植物乳杆菌脂肪酸构成与胆盐耐受性的相关性分析

为分析菌株的脂肪酸构成与胆盐耐受能力的关系,本文对8株分离自发酵乳制品的植物乳杆菌展开研究。以菌体在含有0.3%胆盐的MRS肉汤培养基中的对数存活率作为其胆盐耐受能力评价的指标,并通过气相色谱法分析各菌株的脂肪酸构成。Pearson相关性分析表明,菌体中棕榈酸(C16:0)和19碳环丙烷脂肪酸(cyc C19:0)含量与其胆盐耐受能力呈显著正相关(P0.05),而豆蔻酸(C14:0)和油酸(C18:1)含量与菌体胆盐耐受能力呈显著负相关(P0.05)。细胞完整性评价表明:胆盐敏感型菌株在胆盐环境中具有较弱的细胞完整性,而这一指标受脂肪酸构成影响。本研究结果表明:特定脂肪酸对天然来源的菌体而言,在胆盐环境中维持细胞完整性和提高胆盐耐受性方面扮演着重要角色。     

一株有机溶剂稳定性蛋白酶产生菌的筛选与鉴定

为了筛选分泌有机溶剂稳定性蛋白酶耐有机溶剂极端微生物,利用添加苯10%(V/V)的MLB培养液从油污染水样中分离获得有机溶剂耐受菌株56株。通过产蛋白酶筛选培养基(SMA 培养基)平板初筛和摇瓶发酵复筛从中筛选获得蛋白酶高产菌株DS1。通过形态学、生理生化及16S rDNA序列(genbank EU578329)构建的系统进化树将菌株DS1鉴定为Bacillus aquaemaris。该菌株能耐受多种有机溶剂,并可以分泌有机溶剂稳定性蛋白酶。该蛋白酶在 25%极性常数(logPOW)大于等于1.8的有机溶剂中稳定性好,于30℃、140 r/min,培养14d仍有70%以上的活力。菌株DS1及其所分泌的蛋白酶均能较好的耐受有机溶剂,可以进行有机相催化,具有潜在的工业应用价值。     

全局转录机制工程法筛选丁醇耐受大肠杆菌及性质

作者旨在采用一种快速有效的方法(全局转录机制工程方法)筛选一株具有较高丁醇耐受性的大肠杆菌。通过对全局转录因子σ~(70)进行随机突变,构建rpoD(编码σ~(70)因子)突变库。并采用高通量筛选的方法筛选获得丁醇耐受突变株E. coli JM109/pHACM~(B8),并对该突变株的性质进行了研究。结果表明:丁醇耐受突变株B8能够耐受体积分数2%丁醇,且对其他有机溶剂也具有较高的耐受性,如体积分数3%异丁醇、体积分数8%乙醇、体积分数4%环己烷和体积分数0.3%甲苯。为进一步阐明了B8菌株丁醇耐受机制,分别对B8菌株和对照菌株E. coli JM109/p HACM~(WT)的生理特性进行了研究。结果显示突变株B8胞内的丁醇含量较对照菌株低55%;且在酸性环境下比对照菌株生长更好;此外Mg~(2+)有助于提高菌株B8的丁醇耐受性。本研究为工业化应用中耐溶剂微生物菌株的构建提供了实验依据和理论基础。     

羟基脂肪酸生产菌Bacillus pumilus对油酸的代谢特性和产物分析

一株具有转化油酸羟基化的微生物Bacillus pum ilus BD-12(记作BP BD-12),在摇瓶条件下分批深层培养,研究了菌株在以胰蛋白胨为主要氮源、葡萄糖为基本碳源的条件下对油酸(OA)的代谢特性,并对转化OA生成羟基脂肪酸的规律及产物进行了分析测定。结果表明:在只有葡萄糖作碳源条件下,细胞生长良好,且无羟基脂肪酸生成,OA对菌株BP BD-12细胞生长有抑制作用;用40 h细胞菌龄添加OA条件下其转化产物为ω-1、ω-2和ω-3-羟基脂肪酸,其转化率和羟基脂肪酸得率最大值分别达到63%和12.3%;通过气质联用方法对产物组分分析,其ω-1-羟基脂肪酸占总羟基脂肪酸的70%,细胞培养过程中未有其它羟基脂肪酸检出。因此,菌株BP BD-12是一株较理想的ω-1-羟基脂肪酸工业化生产菌株。     

