低糖面团用耐冷冻酵母的筛选及其性质

从自然界中分离、筛选出100多株酵母,通过对其海藻糖含量、耐冷冻存活率、面团发酵活力以及-22℃冷冻后发酵力变化的测定,确定一株适用于冷冻面团制作的耐冷冻酵母--W122.该菌株在-22℃冻藏6周后存活率达到80%以上,发酵力为冷冻前的78%.在不同含糖量(0%～20%)的面团中发酵力变化不大,均能达到较高的发酵产气量,在含糖量为5%时产气量最高,并可用于无糖面团的制作.因此,该酵母在冷冻面团加工中具有很大的应用前景.     

大豆多肽对酵母细胞增殖及耐冻性的影响

酵母细胞的活性和耐冻融性对于发酵制品和冷冻面团技术具有十分重要的影响。将大豆多肽、酪蛋白胨、酵母氮源三种不同的氮源加入培养基培养酵母细胞,通过对生长曲线、细胞湿重、面团发酵和冷冻后面团发酵及细胞存活率的比较,评价大豆多肽对酵母细胞活性及耐冻能力的影响。结果表明,随着培养基中大豆多肽量的增加,所得的酵母细胞生物量增加,添加量超过25 g/L以后,酵母细胞生物量不再有明显增加,25 g/L是大豆多肽的最适添加量。与相同量的其他氮源相比,大豆多肽作为培养基氮源得到的酵母细胞在冷冻后存活率更高,其发酵面团仍能够保持较好的发酵力。大豆多肽能够促进酵母细胞增殖、增强酵母细胞的耐冻性、提高面团的发酵效果。     

不同酵母对冷冻面团发酵特性及馒头品质的影响

对市场上4种活性干酵母进行了无糖和低糖面团发酵活力及冷藏1周后发酵力的变化进行测定。结果表明:不同酵母在无糖面团和低糖面团中的发酵力存在差异,酵母Y2基本无差别,Y1、Y3和Y5发酵力都有不同程度的提高。冷藏7d后相对发酵力的测定表明:Y1、Y3和Y4在无糖面团中相对发酵力较高;Y2和Y3在低糖面团中的相对发酵力较高。通过无糖冷冻面团馒头感官评价及质构特性的测定,用酵母Y3来发酵的冷冻面团馒头品质较好。     

烘焙酵母取样及冷冻面团的稳定性

评价了冷冻面团中6种商品烘烤醇母菌株在同等条件下生长时的冷冻耐力。观察到经受了快速冷冻（冷冻速率为约10℃／min）的酵母菌株之间存活差别极小。在低速冷冻（约1℃／min）后接着贮存12周，所有菌株呈现出类似的耐冷冻力。如两个实验室合作研究的结果那样，有7个品牌（大多数菌株从中筛选）的21种商品烘焙酵母样品按冷冻面团进行冷冻对比。快速冷冻试验（测量产气量）和3个月的贮存试验（测量产气量、面团醒发时间以及面包比容）表明，用于制作冷冻面团的商品酵母样品之间耐冷冻力变化很大。由于酵母样品间耐冷冻力的差别很大，因此，产于加拿大、法国和美国的7个品牌的酵母无一优于其它。上述结果表明，对冷冻面团稳定性的主要影响是商品烘焙酵母的取样而非菌株或品牌，并且强调了用于冷冻面团生产中烘焙酵母样品耐冷冻力质量控制的重要性。     

超声辅助酶解大米多肽对酵母细胞活性及耐冻性的影响

将超声辅助酶解制取的大米多肽、酪蛋白胨、酵母氮源3种不同氮源加入培养基培养酵母细胞,比较酵母的生长曲线、细胞湿质量、面团发酵和冷冻后面团发酵及细胞存活率,评价大米多肽对酵母细胞活性及耐冻能力的影响。结果表明,与相同量的其他氮源相比, 25 g/L大米多肽作为培养基氮源得到的酵母细胞在冷冻后发酵活力更好,能够促进酵母细胞增殖、增强酵母细胞的耐冻性、提高面团的发酵效果。     

传统面食发酵剂中酵母菌的筛选及性能研究

对山西地区传统面食发酵剂中酵母菌进行筛选分离及初步鉴定,考察酵母的发酵力、耐酒精能力、耐酸性及抗冻性等指标。结果表明:两株酵母菌分别为萨地假丝酵母(编号Q3505)和卡斯特酒香酵母(编号Q5503)。其中菌株Q5503发酵3 h面团体积可达410 m L,产气490 m L。菌株Q3505发酵3 h面团体积可达395m L,产气270 m L。在耐酸性和耐酒精能力上,菌株Q5503优于Q3505;在抗冻性方面,冷冻60 d后的菌株Q5503和Q3505发酵力保持率分别为83.33%和64.39%,表现出较好的抗冷冻性,具有一定的工业应用前景。     

