Development of antimicrobial whey protein-based film containing silver nanoparticles biosynthesised by Aspergillus Niger

Applications of whey protein concentrate (WPC)-based films have been limited in the food industry due to their poor mechanical properties. This research aims to evaluate the effect of silver nanoparticles (AgNPs) synthesised by Aspergillus niger on the mechanical and antimicrobial properties of WPC-based films. The biosynthesised AgNPs solution was added into the WPC film formula at the concentration of 0, 0.25 and 1.25 mm . The film samples containing AgNPs inhibited the growth of Staphylococcus aureus, Escherichia coli O157:H7, Salmonella Enteritidis, Listeria monocytogenes, Williopsis saturnus or Aspergillus sydowii with zones of inhibition ranging from 13 to 19.7 mm. Incorporation of AgNPs improved tensile strength and water barrier properties of the films by 84% and 67%, respectively. However, per cent elongation at the break of the film decreased from 37% to 11% by the addition of 1.25 mm AgNPs. This work provides a protocol for preparing improved antimicrobial WPC films with AgNPs.     

乳糖酶和酿酒酵母的共固定化及其在乳清发酵中的应用

利用凹凸棒土的强吸附作用,首先将乳糖酶吸附于凹凸棒土上,再采用壳聚糖溶液包埋的方法制成乳糖酶与酿酒酵母细胞的共固定化凝胶颗粒。实验结果表明,凹凸棒土与壳聚糖的适宜比例为5：1,加酶量为300u儋凹凸棒土,室温下吸附时间为4h;所制得的共固定化酶-酵母细胞发酵乳糖的适宜pH值和温度分别为6．0和32℃,乳糖浓度13％～15％;在适宜的发酵条件下,以20％的乳清（乳糖含量为13．42％）为底物发酵30h,酒精浓度达8．3％（v／v）,乳糖转化率达93．2％。     

酿酒酵母发酵生产谷胱甘肽的研究

以诱变获得的酿酒酵母突变株YF(ZnCl2r,Ethr)为试验菌株,通过摇瓶发酵、发酵罐补料分批发酵,对突变株发酵生产谷胱甘肽进行研究.确定发酵罐分批发酵的最佳培养条件为:温度30℃,pH 6.0,接种量为20%,搅拌转速为150 r/min,通气量为250 L/h.在补料分批操作方式下,分别考察了摇瓶培养、发酵罐培养...     

Bioconversion of heptanal to heptanol by Saccharomyces cerevisiae

Saccharomyces cerevisiae is widely known for its catalytic activity on substrates such as aldehyde and ketone. Interestingly, the activity of S. cerevisiae on heptanal (C₆H₁₃CHO), in spite of its being a very common aldehyde, has not been explored. The main objective of this study was therefore to investigate the bioconversion of heptanal, using a strain of the yeast S. cerevisiae. Bioconversion parameters such as incubation period, pH, concentration of substrate, yeast and maltose were also optimized. The study revealed heptanol as the major product. The optimum conditions for biotransformation were found to be: 3 days incubation; pH 7.0; heptanal concentration 0.15 ml/100 ml medium; and S. cerevisiae concentration of 0.15 g/100 ml medium. Reduction in maltose content (to 0.3 g maltose/100 ml medium) showed increased conversion of heptanal. Heptanoic acid and 2‐hydroxyheptanoic acid were obtained as two minor co‐products. The overall study showed that S. cerevisiae converted heptanal to heptanol by a yield of 68.9 ± 1.1% w/w under optimum conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

肉桂醛诱导酿酒酵母Persisters细胞的形成

本文研究了肉桂醛对酿酒酵母persister细胞形成的影响。通过96孔板微量法测定肉桂醛对酿酒酵母生长的最小抑制浓度(MIC)为0.4 m M;采用流式细胞仪以及梯度稀释滴平板计数法研究了肉桂醛处理后酿酒酵母persister细胞的形成情况。结果表明,肉桂醛可以抑制酿酒酵母生长,且能够诱导酿酒酵母细胞形成persister状态,该状态下的细胞对两性霉素B产生耐药性。进一步研究发现肉桂醛处理后可以使酿酒酵母细胞停滞在细胞周期的任何阶段,而雷帕霉素诱导的细胞自噬只能停留在G1期,所以酿酒酵母perisister与自噬状态存在区别。目前,对于Persister的研究集中在原核微生物,对真核生物persister的研究非常有限。由于persister群体通常占总群体极小一部分,这就给基因水平上研究persister的形成机制带来很大的挑战。本研究发现肉桂醛处理酿酒酵母细胞后,可以促使其大部分细胞形成persister。这就为从基因水平上认识真核生物persister的形成机制提供了方法,实验结果表明YGL基因也与酿酒酵母persister的形成有很大关系。     

Exclusion of Saccharomyces kudriavzevii from a wine model system mediated by Saccharomyces cerevisiae

