百里醌对阪崎克罗诺肠杆菌的抑制作用

为探究百里醌对阪崎克罗诺肠杆菌的抑制作用及可能的抑制机理,检测了百里醌对阪崎克罗诺肠杆菌的最 小抑菌浓度（minimal inhibitory concentrations,MIC）及对其生长动力学模型的影响,并测定百里醌处理后阪崎肠 杆菌胞内ATP浓度、胞内pH值、膜电位、细胞膜完整性的变化,最后利用场发射扫描电子显微镜观察细胞形态的 改变。结果表明：百里醌对阪崎克罗诺肠杆菌的MIC为0.3～0.6 mg/mL;百里醌使阪崎克罗诺肠杆菌的生长迟滞期 延长,最大生长速率减小;百里醌影响了阪崎克罗诺肠杆菌细胞膜的通透性,表现为：质量浓度为MIC和2×MIC 的百里醌使细胞内ATP浓度由6.52 μmol/L分别降低为0.27 μmol/L和0.17 μmol/L,胞内pH值分别由5.69降低为5.22和 4.99,细胞膜完整菌体比例分别降低至80%和22%,引起细胞膜膜电位超极化;场发射扫描电子显微镜观测表明百 里醌使阪崎克罗诺肠杆菌细胞膜褶皱,菌体干瘪。综上所述,百里醌是通过影响细胞膜通透性和改变细胞形态抑制 阪崎克罗诺肠杆菌。这些结果表明百里醌有潜力作为控制阪崎克罗诺肠杆菌的天然抑菌剂应用于食品中。     

Interaction between pH,autolysis promoters and bacterial contamination on the production of yeast extracts

Bakers' yeast (Saccharomyces cerevisiae) cell suspensions were submitted to autolysis at various pH values (4.0, 5.5, 7.0 and 8.5) and with chemical autolysis promoters (ethyl acetate, chitosan). In one series of assays, bacterial contaminants were added at 10⁸ CFU/ml. Autolysis yields, total nitrogen (total N) and α-amino nitrogen (α-amino N) composition as well as turbidity of the yeast extracts (YE) were examined. The addition of bacterial contaminants at 10⁸ CFU/ml to the yeast cell suspension did not significantly influence any of the response variables tested. There was a significant effect of pH on autolysis yields, total N and α-amino N of YE as well as on the turbidity of the YE. There was an interaction between pH and the autolysis promoter. The highest autolysis yields and total N contents of YE were obtained with a combination of pH 5.5 and the addition of ethyl acetate. The α-amino N represented between 50 and 60% of total N in the YE produced at pH 5.0 and 7.0, suggesting good peptidase activities at these pH values. The YE produced at pH 7.0 and 8.5 had much more turbidity than those obtained by incubating at pH levels of 4.0 and 5.5.     

Antiyeast Potency of Heated Garlic in Relation to the Content of Allyl Alcohol Thermally Generated from Alliin

ABSTRACT:  The appearance of antiyeast activity in heated garlic extract was influenced by the temperature, heating time, and pH. The maximum antiyeast activity was attained at the temperature range between 110 and 130 °C for the heating time range of 90 and 30 min, respectively. Reduced antiyeast activity occurred above 130 °C. More potent antiyeast activity was generated when the pH of the garlic extract was adjusted to and below 4.0. The sensitivity to the antiyeast activity of heated garlic or heated alliin was quite different depending on the yeast strain. Species belonging to Zygosaccharomyces were the least sensitive, while Candida utilis and Pichia membranaefaciens were among the most sensitive. The alliin content of the garlic was in the range of 0.5% to 1.32%. When garlic extracts were heated at 121 °C for 120 min, the content of allyl alcohol generated from alliin through thermal degradation was in the range of 0.08% to 0.16%. The allyl alcohol produced upon heating was positively proportional to the content of alliin in garlic. The antiyeast potency expressed as the minimum inhibitory concentration (MIC) was negatively proportional to the content of allyl alcohol and thus to the content of alliin.     

