factorial design it was found that the two parental strains have different optimal temperature but for the two strains, pH does not have a significant influence on growth. The influence of temperature on biomass productivity for hybrid strains were strictly identical, so we suppose that the main genes coding for temperature sensitivity were not contained in mitochondrial DNA, but in nuclear DNA. Moreover the reactions of hybrid strains to the temperature variations were similar to the one of S. bayanus var. uvarum. This latter strain could have a majority of genes responsible of temperature sensitivity dominant in comparison with those of the strain S. cerevisiae.     

Changes in wine yeast storage carbohydrate levels during preadaptation,rehydration and low temperature fermentations

The metabolism of glycogen and trehalose was analysed in a wine yeast strain fermenting at 25 and 13 degrees C. Trehalose and glycogen degradation were completed during the lag phase of fermentation. Ammonia was taken up rapidly and once it had been reduced to negligible amounts, the synthesis of trehalose started. Glycogen followed a similar pattern. If trehalose synthesis was taken as a stress indicator, the fermentation at 13 degrees C could not be considered stressful because the maximum concentrations are similar at both temperatures. In industrial fermentations, and after a preadaptation in grape must for several hours at 18 degrees C, the lag phase was reduced significantly, and this may be why trehalose and glycogen were completely depleted at the beginning of the low temperature fermentation. Various preadaptation conditions were tested so that their influence on trehalose and glycogen degradation could be determined. The presence of fermentable carbon sources, such as glucose or fructose, triggered the mobilisation and use of trehalose. However, just increasing the osmotic pressure did not reduce the trehalose content. No such differences were observed in glycogen metabolism.     

Molecular cloning of CIF1, a yeast gene necessary for growth on glucose.

The cif1 mutation of Saccharomyces cerevisiae (Navon et al., Biochemistry 18, 4487-4499, 1979) causes inability to grow on glucose and absence of catabolite inactivation. We have cloned the CIF1 gene by complementation of function and located it in a 2.75 kb SphI-BstEII fragment situated at ca. 18 kb centromere distal of LYS2 and ca. 80 kb centromere proximal of TYR1 on chromosome II. Southern analysis demonstrated that CIF1 is present in a single copy in the yeast genome. Northern analysis revealed that the corresponding mRNA of 1.8 kb is more abundant in cells grown on galactose than in those grown on glucose. A protein of ca. 54 kDa was predicted from the open reading frame in the sequenced fragment. In strains carrying the cif1 mutation the intracellular concentration of ATP decreased immediately after addition of glucose while the intracellular concentration of cAMP did not increase. cAMP concentration increased in response to galactose or 2,4-dinitrophenol. Disruption of BCY1 or overexpression of CDC25 in a cif1 background did not restore growth on glucose, suggesting that the absence of cAMP signal is not the primary cause of lack of growth on glucose. Complementation tests showed that cif1 is not allelic to fdp1 although the two genes seem to be functionally related.     

Interactions between yeast autolysates and volatile compounds in wine and model solution

The addition of a commercial yeast autolysate to a model solution of five typical wine aroma compounds (ethyl octanoate, linalool, 2-phenylethanol, β-ionone and octanoic acid) was investigated considering different variables, such as temperature, pH and the presence of highly concentrated natural volatile substances in wine (e.g. 3-methyl-1-butanol). The interactions of such compounds with both yeast walls and released colloids were studied using gas chromatography, with liquid–liquid extraction and solid-phase microextraction. The results were compared with those obtained by adding the commercial product to a white table wine, spiked with the five standard compounds. The data confirmed that yeast walls mainly bind less polar molecules: their loss in synthetic medium seemed to increase at higher pH values. Temperature and pH affected differently the interactions between yeast colloids and volatile compounds in wine and model solution: in complex solutions (as the addition of 3-methyl-1-butanol demonstrated) the interaction mechanisms could be influenced by competitive or other matrix-related effects, which can reduce the binding of single compounds, or even enhance their volatility.     

Simulation of retronasal aroma of white and red wine in a model mouth system. Investigating the influence of saliva on volatile compound concentrations

The influence of saliva on aroma release from white and red wines was studied in a model mouth system. Aroma compounds were analysed in the dynamic headspace of wines by solid phase micro extraction/gas chromatography with flame ionization detection. Volatile compounds were identified by solid phase micro extraction/gas chromatography-mass spectrometry, resulting in a total of 43 compounds in white wine and 41 in red wine. The results showed a greater influence of saliva on aroma release in white wine than red wine. In white wine treated with human saliva, esters and fusel alcohols, responsible for fruity and fusel oil odours, were reduced of 32–80%; by contrast, the concentration of 2-phenylethanol and furfural, responsible for rose and toasted almond notes, increased by 27% and by 155%, respectively. In red wine, treated with human saliva, only a few esters decrease, with a reduction of 22–51% due to protein-binding ability of polyphenols that are able to inhibit the activity of the saliva. C-13 norisoprenoids, vitispirane (eucalyptol) and TDN (kerosene), decreased both in white and red wine, showing a comparable variation while, for β-damascenone, the variation was insignificant.     