This study investigated the competition and potential hybrid generation between the species Saccharomyces cerevisiae and S. kudriavzevii in a wine-model environment. Our main goal was to understand why S. kudriavzevii has not been found in wine fermentations whilst their hybrids are present. Auxotrophic mutants (Ura(-) and Lys(-)) were used to favour the selection of hybrids and to specifically differentiate the two species in mixed fermentations carried out at different temperatures (17 °C, 24 °C and 31 °C). Both yeasts showed a reduction in their maximum specific growth rates in mixed fermentations, indicating a clear antagonistic effect between the two microorganisms. Temperature played an important role in this competition. In this way, S. kudriavzevii was less affected at 17 °C, but S. cerevisiae was clearly the best competitor at 31 °C, preventing the growth of S. kudriavzevii. Population levels of S. kudriavzevii always significantly decreased in the presence of S. cerevisiae. Ethanol was measured throughout the fermentations and in all cases S. kudriavzevii growth was arrested when ethanol levels were < 5 g/l, indicating that this compound did not influence the competitive exclusion of S. kudriavzevii. Killer factors were also discarded due to the K(-) R(-) phenotype of both strains. Finally, no prototrophic interspecific hybrids were isolated in small-scale fermentations at any temperature assayed. Our results show that the lack of competitiveness exhibited by S. kudriavzevii, especially at high temperatures, explains the absence of this species in wine fermentations, suggesting that natural S. cerevisiae × S. kudriavzevii hybrids most likely originated in wild environments rather than in industrial fermentations.     

Saccharomyces cerevisiae SCY1发酵kefir的工艺研究

本文采用Saccharomyces cerevisiaeSCY1和乳酸菌混合发酵牛乳制备kefir,分别研究了接种量、灭菌条件、发酵温度和加糖量对kefir风味的影响,最终确定最佳工艺条件为:XPL-1接种量为0.0400g/L,SCY1接种量为103个/mL;灭菌条件为80~85℃下灭菌10min;发酵温度为32℃;加糖量为4%。通过此工艺条件制备的kefir,具有独特的风味和较高的营养价值。     

酿酒酵母生产谷胱甘肽的培养条件的研究

本实验对酿酒酵母(Saccharomyces cerevisiae)CS10515产谷胱甘肽的培养条件进行了初步研究,确定了其最佳培养基组成为:葡萄糖为5%、酵母膏1.2%、硫酸铵0.6%、硫酸镁0.02%、磷酸二氢钾0.1%;当发酵液初始pH为6.0、装液量50%～60%、振荡速度300r/min时,经过24h振荡培养后,谷胱甘肽的产量为90.20mg/L。     

Saccharomyces cervisiae在食品发酵工业中的研究进展

从基础理论和应用技术等方面综述了国内外对酿酒酵母(Saccharomyces cervisiae)研究进展及其在食品发酵工业中的最新研究成果。     

荧光图像分析法进行酿酒酵母生长过程活力分析

应用荧光标记结合显微图像分析技术检测酿酒酵母摇床培养过程中活力的变化规律,分析酿酒酵母在生长过程中不同时期的活力特点及其与活性关系.结果表明,本技术不但可获得酿酒酵母生长的活力水平的变化趋势,而且还可获得酿酒酵母分裂周期中蛋白质的分布变化情况,并通过对酿酒酵母的连续动态观察而获得酵母分裂时相的信息.说明图像分析法能够替代流式细胞仪作为酿酒酵母活力评价的重要手段.     

Endomitotic diploidization of Saccharomyces cerevisiae by heat treatment during spore germination

Diploid cells with ability to mate, hereafter referred to as diploid mater cells, were obtained at significant frequencies by the heat treatment of haploid spores at the early germination stage in Saccharomyces cerevisiae heterothallic strain CG5M ( a /α diploid cells heterozygous for five auxotrophic markers). The highest frequency (ca. 11%) of diploidization was obtained from viable cells after heat treatment at 55°C for 10 min when spores were precultivated for 30 min in liquid medium to initiate the germination. The diploid mater cells obtained were homozygous for mating type and for the auxotrophic markers. The diploidization of a spore is thus concluded to be due to endomitotic events in germinating heat-treated spores.     

丙烯酰胺诱导酿酒酵母的抗氧化降解动力学研究

目的 研究丙烯酰胺处理酿酒酵母的抗氧化降解动力学。方法 以酿酒酵母为模型, 测定丙烯酰胺对酿酒酵母的生长影响及抗氧化指标。结果 丙烯酰胺对酿酒酵母的生长有抑制作用, 且呈剂量依赖性。与对照组相比, 大部分丙烯酰胺处理组的丙二醛(malondialdehyde, MDA)含量、谷胱甘肽(glutathione, GSH)含量、总超氧化物歧化酶(total superoxide dismutase, T-SOD)活力增加, 总抗氧化能力(total antioxidant capacity, T-AOC)降低, 且MDA含量、T-AOC的变化符合动力学方程。结论 在培养前期, 处理组各抗氧化指标的波动比对照组大, 这表明丙烯酰胺对酿酒酵母具有氧化损伤, 且在培养前期较为明显, 这可能与丙烯酰胺的半衰期及酿酒酵母自身抗氧化防御系统有关。     

酿酒酵母发酵生产S-腺苷甲硫氨酸工艺的优化

目的 优化酿酒酵母LS101发酵生产S-腺苷甲硫氨酸(SAM)的工艺.方法 用单因素实验法,通过测定SAM浓度、细胞浓度、胞内SAM含量以及胞外SAM浓度等参数来确定较为适合的工艺.结果 得到适合的培养基组成为:蔗糖10%～12%,L-甲硫氨酸0.4%,尿素1.5%～2%,酵母粉3%,甘氨酸0.1%,生物素4 mg/L.8 L发酵罐间歇分批补料发酵,培养54 h后SAM产量为3.9 g/L,细胞浓度达到42.2 g/L.结论 得到了优化的酿酒酵母LS101生产SAM发酵工艺,提高了SAM发酵水平.     