太空搭载对酵母菌抗逆性的影响

以茅台大曲中所分离的酵母菌为出发菌株,对其在"神舟五号"搭载前后的细胞抗逆性进行了研究.结果表明,搭载后的菌株在耐有机溶剂、耐酶解,耐酒精、耐热性方面均高于搭载前菌株.太空搭载使菌株的细胞结构发生了变异,菌体的抗逆性增强.     

GC-MS技术在鉴定食源性致病菌研究中的应用

通过有机溶剂提取、TLC分离及GC-MS对食源性致病菌中常见的4个属9种19株病原菌的全细胞脂肪酸组分进行了分析.结果表明:沙门氏菌属、埃希氏菌属、弧菌属和志贺氏菌属全细胞脂肪酸组分都含有十四烷酸、十六烷酸和十八碳烯酸,这三种脂肪酸占总脂肪酸含量的90%左右,含量最高的是十六烷酸,含量在40%以上,其次是十八碳烯酸,含量在30%左右.脂肪酸组成在属间差异显著.大肠杆菌O157不含有十三烷酸和十五烷酸,副溶血弧菌不含有十二烷酸和十三烷酸,志贺氏菌含有特异性的环戊烷十三烷酸.这些特征可作为各个属分类鉴定的依据.模式菌株和地方菌株在含有双键的脂肪酸上,双键的位置有一定的差异,因此通过这些差异可以鉴定模式菌株与地方菌株.     

有机溶剂对黑曲霉Aspergillus niger GIM 3.25的毒性影响

有机溶剂对微生物细胞的毒性作用会影响全细胞催化剂在有机介质中催化反应的效率和稳定性。本文研究了11种log P值不同的有机溶剂对黑曲霉Aspergillus niger GIM 3.25的孢子、菌丝球和催化效率的毒性作用,结果表明:所研究的有机溶剂中,甲醇、乙腈、甲苯、叔戊醇对微生物的孢子形态产生明显的改变;其中甲醇、乙腈、甲苯会导致孢子变形甚至破裂,叔戊醇致使孢子的形态完全变化,孢子的直径变小,表面变光滑。与对照组相比,有机溶剂还对Aspergillus niger GIM 3.25菌丝成球状况、菌丝质量和所成菌丝的催化效应产生损害作用,其中丙酮、异丙醇、异辛烷的毒性作用最低,甲醇、乙腈、氯仿毒性作用较高;氯仿甚至抑制了菌丝球的形成。有机溶剂对孢子和菌丝体的毒性作用未与有机溶剂的log P值呈现出相关关系。本研究将为推动真菌全细胞催化剂在非水介质中的广泛应用及具有溶剂抗性真菌菌株的筛选提供良好的依据和参考。     

水/正己烷双相体系全细胞合成D-苯基丙酸的研究

利用前期筛选出的耐受苯基乳酸的突变菌株E. coli Z2016 (CCTCC保藏编号为M2016332),在水相和有机溶剂正己烷组成的双相体系中转化生产苯基乳酸。实验还研究了转化温度、摇床转速、底物浓度、湿菌体浓度和有机溶剂正己烷的体积分数对PLA产量的影响。当转化温度为40℃、摇床转速为300 r/min、底物浓度和耐受PLA突变菌株E. coli Z2016菌体浓度均为15 g/L、正己烷的体积分数为40%的时候,PLA的产量最大,为10. 9±0. 08 g/L/h。     

现代微生物分类鉴定技术在白酒酿造中的应用

该文综述了基因序列的同源性分析技术、以聚合酶链式反应（PCR）为基础的脱氧核糖核酸（DNA）指纹图谱分类鉴定技术、磷脂脂肪酸法分类技术、Biolog微平板、元基因组技术等现代微生物分类鉴定技术在白酒酿造中的应用,为研究白酒酿造过程的微生物群落结构和微生物多样性以及分离、鉴定功能微生物菌株提供坚实技术基础。     

