啤酒花的萃取

本文综述了使用啤酒花萃取物的优点以及啤酒花的超临界二氧化碳萃取和液态二氧化碳萃取的特点。     

啤酒腐败菌的酒花抗性

酒花苦味物质具有抗菌活性,能抑制多种细菌生长。未解离的苦味物质作为一个离子载体,驱散细胞跨膜pH梯度(ΔpH),影响细胞吸收营养物质,使细胞因饥饿而死亡。小部分乳酸菌具有酒花抗性,使其能在啤酒中生长。这种酒花抗性是菌株特异性的,并需要诱导产生。研究表明它与多种抗性机制有关,如细胞壁成分、多个膜上运输载体。已有数个与酒花抗性相关的基因被报道,并用它们可作为PCR快速检测啤酒腐败菌的跨种基因标记。     

乳链菌肽(nisin)抗性机制的研究进展

乳链菌肽(nisin)是某些乳酸乳球菌产生的一种羊毛硫细菌素。其对包括食品腐败菌和致病菌在内的许多革兰氏阳性菌具有强烈的抑制作用,是目前世界上唯一被允许用作食品添加剂的细菌素。nisin的广泛使用虽未引发大范围的抗性,但在自然界或实验室的选择压力下,某些非nisin产生菌也获得了抵御nisin攻击的抗性机制。nisin抗性机制通常涉及两种方式,即非特异性的生理适应机制和特异性蛋白酶介导的主动防御机制。本文综述了近年来nisin抗性机制的研究进展。     

铅胁迫下植物抗性机制的研究进展

综述了近10多年来国内外研究重金属铅对植物的伤害机理,以及植物对铅的耐性机制的研究进展.首先从细胞分裂、细胞膜透性、光合作用和抗氧化酶系统等生理生化方面讨论了铅对植物的伤害机理,其次分析了铅离子跨膜运输、根系分泌物、金属配位体、铅离子区域化分布与植物抗性的关系.     

微生物铬转化和抗性机制与生物修复研究进展

铬(Chromium,Cr)是过渡金属元素,在自然界中以六价[CrO_4~(2-),Cr_2O_7~(2-),Cr(Ⅵ)]和三价[Cr(OH)_3,Cr(Ⅲ)]为主。很多微生物在长期铬胁迫的条件下,进化出了一系列铬转化和抗性机制。微生物对铬的转化包括Cr(Ⅵ)的还原和Cr(Ⅲ)的氧化。微生物的Cr(Ⅵ)还原可以将毒性强的六价铬转化为毒性弱或无毒的三价铬,这类微生物有较强的土壤和水体铬污染治理潜力。Cr(Ⅲ)的氧化也在铬的生物地球化学循环过程中起着至关重要的作用。除了Cr(Ⅵ)的还原,微生物对铬的抗性机制还有:(1)减少摄入;(2)外排;(3)清除胞内氧化压力;(4)DNA修复。本文主要介绍微生物的铬转化和抗性机制,以及其在铬污染生物修复中应用的最新研究进展。     

狄斯瓦螨对杀螨剂抗性机制的研究进展

狄斯瓦螨Varroa destructor是严重危害西方蜜蜂Apis mellifera的主要寄生螨之一,由于杀螨剂长期大量、单一和连续使用,狄斯瓦螨对杀螨剂的抗性发展日趋严重,探明狄斯瓦螨抗性机制对于治理狄斯瓦螨具有重要意义。狄斯瓦螨抗性形成受遗传因素、人为操作因素及其他生态因素的影响,其抗性机制与化学杀螨剂的种类有关,目前研究较多的是靶标不敏感性机制和解毒代谢增强机制,对拟除虫菊酯类杀螨剂抗性机制研究较为透彻,而对有机磷类和甲咪类杀螨剂抗性机制研究有限。本文基于文献,阐述了狄斯瓦螨对拟除虫菊酯类、有机磷类和甲咪类杀螨剂抗性机制的最新研究进展,讨论了抗性治理的最新研究成果及该领域未来的研究方向,以期为狄斯瓦螨有效治理、杀螨剂的安全有效使用及新型杀螨剂开发等研究提供参考。     

细菌抗生素和重金属协同选择抗性机制研究进展

随着各类抗生素和新型复合金属材料的不断开发和使用,环境中抗生素和重金属离子协同污染的机率不断提高,对环境选择最为敏感的细菌通过自身的进化和发展形成了二者协同选择的抗性机制,如协同抗性、交叉抗性、协同调控和生物膜诱导机制。     

啤酒腐败微生物与啤酒微生物稳定性研究进展

尽管生产环境和卫生条件已经得到大幅改善,但啤酒生产过程中仍然会发生微生物污染,因此,真正意义上的啤酒纯种酿制是很难实现的。为了有效控制生产过程中的微生物污染,本文系统介绍了啤酒微生物的多样性及其在生产工序中的分布,探讨了啤酒环境对抑制啤酒微生物污染的影响,讨论了啤酒微生物对啤酒质量与风味的积极贡献,提出合理控制外源微生物侵染是形成不同啤酒典型特征的关键。     

Heat resistance of Pectinatus sp., a beer spoilage anaerobic bacterium

D. WATIER, I. LEGUERINEL, J.P. HORNEZ, I. CHOWDHURY AND H.C. DUBOURGUIER. 1995. The heat resistance of three strains of Pectinatus (Pectinatus cerevisiiphilus DSM 20466, Pectinatus sp. DSM 20465 and Pectinatus frisingensis ATCC 33332) were measured at different temperatures (50–60°C), different pH (4–6·3), in two media (MRS and wort). Similar D ₆₀ values were obtained for DSM 20465 and ATCC 33332, but DSM 20466 was more resistant in MRS. Moreover the z values were higher in MRS than in wort for the three strains. Thermal destruction at different pH was variable. Results were discussed in relation to factors affecting heat resistance.     