The role of light,temperature and wine bottle colour on pigment enhancement in white wine

Pigmentation enhancement in a Chardonnay wine with high flavan-3-ol concentration was examined by irradiating the wine under controlled conditions. Heating the wine in darkness required temperatures in excess of 50 °C before enhanced pigmentation became apparent. It was found that ultraviolet and, to a lesser extent, low wavelength visible light contributed to pigment production. The development of pigmentation depended on wine bottle glass colour: Flint > Arctic Blue > French Green > Antique Green. This is in agreement with the transmission characteristics of the bottles with even the darkest (Antique Green) allowing the transmission of some ultraviolet light. Riboflavin, when added to the wine, degraded rapidly when exposed to radiation <400 nm. The degradation of riboflavin and the onset of colour development depended on the actual amounts as well as the ratio of riboflavin to flavan-3-ol, suggesting that a complex series of reactions are occurring. A degradation product of riboflavin may be contributing to the increase in absorbance in the visible region observed during light exposure.     

不同酵母菌株对霞多丽冰葡萄酒香气成分的影响

通过从霞多丽葡萄渣中分离筛选出5株不同的酵母菌株,1号菌、12号菌、X7号菌、V10号菌和15号菌,分别进行冰葡萄酒发酵实验,并采用固相微萃取结合气质色谱的方法对葡萄酒中的香气成分进行检测。结果表明,采用计算机谱图库检索定性的方法共检测出40种化合物,主要为酯类、醇类、醛类;5种酵母发酵的霞多丽冰葡萄酒样中分别检测到20种、21种、19种、23种、20种香气成分,其种类和含量均具有明显差异,说明这些菌株具有不同的发酵功能。     

砧木对酿酒葡萄生长和结果状况的影响

以SO4、5BB两种砧木与宁夏主栽的赤霞珠、美乐、霞多丽进行绿枝嫁接,研究砧木对酿酒葡萄生长、果实品质的影响。结果表明,对于同一接穗品种,以5BB为砧木越冬保存率高,接穗与砧木增粗的速度接近,亲和性更好。SO4和5BB两种砧木显著增加赤霞珠葡萄的单粒质量,但对3个品种的穗质量没有明显影响。5BB做砧木提高霞多丽、赤霞珠可溶性固形物含量,降低霞多丽、美乐可滴定酸含量;以SO4为砧木显著降低3个品种可溶性固形物含量,提高赤霞珠酸含量。综合来看,以5BB为砧木可提高果实品质,而SO4为砧木降低果实品质或推迟成熟。     

不同酵母多糖对霞多丽干白葡萄酒品质的影响

以霞多丽干白葡萄基酒为材料,分别添加酵母甘露聚糖、酵母细胞壁、非活性酵母与酵母葡聚糖等4种商业酵母多糖,采用顶空固相微萃取和气相色谱-质谱联用技术对所得酒样进行分析,以了解不同商业酵母多糖的添加对于白葡萄酒感官品质的影响。结果表明,与对照相比4种酵母多糖的添加均可提高葡萄酒总酸并降低挥发酸含量,其中酵母甘露聚糖挥发酸含量相比对照降低了51.40%;通过对挥发性香气物质贡献值(OAV)的分析表明,4种多糖处理酒样之间重要香气活性物质的种类和贡献程度差别较大,其中酵母葡聚糖处理获得的重要香气活性物质最多;感官分析也表明,4种多糖处理组酒样其香气浓郁度,感官平衡性均高于对照组,其中酵母甘露聚糖处理组的最为突出。     

Degradation kinetics of grape skin and seed proanthocyanidins in a model wine system

Catechin (monomer), purified grape skin proanthocyanidin (polymer), and purified grape seed proanthocyanidin underwent monitored accelerated oxidation under continuous oxygenation and UV light, at a constant 20 °C. Compounds were dissolved in model wine solutions with (and without) catechol. Solutions were examined and then contrasted by absorbance measurements, phloroglucinolysis, and subsequent HPLC analysis. Oxidation of these monomers and polymers revealed significant colour changes (measurable increase in colour density). The presence of catechol increased the half-life of catechin, but the opposite was observed for total skin and seed proanthocyanidins. Skin and seed proanthocyanidin degradation half-life decreased with the addition of catechol. In general, based on second order rate reactions, total subunits of seed proanthocyanidin solutions degraded faster than that of skin proanthocyanidin solutions. As expected, there were decreases of measurable phenolics in both monomer and polymer solutions. Under the study conditions, flavanol monomer and polymer oxidation was chiefly dependant upon initial solution concentration.     

