赤藓糖醇高产菌株的研究进展

赤藓糖醇为分子量最小、热量值最低的功能性多元醇,具有优良的物理化学性质和保健功能。目前赤藓糖醇的工业化生产方法为微生物发酵法,如何选育高产的发酵菌株是工业化生产的关键。本文就赤藓糖醇的产生菌、合成方式和育种方法等方面进行了讨论。      

酵母菌发酵生产赤藓糖醇的研究进展

赤藓糖醇是一种新型甜味剂,具有低热量、高稳定性、食用安全性高等优点,可广泛应用于食品及日用品方面。目前赤藓糖醇最佳的工业化生产方式是微生物发酵法,其中主要使用的菌种是酵母菌,此类菌种的安全性高,生产赤藓糖醇的能力强。从菌种选育、赤藓糖醇的合成途径、基因工程和发酵工艺等方面综述酵母菌发酵生产赤藓糖醇的现状,旨在为增强酵母菌生产赤藓糖醇的能力提供参考。     

赤藓糖醇的科学共识

随着健康饮食理念的盛行及减糖、低糖需求的增长,甜味剂——赤藓糖醇备受市场和行业关注。本文通过文献检索分析与专题研讨的形式开展研究,在综合分析赤藓糖醇国内外研究与应用现状的基础上,结合食品添加剂、食品科学等科技界与产业界相关专家意见,形成赤藓糖醇的科学共识,即:赤藓糖醇是一种四碳多元醇,在自然界中广泛存在,具有低能量、高耐受量等特性,目前工业化生产以微生物发酵法为主;赤藓糖醇作为食品添加剂的安全性虽已得到国内外权威机构的认可,但仍需加强其生产与应用等方面的科学研究,推动科学认知。本共识对引导行业科学认识、企业规范使用、公众合理消费赤藓糖醇具有重要的指导意义,有助于推动含赤藓糖醇食品的创新发展。     

RP-HPLC法测定PC12细胞内外液中甜味剂赤藓糖醇的含量变化

目的:应用反相高效液相色谱法(RP-HPLC)检测甜味剂赤藓糖醇在PC12细胞内外液中的含量变化情况,明确赤藓糖醇能否进入PC12细胞。方法:采用RPMI-1640培养基培养PC12细胞,提取对数期细胞并使用不同浓度赤藓糖醇处理细胞,应用RP-HPLC法(含示差折光检测器)检测PC12细胞内外液中赤藓糖醇的含量。结果:当PC12细胞外液中赤藓糖醇浓度为0.4mg/m L时,细胞内液中出现赤藓糖醇色谱峰,在浓度0.4~2.0mg/m L范围内,随着细胞外液中赤藓糖醇浓度的增加,细胞内液中赤藓糖醇峰面积呈现逐渐增加的趋势,当浓度为2.0mg/m L时,细胞内液中峰面积达到最大值。结论:PC12细胞内液中出现赤藓糖醇的色谱峰,提示赤藓糖醇能够进入PC12细胞,随着细胞外液中赤藓糖醇浓度不断增加,细胞内液中赤藓糖醇浓度也不断增高,为PC12细胞内外液中甜味剂赤藓糖醇的食品学及药效学研究提供一定的基础。     

赤藓糖醇的特性及其应用研究进展

赤藓糖醇,一种天然活性物质,被广泛应用于食品、医药保健品、日化产品和化工产品中。近年来,随着人们对于营养健康的关注度逐渐增加,学者对其理化及生物学特性研究的不断深入,赤藓糖醇的安全性得到证实,应用范围逐渐扩大。为此,本文对赤藓糖醇的来源、提取方法、理化特性进行了简要介绍,从机理和应用的角度阐述了赤藓糖醇在不同领域的研究。赤藓糖醇独特的代谢方式,使其被应用于糖尿病、葡萄糖不耐受症等特殊人群的功能食品中。赤藓糖醇的防龋性、抗氧化性、保湿性和不可燃性等特性使其在医药、日化领域的应用不断扩展。此外,本文结合国内外赤藓糖醇的最新研究进展,重点阐述了赤藓糖醇作为食品添加剂和化工原料的应用的扩展,进一步分析了赤藓糖醇优良的特性,以期为赤藓糖醇的应用研究和资源化利用提供理论依据与一定的参考。     

