腊肠中降胆固醇乳酸菌的筛选及鉴定

通过硫磷铁比色法,该试验从腊肠中共分离到具有降胆固醇能力的乳酸菌35株,胆固醇的清除能力为9.65％～48.23％,清除率在40％以上的有11株,而乳酸菌HC12的胆固醇清除率最高(48.23％).通过对乳酸菌HC12的形态观察、生理生化试验、糖发酵试验及16S rDNA序列分析等研究,鉴定HC12为干酪乳杆菌.     

乳酸菌MR25的筛选、鉴定及降胆固醇益生特性

通过气相色谱法,从萝卜干中共分离到31株具有清除培养基中胆固醇能力的乳酸菌,其中乳酸菌MR25的胆固醇清除率最高(42.48％).通过形态观察、生理生化试验、糖发酵试验等,鉴定MR25为米酒乳杆菌.乳酸菌MR25具有酸耐受性、胆盐耐受性和一定的胆固醇降低能力.在pH 2.0、培养2h条件下菌株浓度仍能达到106 cfu/mL.加胆盐(0.3％～0.4％)对菌株生长量(OD值)的影响很小.热杀死和休眠的细胞能去除很少的胆固醇,分别是3.26 mg/mL和8.42 mg/mL,而生长的细胞去除的胆固醇达到44.06 mg/mL.胆固醇去除与菌体的生长有一定的相关性.乳酸菌MR25去除胆固醇的机理是菌体对胆固醇的吸附作用,以及菌体在生长过程中对胆固醇的吸收利用.     

抗氧化乳酸菌的筛选及其益生特性评价

为筛选出具有高抗氧化能力和优良益生特性的乳酸菌，该研究应用乳酸菌选择性培养基从传统发酵浆水中分离纯化得到120株乳酸菌，利用DPPH自由基清除率对120株乳酸菌进行初选，获得10株DPPH自由基清除率>30%的乳酸菌，通过羟自由基、超氧阴离子自由基清除率复选，获得5株羟自由基清除率>50%,超氧阴离子自由基清除率>40%的乳酸菌。经16S rDNA序列鉴定，5株乳酸菌中有2株为植物乳杆菌(Z12、Z13)、2株为副干酪乳杆菌(Z33、Z45)、1株为鼠李糖乳杆菌(Z41)。对5株乳酸菌的益生特性研究表明，Z12、Z45、Z33菌株在pH 2～3的酸性环境中存活率>50%,在胆盐质量分数为0.1%～0.5%环境下存活率>10%,自凝聚率>29%,表明这3株乳酸菌具有较强的耐酸、耐胆盐能力及较高的黏附特性，可用于抗氧化功能食品的开发。     

酸菜汁中降胆固醇乳酸菌的分离鉴定

目的为开发降血脂和预防心血管疾病的保健食品.从自然发酵的酸菜中筛选安全、高效的降胆固醇的乳酸菌,并进行鉴定.方法用乳酸菌分离培养基从自然发酵的酸菜汁中分离、筛选乳酸菌;选取体外降胆固醇能力最强的菌株做耐酸及耐胆汁盐试验.并用其灌胃高脂模型大鼠,研究其对大鼠血清总胆固醇(TC)、血清甘油三酯(TG)、血清高密度脂蛋白(HDL-C)以及体重和肝、肾、脾质量的影响;用VITEK 32全自动微生物鉴定系统对其进行鉴定.结果筛选出11株乳酸菌,其中,菌株2体外降胆固醇能力最强,达47.58%.并具有较强的耐酸、耐胆汁盐能力;能降低高血脂肥胖大鼠体重、血清总胆固醇、血清甘油三酯和脂肪在大鼠肝脏内的存积量,提高大鼠血清高密度脂蛋白,对大鼠没有明显毒副作用;菌株2被鉴定为乳酸乳球菌(Lactococcus lactis).结论从自然发酵的酸菜中分离的乳酸乳球菌可用于开发安全、高效的降血脂和预防心血管疾病的保健食品.     

