酸奶发酵剂和乳酸菌生物技术育种

由新鲜牛奶制成的酸奶由于其丰富的营养、特殊的风味、爽滑的质构和良好的生理功能 ,倍受人们青睐。对酸奶乳酸菌的微生物种类、功能及其组成的酸奶发酵剂进行了综述 ,并简要介绍了乳酸菌生物工程育种方面的研究进展及酸奶乳酸菌研究领域一些令人感兴趣的课题。     

酸奶后酸化控制措施的研究进展

酸奶在储存、运输到消费者食用前,乳酸菌会继续产酸,从而使酸奶的酸度增加,出现后酸化现象,影响酸奶的口感和风味。本文简要介绍了酸奶后酸化机理和乳酸菌的耐酸机制,并从物理、化学、生物方法三个方面对目前酸奶后酸化防治措施进行了阐述与展望。     

富硒活性乳酸菌发酵剂的研制

通过L9(33)正交试验确定了富硒活性乳酸菌发酵剂的适宜发酵条件为发酵温度39℃,加硒量5μg/mL,接种量7%。经检验,研制的发酵剂富硒率达50.38%,冷藏5 d后发酵活力达0.48,冷藏7 d后活菌数达7.2×108cfu/mL,符合发酵剂的各项质量要求。     

直投式酸奶发酵剂中双歧杆菌的分离

介绍一种简便可行的从直投式酸奶发酵荆中分离双歧杆菌的方法。发酵剂在液体培养基中活化后,在不同选择培养基上划线分离,根据菌落及菌体形态确定双歧杆菌。然后进行初步鉴定。     

植物抗逆诱变育种技术研究进展

随着分子生物学技术的飞速发展,通过基因工程方法可以更快更好地获得农作物抗逆新品种,其首要任务是通过分离相应的表型改变的突变体来鉴定、克隆在胁迫条件下表达模式发生改变的基因。主要介绍几种常用的及最新的突变体诱变和筛选技术,并分析每种技术的优缺点。     

食用菌育种技术的研究进展

食用菌育种技术近年有了很大进展。本文是对野生食用菌驯化、诱变育种、杂交育种、原生质体融合技术育种及食用菌“种”的鉴定方法方面研究进展的综合论述。     

市售酸奶中乳酸菌的鉴定与耐药性

[目的]检测市售酸奶中乳酸菌的种类及其耐药情况.[方法]收集10种来自5个不同厂家的酸奶,通过细菌基因组重复基因外回文序列-PCR (repetitive extragenic palindromic-PCR,rep-PCR)结合16S rRNA同源性分析的方法对分离的乳酸菌进行基因分型和菌种鉴定.利用药敏纸片扩散法(K-B法)对分离的乳酸菌进行针对7种抗生素的药敏实验,用PCR特异性扩增结合测序的方法检测每个样品中不同基因型菌株的耐药基因(包括红霉素耐药基因erm A、erm B和四环素耐药基因tetM、tetK、tet S、tetQ、tetO、tetL、tetW).[结果]10种市售酸奶中分离到100株乳酸菌.其中,德氏乳杆菌保加利亚亚种(Lactobacillus delbrueckii ssp.bulgaricus)23株,干酪乳杆菌(Lactobacillus casei)26株,嗜热链球菌(Streptococcus thermophilus)30株,嗜酸乳杆菌(Lactobacillus acidophilus)5株,植物乳杆菌(Lactobacillus plantarum)6株,副干酪乳杆菌(Lactobacillus paracasei)10株.药敏实验发现所有100株乳酸菌均对链霉素和庆大霉素耐药,42株对万古霉素耐药,没有菌株对头孢氨苄,四环素,红霉素以及土霉素耐药.在28株经过16S rRNA测序的乳酸菌中检测到5种不同的耐药基因,在8株乳酸菌中检测到erm B基因,4株检测到tetK基因,2株菌检测到tetL基因,4株菌检测到tet M基因,2株菌检测到tet O基因,没有检测到erm A,tet S,tet Q,tet W基因.28株乳酸菌中有15株(53.57%)检测到耐药基因,其中有4株L delbrueckii ssp.bulgaricus检测到2-3种不同的耐药基因.[结论]本研究在市售酸奶中除了检测到商品标签上标注的L.delbrueckii ssp.bulgaricus和S.thermophilus以外,还检测到商标上没有标注的乳酸菌;作为常用发酵剂的德氏乳杆菌保加利亚亚种和嗜热链球菌更容易检测到耐药基因;分离得到的乳酸菌均对红霉素和四环素敏感却检测到相应的耐药基因,再一次证明了没有耐药表型的菌株也可能携带耐药基因.     

