NISIN: A BACTERIOCIN WITH A POTENTIAL USE IN BREWING

Depending on the amount used and the strain of bacteria involved, nisin either kills lactic acid bacteria or inhibits their growth. In medium inoculated with approximately 10⁵ cells ml^?1 of a sensitive strain of Lactobacillus (BSO 375) nisin, added at levels recommended for commercial use (100 International Units ml^?1, killed all the cells in less than 6 h. In the absence of nisin this inoculum grew to a concentration of 10¹⁰ cells ml^?1 in about 50 h. Lower nisin concentrations killed fewer cells but inhibited the growth of those still viable. For the more resistant strain Lactobacillus (BSO 343) growth was only inhibited at the higher nisin concentrations. Nisin maintained its activity against lactic acid bacteria in brewing fermentations. It had no effect on the growth and fermentative performance of the 9 brewing yeast strains tested, and, in a pilot brewery fermentation, had no deleterious affect on the taste of the beer produced. Nisin could be used either as a preventative measure by regular addition to fermentations, or as a remedial measure once contamination by lactic acid bacteria had been detected.     

THE ACTION OF NISIN ON BEER SPOILAGE LACTIC ACID BACTERIA

Within one minute of adding nisin to suspensions of Lactobacilli clumping of cells was observed. This happened with all the strains assayed, irrespective of their sensitivity or resistance to nisin. There was, however, no evidence of cell lysis. Two different assays for cell viability were used to show that the vast majority of cells of sensitive strains were killed within one minute of contact with nisin. The time needed to kill all the cells depended on the concentrations of both nisin and cells. One strain was more resistant and only 50–60% of the cells died within one minute of nisin addition . Using an ATP-bioluminescence assay it was shown that the addition of nisin to both Lactobacilli and Pediococci caused a rapid fall in intracellular ATP levels, which was reflected in a simultaneous appearance of ATP in the extracellular medium. Actively growing cells lost ATP more rapidly than did those in stationary phase. The amount of intracellular ATP lost was affected both by the concentration of nisin used and the sensitivity of the bacteria. It appears that an initial effect of nisin is to make the cell membrane ‘leaky’ as happens with many antibiotics, yeast killer factors (zymocins), colicins, and other gram-positive bacteriocins .     

乳酸菌发酵混合乳研究

着重探讨乳酸菌发酵不同比例的混合乳（牛乳和豆乳）的产酸和凝乳工艺条件．结果表明：对豆乳∶牛乳＝２∶１的混合乳中添加１．０％葡萄糖，３．０％蔗糖和２．０％海藻酸钠，接种５％活化的嗜热链球菌和保加利亚杆菌，在４２℃培养６ｈ可获得具有清新的乳酸发酵风味、无豆腥、有乳香、酸味爽口、凝乳良好、口感细腻的混合酸乳     

NISIN AND BREWING

Nisin, an internationally accepted food preservative has been shown to inhibit the growth of almost all Gram-positive beer-spoilage bacteria investigated. The initial effects on these bacteria appear to be upon the cell membrane. Nisin has little effect on most Gram-negative bacteria and has no effect upon the growth and fermentation properties of brewing yeasts. Nisin activity survives kieselguhr filtration, fining and pasteurisation and has no effect on beer shelf life. Nisin has potential applications in preventing spoilage of worts or beers by Gram-positive bacteria (particularly lactic acid bacteria).     

嗜热菌合成乳酸的研究

从467株原始菌株保藏物中筛选获得了产乳酸的嗜热菌29株.进一步复筛确定19株为产乳酸水平较高的嗜热菌,且均为Bacillus coagulans.采用高效液相色谱法对19株Bacillus coagulans的主要发酵产物进行分析.55℃下发酵54h,总乳酸产量最高的为74.80 g/L,最低的为49.55 g/L.选择总乳酸产量较高的四株菌和产物中杂酸最少的一株菌作为进一步研究的菌株,分析所形成乳酸光学构型发现,5株菌所产L-乳酸的光学纯度均在98%以上,同时皆形成少量D-乳酸.     

