单宁酸络合镁与DNA的作用机制研究

单宁酸(tannic acid,TA)具有抑菌性、抗氧化性性能,镁离子具有重要的生理调节作用,通过络合反应将单宁酸和氯化镁制备成单宁酸络合镁(tannic acid complexing magnesium,T-Mg)。为了进一步了解T-Mg的一些功能,本文利用紫外光谱法、荧光光谱法、黏度法和热变性等方法在体外模拟体内环境研究了单宁酸络合镁与脱氧核糖核酸(DNA)的相互作用方式并进行分析。T-Mg与DNA相互作用后,随着DNA浓度的增加,T-Mg-DNA体系紫外吸收峰呈现先减色效应和微弱的红移,最大减色率为1.82%,后增色效应,增色率为5.2%;采用摩尔比法,在pH=7.4的缓冲溶液中,25℃时,最大吸收波长222nm处,求得T-Mg与DNA结合比为n(T-Mg):n(DNA)=5.88:1,结合常数为6.20×10~7L/mol;由于T-Mg嵌入到DNA碱基对之间,使得T-Mg-DNA体系荧光吸收强度增强,最大增幅为2.14倍。黏度法和热变性法表明,T-Mg可使DNA的黏度降低、热变性温度升高,进一步证实了T-Mg与DNA之间作用方式为以T-Mg部分插入为主导,镁离子促进了T-Mg和DNA之间的作用。     

光谱法探究苯乳酸与小牛胸腺DNA的作用机制

为深入研究苯乳酸的防腐作用机制,采用紫外-可见光谱法和荧光光谱法研究苯乳酸与小牛胸腺DNA(Thymus DNA,ct-DNA)的相互作用。紫外光谱法测定ct-DNA在苯乳酸浓度逐渐增加的情况下呈现增色效应和微小的蓝移(3 nm),紫外结合常数为Kb=8.4×10~3 M~(-1)(R=0.98849);在苯乳酸存在的情况下ct-DNA的激发波长280 nm,发射波长(300～500)nm下荧光强度明显增加,同时EB-DNA复合体系的荧光强度逐渐减弱,发生荧光猝灭;根据Sterm-Volmer方程得到PLA与EB属于静态和动态混合的猝灭方式。综合紫外和荧光光谱法分析苯乳酸与ct-DNA发生了静电结合和嵌插结合的作用。将光谱学应用于天然抑菌物质的抑菌机制研究中,为后续研究奠定一定的理论基础。     

多波长紫外吸收光谱法快速测定饮料及糕点中的山梨酸

建立快速、准确测定饮料及糕点中山梨酸的多波长紫外吸收光谱法。在p H 3.25 Tris-盐酸溶液中,碱性紫与山梨酸反应,在紫外区生成具有3个正吸收峰的二元离子缔合物。最大吸收峰位于254 nm,另两个吸收峰分别位于305 nm和223 nm,线性范围为0.03~1.4 mg/L,表观摩尔吸光系数(κ)分别为4.50×10^4L/(mol·cm)(254 nm)、2.09×10^4L/(mol·cm)(305 nm)和2.53×10^4L/(mol·cm)(223 nm),检出限为0.028 mg/L(254nm)、0.030 mg/L(305 nm)和0.025 mg/L(223 nm),当以单波长法(以254 nm为例)测定时,饮料的定量限为4.66 mg/L,糕点的定量限为1.68 mg/kg。当用双波长(254 nm+305 nm)或三波长法(254 nm+305 nm+223nm)测定时,表观摩尔吸光系数(κ)分别为6.59×10^4L/(mol·cm)和9.12×10^4L/(mol·cm),检出限分别为0.014 mg/L和0.0098 mg/L,饮料的定量限分别为2.33 mg/L和1.63 mg/L,糕点的定量限分别为0.843 mg/kg和0.590 mg/kg。以双波长法为例,样品的加标回收率和相对标准偏差RSD(n=5)分别为97.3%~102%和2.0%~2.7%。该法适于糕点及饮料中山梨酸的快速测定。     