高活性乳酸菌发酵剂培养条件优化及活性测定

采用自行分离选育的乳酸菌进行混合培养,对浓缩培养条件进行正交试验,以德氏乳杆菌保加利亚亚种和嗜热链球菌的菌数及其比值作为考察指标。结果为以改良MRS为基础培养基,以6%番茄汁、0.3%玉米浆作为生长因素,42℃培养,过程采用流加氨水作中和试剂,使培养基酸度控制在pH 6.0,浓缩培养液中菌数可达9.15×109个/mL,球菌与杆菌比例为1.2∶1;最佳菌体收集时间为7.5 h;-30℃下冷冻干燥得到的乳酸菌发酵剂含活菌数达到8.2×1010个/g,球菌与杆菌比例为1.5∶1,发酵剂活性达0.435;0~4℃冷藏6个月,乳酸菌活性没有损失。产品可直接加入到灭菌奶中发酵,具有大众化特点,广泛用于各类乳品厂、饭店、食堂及家庭。     

物理诱变技术及其在香蕉育种中的研究进展

我国是世界产蕉大国,香蕉总产量已居世界第2位,香蕉产业已成为我国南亚热带地区农民脱贫致富的重要支柱产业。但目前我国香蕉品种更新缓慢,现有品种的高产性、抗寒性、抗病性均存在一定程度的缺陷,而物理诱变技术在培育改良品种特性上具有独特的优势。本文综述了物理诱变技术及其在香蕉育种中的研究进展,包括物理诱变定义、种类及应用等方面,以期对香蕉诱变研究及新品种选育实践提供参考。     

抗生素产生菌诱变育种的研究进展

一种抗生素能否产业化决定于抗生素产生菌菌种的产素水平。因而如何提高抗生素产生菌的产素水平成为抗生素研究工作者长期不懈探索的重要课题。其中,诱变育种以其技术设备简单、省时省力等优点得到了微生物育种工作者的青睐,在诱变育种技术上取得了巨大进展,为抗生素工业化生产发挥了重要作用。综述了抗生素产生菌的诱变育种研究进展。     

乳酸菌低温菌株的复合诱变选育

【目的】采用复合诱导的方法,选育出能在低温条件下性状稳定、生长良好且具有工业生产价值的低温乳酸菌菌株。【方法】使用紫外照射和亚硝基胍处理的方法对分离的Q1菌株进行诱变处理,将选育得到的低温菌株Q1-4-6与出发菌株Q1在15°C、20°C、37°C下,比较其生长速率、产酸量和糖降解量。【结果】从玛曲牧民自制酸奶中分离得到一株乳酸菌Q1,根据其形态学特征、生理生化特性,同时结合16SrDNA序列分析结果,将其鉴定为肠球菌属棉籽糖肠球菌(Enterococcus raffinosus)。经过多轮诱变选育出一株能在低温下良好生长、遗传性状稳定的菌株Q1-4-6,将出发菌株与诱变菌株在15°C、20°C比较其生长、产酸和糖降解量发现,诱变菌株均好于出发菌株。在37°C的自然条件下,诱变菌株和出发菌株的生长速率差异不大,但均略高于出发菌株。在15°C培养发现,诱变菌株生长速率、产酸量均高于购买菌株干酪乳杆菌(CL04)和嗜热链球菌(CL05)。【结论】通过UV+NTG复合诱变,最终选育出一株在低温下生长良好、遗传性状稳定的菌株Q1-4-6。     

Progress and potential in the biotechnology of lactic acid bacteria

Abstract: Current activities and future prospects for the biotechnology of lactic acid bacteria are reviewed. Genetic engineering technology, including advances and limitations of plasmid vectors and chromosomal integration strategies are discussed together with the status of gene expression and the importance of in vivo gene transfer systems and transposition. Areas of biotechnological application considered include proteolysis and flavour generation, bacteriophage resistance, antimicrobials, metabolic engineering and the possible uses of lactic acid bacteria in relation to health.     