风干香肠中乳酸菌的分离鉴定及益生特性研究

由风干香肠中分离纯化得到的3株乳酸菌ORC2、QM7和QM8,均能产乳酸、革兰氏染色阳性、接触酶阴性。经系统发育分析,结合菌落形态、细胞形态、生化反应试验,确定菌株ORC2和QM7为肠膜明串珠菌,QM8为柠檬明串珠菌。乳酸菌ORC2、QM7和QM8均能降低培养基中的胆固醇,且对·OH、DPPH·和O-2·有一定的清除能力,其清除率都与细胞浓度呈正相关。在细胞浓度为5×108CFU/mL时,菌株ORC2对·OH的清除率最高,为65.36%;菌株QM8对DPPH·的清除率最高,为61.21%;而对O-2·的清除率最高的菌株为QM7,达到75.70%。菌株QM7在培养96 h能清除最多的胆固醇,清除率为51.2%。     

新疆自然发酵骆驼酸乳中乳酸菌降解胆固醇能力研究

以新疆骆驼酸奶分离出的10株初步鉴定为乳酸菌的菌株为研究对象,进行体外胆固醇降解能力的研究。用富集培养方法筛选出具有降解胆固醇能力的乳酸菌,然后将菌株接种到发酵培养基中进行发酵产酶,离心得酶液,用分光光度法测定其酶液对胆固醇的降解率,进而分析研究各菌株降解胆固醇的能力。有9株乳酸菌能够在以胆固醇为唯一碳源和能源的液体培养基中生长,其中3株菌对胆固醇降解率达到了60%。实验通过对自然发酵的骆驼酸乳中分离得到的乳酸菌的体外降解胆固醇的实验研究,表明骆驼酸乳中的乳酸菌具有一定的降解胆固醇的能力。     

猪源降胆固醇乳酸菌的分离鉴定

乳酸菌是一种重要的益生菌,具有降解胆固醇能力。作者从猪消化道中分离出31株疑似菌株,在高胆固醇培养基中培养后有18株菌株生长。利用磷硫铁法对体外降胆固醇进行了研究,结果表明,胆固醇降解率在0～47.26%,其中4株乳酸菌的胆固醇降解率大于30%,分别是r16、r53、r762和m661。通过细胞形态、生理生化试验和16SrDNA分子生物学鉴定,最终鉴定r16、r53和r762为植物乳杆菌,m661为鹑鸡肠球菌。     

发酵食品乳酸菌分离鉴定及功能特性研究

对发酵食品中分离出的7株乳酸菌进行了亚硝酸钠、乳糖、胆固醇降解试验、抗氧化活性试验和抑菌试验,筛选出益生功能较强的乳酸菌菌株。结果表明:菌株A1对亚硝酸钠和胆固醇的降解率都是最高,分别为91.8%和56.6%,对乳糖降解率最高的是A2,降解率为73.9%,菌株A2对亚硝酸钠的降解率也超过90%。3种抗氧化试验的结果各不相同,自由基清除率最高的是A4,为94.6%;羟基清除率最高的是A7,为40.9%;亚铁离子清除率最高的是A1,为71.1%。经过100℃处理后的乳酸菌抑菌效果没有发生太大的改变;经酶处理后,加入胃蛋白酶和胰蛋白酶的A6菌液对大肠杆菌,没有产生抑菌效果。     