防腐剂对地衣芽孢杆菌的抑制效果

通过药敏纸片法、最小抑菌质量浓度(MIC)法测定地衣芽孢杆菌对不同防腐剂的敏感性,利用正交试验设计筛选出最佳的防腐剂组合,并对获得的最佳防腐剂组合的抑菌效果进行验证。结果表明:地衣芽孢杆菌对山梨酸钾、乳酸钠不敏感;对Nisin、ξ-聚赖氨酸和尼泊金乙酯较为敏感,在20mg/mL时其抑菌圈直径分别为9.25、10mm和7.5mm,MIC分别为0.078、0.078mg/mL和2.5mg/mL。正交试验结果表明:当Nisin、ξ-聚赖氨酸和尼泊金乙酯质量浓度分别为0.313、0.313mg/mL和0.125mg/mL时,对地衣芽孢杆菌的抑制效果最佳,可使基质中的地衣芽孢杆菌数(空白样品中为5.48(lg(CFU/g))降低2(lg(CFU/mL))。选择这一最佳组合分别对其在肉制品、乳制品、果汁中的应用效果进行测定,结果显示在0～4℃条件下,复配防腐剂的效果较好。     

ε-聚赖氨酸与纳他霉素复配剂抑菌性能的研究

研究了ε-聚赖氨酸(ε-PL)与纳他霉素复配剂的抑菌活性.以典型菌株大肠杆菌、伤寒沙门氏菌、金黄色葡萄球菌、枯草芽孢杆菌、酿酒酵母和热带假丝酵母为研究对象,采用二倍稀释法确定ε-PL和纳他霉素的最小抑菌浓度,96孔板法确定ε-PL与纳他霉素对酵母菌最佳复配抑菌浓度,通过测定胞内物质渗漏来反映酵母细胞膜的完整性.结果表明,二者抑制酿酒酵母的最佳复配浓度为ε-PL 100μg/mL、纳他霉素4μg/mL,抑制热带假丝酵母的最佳复配浓度为ε-PL 400μg/mL、纳他霉素2μg/mL,且两种复配剂均能抑制大部分细菌.通过测定抑菌剂作用于酿酒酵母在260nm、280nm的吸光度以及电导率的变化,可知复配剂对酿酒酵母细胞膜的破坏性最强.总之,ε-PL与纳他霉素复配使用,能够减少用量,拓宽抑菌范围,能更好的抑制食品中腐败微生物的生长.     

Effect of vanillin, ethyl vanillin, and vanillic acid on the growth and heat resistance of Cronobacter species

Preservatives could be part of an effective intervention strategy for the control of Cronobacter species in foods, but few compounds with the desired antimicrobial properties have been identified to date. We examined the antibacterial activity of vanillin, ethyl vanillin, and vanillic acid against seven Cronobacter spp. in quarter-strength tryptic soy broth with 5 g/liter yeast extract (TSBYE) adjusted to pH 5.0, 6.0, and 7.0 at 10, 21, and 37°C. All compounds exhibited pH- and temperature-dependant bacteriostatic and bactericidal activity. MICs of vanillin and ethyl vanillin consistently increased with decreasing pH and temperature, but vanillic acid had little activity at pH values of 6.0 and 7.0. The MICs for all temperatures, pH values, and bacterial strains tested were 2 mg/ml ethyl vanillin, 3 mg/ml vanillin, and >8 mg/ml vanillic acid. MBCs also were influenced by pH, although significantly higher concentrations were needed to inactivate the bacteria at 21°C than at 10 or 37°C. Survivor curves for Cronobacter sakazakii strains at the MBCs of each compound revealed that all treatments resulted in immediate loss of cell viability at 37°C. Measurements of propidium iodide uptake indicated that the cell membranes were damaged by exposure to all three compounds. The thermal resistance of C. sakazakii was examined at 58°C in TSBYE supplemented with MBCs of each compound at pH 5.0 and 6.0. D-values at pH 5.0 were reduced from 14.56 ± 0.60 min to 0.93 ± 0.01, 0.63 ± 0.01, and 0.98 ± 0.02 min for vanillin, ethyl vanillin, and vanillic acid, respectively. These results suggest that vanillin, ethyl vanillin, and vanillic acid may be useful for the control of Cronobacter spp. in food during preparation and storage.     