不同合成方法对4种渔药人工抗原免疫 原性的影响

目的建立4种常用渔药磺胺甲恶唑(sulfamethoxazole,SMZ)、新霉素(neomycin,NEO)、恩诺沙星(enrofloxacin,EF)和氟苯尼考(florfenico,FF)人工抗原合成及免疫原性的检测方法,为其单克隆抗体制备及渔药残留快速检测奠定基础。方法对4种渔药分别采用重氮化法、戊二醛法(GA)、碳二亚胺法(EDC)和混合酸酐法合成人工抗原。用紫外扫描法(UV)和聚丙烯酰胺凝胶电泳法(SDS-PAGE)对人工合成抗原进行鉴定,并用ELISA法检测人工抗原的免疫原性。结果重氮化法与GA法都能合成SMZ人工抗原,重氮化法合成抗原的紫外峰值与电泳条带位移更明显,抗体效价为1×10~4;EDC法与GA法均可合成NEO人工抗原,但EDC法合成抗原的电泳条带位移更加明显,且抗体效价为1×10~4;混合酸酐法合成EF人工抗原失败,EDC法可合成EF人工抗原且合成抗原的紫外峰值与电泳条带位移明显,抗体效价为1×10~4;GA法合成的FF人工抗原的紫外峰值与电泳条带位移明显,抗体效价高达1×10~5。结论 SMZ人工抗原的合成采用重氮化法较好,FF人工抗原的合成采用戊二醛法较好,NEO与EF人工抗原的合成采用碳二亚胺法较好。     

微波消解-原子吸收光谱法测香菇中的微量元素

目的:建立微波消解-火焰原子吸收光谱法测定香菇中Cu、Zn、Mn三种微量元素含量的分析方法。方法:在微波环境下用高氯酸和浓硝酸(1∶3)对已粉碎的香菇按照一定的升温程序进行消解,以火焰原子吸收光谱法分别于324.7nm、213.9nm、279.5nm波长处对消解液中的Cu、Zn、Mn三种元素进行了测定。结果:实验结果表明,Cu、Zn、Mn三种元素的检出限分别为6.8×10~(-9) g/m L、5.6×10~(-9) g/m L和8.6×10~(-9)g/m L。香菇样品中Cu、Zn、Mn三种元素的含量分别为10.9mg/kg、88.2mg/kg和9.65mg/kg,回收率为100.3%～100.8%。结论:该方法检测操作简单、灵敏度、精密度及准确度较高,用于香菇中Cu、Zn、Mn等微量元素的测定,获得令人满意的结果。     

多波长褪色光度法测定鲜柠檬中的柠檬酸

建立了测定柠檬酸的多波长分光光度法。在pH 6.15的Tris-盐酸缓冲溶液中,灿烂绿与柠檬酸在可见光区发生褪色反应,生成具有3个明显负吸收峰的绿色离子缔合物,并出现褪色现象。最大、次大和最小的负吸收波长分别位于652、582和426 nm处。柠檬酸在0.02~3.84 mg/L(652 nm和582 nm)和0.48~3.84 mg/L(426 nm)内遵从比尔定律,表观摩尔吸光系数(κ)分别为3.33×10~4、2.84×10~4和1.44×10~4L/(mol·cm),定量限为0.019 g/100 g(652 nm和582 nm)和0.45 g/100 g(426 nm)。采用双波长或三波长叠加法测定,它们的灵敏度分别可达6.16×10~4L/(mol·cm)和7.61×10~4L/(mol·cm),定量限均为0.019 g/100 g。还探讨了适宜的反应条件、主要分析化学性质及络合比。方法用于新鲜柠檬中柠檬酸含量的测定,回收率为98.85%~101.1%,相对标准偏差(n=6)为2.2%~2.5%。     