青藏高原牦牛酸奶中降胆固醇乳酸菌的筛选及特性研究

目的:本研究旨在从天祝、那曲、若尔盖、玉树、红原和玛曲采集的202份牦牛酸奶样品中,筛选出具有高降胆固醇特性的优良菌株。方法:选择MRS、M17和SL培养基(MRS培养基是培养乳酸菌的基础培养基,M17培养基和SL培养基均为分离乳酸菌的培养基,其中SL培养基为分离嗜酸性乳酸菌的培养基)进行分离纯化,过氧化氢筛选阴性菌。根据邻苯二甲醛法测定胆固醇,筛选具有降解脂溶性胆固醇能力的菌株,水溶性胆固醇法复筛验证菌株降解能力,16SrDNA分子生物学法鉴定其种属。结果:分离纯化后总计720株乳酸菌,所有菌株经初筛都具有一定的胆固醇降解能力,其中降解率在68%以上的菌株,共有52株,菌株BX39的胆固醇降解率高达90.05%;复筛发现菌株BT18胆固醇降解率高达96.26%;16S rDNA分子生物学法分析比对后发现,72株乳酸菌中有64株罗伊氏乳杆菌、4株乳酸片球菌、3株瑞士乳杆菌和1株植物乳杆菌。结论:罗伊氏乳杆菌BT18具有高降胆固醇特性,可作为后备菌株进一步的研究和利用。     

分离自传统自然发酵食品中降胆固醇乳酸菌的筛选与评价

为了筛选优良的降胆固醇乳酸菌,本分析了从传统自然发酵食品中分离的30株乳酸菌,从中筛选出WS1、LP2、LP3、LP4、LP5和LP6 6株具有较强降胆固醇能力的乳酸菌,并通过对其胆盐耐受性及在含胆盐MRS培养基中的降胆固醇效率的分析,复筛出其中的WS1、LP2、LP3和LP6 4株乳酸菌。对4株乳酸菌的生长特征、产酸特征、不同生长阶段的种子液对胆固醇的降低效率的影响、耐酸特征及人工胃酸的耐受性进行分析和评价。结果显示,4株优选的乳酸菌降胆固醇能力较好,在胆盐中具有一定的存活力。胆盐的存在对降胆固醇能力具有一定的促进作用,4株菌在常规MRS培养基中生长和产酸特征稳定。不同生长时期的种子液对乳酸菌的降胆固醇能力有一定影响,对数期优于稳定期。耐酸性分析表明, pH越高,乳酸菌耐受性越好。pH 2.5,处理2h,乳酸菌依然具有一定的存活力;pH 3.5,乳酸菌存活力和存活时间都有所提高,pH 4.5时的存活力基本和自然pH的保持一致。在人工胃酸条件下,4株复筛乳酸菌在pH 2的条件下,存活时间超过4 h,随着pH的升高,存活率和存活时间都有所提高。本试验结果表明,4株乳酸菌均具有降胆固醇的特征,为后续优良菌株的降胆固醇机理研究打下了基础。     

降胆固醇乳酸菌的筛选及其鉴定

对19株乳杆菌进行体外实验,研究它们在MRS-CHOL培养基中对胆固醇的降解量,进而分析各菌株降胆固醇的能力。结果表明,所有试验菌株均有降解培养物中胆固醇的能力,去除率在3.84%～42.28%之间。其中有2株试验菌对培养物中胆固醇的降解率大于40%,这2株菌对胆固醇的脱除效力也较高。这2株菌WE43-1-2和WE57-1经形态学、生理生化反应以及糖类发酵试验被鉴定为敏捷乳杆菌(Lactobacillus agilis)和干酪乳杆菌干酪亚种(Lactobacillus casei subsp casei)。     

Removal of cholesterol by lactobacilli via incorporation and conversion to coprostanol

Fifteen strains of Lactobacillus and Bifidobacterium were screened based on their ability to adhere to hydrocarbons via the determination of cellular hydrophobicity. Lactobacillus acidophilus ATCC 314, L. acidophilus FTCC 0291, Lactobacillus bulgaricus FTCC 0411, L. bulgaricus FTDC 1311, and L. casei ATCC 393 showed greater hydrophobicity and, thus, were selected for examination of cholesterol-removal properties. All selected strains showed changes in cellular fatty acid compositions, especially total fatty acids and saturated and unsaturated fatty acids in the presence of cholesterol compared with those grown in the absence of cholesterol. In addition, we found that cells grown in media containing cholesterol were more resistant to sonication and enzymatic lysis compared with those grown without cholesterol. We further evaluated the location of the incorporated cholesterol via the insertion of fluorescence probes into the cellular membrane. In general, enrichment of cholesterol was found in the regions of the phospholipid tails, upper phospholipids, and polar heads of the cellular membrane phospholipid bilayer. Our results also showed that lactobacilli were able to reduce cholesterol via conversion of cholesterol to coprostanol, aided by the ability of strains to produce cholesterol reductase. Our results provided experimental evidence to strengthen the hypothesis that probiotics could remove cholesterol via the incorporation of cholesterol into the cellular membrane and conversion of cholesterol to coprostanol. The strains studied may be potential health adjunct cultures in fermented dairy products with possible in vivo hypocholesterolemic effects.     