Lactobacilli isolated from the Armenian fermented milk product matsoun: Growth properties,antibacterial and proteolytic activity and their dependence on pH

Growth, antibacterial and proteolytic activities of two new lactobacilli strains isolated from matsoun (Armenian traditional dairy product) and their pH dependence were studied. The results demonstrated the antibacterial activity of lactobacilli against Gram‐positive and Gram‐negative test strains. This activity was stable when pH of cell culture medium was adjusted to the value of 6.5. At pH 8, the antibacterial activity of only one strain was stable. Both strains were able to hydrolyse casein in pH range of 5.5–8 with maximal activity at pH 5.5. Controlled pH conditions were suitable for biomass yield, while noncontrolled pH was better for expression of antibacterial activity.     

Effects of Nisin and Lysozyme on Growth Inhibition and Biofilm Formation Capacity of Staphylococcus aureus Strains Isolated from Raw Milk and Cheese Samples

Effects of nisin and lysozyme on growth inhibition and biofilm formation capacity of 25 Staphylococcus aureus strains isolated from raw milk (13 strains) and cheese (12 strains) were studied. Nisin was tested at concentrations between 0.5 and 25 μg/ml; the growth of all strains was inhibited at 25 μg/ml, but the resistances of strains showed a great variation at lower nisin concentrations. In contrast, lysozyme tested at concentrations up to 5.0 mg/ml showed no inhibition on the growth of strains. Nisin used at the growth inhibitory concentration prevented the biofilm formation of strains, but strains continued biofilm formation at subinhibitory nisin concentrations. Lysozyme did not affect the biofilm formation of 19 of the strains, but it caused a considerable activation in the biofilm formation capacity of six strains. Twelve of the strains contained both biofilm-related protease genes (sspA, sspB, and aur) and active proteases; eight of these strains were nisin resistant. These results suggest a potential risk of S. aureus growth and biofilm formation when lysozyme is used in the biopreservation of dairy products. Nisin can be used to control growth and biofilm formation of foodborne S. aureus, unless resistance against this biopreservative develops.     

Inhibition of aflatoxin-producing fungi by Welsh onion extracts.

Welsh onion ethanol extracts were tested for their inhibitory activity against the growth and aflatoxin production of Aspergillus flavus and A. parasiticus. The survival of spores of A. flavus and A. parasiticus depended on both the extract concentration and the exposure time of the spores to the Welsh onion extracts. The mycelial growth of two tested fungi cultured on yeast extract-sucrose broth was completely inhibited in the presence of the Welsh onion ethanol extract at a concentration of 10 mg/ml during 30 days of incubation at 25 degrees C. The extracts added to the cultures also inhibited aflatoxin production at a concentration of 10 mg/ml or permitted only a small amount of aflatoxin production with extract concentration of 5 mg/ml after 2 weeks of incubation. Welsh onion ethanol extracts showed more pronounced inhibitory effects against the two tested aflatoxin-producing fungi than did the same added levels of the preservatives sorbate and propionate at pH values near 6.5.     

In vitro assessment of the upper gastrointestinal tolerance of potential probiotic dairy propionibacteria

This study aimed to assess the transit tolerance of potential probiotic dairy propionibacteria strains in human upper gastrointestinal tract in vitro, and to evaluate the effect of food addition on viability of these strains in simulated pH 2.0 gastric juices. The transit tolerance of 13 dairy propionibacteria strains was determined at 37 degrees C by exposing washed cell suspensions to simulated gastric juices at pH values at 2.0, 3.0, and 4.0, and simulated small intestinal juices (pH 8.0) with or without 0.3% bile salts. The viability of dairy propionibacteria in pH 2.0 simulated gastric juice with So-Good original soymilk or Up & Go liquid breakfast was also determined. The simulated gastric transit tolerance of dairy propionibacteria was strain-dependent and pH-dependent. All tested strains were tolerant to simulated small intestinal transit. The addition of So-Good original soymilk or Up & Go liquid breakfast greatly enhanced the survival of dairy propionibacteria strains in pH 2.0 simulated gastric juices. Dairy propionibacteria strains demonstrate high tolerance to simulated human upper gastrointestinal tract conditions and offer a relatively overlooked, yet alternative source for novel probiotics besides Lactobacillus and Bifidobacterium.     