Effect of the ethanol content of beer on the heat resistance of a spoilage Lactobacillus

D -values of a heterofermentative beer spoilage lactobacillus were measured at 55°C, 60°C and 65°C in beers containing <0·05% to 4·4% v/v ethanol. Z -values for the different beers varied between 9·17 and 12·13°C. At each temperature an increase in ethanol reduced the measured D -value. The maximum, 5·01 min was observed in alcohol-free beer (<0·05%) at 55°C and the minimum, 0·31 min, at 60°C and 65°C in beer containing 4·4% ethanol. D -values could be increased by prior growth in the presence of ethanol. They could be reduced by adding ethanol to alcohol-free beer or by increasing its hop extract content. The implications for the pasteurization of low-alcohol beers are discussed.     

Potential use ofGarcinia kola as hop substitute in lager beer brewing

The chemical, brewing and anti-microbial properties of a tropical seed,Garcinia kola, were compared with traditional hops. Treatment ofGarcinia kola with methanolic lead acetate produced a yellow precipitate from which organic acids (alpha acids) were contirmed to be present by thin-layer chromatography. Hops, however, had a higher concentration of organic acids thanGarcinia kola. Laboratory brewing trials withGarcinia kola and hops gave beers with simillar chemical properties. Organoleptically,Garcinia kola beer was as acceptable to tasters as hopped beer except that it had an improved bitterness.Garcinia kola and hop extracts exerted similar anti-microbial effects on two beer spollage micro-organisms (Lactobacillus delbruckii andCandida vini).

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Résumé On a comparé les propriétés chimiques, brassicoles, et antiseptiques d'une graine tropicale,Garcinia kola, à celles des houblons traditionnels. Le traitement deGarcinia kola à l'acétate de plomb en milieu méthanolique a produit un précipité jaune dans lequel on a confirmé la présence d'acides organiques ou acides . Les houblons, toutefois, avaient une concentration plus élevée en acides organiques queGarcinia kola. Des essais de brassage au laboratoire avecGarcinia kola ont produit des bières aux propriétés chimiques sembiables. Sur le plan organolètique, la bière deGarcinia kola a été aussi acceptable pour les goûteurs que la bière de houblon à ceci prés que la première avait une amertume améliorée. Les extraits deGarcinia kola et de houblon ont exercé des effets antimicrobiens semblables sur deux microorganismes contaminant la bière (Lactobacillus delbruckii etCandida vini).

     

Hop resistance in the beer spoilage bacterium Lactobacillus brevis is mediated by the ATP-binding cassette multidrug transporter HorA

Lactobacillus brevis is a major contaminant of spoiled beer. The organism can grow in beer in spite of the presence of antibacterial hop compounds that give the beer a bitter taste. The hop resistance in L. brevis is, at least in part, dependent on the expression of the horA gene. The deduced amino acid sequence of HorA is 53% identical to that of LmrA, an ATP-binding cassette multidrug transporter in Lactococcus lactis. To study the role of HorA in hop resistance, HorA was functionally expressed in L. lactis as a hexa-histidine-tagged protein using the nisin-controlled gene expression system. HorA expression increased the resistance of L. lactis to hop compounds and cytotoxic drugs. Drug transport studies with L. lactis cells and membrane vesicles and with proteoliposomes containing purified HorA protein identified HorA as a new member of the ABC family of multidrug transporters.     

Selective antimicrobial activity of chitosan on beer spoilage bacteria and brewing yeasts

Chitosan (0.1 g l(-1)), assayed in a simple medium, reduced the viability of four lactic acid bacteria isolated during the beer production process by 5 logarithmic cycles, whereas activity against seven commercial brewing yeasts required up to 1 g chitosan l(-1). Antimicrobial activity was inversely affected by the pH of the assay medium. In brewery wort, chitosan (0.1 g l(-1)) selectively inhibited bacterial growth without altering yeast viability or fermenting performance.     

Bacterial surface antigen-specific monoclonal antibodies used to detect beer spoilage pediococci.

Fourteen monoclonal antibodies (Mabs) were isolated that react with surface antigens of Pediococcus beer spoilage organisms, including P. damnosus, P. pentosaceous, P. acidilactici, and unspeciated isolates. Immunoblotting, enzyme immunoassays (EIAs) of protease- and neuraminidase-treated surface antigen extracts, carbohydrate competition EIAs, and cardiolipin EIAs were used to characterize the bacterial antigens involved in Mab binding. Antigen stability in situ was tested by protease treatment or surface antigen extraction of washed bacteria. In most cases, the Mabs bind to Pediococcus surface antigens that appear to be covalently bound cell wall polymers resistant to alteration or removal from the bacterial surface. These bacterial surface antigen reactive Mabs show good potential for rapid, sensitive, and specific immunoassay detection of Pediococcus beer spoilage organisms.