赤藓糖醇特性及其硬糖研究

以赤藓糖醇为主要原料,在研究赤藓糖醇加工特性的基础进行无糖硬糖工艺研究。对赤藓糖醇加工特性研究的结果表明:赤藓糖醇在200℃条件下比较稳定,不会发生分解、变色。经由配方及加工工艺优化试验考察液体麦芽糖醇添加量、熬糖温度、熬糖时间对赤藓糖醇硬糖感官品质、硬度和脆度的影响,得到赤藓糖醇硬糖的最优工艺为:液体麦芽糖醇添加量为80%,熬糖温度为165℃,熬糖时间为20 min。     

响应曲面法优化赤藓糖醇结晶工艺

为了开发一套赤藓糖醇的结晶工艺,该文研究了包括晶种添加量、溶液初始浓度、结晶时间和结晶温度在内的4个主要因素对赤藓糖醇结晶收率的影响。然后根据单因素试验的结果,采用响应曲面法整体优化了赤藓糖醇的结晶工艺参数。响应面优化结果显示,水溶液中赤藓糖醇结晶的最优操作条件为,晶种添加量1.0%,赤藓糖醇溶液初始质量浓度550 mg/mL,结晶时间3 h,结晶温度-4.5℃。上述条件下,赤藓糖醇的一次结晶率为52.78%。该文得到的模型可以用来优化赤藓糖醇在水溶液体系中的结晶过程。该模型化的工艺获得了较高的赤藓糖醇结晶收率。     

赤藓糖醇高产菌选育及发酵条件研究

为了提高赤藓糖醇的产量,对自选耐高渗酵母菌T-3-2进行紫外线与亚硝酸复合诱变处理,并采用响应曲面法优化了其发酵条件。复合诱变得到1株稳定高产突变株UN-11,其赤藓糖醇的产量达到78.3mg/mL,比T-3-2提高了38.8%;通过响应面分析建立了关键影响赤藓糖醇产量的二次多项式数学模型,得到最佳生产工艺条件为:发酵温度31℃、转速170r/min、接种量9.8%。模型预测结果产物浓度达到84.93mg/mL,验证实验结果产物浓度为85.25mg/mL。该模型对赤藓糖醇工业化生产有一定的指导意义。      

微生物发酵法生产赤藓糖醇的研究

赤藓糖醇是一种低热量、口感清凉,食用安全的填充性甜味剂。现介绍赤藓糖醇的生产和研究现状,耐高渗酵母赤藓糖醇的合成途径和赤藓糖醇的应用,并对其研究和发展提出看法。     

从赤藓糖醇生产废弃母液中回收赤藓糖醇

赤藓糖醇生产废弃母液的成分分析表明,母液中固形物含量约为70%,其中赤藓糖醇约占干物的30%,灰分约占干物的20%,检测不到葡萄糖。液相色谱分析结果表明,母液中有机固形物除赤藓糖醇外,还含有另外2种未知糖醇组分。实验主要探讨了从赤藓糖醇生产废弃母液中回收赤藓糖醇的可行性,重点考察了废弃母液的脱盐效果及其对赤藓糖醇回收的影响。以交换容量和产物的吸附为考察指标,筛选出D315和001*7阴阳2种离子交换树脂用于母液脱盐除杂,采用双柱串联工艺,活性炭脱色处理后的母液脱盐率可达98.5%。经减压蒸馏、降温结晶,母液赤藓糖醇结晶回收率达47.3%,纯度达99%以上。     

Mechanisms of erythromycin resistance of Campylobacter spp. isolated from food, animals and humans