Growth/no growth interfaces of table olive related yeasts for natamycin, citric acid and sodium chloride

The present work uses a logistic/probabilistic model to obtain the growth/no growth interfaces of Saccharomyces cerevisiae, Wickerhamomyces anomalus and Candida boidinii (three yeast species commonly isolated from table olives) as a function of the diverse combinations of natamycin (0-30 mg/L), citric acid (0.00-0.45%) and sodium chloride (3-6%). Mathematical models obtained individually for each yeast species showed that progressive concentrations of citric acid decreased the effect of natamycin, which was only observed below 0.15% citric acid. Sodium chloride concentrations around 5% slightly increased S. cerevisiae and C. boidinii resistance to natamycin, although concentrations above 6% of NaCl always favoured inhibition by this antimycotic. An overall growth/no growth interface, built considering data from the three yeast species, revealed that inhibition in the absence of citric acid and at 4.5% NaCl can be reached using natamycin concentrations between 12 and 30 mg/L for growth probabilities between 0.10 and 0.01, respectively. Results obtained in this survey show that is not advisable to use jointly natamycin and citric acid in table olive packaging because of the observed antagonistic effects between both preservatives, but table olives processed without citric acid could allow the application of the antifungal.     

Technical note: High-throughput method for antifungal activity screening in a cheese-mimicking model

In this study, we developed a high-throughput antifungal activity screening method using a cheese-mimicking matrix distributed in 24-well plates. This method allowed rapid screening of a large variety of antifungal agent candidates: bacterial fermented ingredients, bacterial isolates, and preservatives. Using the proposed method, we characterized the antifungal activity of 44 lactic acid bacteria (LAB) fermented milk-based ingredients and 23 LAB isolates used as protective cultures against 4 fungal targets (Mucor racemosus, Penicillium commune, Galactomyces geotrichum, and Yarrowia lipolytica). We also used this method to determine the minimum inhibitory concentration of a preservative, natamycin, against 9 fungal targets. The results underlined the strain-dependency of LAB antifungal activity, the strong effect of fermentation substrate on this activity, and the effect of the screening medium on natamycin minimum inhibitory concentration. Our method could achieved a screening rate of 1,600 assays per week and can be implemented to evaluate antifungal activity of microorganisms, fermentation products, or purified compounds compatible with dairy technology.     

Combinations of antimycotics to inhibit the growth of molds capable of producing 1,3-pentadiene

Some species of molds are capable of degrading sorbic acid to produce 1,3-pentadiene, a volatile compound with an unpleasant hydrocarbon-like odor. The effectiveness of reduced concentrations of sorbate, in combination with other antimycotics, to control the growth of these molds has not been described. We did a study to evaluate potassium sorbate, sodium benzoate, calcium propionate, disodium ethylenediaminetetraacetic acid (EDTA), and natamycin, alone and in combination, for their effectiveness in preventing the growth of five molds isolated from Parmesan cheese and a lemon-flavored drink subjectively judged to contain 1,3-pentadiene. Growth of Penicillium brevicompactum, Penicillium roqueforti, Paecilomyces variotii, Aspergillus niger, and Cephaloascus fragrans on model agar media containing Parmesan cheese (PRM agar) (pH 5.5) and lemon-flavored drink (LD agar) (pH 2.6) supplemented with antimycotics was studied. All molds grew well at 21 degrees C on PRM agar containing potassium sorbate (3500microg/ml), calcium propionate (3000microg/ml), or natamycin (20microg/ml). Combinations of potassium sorbate (250-1000microg/ml), calcium propionate (250-1000microg/ml), and/or natamycin (10-18microg/ml) greatly inhibited or prevented growth of molds on PRM agar, indicating their potential as preservative systems at pH values resulting in large percentages of the acids in dissociated forms. Three of the five molds grew on LD agar containing potassium sorbate or sodium benzoate at a concentration of 200microg/ml. Growth did not occur within 70 days on LD agar containing EDTA (30microg/ml) in combination with potassium sorbate and sodium benzoate at 50 and 175microg/ml, respectively, or 175 and 50microg/ml, respectively. Results of this study show that preservative systems containing a reduced concentration of potassium sorbate, in combination with other antimycotics, particularly natamycin, have potential for controlling the growth of molds thought to be capable of producing 1,3-pentadiene.     