高效抑菌作用乳酸菌的选育

对从自然发酵辣椒中分离出的66株乳酸菌的抑菌特性进行了研究,结果发现66株乳酸菌中仅有28株对指示菌表现出抑菌活性,从这28株中选育出了三株具有广谱、高效抑菌作用乳酸菌,对这三株乳酸菌的抑菌成分进行了研究,最后发现起抑菌作用的物质是细菌素。     

乳酸菌的固定化方法及其发酵特性的研究

对乳酸菌固定化工艺参数及发酵特性进行了研究,结果表明,乳酸菌包埋法固定最佳工艺条件为:海藻酸钠的浓度为2%,菌体的稀释比例为1:1,CaCl2溶液的浓度为1.5%,菌种的固定化温度为42℃。固定化菌种胶珠含菌量为4.59×109个/g。固定化乳酸菌产酸和耐酸能力强,菌种活力得到保持,具有持久和可重复利用的特点。     

乳酸发酵鲜菇汁技术研究

以鲜菇汁为原料，经乳酸发酵而制成鲜菇汁发酵饮料，通过对接种量、发酵时间、乳粉量、糖酸比进行试验．从而确定最佳工艺参数为：接种量3％，乳粉量5％，发酵时间3．75h，蔗糖12％，柠檬酸0．04％。     

VARIATIONS AMONGST BEERS AND LACTIC ACID BACTERIA RELATING TO BEER SPOILAGE

The ability of lactic acid bacteria to grow in beer has been studied using 31 beers, 13 strains of Lactobacillus and 3 strains of Pediococcus isolated from wort or beer. In 3 beers all the micro-organisms were able to grow, in 5 beers none of them developed and diverse results were obtained with the remaining 23 beers. Resistance of the beers to spoilage was not correlated with values of pH, specific gravity, total or free amino nitrogen, individual or total fermentable sugars, colour or levels of sulphur dioxide. Resistant beers became sensitive after certain filtration treatments and after heating at 80° for 15 minutes, but not after treatment at 60°. Resistance to spoilage is tentatively attributed to the presence of a yeast metabolite which is heat-labile. The lactic acid bacteria varied in their ability to grow in beer but those possessing a broad range of biochemical abilities had the greater propensity to cause spoilage.     

乳酸菌基础培养基比较研究

研究了脱脂乳中性蛋白酶的最适酶解条件，并以保加利亚乳杆菌和嗜热链球菌为混合发酵菌种，对MRS、脱脂乳和脱脂乳酶解液3种基础培养基进行了比较研究。结果表明：（1）脱脂乳中性蛋白酶的适宜酶解条件为：加酶量5000U／g蛋白质，在pH=7．0，50℃下酶解2h；（2）脱脂乳酶解液是保加利亚乳杆菌和嗜热链球菌混合菌种较好的基础培养基，其冻干发酵剂的质量和数量均优于脱脂乳培养基。以脱脂乳酶解液为基础培养基制备的冻干发酵剂的活菌数达到3．5×10^11cfu／g，冻干发酵剂的重量是脱脂乳的1．93倍。     

冷藏鲜肉中腐败乳酸菌的分离及鉴定

利用稀释平板法从冷藏3 d的肉样品中共分离出60株疑似乳酸菌菌株,经过2次划线分离,然后进行革兰氏染色、镜栓、过氧化氢酶试验、明胶液化试验、硝酸盐还原试验和H2S检验,得到36株乳酸菌.将分离出的这36株乳酸菌,经过形态学和生理生化鉴定,确定他们属于5大类,即清酒乳杆菌,13株;马里乳杆菌,8株;消化乳杆菌,7株;口乳杆菌,4株;未知乳杆菌,4株.     

CLEANSING CONTAMINATED PITCHING YEAST WITH NISIN

The ability of solutions of nisin to cleanse pitching yeast of contaminating gram-positive lactic bacteria (at levels of about 1% by cell numbers) was compared to that of three different acid-washing procedures: ammonium persulphate, acidified ammonium persulphate or phosphoricacid. 1000 international units ml^?1 of nisin killed all the cells of more sensitive bacterial strains in less than 30 minutes, equivalent to the killing ability of the acid-washing procedures, and more than 99·9% of cells of a more resistant strain in 2 hours. Washing contaminated pitching yeast with nisin has several advantages over acid-washing methods. It has no effect on yeast viability and vitality, and, in subsequent fermentations, the yeast shows unchanged flocculation characteristics and fermentative performance.     

ASSESSMENT OF POTENTIAL PROBIOTIC PROPERTIES OF LACTIC ACID BACTERIA AND YEAST STRAINS

ABSTRACT

Four lactic acid bacteria (LAB) and three yeast strains isolated from a traditional Bulgarian cereal-based fermented beverage were assessed for potential probiotic properties. Acid and bile resistance, antipathogenic activity and antibiotic resistance of the strains were evaluated. Tolerance to low pH values (2.0–3.0) and high bile concentrations (0.2–2.0%) of the LAB and yeast strains varied, but all strains kept viable throughout the experiments. Antagonistic activity towards most of the eight test-pathogens was observed for one LAB (Lactobacillus plantarum B28) and two yeast strains (Candida rugosa Y28 and Candida lambica Y30). Antibiotic resistance (39 antibiotics) of the LAB strains was variable, but showed their potential for therapeutic application.     