抗冻酵母的筛选及发酵特性研究

采用模拟面团预发酵法筛选出应用于冷冻面团的菌株,研究菌株胞内化合物含量与其抗冷冻能力、相对发酵力的相关性,并且根据菌株菌落形态和26SrDNA序列分析法鉴定抗冻性能或发酵性能优良的菌株。结果表明,4个样品中筛选了7株酵母菌,存活率为9%~86%,相对发酵力为9%~67%,其中菌株Y-3的存活率较高,达到86%,菌株H-1的相对发酵力最高,达到67%。相关性分析结果表明,细胞存活率与海藻糖含量、甘油、脯氨酸含量呈正相关,与精氨酸、天冬氨酸、谷氨酸及相对发酵力呈负相关;相对发酵力与天冬氨酸、谷氨酸含量呈显著正相关,与海藻糖、甘油、脯氨酸、精氨酸呈负相关。菌株鉴定结果表明,菌株Y-3为汉逊德巴利酵母(Debaryomyces hansenii),菌株H-1为酿酒酵母(Saccharomyces cerevisiae)。综合抗冷冻性能、发酵力和食用安全性,后续研究拟将菌株Y-3和H-1进行混合发酵,最终应用于冷冻面团的制作。     

冷冻面团面包工艺的研究进展

叙述了耐低温面包酵母的耐冻机理和决定冷冻面团质量的因素。冷冻面团的稳定性与酵母质量、面团配方、冷冻前发酵工艺和冻融速率等有关,筛选耐低温酵母菌种是冷冻面团面包的关键因素;海藻糖含量、酵母的培养条件和冻融条件在酵母的耐冻机制中起着重要的作用。     

市售酵母发酵特性和抗冻性的比较

采用蒽酮比色法测定不同市售酵母中海藻糖的含量,并结合F3流变发酵仪测出面团冷冻前后酵母发酵特性的变化,对不同酵母的抗冻性进行比较,用以筛选出合适的抗冻酵母来生产冷冻面团。结果表明:5#酵母的海藻糖含量最高,15#、12#和10#酵母制成的新鲜和冷冻面团的发酵力均较大,8#、20#和25#的抗冻力最强且全为高糖型酵母。综合比较得出,在冷冻面团的制作中应首先选择8#酵母。     

新型耐冷冻酵母开发上市

日本协和发酵食品公司今年在市场上推出了具有优良耐冷冻性能的酵母新品种“答伊耶酵母VS”。该酵母即使在高糖度面团中使用也具有高发酵力。     

Identification of genes whose expressions are enhanced or reduced in baker's yeast during fed-batch culture process using molasses medium by DNA microarray analysis

Genes whose expression levels are enhanced or reduced during the cultivation process that uses cane molasses in baker's yeast production were identified in this study. The results showed that baker's yeast grown in molasses medium had higher fermentation ability and stress tolerance compared with baker's yeast grown in synthetic medium. Molasses apparently provided not only sugar as a carbon source but also provided functional components that enhanced or reduced expression of genes involved in fermentation ability and stress tolerance. To identify the genes whose expression is enhanced or reduced during cultivation in molasses medium, DNA microarray analysis was then used to compare the gene expression profile of cells grown in molasses with that of cells grown in synthetic medium. To simulate the commercial baker's yeast production process, cells were cultivated using a fed-batch culture system. In molasses medium, genes involved in the synthesis or uptake of vitamins (e.g., biotin, pyridoxine and thiamine) showed enhanced expression, suggesting that vitamin concentrations in molasses medium were lower than those in synthetic medium. Genes involved in formate dehydrogenase and maltose assimilation showed enhanced expression in molasses medium. In contrast, genes involved in iron utilization (e.g., siderophore, iron transporter and ferroxidase) showed enhanced expression in synthetic medium, suggesting that iron starvation occurred. The genes involved in the metabolism of amino acids also showed enhanced expression in synthetic medium. This identification of genes provides information that will help improve the baker's yeast production process.     

面包酵母发酵力测定方法的探讨

探讨了面包酵母发酵力的测定方法。试验结果表明 ,采用发酵 0 .5h内面团的产气量 (mL)作为面包酵母发酵力的指标 ,能较好地反映面包酵母产品的质量 ;面团浮水法设备简单、重复性好 ,且与排水法之间有良好的相关关系 ,亦可作为面包酵母发酵力检测的方法。     

酵母内海藻糖积累条件的优化

对面包酵母 (BY 11)海藻糖积累条件进行了较系统的研究 ,采用了PB和响应曲面设计法 ,得到了 1个优化的培养基。采用此培养基 ,以 3 g/L(以酵母干固物计 )的接种量 ,3 7℃震荡培养 3h可积累海藻糖 0 96g/L ,从而大大提高了海藻糖的产量 ,为工业生产提供了可行性。     