乳杆菌在胆盐MRS培养基中的传代稳定性

该实验探究提高乳杆菌传代稳定性的方法以提高乳杆菌在胃肠道的定植能力,为工业生产提供依据。该研究以植物乳杆菌M547、M621、M748、戊型乳杆菌M750为研究对象,研究胆盐环境对菌株生长的影响,利用生长曲线仪确定合适胆盐培养菌株的浓度,对比胆盐培养和MRS培养的菌株在耐胆盐能力、产酸能力、耐酸能力的表现。0.04%的胆盐培养后,菌株在传代过程中对于0.075%胆盐的耐受存活率提升11%~18%左右,0.1%胆盐的耐受存活率提升20%~34%。胆盐培养对于产酸能力,耐酸能力及稳定性的提高没有明显作用,但对菌株的耐胆盐能力及传代稳定性有提高作用,可为研究改善益生菌的益生特性的方法提供理论支持。     

METHODS FOR THE ANALYSIS OF C4 TO C10 FATTY ACIDS IN BEER,WORT AND CARBOHYDRATE SYRUPS

Methods have been developed for the analysis of C4 to C10 fatty acids in beer, wort and carbohydrate syrups. The methods are based on the adsorption of the aqueous samples on to solid supports followed by removal of the fatty acids with organic solvents. The methods are suitable for routine batchwise analysis of fatty acids and the reproducibility of the analysis and recoveries of the acids are generally good. Problems often encountered with analysis of C4 to C10 fatty acids and possible solutions are also discussed.     

Swelling and Reactivity of Maize Starch Granules

It is concluded that granule swelling is required for any chemical derivatization of common yellow dent maize starch with fatty acyl chlorides in organic solvents, even for reaction at granule surfaces. It was also concluded that progressively less of hot pyridine-swollen granules is available for reaction with fatty acyl chlorides as the carbon chain length increases from C₆ to C₁₄, with those two lengths being the approximate outside limits for partial exclusion.     

A novel lipolytic activity of Rhodotorula glutinis cells: production, partial characterization and application in the synthesis of esters

Cell-bound lipase activity (10 pNPL units/g dry cell weight) was released when the yeast Rhodotorula glutinis was cultured in a 7-l stirred tank fermentor using palm-oil as the sole carbon source. The enzyme showed relative specificity towards medium chain organic acids since the apparent K(m) values for pNPB (p-NitroPhenyl-Butyrate) and pNPL (p-NitroPhenyl-Laurate) were equal to 2.7 and 0.7 mM, respectively. In addition, 80% of this activity could be detected on the surface of the cells. The cell-bound nature of the enzyme increased its thermal stability showing half-life times of 200 and 60 min at 50 and 60 degrees C, respectively, as well as good stability in organic solvents. Freeze-dried cell preparations were successfully used to catalyze the synthesis of fatty acid esters of butanol and heptanol in nearly anhydrous organic solvents. A conversion of 60-62% was obtained upon esterification of palmitic or oleic acid with butanol, within 96 h. The enzyme preparation was used in four consecutive batch reactions with only 10% loss of activity.     

Effects of organic solvents on transesterification of phospholipids using phospholipase A2 and lipase

The transesterification abilities of phospholipase A₂ and Mucor javanicus lipase in various organic solvents were studied. Phosphatidylcholine and caprylic acid (molar ratio, 1:6) were transesterified by incubation at 40°C in three organic solvents using phospholipase A₂ and M. javanicus lipase. The fatty acid composition of the reaction product was measured using gas chromatography. Caprylic acid was incorporated into the sn-1 and -2 positions at a rate of 87.7% using phospholipase A₂ in hexane, and 36.7% using M. javanicus lipase in diethyl ether. Higher acyl migration into sn-2 was observed in diethyl ether than in hexane during transesterification using M. javanicus lipase, however, there was no substantial difference in the caprylic acid content at the sn-2 position. Acyl migration during transesterification in methanol was lower than in other organic solvents. Non-polar hexane and diethyl ether were more effective for transesterification than methanol.     