Effect of growth temperature on yeast lipid composition and alcoholic fermentation at low temperature

The loss of viability of wine yeast strains due to low-temperature fermentations could be overcome by increasing their stress tolerance and adaptability. Changes in membrane lipid composition are one of the first responses to cold stress. The aim of this study was to analyze the various adaptation mechanisms to low temperatures by comparing the better adapted Saccharomyces species. The viability, vitality, fermentation capacity, and lipid composition of different Saccharomyces species (S. cerevisiae, S. bayanus, S. uvarum, and a hybrid S. cerevisiae/S. uvarum) with different fermentative origins (wine, beer, and baker’s strains together with a laboratory strain) were compared after culturing at low (13 °C) and optimal (25 °C) temperatures. In spite of specific responses of the different strains/species, the results showed that at low temperature, the medium-chain fatty acid and the triacylglyceride content increased, whereas the phosphatidic acid content and the phosphatidylcholine/phosphatidylethanolamine ratio decreased. Only the laboratory strain was not able to ferment the sugars, and after growing at both temperatures, its lipid composition was very different from that of the other strains. The hybrid strain showed the highest sugar consumption at 13 °C and the best vitality whatever the preculture temperature used. The rest of the species needed a preadaptation at low temperature involving a change in their lipid composition to improve their fermentation rate at 13 °C.     

Glucagon, insulin, growth hormone, and glucose concentrations in blood plasma of lactating dairy cows

Concentrations of glucose, growth hormone, insulin, and glucagon in blood plasma relative to days in milk, milk production, type of housing, and season were measured. Blood samples were obtained from 133 to 150 lactating Holstein cows on 3 consecutive days in July, October, January, and April. Glucose, insulin, and ratio of insulin to glucagon increased with increasing days in milk. Growth hormone and ratio of growth hormone to insulin decreased with increasing days in milk. Glucagon concentrations were similar throughout lactation. Above average milk production throughout lactation was associated with above average glucagon, lower insulin, and lower glucose. The relationship was not significant between growth hormone concentration and milk production, however. Cows on summer pasture with limited grain supplement had higher growth hormone and lower glucose, insulin, and glucagon than cows eating ad libitum in barns or feedlot. In general, however, all cows had higher glucose and lower growth hormone, insulin, and ratio of insulin to glucagon in July than in cooler months.     

香雪酒中的黄酒酵母选育

为了分离出优良的黄酒酵母菌种,通过对香雪酒中的酵母复壮和TTC选育,将分离出的酵母经酵母水试验、锥型瓶发酵、耐酒精、耐温、速酿酒母制作和锥型瓶模拟大缸发酵试验等,可使黄酒生产企业根据自己产品的类型特点和消费者的口味需求,选育出产生不同口感的黄酒的菌株来生产不同类型的黄酒.     

树莓果酒酿造酵母的分离、筛选

从天然浆果中分离酿酒酵母并进行生理生化分类鉴定,通过红树莓汁的发酵试验从分离到的酿酒酵母中筛选得到适合发酵红树莓果酒的天然酵母。首先通过自然发酵法从不同来源的新鲜树莓、山葡萄、蓝莓中分离得到30株酵母,利用形态及生理生化鉴定方法将30株酵母分成25组;然后在相同条件下接入等量的不同酵母进行发酵,以红树莓果酒的总酸、残糖、乙醇体积分数及感官评价分数为评价指标,从而筛选出适合红树莓果酒酿造的最佳酵母。结果表明,第7组酵母最适于发酵红树莓果酒,所得果酒总酸10.55g/L,残糖4.14g/L,乙醇体积分数为12.2%,果酒具有鲜亮的宝石红色,澄清透亮,果香浓郁,酒体丰满,口味纯正。     

红葡萄酒酿酒酵母的分离筛选研究

流行性病学研究发现适量的饮用红葡萄酒可以降低心血管疾病、动脉粥样硬化和癌症等多种疾病的发病率。在酿造设备、生态条件与葡萄品种、工艺条件三个因素相对稳定的情况下,酵母菌的酿造学特性直接影响葡萄酒的质量和风格。山东省烟台地区是我国葡萄酒的主产区之一,历史悠久,酒厂众多,因而选育适合本产区葡萄特性、土壤特点、地域特性的优良酵母并酿出风格独特、具有品种典型性的葡萄酒显得尤为重要。本研究从葡萄、葡萄园土壤分离获得32株酵母菌株,通过杜氏管发酵、耐酒精、耐糖、耐酸、耐SO2和葡萄酒发酵试验,筛选出一株优良葡萄酒酿酒酵母QY-29。QY-29菌株发酵的葡萄酒具有酒体澄清、透明、果香浓郁、酒体丰满等特点,将进一步提高当地葡萄酒的市场竞争力和商业价值。