Study on chemical composition and biological activities of essential oil and extract from Salvia pisidica

In this study, total contents of phenolic, flavanol and flavonol, antioxidant activities and antimicrobial activities of the Turkish endemic Salvia pisidica Boiss. & Heldr. ex Bentham (Lamiaceae) extract and essential oil were assessed in vitro. Total phenolic, flavanol and flavonol contents in the extract were 54.57 mg gallic acid equivalents (GAE)/g, 16.70 mg catechine equivalents (CE)/g and 18.19 mg rutin equivalents (RE)/g, respectively. Antioxidant activities (IC₅₀ value) of the extract and essential oil were determined as 4.88 and 6.41 mg/mL by DPPH assay, respectively. 31 compounds were determined in the essential oil using GC-MS and the major compounds (%) were camphor (23.76), sabinol (19.2), α-thujone (14.2) and eucalyptol (1.8-cineole) (5.8).The antimicrobial activity of the methanolic extract and the essential oil against 13 bacterial and two yeast strains was determined. The extract (concentration 5 g/100 ml or 10 g/100 ml) was effective against most of the strains tested, yet not against Bacillus cereus, Staphylococcus aureus, Aeromonas hydrophila and the two yeast strains tested. The essential oil (2 g/100 ml) showed an antimicrobial effect against all the gram (+) bacteria tested, against Saccharomyces cerevisiae, but was not effective against all gram (−) bacteria and Candida albicans. These results show that S.piscidica essential oil and extract could be considered as a natural alternative to traditional food preservatives and be used to enhance food safety and shelf life.     

ε-聚赖氨酸复配防腐剂在酱腌菜中的应用

为延长酱腌菜保质期,研究ε-聚赖氨酸（ε-ploy-L-lysine,ε-PL）与其他防腐剂和抗氧化剂复配对酱腌菜的防腐效果。结果表明,生物防腐剂乳酸链球菌素（Nisin）、纳他霉素和抗氧化剂茶多酚对酱腌菜中的腐败微生物有很好的抑制作用,并且同时使用具有协同增效的作用。通过响应面法复配防腐剂各成分配比为：ε-PL?0.06?μg/mL、Nisin?0.06?μg/mL、纳他霉素0.035?μg/mL和茶多酚0.40?μg/mL。经验证在酱腌菜拌料时添加复配防腐剂比在干制萝卜复水时添加防腐剂效果更好,可以延长其保质期至21?d,品质较好,总菌落数、大肠菌群数、总酸及氨基酸态氮含量符合国家标准,为ε-PL在酱腌菜中的应用提供了理论支持。     

Characterization of butter spoiling yeasts and their inhibition by some spices

This study was designed to identify the yeasts in packaged and unpackaged butters and screen antiyeast activity of spices, including marjoram (Origanum majorana L.), summer savory (Satureja hortensis L.), and black cumin (Nigella sativa L.) against the most dominant yeast species in the packaged and unpackaged butters. Mean total yeast populations were 5.40 log CFU/g in unpackaged butter samples and 2.22 log CFU/g in packaged butter samples, indicating better hygienic quality of packaged samples. Forty-nine yeast species were isolated and identified from butter samples with the most prevalent isolates belonging to genera Candida-C. kefyr, C. zeylanoides, and C. lambica-and with moderate number of isolates belonging to genera Cryptococcus, Rhodotorula, Saccharomyces, and Zygosaccharomyces. Black cumin exhibited the highest antiyeast activity against C. zeylanoides and C. lambica species, even inhibited these species, while summer savory inhibited C. kefyr. The results of this study revealed clear antimicrobial potential of black cumin against the yeast species isolated from butters. Marjoram, summer savory, and black cumin could be used as natural antimicrobial agents against spoilage yeasts in food preservation, especially in butter.     