Enzymes which are stable in the presence of organic solvents

There are numerous advantages of employing enzymes as catalysts in organic solvents or aqueous solutions containing organic solvents instead of water. A few natural enzymes which are stable in the presence of organic solvents have been discovered. However, almost all natural enzymes are easily denatured and inactivated in the presence of organic solvents. Therefore, several physical and chemical methods, such as immobilization, modification, and entrapment, for stabilizing enzymes in the presence of organic solvents were developed. Protein engineering using site directed mutagenesis and directed evolution are useful for clarifying why organic solvent-stable enzymes are stable in the presence of organic solvents and for developing organic solvent-stable mutant enzymes.     

Comparative study of the oxidative and physical stability of liposomal and nanoliposomal polyunsaturated fatty acids prepared with conventional and Mozafari methods

The relative oxidative stability of freshly prepared and stored liposomal and nanoliposomal systems of docosahexaenoic acid (DHA, 22:6 n−3) and eicosapentaenoic acid (EPA, 20:5 n−3) were investigated. The effects of organic solvents on the oxidative stability of liposomal polyunsaturated fatty acids (PUFAs) produced by two methods, the Bangham thin-film hydration (conventional rotary evaporation method and using organic solvents) and Mozafari (direct hydration and without using organic solvents) methods, were compared. The highest physicochemical stability was observed in PUFA liposomes prepared by the Mozafari method, followed by conventional liposomes and bulk PUFAs. There was no significant change in physicochemical stability during 10 months of cold storage (4 °C) in the dark. Moreover, the comparison between liposomes (>200 nm) and nanoliposomes (50–200 nm) revealed that the surface charge, physical stability and oxidative stability of liposomal PUFAs increased as the size of the liposomes decreased. The differences in the oxidative stability of PUFAs may be due to the protective effects of aqueous systems, which indicate the advantage of using non-organic solvent (water and CO₂) techniques in liposome manufacturing.     

Lipase-catalyzed synthesis of fatty acid fructose esters

Fatty acid sugar esters are non-ionic surfactants which are widely used in food, cosmetic and pharmaceutical industry. Lipase-catalyzed synthesis of fructose with fatty acid in organic medium was performed in a batch reactor at atmospheric pressure. Influence of different reaction parameters, such as different kinds of lipase preparations and organic solvents, biocatalyst concentration, molecular sieve concentration, temperature, stirring rate and the use of different fatty acids as acyl donors was studied. Optimum conditions were found using 10% (w/w of substrates) lipase from Candida antarctica B (Novozym 435) and 12.1% (w/w) of molecular sieves at 60 °C and stirring rate of 600 rpm. The highest conversion was obtained in ethyl methylketon (82%), which is permitted for general use in the manufacture of food additives.     

Modification of the vermont test for monitoring fat adulteration of dairy products

The Vermont test was developed for the routine screening of dairy products for vegetable fat adulteration. A slight modification of the test procedure made it more rapid and reduced costs. Gas-liquid chromatographic analysis of saponified fatty acids in the first and second Mojonnier extractions were proportional; thus, only the first extraction was needed to determine the purity of a milk lipid sample. This modification saves about 8 min/series of four samples and conserves 48% of the volume of organic solvents necessary to perform the classical Mojonnier extraction.     

Validation of a Single-Extraction Procedure for Sequential Analysis of Vitamin E, Cholesterol, Fatty Acids, and Total Fat in Seafood

Food lipid major components are usually analyzed by individual methodologies using diverse extractive procedures for each class. A simple and fast extractive procedure was devised for the sequential analysis of vitamin E, cholesterol, fatty acids, and total fat estimation in seafood, reducing analyses time and organic solvent consumption. Several liquid/liquid-based extractive methodologies using chlorinated and non-chlorinated organic solvents were tested. The extract obtained is used for vitamin E quantification (normal-phase HPLC with fluorescence detection), total cholesterol (normal-phase HPLC with UV detection), fatty acid profile, and total fat estimation (GC-FID), all accomplished in <40 min. The final methodology presents an adequate linearity range and sensitivity for tocopherol and cholesterol, with intra- and inter-day precisions (RSD) from 3 to 11 % for all the components. The developed methodology was applied to diverse seafood samples with positive outcomes, making it a very attractive technique for routine analyses in standard equipped laboratories in the food quality control field.