Macrolides are regarded as drugs of choice for treatment of human campylobacteriosis. The use of antimicrobials for this purpose as well as in food animal production could result in macrolide resistance in Campylobacter species. Campylobacter isolates exhibit two different phenotypes with regard to erythromycin resistance: high-level resistance (HLR) and low-level resistance (LLR). Thirty-six food/animal and human isolates of Campylobacter jejuni and C. coli were examined for their mechanisms of resistance to erythromycin. The data presented here confirm the previous findings that the A2075G mutation in the 23S rRNA gene is the most frequently reported mechanism of high-level erythromycin resistance in Campylobacter isolates. The efflux pump inhibitor PAbetaN increased susceptibility to erythromycin for at least 16-32-fold in all examined HLR isolates, suggesting that the efflux mechanism acts in synergy with the 23S rRNA mutation to confer high-level erythromycin resistance. This was also confirmed in the isolates with sequence variation in the efflux pump cmeB gene. Additionally, the PAbetaN restored the susceptibility of LLR strains to the level of minimal inhibitory concentrations (MICs) of the susceptible strains and also reduced the MICs of the susceptible C. jejuni and C. coli isolates. The data suggest that active efflux contributes to the intrinsic resistance to erythromycin in Campylobacter and also contribute to high-level resistance.     

High-level coproduction of the bacteriocins nisin A and lactococcin A by Lactococcus lactis

In this study, a two-plasmid system for enhanced and consistent biosynthesis of the model lactococcal bacteriocin lactococcin A in non-producing Lactococcus lactis hosts was developed. The system comprised a plasmid carrying the genes lcnA and lciA under the control of the nisin-inducible nisA promoter, and a second plasmid harbouring the lcnC and lcnD genes. The introduction of both plasmids into two strains containing the nisRK genes required for nisin-controlled expression, Lc. lactis FI5876 (a nisin A-producer strain) and FI7847, resulted in production of extracellular lactococcin A at a higher level than that for the parental strain, Lc. lactis WM4. In addition, transformation of the nisin-producing host with both plasmids led to a high-level production of both lactococcal bacteriocins, which may provide a means to exploit their complementary properties in cheese ripening.     

The effect of ethanol and acetate on protein expression in Pichia pastoris

Pichia pastoris is an excellent host for high-level heterologous gene expression, but there is still much interest in improving the productivity of recombinant protein production. P. pastoris produces a small amount of ethanol as a by-product during the glycerol fed-batch phase and the mixed-feed induction phase (glycerol-methanol) of high cell density fermentations, regardless of the phenotype (Mut+, Mut(s), or Mut-). We have nvestigated ethanol repression of the AOX1 promoter using strains, GS115 (Mut+) and MC100-3 (Mut-), expressing an AOX1-lacZ fusion. The addition of 10 mg l(-1) ethanol at the start of methanol induction delayed beta-galactosidase production and methanol utilization for four hours in shake flask experiments. When ethanol and acetate were added together, all of the ethanol was converted to acetate, which also represses the AOX1 promoter. The effects of ethanol and acetate on protein expression in P. pastoris at shake flask and fermentor conditions are discussed.     

中国金顶侧耳菌株遗传多态性的ISSR分析

金顶侧耳是重要的食药用真菌。本实验收集全国各地18种金顶侧耳菌株,通过ISSR分子标记技术分析金顶侧耳菌株种内遗传多态性,11种引物扩增出102个条带,其中78个条带具有多态性,多态率为76.4%。结果表明,金顶侧耳菌株内具有丰富的遗传多样性,遗传相似系数在0.50～0.96。采用平均分类法UPGMA分析表明,在遗传相似系数为0.62时,18种菌株分为两大类。当遗传相似系数增大到0.75时,它们分为7类。16号菌株具有独立的遗传体系。     