不同菌株对发酵大豆后熟期间品质特性的影响

为研究利用细菌和霉菌进行混合发酵的不同效果,开发新的混菌发酵工艺,本研究采用不同接种方式,得到3个单一菌株发酵样品,4个混合菌株发酵的样品,研究不同菌株对发酵大豆品质特性的影响。按照韩国清麴酱的方法,利用Bacillus subtilis菌株发酵制得样品B,按照豆豉的发酵方法利用Aspergillus oryzae和Mucor racemosus菌株制得样品A和M。混合菌株发酵样品中依据两种菌株接种的顺序不同,分别制得AB、BA、MB和BM。结果表明,后熟0~9 d期间,样品B的蛋白酶活性最高(257.32±3.04)U/g;样品M的还原糖在后熟第1 d达到1.17%,高于其他样品。样品A和MB氨基态氮含量较高,样品B中测得铵态氮含量最高。所有样品的pH呈下降趋势,而滴定酸度变化范围则相反,从0.02%上升到0.19%。在后熟9 d期间,各样品色度中的L*值呈持续下降趋势,样品MB褐变现象明显。在7个实验组中,样品MB通过混菌发酵工艺提高了发酵大豆的品质特性,验证了利用细菌和霉菌进行混菌发酵技术能够改善发酵大豆的品质特性。     

Assimilation of cholesterol and probiotic characterisation of yeast strains isolated from raw milk and fermented foods

In this study, cholesterol assimilation ratios and some probiotic characteristics of yeasts were investigated. For this purpose, yeasts were isolated from milk and foods that were naturally fermented and not containing starter culture. In vitro cholesterol assimilation properties were determined in media. The Cholesterol assimilation by yeast strains ranged between 1.36 and 73.33%. Twenty‐one yeast strains showing high assimilation percentage were selected, and their acid tolerance, bile tolerance, bile salt deconjugation activity and survival in simulated gastrointestinal conditions were investigated. Among the strains assessed, 12 of them showed probiotic characteristics.     

Resistance of Clostridium perfringens to Varying Degrees of Acidity during Growth and Sporulation

SUMMARY: Viable cells of each of 6 strains of Clostridium perfringens were exposed to 4 levels of acidity during phases of the growth cycle. The selected strains included 4 which had been recovered in association with food poisoning outbreaks and 2 strains not so associated. The growth media tested included Fluid Thioglycollate Medium, DS-sporulation medium and the CP-2V medium proposed by Hauschild.
The level of acidity, length of exposure of the cells, the growth medium employed and the phase in the growth curve influenced the survival of C. perfringens. Exposure of cells grown in DS-sporulation medium to buffers pH 6.0 had little effect on the survival over the 8-hr test period, with somewhat greater sensitivity of cells being demonstrated at pH 4.5. Exposure of cells, similarly produced, to buffer pH 1.0 or 2.0 was much more effective in reducing the percentage of survival, particularly during early log phase and at the onset of sporulation. Based on the 3 growth media utilized, calculated survival curves resulting from exposure of cells to pH 1.0 or 2.0 were erratic in shape, and percentage survival was almost universally less than 10%.
Source of the strain, whether food poisoning or non-food poisoning associated, appeared to have no significant effect on the acid resistance of the cells. The comparatively regular increase in the percentage of survivors after the initiation of sporulation suggests that spores exhibit a greater resistance to acid stress than vegetative cells.
Incubation at temperatures of 37° or O°C, during the time of treatment with the test buffers pH 1.0 or 2.0, produced no consistent change in the percentage of survivors when the cells were grown in FTG.     