苯乳酸与单增李斯特菌和大肠杆菌胞内外基因组的抑菌作用机制

为研究苯乳酸与食源性致病菌基因组的相互作用机制,选取单增李斯特菌(Listeria monocytogenes 10403s)和大肠杆菌(E.coli 44752)采用凝胶电泳阻滞实验法和紫外-可见光谱法研究苯乳酸与胞内、胞外基因组DNA的作用机制。实验结果表明苯乳酸与单增李斯特菌和大肠杆菌的胞内DNA迁移率和条带亮度均未发生变化,无相互作用;苯乳酸对单增李斯特菌和大肠杆菌的胞外DNA发生结合作用。单增李斯特菌体外DNA在苯乳酸16~32 mmol/L浓度下,与苯乳酸发生结合作用,结合常数为9.16×10~5M~(-1);大肠杆菌体外DNA在苯乳酸2~16 mmol/L的浓度下,与苯乳酸发生结合作用,结合常数为7.36×10~5M~(-1)。两者的结合方式为静电结合和嵌插结合。     

双极制界面电位法测定鲱鱼精dsDNA与联苯胺的结合参数

将鲱鱼精dsDNA通过自吸附方式固定在铅笔芯电极(CP)表面制备出DNA/CP.在pH7.38磷酸缓冲溶液(PBS)中,考察联苯胺(BZ)与铅笔芯电极表面鲱鱼精dsDNA相互作用后所导致的DNA/CP零流电位Ezcp变化.结果显示,随着BZ浓度或结合时间的增加,DNA/CP的Ezcp均正移;且当BZ浓度在8.0×10~(-7)~1.0×10~(-5) mol·L~(-1)或结合时间在2~18min内,Ezcp与BZ浓度对数lg[BZ]或结合时间呈正比关系.由此计算出dsDNA与BZ结合反应呈现一级动力学反应方程,其结合比为1∶1,表观结合常数为3.98×106L·mol~(-1),表观速率常数为2.06×104s~(-1),半衰期为3.36×10~(-5)s.本方法简单灵敏安全,对拓宽致癌或致毒小分子与DNA作用的研究方法有参考价值.     

烟草蚀纹病毒(TEV)生物学及理化特性的研究

从自然感病的烟草上分离到烟草蚀纹病毒(TEV)。其寄主范围较宽,经汁液摩擦接种普通烟产生明脉和坏死性蚀纹,在蔓陀萝上为斑驳和畸形,不侵染苋科的千日红及豆科和葫芦科植物。致死温度为53℃,稀释限点为3×10~(-3),体外保毒期为4天。蚜虫传毒试验表明,可经桃蚜进行非持久性传毒。粗提纯的病毒制品在电镜下为稍弯曲的线状粒子,大小约728×12-13nm。病毒粒子经5-40％的蔗糖密度梯度离心后,显示出单一主峰,其紫外吸收值最大为258.5nm,最小为241.7nm,A280/260之比值为1.27。降解病毒所得核酸和蛋白的紫外吸收值分别为最大258nm及273.9nm,最小为233nm及250nm,经PAGE测定其分子量分别为3.16×10~6道尔顿及2.98×10~4道尔顿。用提纯病毒制备所得抗血清效价为1:512;经琼脂双扩散试验证明只与分离的病毒起沉淀反应,而与CMV、TMV、ToRSV、TNV、PVY则无反应。     

四种黄酮类化合物与DNA相互作用关系研究

本实验分别从紫外吸收、热变性、结合平衡三个方面研究了四种黄酮类化合物桑色素、山萘酚、槲皮素和杨梅素与鲱鱼精DNA的相互作用。紫外吸收光谱表明:这四种黄酮化合物与DNA作用后,均导致DNA的最大吸收峰发生增色效应,桑色素和山萘酚使最大吸收峰红移,而槲皮素或杨梅素则使最大吸收峰发生蓝移。采用双倒数法,测得四种黄酮化合物与DNA作用的结合常数。通过热变性实验发现,四种黄酮化合物均使DNA的熔解行为发生变化。     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.     