沙拉沙星体外诱导鼠伤寒沙门菌耐药实验

目的为获得体外鼠伤寒沙门菌(Salmonella typhimurium)对盐酸沙拉沙星(sarafloxacin hydrochloride)的活性耐药菌株,研究诱导其产生耐药的盐酸沙拉沙星最低浓度,为评价食品中沙拉沙星残留导致的微生物耐药提供依据。方法设置盐酸沙拉沙星0.001、0.002 5、0.005、0.025、0.05、0.1μg/ml实验组和空白对照组、NaOH溶剂对照组,采用NCCLS法测试最小抑菌浓度,对鼠伤寒沙门菌进行耐药诱导,耐药判断为≥8×MIC(0.25μg/ml)。对产生耐药的鼠伤寒沙门菌的gyrA基因片段进行PCR扩增,焦磷酸凝胶测序法鉴定gyrA基因常见5个位点观察突变。结果盐酸沙拉沙星在0.005μg/ml水平传到第10代时,MIC增大32倍,抑菌浓度增加到1μg/ml,耐药菌增殖停止;传到第25代时,鼠伤寒沙门菌gyrA基因Ser83位点发生突变,获得多株稳定、有生物活性的耐药菌株。沙拉沙星浓度≥0.025μg/ml时,细菌不生长;沙拉沙星浓度≤0.002 5μg/ml时细菌生长,不产生耐药。结论沙拉沙星浓度为0.005μg/ml时可体外诱导鼠伤寒沙门菌产生耐药,经传代后获得具生物活性的耐药菌株。     

纳他霉素和茶多酚在酱油中的应用研究

酱油是常用调味品,目前市售的酱油中添加的防腐剂多为化学合成的,而天然防腐剂较少在酱油使用.文章分别对天然防腐剂纳他霉素和茶多酚在酱油中的防腐效果及其复配使用后的效果进行了研究,并与化学合成防腐剂山梨酸钾进行了对照实验,得知天然防腐剂纳他霉素和茶多酚在酱油中都具有一定的防腐作用,两者复配使用后与山梨酸钾具有等同的防腐效果,可达到酱油的国家标准,但安全性大大提升.而且茶多酚具有一定的保健功效,对人体健康十分有利,可提高酱油的营养价值和保健功能.     

发酵肉制品中乳酸菌计数培养基的优化

采用平板计数法比较了5种乳酸菌在4种培养基(MRS、SL、TJA与酪蛋白山梨酸培养基)上的生长情况,选择乳酸菌生长最好的培养基,对其pH值、添加山梨酸和纳他霉素进行改良,检测了5种乳酸菌及6种杂菌在此培养基上的生长情况,并用发酵肉制品样品进行验证.结果表明,采用改良TJA培养基对发酵肉制品中乳酸菌计数效果最好,在pH 5.5、添加山梨酸(1000mg/L)和纳他霉素(20mg/L)条件下能排除其他杂菌的干扰,提高乳酸菌计数的准确性.优化后的改良TJA培养基能较好地排除发酵肉制品中的杂菌对乳酸菌计数的影响,可应用于发酵肉制品中乳酸菌的计数.     

Optimised quantification of the antiyeast activity of different barley malts towards a lager brewing yeast strain

The brewing of beer involves two major biological systems, namely malted barley (malt) and yeast. Both malt and yeast show natural variation and assessing the impact of differing malts on yeast performance is important in the optimisation of the brewing process. Currently, the brewing industry uses well-established tests to assess malt quality, but these frequently fail to predict malt-associated problem fermentations, such as incomplete fermentations, premature yeast flocculation (PYF) and gushing of the final beer product. Antimicrobial compounds, and in particular antiyeast compounds in malt, may be one of the unknown and unmeasured malt factors leading to problem fermentations. In this study, the adaptation of antimicrobial assays for the determination of antiyeast activity in malt is described. Our adapted assay was able to detect differing antiyeast activities in nine malt samples. For this sample set, malts associated with PYF during fermentation and gushing activity in beer showed high antiyeast activity. Both PYF and gushing are malt quality issues associated with fungal infection of barley in the field which may result in elevated antimicrobial activity in the barley grain. Also, two more malts that passed the normal quality control tests were also observed to have high antiyeast activity and such malts must be considered as suspect. Based on our results, this assay is a useful measure of malt quality as it quantifies the antiyeast activity in malt which may adversely impact on brewery fermentation.