ASSESSMENT OF POTENTIAL PROBIOTIC PROPERTIES OF LACTIC ACID BACTERIA AND YEAST STRAINS

Four lactic acid bacteria (LAB) and three yeast strains isolated from a traditional Bulgarian cereal-based fermented beverage were assessed for potential probiotic properties. Acid and bile resistance, antipathogenic activity and antibiotic resistance of the strains were evaluated. Tolerance to low pH values (2.0-3.0) and high bile concentrations (0.2-2.0%) of the LAB and yeast strains varied, but all strains kept viable throughout the experiments. Antagonistic activity towards most of the eight test-pathogens was observed for one LAB (Lactobacillus plantarum B28) and two yeast strains (Candida rugosa Y28 and Candida lambica Y30). Antibiotic resistance (39 antibiotics) of the LAB strains was variable, but showed their potential for therapeutic application.     

FUNDAMENTALS AND PERSPECTIVES FOR THE USE OF BACTERIOCINS PRODUCED BY LACTIC ACID BACTERIA IN MEAT PRODUCTS

Bacteriocins of lactic acid bacteria (LAB) are proteinaceous compounds that may present antimicrobial activity towards important foodborne pathogens and spoilage-related microflora. Due to these properties, bacteriocin-producing strains or purified bacteriocins have a great potential of use in biologically based food preservation systems. Despite the growing number of articles describing the isolation of bacteriocinogenic strains, genetic determinants for production, as well as the purification and biochemical characterization of these inhibitory substances, there are only limited reports of successful application of bacteriocins to meats.

This paper presents a critical review of the methods available for screening of bacteriocin-producing LAB strains from meats and also discusses the proposed mechanisms of action for LAB bacteriocins. Additionally, an overview of the Brazilian experience in the application of LAB bacteriocins to meats and meat products is given.     

FUNDAMENTALS AND PERSPECTIVES FOR THE USE OF BACTERIOCINS PRODUCED BY LACTIC ACID BACTERIA IN MEAT PRODUCTS

Bacteriocins of lactic acid bacteria (LAB) are proteinaceous compounds that may present antimicrobial activity towards important foodborne pathogens and spoilage-related microflora. Due to these properties, bacteriocin-producing strains or purified bacteriocins have a great potential of use in biologically based food preservation systems. Despite the growing number of articles describing the isolation of bacteriocinogenic strains, genetic determinants for production, as well as the purification and biochemical characterization of these inhibitory substances, there are only limited reports of successful application of bacteriocins to meats.

This paper presents a critical review of the methods available for screening of bacteriocin-producing LAB strains from meats and also discusses the proposed mechanisms of action for LAB bacteriocins. Additionally, an overview of the Brazilian experience in the application of LAB bacteriocins to meats and meat products is given.     

LACTIC ACID BACTERIA AND MALOLACTIC FERMENTATION IN THE MANUFACTURE OF SPANISH CIDER

Numeration, isolation and identification of the lactic acid bacteria found in Asturian cider during processing and storage has been carried out. The species Leuconostoc oenos was predominant during both alcoholic and malolactic fermentations. In most of the ciders studied the malolactic fermentation and the alcoholic fermentation started at the same time; production of D-lactate as well as a decrease of L-lactate were to be found once the malolactic fermentation was complete .     

乳酸菌代谢工程的研究与应用

综述了乳酸菌代谢工程的研究与应用，阐述了利用基因工程技术改良乳酸菌发酵剂产双乙酰能力、蛋白质水解能力、胞外多糖的合成能力以及抗杂菌病原菌污染能力4个方面的最新研究进展。     

多菌种混合乳酸菌发酵酸豆奶工艺研制

本文研究了市售酸牛奶和自制酸泡菜中分离筛选菌种，确定菌种间的比例。通过对生产过程中的条件进行初步摸索，以鲜豆奶为主要原料，采用多菌种混合液态发酵，可生产出色、香、味俱佳，不舍任何防腐剂的纯天然酸豆奶新产品，从而为工业化生产乳酸菌发酵酸豆奶提供技术依据。