动物性食品源大肠杆菌质粒介导喹诺酮的耐药机制研究

本研究以动物性食品源大肠杆菌为研究对象,采用琼脂二倍稀释法调查菌株对抗生素的药物敏感性,通过PCR扩增及产物测序检测质粒介导喹诺酮耐药(PMQR)基因的分布以及喹诺酮耐药决定区(QRDR)靶基因突变,旨在更好的了解食源性大肠杆菌对喹诺酮类药物产生耐药性的分子机制。645份动物性食品样品中共检出大肠杆菌179株,总检出率为27.7%。179株动物性食品源大肠杆菌对15种抗生素均表现出不同程度的耐药性,其中对四环素、链霉素、萘啶酸和复方新诺明的耐药水平较高。PMQR基因阳性菌株共14株,占受试菌株的7.8%,其中有11株能通过接合转移将PMQR基因转移至受体菌中。QRDR靶位突变在PMQR阳性菌株中普遍存在,介导菌株对喹诺酮的高水平耐药。研究结果表明,动物性食品可能成为耐药菌株的潜在"蓄水池",并通过食物链将耐药性传递给人类,从而引起人类的感染以及耐药菌株的流行。     

高大平房仓稻谷粮层霉菌量与优势霉菌的差异性研究

采用传统培养法对湖南与湖北两省粮库中的稻谷进行研究,对高大平房仓粮仓上中下三层的稻谷霉菌量及优势霉菌进行研究。研究结果表明:湖南省储藏一年稻谷与新入库稻谷中层霉菌数分别为6.4×10~3 CFU/g、1.3×10~3 CFU/g,相比上、下层,中层最多;湖北省储藏一年稻谷下层霉菌数为1.4×10~4 CFU/g,相比上、中层,下层最多,湖北省新入库稻谷上层霉菌数为1.4×10~4 CFU/g,相比中、下层,上层最多。通过传统的菌落培养及菌丝、孢子观察,初步判断上中下三层的优势霉菌,并结合分子生物学的方法对其ITS序列进行分析,通过PCR扩增,将扩增出来的基因序列,在GenBank进行BLAST,最终鉴定优势菌株为黄曲霉、白曲霉、聚多曲霉、内生真菌、黑曲霉。     

Biochemical characteristics of Enterobacter agglomerans and related strains found in buckwheat seeds

Thirty strains of bacteria were randomly isolated and identified from buckwheat seeds. The phenotypic characteristics of these strains agree well with those of the Enterobacter agglomerans-Erwinia herbicola complex. On the basis of the difference in indole production and gas production from D-glucose, the isolates were divided into 3 phenotypic groups, viz. I, II and III. Twenty two strains were in phenotypic group I, which is negative for indole production and gas production from D-glucose, and resembles Pantoea agglomerons. All six strains in phenotypic group II, which is positive for indole production and negative for gas production from D-glucose, were identified as Erwinia ananas. Two strains in phenotypic group III, which is negative for indole production and positive for gas production from D-glucose, were identified as Rahnella aquatilis.     

Resistance to gentamicin and vancomycin in enterococcal strains isolated from retail broiler chickens in Japan

A total of 137 Enterococcus strains isolated from chicken meat were subjected to antimicrobial susceptibility tests. Strains with the vanCl gene were isolated from seven of nine samples of chicken meat processed in Japan and from all chickens from China and Brazil between July 2001 and April 2002. The pulsed-field gel electrophoresis (PFGE) patterns of the isolates were distinguishable from each other, suggesting that VanCl-type vancomycin-resistant Enterococcus is preferentially colonized in broiler chickens in these countries. The incidence of high-level gentamicin resistant (HLGR) enterococci that harbored the aac(6')-le-aph(2")-la or aph(2')-Id gene varied among the countries from which the chickens originated (Japan, 2 of 65; China, 11 of 43; Brazil, 6 of 29). Moreover, the PFGE patterns of the HLGR strains were distinguishable from each other, except for two strains obtained from chickens from Brazil. The results suggest that HLGR Enterococcus is highly prevalent in broiler chickens.     

织造行业技术改造和技术进步的现状及方向

目前我国织造行业低水平生产能力过剩，高水平生产能力不足，产品档次低，品质差。加快织造行业技术进步步伐，加大我国织机无梭化比重，是进行产品结构调整和提升产品档次的根本捷径。文章指出中高档无梭织机是我国新型织机发展的主流，应多渠道多层次地发展我国剑杆和喷气织机。