固定化酿酒酵母发酵香蕉酒的研制

介绍了以香蕉为原料采用固定化酿酒酵母发酵香蕉酒的工艺，并对分批和连续发酵工艺的关键点进行了研究。     

Recovery of gene function by gene duplication in Saccharomyces cerevisiae

A prototroph revertant (Rev9) selected from an ATCase^? mutant of the URA2 gene containing three nonsense mutations was shown to contain two ATCase coding sequences. We cloned both ATCase coding areas to show that the duplicated locus (dl9) was the only functional one. Its size corresponded roughly to the second half of the URA2 wild-type gene. Sequence analysis of the 5′ end of dl9 indicated that this duplicated sequence was inserted within the intergenic region close to the MRS3 gene and was transcribed from an unknown promoter divergently from the MRS3 gene. The event leading to the revertant strain Rev9 included a rearrangement that increased the size of chromosome X by about 60 kb. In agreement with such a rearrangement, recombination was undetectable in the vicinity of the locus dl9. Genetic mapping confirms that the MRS3 gene is 2 cM distal to the URA2 gene on the right arm of chromosome X.     

流式细胞术检测单增李斯特菌与酿酒酵母

为探讨流式细胞术对单增李斯特菌和酿酒酵母的活菌与热灭活菌的检出效果,本文采用荧光染色试剂SYTO-9和碘化乙锭(PI)对单增李斯特菌和酿酒酵母的活菌与热灭活菌的细胞悬液进行染色,采用流式细胞仪同时测量红色荧光与绿色荧光从而得出细胞悬液中的细菌和酵母的含量。结果表明经核酸荧光染料染色后,再结合流式细胞术对细菌与酵母菌进行检测,步骤简单、耗时短。该法不仅简化了测量步骤且分辨率高,对单增李斯特菌和酿酒酵母均具有良好的检出结果,能分辨同一体系中同一菌种的活细胞与热灭活细胞和同一体系中的细菌与酵母活细胞;该法检出限低,将单增李斯特菌稀释后,最低检出限可达1.2×104 cells/mL,将酿酒酵母稀释后,最低检出限可达6×103 cells/mL,因此能大大缩短增菌时间或者避免繁复的增菌步骤。     

α-乙酰乳酸脱羧酶基因在酿酒酵母中稳定表达的策略

综述了宿主细胞的表达特点，外源基因的来源，表达载体和转化方法对α-乙酰乳酸脱羧酶基因在酿酒酵母中稳定表达的影响，并在此基础上提出了相应的策略。     

WL培养基在酿酒酵母筛选中的应用

从葡萄果皮自然发酵液中分离酵母菌株。利用WL琼脂培养基及赖氨酸培养基筛选酿酒酵母,结果显示,在葡萄果皮自然发酵的早期不存在酿酒酵母,酿酒酵母最初出现在发酵中期即发酵后第4d。经过生理生化和分子鉴定结果表明,WL培养基对酿酒酵母的筛选可信度达到100%。     

Thermal Resistance of Saccharomyces cerevisiae in Pilsen Beer

The thermal resistance of S. cerevisiae (CMOJ896) was determined in Pilsen beer (pH = 4.28 ± 0.05; extract of original wort (EOW %) = 11.30 ± 0.08; percentage of alcohol by volume (% at 20°C) = 4.97 ± 0.05; total nitrogen content (mg/L) = 590 ± 37; bitterness units (BU) = 20.5 ± 1.3; carbonation of the beer (Vol. CO₂) = 2.89 ± 0.09; color (SRCM) = 3.3 ± 0.4). The flask method was used for an initial population of 1 × 10⁴ cells/mL. Decimal reduction times of D_47°C = 3.16 min, D_48°C = 2.65 min, D_49°C = 1.74 min and D_50°C = 0.68 min were obtained at the temperatures studied. Values of D_60°C = 0.01 min and z = 4.6° were obtained for this microorganism.     

A Review of Phenotypes in Saccharomyces cerevisiae

A summary of previously defined phenotypes in the yeast Saccharomyces cerevisae is presented. The purpose of this review is to provide a compendium of phenotypes that can be readily screened to identify pleiotropic phenotypes associated with primary or suppressor mutations. Many of these phenotypes provide a convenient alternative to the primary phenotype for following a gene, or as a marker for cloning a gene by genetic complementation. In many cases a particular phenotype or set of phenotypes can suggest a function for the product of the mutated gene. © 1997 John Wiley & Sons, Ltd.