Lactobacillus delbrueckii subsp. bulgaricus和Streptococcus thermophilus接种比例对Bifidobacterium lactis益生菌发酵乳品质的影响

将Lactobacillus delbrueckii subsp.bulgaricus ND02(LB-ND02)和Streptococcus thermophilus ND03(ST-ND03)按1∶1、1∶10、1∶100、1∶1000接种于脱脂乳中,同时接入益生菌Bifidobacterium lactis V9(B.lactis V9,接种量为2.0×107g-1),于42℃进行发酵。通过对发酵及贮藏过程中发酵乳指标的测定,评价LB-ND02和ST-ND03的接种比例对发酵乳品质的影响。结果表明,随着LB-ND02接种比例减小,凝乳时间显著延长,B.lactis V9活菌数显著提高。4℃贮藏28 d后,随LB-ND02接种比例减小,B.lactis V9存活率差异显著,后酸化也显著减弱。研究发现,LB-ND02和ST-ND03的接种比例,显著影响发酵乳的发酵时间、B.lactis V9活菌数、后酸化及黏度。     

Production of human growth hormone by Lactococcus lactis

A synthetic gene coding for human growth hormone was expressed in Lactococcus lactis. The presence of the recombinant protein was assayed and quantified using ELISA tests. Human growth hormone was detected at high concentrations and displayed a biological activity similar to the one shown by commercial human growth hormone.     

Monitoring of the bacterial communities of bamboo shoots (Dendrocalamus latiflorus) during pickling process

The diversity and dynamics of the dominant bacterial communities arising during the pickling process of bamboo shoots (Dendrocalamus latiflorus) were investigated by nested polymerase chain reaction denaturing gradient gel electrophoresis combined with quantitative real‐time polymerase chain reaction. Results showed only several kinds of halophilic bacteria during early sampling time (0?3 days). After pickling for 7 days, Lactococcus lactis significantly increased (P < 0.05, quantities were 6.39 × 10⁵ copies μL^?1) and became the first dominant bacterium. After pickling for 14 days, Weissella sp. bands appeared and quickly became dominant on the 21st day (4.07 × 10⁶ copies μL^?1). As maturation progressed, Lc. lactis decreased in intensity whereas Weissella sp. increased in intensity. Finally, the quantities of Weissella sp. (2.50 × 10⁷ copies μL^?1) became higher than those of Lc. lactis (1.43 × 10⁷ copies μL^?1) after pickling for 56 days. The pickling process was initiated by Lc. lactis, followed by Lc. lactis and Weissella sp., and was finally succeeded by Weissella sp.     

Probiotic potential and sensory properties of coconut flan supplemented with Lactobacillus paracasei and Bifidobacterium lactis

The effect of probiotic cultures on sensory performance of coconut flan during storage at 5 °C and the viability of these micro organisms for up to 28 days were investigated. Sensory analyses of the product were performed after 7, 14 and 21 days of storage. Coconut flans were produced with no addition of cultures (T1, control), or supplemented with Bifidobacterium lactis (T2), Lactobacillus paracasei (T3) and B. lactis  +  L. paracasei (T4). Populations of L. paracasei and B. lactis as single or in co-culture remained above 7 log CFU g⁻¹ during the entire storage period. Viability of L. paracasei was higher for T3. All products were well accepted and no significant differences ( P  > 0.05) were detected between the coconut flans studied. The addition of L. paracasei and B. lactis to coconut flan resulted in its having great potential as a functional food, which has high sensory acceptability.     

LYS2 gene and its mutation in Kluyveromyces lactis

The KlLYS2 gene, encoding the alpha-aminoadipate reductase of Kluyveromyces lactis, was isolated by complementation of a lysA1 mutant. The deduced amino acid sequence shared an identity of 73% with the LYS2 product of Saccharomyces cerevisiae. Despite the high sequence homology of the alpha-aminoadipate reductase genes, the two yeast species differently responded to the presence of alpha-aminoadipate in the medium. Wild-type S. cerevisiae is known to be sensitive to alpha-aminoadipate, but becomes resistant when mutated to lys2. In contrast, K. lactis strains were found to be naturally resistant to alpha-aminoadipate. Therefore, the positive selection procedure for the isolation of lys2 mutants on alpha-aminoadipate, as practised in S. cerevisiae, cannot be applied to K. lactis. A possible reason of this difference may be that the catalytic rate of the alpha-aminoadipate reductase differs in the two yeasts. The EMBL/Genbank Accession No. for the KlLYS2 gene is AJ504405.     

低温长时间发酵酸乳加工关键技术及品质研究

选用乳酸链球菌和保加利亚乳杆菌制作低温长时间发酵酸乳,利用DPS软件设计正交实验优化酸乳生产工艺,并对发酵结束和经4℃、后熟24h后以及4℃、冷藏3d后酸乳的酸度、pH值、纯蛋白、游离氨基酸、脂肪、双乙酰、乙醛、乳酸菌活菌数量等质量指标和风味成分进行分析检测。结果表明,最佳工艺为乳酸链球菌和保加利亚乳杆菌二4∶1,接种量3%,添加蔗糖8%,34℃培养10h左右。低温长时间发酵酸乳的酸度为69·35°T,乙醛含量为14·46mg/kg,双乙酰含量为4·72mg/kg,乳酸菌活菌数为7·15×109cfu/mL。经感官评定,酸乳的凝乳组织状态均匀细腻,香气浓郁纯正,酸甜适口,品质优良。     

RAG1 and RAG2: nuclear genes involved in the dependence/independence on mitochondrial respiratory function for growth on sugars

The analysis of five independent isolates of Kluyveromyces lactis shows that CBS 2359, CBS 683 and CBS 4574 could grow in the presence of mitochondrial inhibitors (antimycin A, oligomycin or erythromycin) and that CBS 2360 and CBS 141 were unable to grow in the presence of drugs. The resistant growth was observed only on glucose and not on other fermentable carbon sources (galactose, lactose). The phenotype 'growth on glucose in the presence of mitochondrial inhibitors' was called Rag+. This phenotype was found to be controlled by two unlinked nuclear genes: RAG1 and RAG2. Either of their recessive alleles, rag1 and rag2, led to the Rag- phenotype (i.e. the failure of growth on glucose in the presence of antimitochondrial drugs). Rag- strains represent the case in which fermentative growth becomes absolutely dependent on the functioning of the normal respiratory chain.     

乳酸乳球菌NICE系统食品级载体pRNB48的构建

乳酸菌食品级NICE系统是目前较理想的可控制蛋白质生产的食品级诱导表达系统。实验构建的食品级表达载体pRNB48含α-aga食品级选择标记、θ型复制子和nisA启动子,与宿主菌L.lactisNZ9000共同构成乳酸乳球菌食品级NICE系统,可用于目的基因在乳酸乳球菌中高效诱导表达。     

Nisin的生产、提纯和检测

Nisin是一种由乳酸乳球菌产生的羊毛硫氨酸类细菌素 ,在许多国家被许可作为生物防腐剂。Nisin的产量受许多因素的制约 ,如产生菌性能、培养基组成 (碳源、氮源、磷源和阳离子 )、发酵条件 (pH、温度、搅拌、通风 )、发酵类型 (分批发酵、连续发酵、自由细胞、固定化细胞 )等 ;大规模回收和纯化Nisin主要采用一些基于吸附-解析或者相分配原理的方法 ;最常用的定量检测Nisin的方法主要有生物分析法和免疫检测法 ,采用各种特定nisin抗体的免疫检测方法具有迅速、灵敏、准确等特性并能实现Nisin的在线检测。