Occurrence of bisphenol-F-diglycidyl ether (BFDGE) in fish canned in oil

The levels of bisphenol-F-diglycidyl ether (BFDGE) were quantified as part of a European survey on the migration of residues of epoxy resins into oil from canned fish. The contents of BFDGE in cans, lids and fish collected from all 15 Member States of the European Union and Switzerland were analysed in 382 samples. Cans and lids were separately extracted with acetonitrile. The extraction from fish was carried out with hexane followed by re-extraction with acetonitrile. The analysis was performed by reverse phase HPL C with fluorescence detection. BFDGE could be detected in 12% of the fish, 24% of the cans and 18% of the lids. Only 3% of the fish contained BFDGE in concentrations considerably above 1mg/kg. In addition to the presented data, a comparison was made with the levels of BADGE (bisphenol-A-diglycidyl ether)analysed in the same products in the context of a previous study.     

Contribution of European research to risk analysis

The European Commission's, Quality of Life Research Programme, Key Action 1—Health, Food & Nutrition is mission-oriented and aims, amongst other things, at providing a healthy, safe and high-quality food supply leading to reinforced consumer confidence in the safety of European food. Its objectives also include the enhancing of the competitiveness of the European food supply. Key Action 1 is currently supporting a number of different types of European collaborative projects in the area of risk analysis. The objectives of these projects range from the development and validation of prevention strategies including the reduction of consumers risks; development and validation of new modelling approaches; harmonization of risk assessment principles, methodologies, and terminology; standardization of methods and systems used for the safety evaluation of transgenic food; providing of tools for the evaluation of human viral contamination of shellfish and quality control; new methodologies for assessing the potential of unintended effects of genetically modified (genetically modified) foods; development of a risk assessment model for Cryptosporidium parvum related to the food and water industries; to the development of a communication platform for genetically modified organism, producers, retailers, regulatory authorities and consumer groups to improve safety assessment procedures, risk management strategies and risk communication; development and validation of new methods for safety testing of transgenic food; evaluation of the safety and efficacy of iron supplementation in pregnant women; evaluation of the potential cancer-preventing activity of pro- and pre-biotic ('synbiotic') combinations in human volunteers. An overview of these projects is presented here.     

低温带皮菜籽粕微粉的不同粒级部分的功能特性

为研究低温带皮菜籽粕微粉的不同粒级部分的功能特性,以经低温脱脂的带皮菜籽粕为原料,经微粉碎后筛分成212~425μm、150~212μm和106~150μm的3个不同粒级的微粉样品,检测这些样品的吸水性、吸油性、乳化性和乳化稳定性、蛋白质体外消化率。结果表明:1 3个不同粒级的微粉样品之间的粗纤维含量存在显著差异,表明三者的结构组成成分有一定差异。23个微粉样品的乳化活性和乳化稳定性随粒度级别的减小而显著增加(P0.01)。33个微粉样品的蛋白质体外消化率随粒度级别的减小而显著增加(P0.01)。4不同粒级带皮菜籽粕微粉样品的吸水性与吸油性受其结构组成物质不同和粒度的双重影响,与粒度的相关性不明显。     

Microbiology of food taints

Fresh and processed foods are often spoilt by the presence of undesirable flavours and odours caused by microbial action. The aim of this paper is to review the current knowledge of microbiologically induced taints that occur in a wide range of foodstuffs, including meats, poultry, fish, crustaceans, milk, dairy products, fruits, vegetables, cereals and cereal products. Examples have been chosen where the compounds responsible for the taint have been identified and sufficient data obtained to demonstrate the involvement of microorganisms. However, in some cases the full identity of the causative organism may not have been elucidated. The types of microorganisms covered by this review include bacteria, fungi, yeasts, actinomycetes and cyanobacteria. Although cyanobacteria do not in general infect foods, their presence in aqueous systems and water supplies can lead to off-flavours in aquatic organisms and processed foodstuffs. Several examples of each of these processes are discussed. Wherever possible, the likely biosynthetic pathway used by the microorganism to produce the offending compound in a foodstuff is indicated.     