Proline accumulation in baker's yeast enhances high-sucrose stress tolerance and fermentation ability in sweet dough

During bread-making processes, yeast cells are exposed to various baking-associated stresses. High-sucrose concentrations exert severe osmotic stress that seriously damages cellular components by generation of reactive oxygen species (ROS). Previously, we found that the accumulation of proline conferred freeze-thaw stress tolerance and the baker's yeast strain that accumulated proline retained higher-level fermentation abilities in frozen doughs than the wild-type strain. In this study, we constructed self-cloning diploid baker's yeast strains that accumulate proline. These resultant strains showed higher cell viability and lower intracellular oxidation levels than that observed in the wild-type strain under high-sucrose stress condition. Proline accumulation also enhanced the fermentation ability in high-sucrose-containing dough. These results demonstrate the usefulness of proline-accumulating baker's yeast for sweet dough baking.     

Simultaneous accumulation of proline and trehalose in industrial baker's yeast enhances fermentation ability in frozen dough

Freeze tolerance is a necessary characteristic for industrial baker's yeast because frozen-dough baking is one of the key technologies for supplying oven-fresh bakery products to consumers. Both proline and trehalose are known to function as cryoprotectants in yeast cells. In order to enhance the freeze tolerance of yeast cells, we constructed a self-cloning diploid baker's yeast strain with simultaneous accumulation of proline, by expressing the PRO1-I150T allele, encoding the proline-feedback inhibition-less sensitive γ-glutamyl kinase, and trehalose, by disrupting the NTH1 gene, encoding neutral trehalase. The resultant strain retained higher tolerance to oxidative and freezing stresses than did the single proline- or trehalose-accumulating strain. Interestingly, our results suggest that proline and trehalose protect yeast cells from short-term and long-term freezing, respectively. Simultaneous accumulation of proline and trehalose in industrial baker's yeast also enhanced the fermentation ability in the frozen dough compared with the single accumulation of proline or trehalose. These results indicate that baker's yeast that accumulates both proline and trehalose is applicable for frozen-dough baking.     

采用面包酵母制备三磷酸肌醇和四磷酸肌醇的研究

检测了不同厂家生产的面包酵母的植酸酶活力,建立了利用面包酵母降解植酸钠来制备三磷酸肌醇(IP3)和四磷酸肌醇(IP4)的方法.对植酸盐水解液进行阴离子交换树脂吸附之前进行预处理有助于提高其分离IP3和IP4的效率.采用这种方法所制备的IP3和IP4均只有一种异构体,即肌醇(1,2,6)三磷酸[D-I(1,2,6)P3]和肌醇(1,2,5,6)四磷酸[D-I(1,2,5,6)P4].     

Construction of a lactose-assimilating strain of baker's yeast.

A recombinant strain of baker's yeast has been constructed which can assimilate lactose efficiently. This strain has been designed to allow its propagation in whey, the byproduct resulting from cheese-making. The ability to metabolize lactose is conferred by the functional expression of two genes from Kluyveromyces lactis, LAC12 and LAC4, which encode a lactose permease and a beta-galactosidase, respectively. To make the recombinant strain more acceptable for its use in bread-making, the genetic transformation of the host baker's yeast was carried out with linear fragments of DNA of defined sequence, carrying as the only heterologous material the coding regions of the two K. lactis genes. Growth of the new strain on cheese whey affected neither the quality of bread nor the yeast gassing power. The significance of the newly developed strain is two-fold: it affords a cheap alternative to the procedure generally used for the propagation of baker's yeast, and it offers a profitable use for cheese whey.     

高适应性面包酵母菌株的杂交选育

为了改善耐高糖酵母在不同含糖量面团中的发酵力,首先制备了2 4 0株耐高糖酵母单倍体,通过高麦芽糖发酵筛选培养基筛选出了2 8株麦芽糖发酵性能良好的单倍体菌株,通过测定这些单倍体在无糖面团中的发酵力,发现9株单倍体菌株的发酵力优于或等于其亲本,其中4株为a型,5株为α型。通过它们之间的杂交得到2 0 0株杂交株,在无糖、中糖、高糖面团中测定这些杂交株的发酵力,获得4株在不同含糖量(0～30 % )面团中都具有高发酵力的高适应性面包酵母杂交株。研究表明,来自同一亲本单倍体之间的杂交有可能改善面包酵母的某些特征。     

面包酵母耐冷冻性影响因子的研究进展

论述了影响面包酵母耐冷冻性的各种因子。耐冷冻面包酵母是冷冻面团技术的关键,许多因素与酵母冷冻耐受性有关,如酵母胞内海藻糖含量、甘油含量、酒精含量、热休克蛋白含量、不同脂肪成分的比例、某些带电荷的氨基酸含量、呼吸能力、控制质膜的水运送的基因的表达等等,而海藻糖在酵母胞内起到的耐冷冻作用被广泛证明。