乳酸菌代谢组学研究进展

代谢组学作为系统生物学的重要分支,近年来在微生物研究领域受到广泛关注,并取得了重要进展。目前乳酸菌代谢组学正日益成为研究的热点,就乳酸菌代谢组学研究中有关样品的制备、分析鉴定和数据分析等涉及的主要方法进行概述,并介绍一些乳酸菌代谢组学应用的典型实例,对乳酸菌代谢组学研究中潜在的问题和未来发展趋势进行讨论。     

乳酸菌对肠免疫调节功能研究进展

乳酸菌作为益生菌是人体肠道中的重要生理菌群,对维持肠道的微生态平衡,缓解过敏,抑制肠道炎症反应等免疫调节方面有重要作用。本文综述了乳酸菌对肠免疫系统的调节作用,主要从调节先天性免疫和获得性免疫系统角度出发,讨论相关研究进展,并对乳酸菌在免疫调节方面的应用前景作了展望。     

Looking backward and forward at the practical applications of genetic researches on lactic acid bacteria

Abstract Background research findings which have led to current knowledge on the genetics of lactic acid bacteria are reviewed. Important early contributions by researchers with other microorganisms are highlighted to acknowledge milestone discoveries, especially those which have made genetic engineering of industrially important genera a reality. Current genetics in the dairy Streptococcus , Lactobacillus , Pediococcus , Leuconostoc , Bifidobacterium and Propionibacterium genera are discussed. Regulatory, environmental, and research funding concerns also are discussed.     

Responses of lactic acid bacteria to oxygen

Abstract A small number of flavoprotein oxidase enzymes are responsible for the direct interaction of lactic acid bacteria (LAB) with oxygen; hydrogen peroxide or water are produced in these reactions. In some cultures exposed to oxygen, hydrogen peroxide accumulates to inhibitory levels.
Through these oxidase enzymes and NADH peroxidase, O₂ and H₂O₂ can accept electrons from sugar metabolism, and thus have a sparing effect on the use of metabolic intermediates, such as pyruvate or acetaldehyde, as electron acceptors. Consequently, sugar metabolism in aerated cultures of LAB can be substantially different from that in unaerated cultures. Energy and biomass yields, end-products of sugar metabolism and the range of substrates which can be metabolised are affected.
Lactic acid bacteria exhibit an inducible oxidative stress response when exposed to sublethal levels of H₂O₂. This response protects them if they are subsequently exposed to lethal concentrations of H₂O₂. The effect appears to be related to other stress responses such as heat-shock and is similar, in some but not all respects, to that previously reported for enteric bacteria.     

乳酸菌与酵母菌共生机理的研究进展

早期研究者从营养角度分析乳酸菌与酵母菌的共生机制,发现混合培养过程中乳酸菌与酵母菌不仅存在互补机制,代谢产物相互之间能够产生促进或抑制作用。随着Lux S/AI-2介导的群体感应现象(QS)的发现与发展,目前研究者多从群体感应角度来探讨乳酸菌与酵母菌种间的信息交流模式。本文着重从营养及信号分子这两个角度阐述目前乳酸菌与酵母菌共生机理的研究进展。     

Heteropolysaccharides from lactic acid bacteria

Microbial exopolysaccharides are biothickeners that can be added to a wide variety of food products, where they serve as viscosifying, stabilizing, emulsifying or gelling agents. Numerous exopolysaccharides with different composition, size and structure are synthesized by lactic acid bacteria. The heteropolysaccharides from both mesophilic and thermophilic lactic acid bacteria have received renewed interest recently. Structural analysis combined with rheological studies revealed that there is considerable variation among the different exopolysaccharides; some of them exhibit remarkable thickening and shear-thinning properties and display high intrinsic viscosities. Hence, several slime-producing lactic acid bacterium strains and their biopolymers have interesting functional and technological properties, which may be exploited towards different products, in particular, natural fermented milks. However, information on the biosynthesis, molecular organization and fermentation conditions is rather scarce, and the kinetics of exopolysaccharide formation are poorly described. Moreover, the production of exopolysaccharides is low and often unstable, and their downstream processing is difficult. This review particularly deals with microbiological, biochemical and technological aspects of heteropolysaccharides from, and their production by, lactic acid bacteria. The chemical composition and structure, the biosynthesis, genetics and molecular organization, the nutritional and physiological aspects, the process technology, and both food additive and in situ applications (in particular in yogurt) of heterotype exopolysaccharides from lactic acid bacteria are described. Where appropriate, suggestions are made for strain improvement, enhanced productivities and advanced modification and production processes (involving enzyme and/or fermentation technology) that may contribute to the economic soundness of applications with this promising group of biomolecules.