Analysis for organic residues from aids to polymerization used to make plastics intended for food contact

Polymers intended for food contact use have been analysed for organic residues which could be attributed to a range of substances employed as polymerization aids (e.g. initiators and catalysts). A wide range of polymers was extracted with solvents and the extracts analysed by gas chromatography-mass spectrometry (GC-MS). The overwhelming majority of substances identified were not derived from aids to polymerization but were oligomers, additives and adventitious contaminants. However, a small number of substances were identified as initiator residues. These included tetramethylsuccinonitrile (TMSN) which was observed in two polymers and it derived from recombination of two azobisisobutyronitrile (AIBN) initiator radicals. Methyl benzoate, benzoic acid, biphenyl and phenyl benzoate were detected in one poly(methyl methacrylate) sample and in two polyvinylchlorides and they are thought to be derived from benzoyl peroxide initiator. TMSN was subsequently targeted for analysis of poly-(methyl methacrylate) plastics using proton nuclear magnetic resonance spectrometry (¹     

Tests of potential functional barriers for laminated multilayer food packages. Part II: Medium molecular weight permeants

Experiments were performed to characterize the kinetics of the permeation of different medium molecular weight model permeants: bisphenol A, warfarin and anthracene, from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick orientated polypropylene--OPP) into the food simulants olive oil and 3% (w/v) acetic acid. The characterization of permeation kinetics generally observed the permeation models previously reported to explain the experimental permeation results obtained for a low molecular weight group of model permeants. In general, the model permeants exhibited behaviour consistent with their relative molecular weights with respect to (a) the time taken to attain steady-state permeation into the food simulant in which they were more soluble, (b) their subsequent steady-state permeation rates, and (c) their partition between liquid paraffin and the OPP membrane.     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. I: Interlaboratory studies of methods of analysis

This paper describes the first part of a project undertaken to develop mussel reference materials for Paralytic Shellfish Poisoning (PSP) toxins. Two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin (STX) and decarbamoyl-saxitoxin (dc-STX) in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the second part of the project: the certification exercise. In the first study, 18 laboratories were asked to measure STX and dc-STX in rehydrated lyophilized mussel material and to identify as many other PSP toxins as possible with a method of their choice. In the second interlaboratory study, 15 laboratories were additionally asked to determine quantitatively STX and dc-STX in rehydrated lyophilized mussel and in a saxitoxin-enriched mussel material. The first study revealed that three out of four postcolumn derivatization methods and one pre-column derivatization method sufficed in principle to determine STX and dc-STX. Most participants (13 of 18) obtained acceptable calibration curves and recoveries. Saxitoxin was hardly detected in the rehydrated lyophilized mussels and results obtained for dc-STX yielded a CV of 58% at a mass fraction of 1.86 mg/kg. Most participants (14 out of 18) identified gonyautoxin-5 (GTX-5) in a hydrolysed extract provided. The first study led to provisional criteria for linearity, recovery and separation. The second study revealed that 6 out of 15 laboratories were able to meet these criteria. Results obtained for dc-STX yielded a CV of 19% at a mass fraction of 3.49mg/kg. Results obtained for STX in the saxitoxin-enriched material yielded a CV of 19% at a mass fraction of 0.34mg/kg. Saxitoxin could not be detected in the PSP-positive material. Hydrolysis was useful to confirm the identity of GTX5 and provided indicative information about C1 and C2 toxins in the PSP-positive material. The methods used in the second interlaboratory study showed sufficiently consistent analysis results to undertake a certification exercise to assign certified values for STX and dc-STX in lyophilized mussel.     

Focus on China's Paper Industry

In the English section of this issue, 〈China Paper Newsletters〉 will introduce ＂National Development and Reform Commission Issued Announcement for Selection of Major Preliminary Research Projects for the ＇13th Five-Year Plan＇＂, ＂2013 Annual Report of China＇s Paper Industry＂, and news of projects and other policies.     

Listen to downstream & search for innovation

正Nowadays,textile enterprises are all taking efforts in transformation and upgrading,like improving producing capacity and optimizing production structure to face market downturn.It claimed a higher request to the standard of textile equipments.In the upcoming of ITMA ASIA+CITME 2014exhibition,this magazine have interviewed several branch associations and a series of relative enterprises,to summarize industrial developing status