Enterotoxigenic Profiling of Emetic Toxin‐ and Enterotoxin‐Producing Bacillus cereus,Isolated from Food,Environmental, and Clinical Samples by Multiplex PCR

Bacillus cereus comprises the largest group of endospore‐forming bacteria and can cause emetic and diarrheal food poisoning. A total of 496 B. cereus strains isolated from various sources (food, environmental, clinical) were assessed by a multiplex PCR for the presence of enterotoxin genes. The detection rate of nheA, entFM, hblC, and cytK enterotoxin genes among all B. cereus strains was 92.33%, 77.21%, 59.47%, and 47.58%, respectively. Enterotoxigenic profiles were determined in emetic toxin‐ (8 patterns) and enterotoxin‐producing strains (12 patterns). The results provide important information on toxin prevalence and toxigenic profiles of B. cereus from various sources. Our findings revealed that B. cereus must be considered a serious health hazard and Bacillus thuringiensis should be considered of a greater potential concern to food safety among all B. cereus group members. Also, there is need for intensive and continuous monitoring of products embracing both emetic toxin and enterotoxin genes.     

用于高效空气过滤器的过滤介质的研究

对驻极熔喷材料、超细玻璃纤维纸、ePTFE薄膜和静电纺纳米纤维网等过滤介质进行了有关高效空气过滤(HEPA)性能的实验。研究结果表明,在达到相同HEPA过滤要求时,驻极熔喷材料的压降比其他材料的压降低很多;对空气中含有的不同微粒各过滤介质的过滤效率和压降呈现出不同的变化趋势。     

两种弧菌显色培养基在疑似副溶血性弧菌鉴定中的效果比较

为了比较环凯和科玛嘉弧菌显色培养基对食品中可疑菌株的初步鉴定作用,本文按国标(GB/T4789.7-2008)程序,以环凯和科玛嘉弧菌显色培养基初步鉴定硫代硫酸盐-柠檬酸盐-胆盐-蔗糖琼脂(TCBS)的副溶血性弧菌可疑菌株,最后用API和MID鉴定证实。在97份食品样品的定性与定量检测中,TCBS疑似菌株有109株,对应样品有31份。环凯和科玛嘉弧菌显色培养基对109株TCBS可疑菌株初步鉴定的结果相同,均检出64株显紫色的可疑菌株,对应样品22份。经API和MID确认,阳性菌株60株,阳性样品为22份,阳性率为22.68%。两种培养基初步鉴定TCBS可疑菌株的敏感性、特异性和符合性均分别为100.00%、91.84%和96.33%。环凯和科玛嘉弧菌显色培养基对TCBS的可疑菌株具有较好的初步鉴定效果。     

2004—2012年分离自北京口岸进出口食品的沙门菌耐药性分析

目的 了解北京口岸进出口食品中分离沙门菌的耐药状况及耐药谱情况,分析耐药趋势,为制定食品安全监管措施和抗生素的使用提供依据。方法 对65株本实验室分离的沙门菌以及17株参比菌株,共82株沙门菌采用Kindy-Bauer(KB)法检测其对15种抗生素的敏感性,根据美国临床实验室标准化研究所(CLSI)标准进行判断,并对药敏试验结果进行数据分析。结果 65株沙门菌分离株除对头孢吡肟、头孢曲松、阿米卡星、头孢噻肟全部敏感外,对其余11种抗生素均有不同程度的耐药,其中氨苄西林耐药率最高为16.9%(11/65),其次为哌拉西林(13.8%,9/65)、四环素(13.8%,9/65)、卡那霉素(9.2%,6/65)和链霉素(7.7%,5/65)。在所有65株沙门菌分离株中,对1种抗生素耐药的菌株共11株,占16.9%(11/65),对2种抗生素耐药的菌株为1株,占1.5%(1/65),对3种及以上抗生素耐药的多重耐药株为7株,多重耐药率为10.8%(7/65)。结论 北京口岸进出口食品中分离的沙门菌对多种抗生素耐药。