米曲氨基酰化酶的提取及其酶学性质的表征

通过硫酸铵分级沉淀、SephadexG5 0凝胶层析和DEAE Sepharose阴离子交换层析 ,从米曲霉 3 0 42中提取得到了米曲氨基酰化酶 ,该酶的纯化倍数为 5 4.2 9,比活为 647.66U/mg ,总收率为49 5 3 %。详细考察了温度、pH、缓冲体系的离子强度和金属离子对米曲氨基酰化酶酶活的影响。结果表明 ,该酶促反应的最适pH为 7 5～ 8 0 ,最适反应温度随催化反应时间的延长而降低 ,缓冲体系中的离子对酶活有抑制作用 ,而低浓度的Co2 +对酶活有激活作用。     

基于不同缓冲体系的纤维素酶活力及其稳定性研究

采用柠檬酸、醋酸和磷酸3种不同的缓冲体系、分别在pH为4.8、6.0,温度为40℃、50℃、60℃的条件下,测试纤维素酶的滤纸酶活力,分析酶活数值的高低和稳定性。结果表明,在pH=4.8的条件下,醋酸缓冲体系中的酶活数值最高,数值稳定性则是柠檬酸缓冲体系最好;在pH=6.0的条件下,无论酶活数值还是稳定性都是磷酸缓冲体系高于醋酸和柠檬酸缓冲体系。     

微生物弹性蛋白酶催化动力学特性研究

研究了弹性蛋白酶的酶学性质与酶促反应动力学.研究表明,弹性蛋白酶的作用最适pH值与所用缓冲体系有关,在硼砂-硼酸缓冲体系中,最适pH值为7.8,而在Tris缓冲体系中,最适pH值为8.48;酶的作用最适温度为50℃,当温度高于60℃时,酶活性下降辐度较大,差异极显著.酶在pH3～7即酸性条件下,酶活较低,而在pH7～12时酶活较高,且趋于稳定.大部分金属离子对酶的活性有抑制作用,尤其是Ba+、Ca+、Al+和Cu+等金属离子可使酶的活性直线下降,而钠离子对酶的活性没有明显影响.采用Lineweaver-Burk方法,获得酶催化动力学参数Vmax=0.09512U/mL,km=0.00741m/ml,应用Michaelis-Menten方程求得弹性蛋白酶以弹性蛋白为底物的催化动力学方程为V=0.09512[S]/0.00741+[S].     

重组黄杆菌肝素酶测活性方法的改进及影响因素的研究

目的提高Azure A法测活重组肝素酶的效率。方法通过缩短测定反应时间,提高酶活测定的效率。采用改进后的测活方法研究了温度、pH、盐离子浓度、不同金属离子对测活体系的影响。结果改进后的方法使肝素酶的测活效率提高了4倍,新的酶活测定方法最适反应条件为30℃,pH 7.0,盐离子浓度250 mmol/L。Cu2 对酶有轻微的激活作用,Pb2 、Mn2 则有较强的抑制作用。结论改进后的测活方法重复性好,测活效率大大提高。     

缬氨酸转氨酶拆分DL-缬氨酸的催化条件

利用具有缬氨酸转氨酶活性的工程菌对DL-缬氨酸进行拆分,考察了反应温度、pH值、底物摩尔比、底物浓度和金属离子对酶活性和底物转化率的影响。结果显示,该催化反应的最适反应条件为:反应温度是45℃,pH=9,L-缬氨酸与丙酮酸的摩尔比1∶8,DL-缬氨酸初始浓度为0.6 mol/L、丙酮酸初始浓度为2.4 mol/L,0.5 mmol/L的Mg2+和Na+对酶活性有明显的促进作用。     

类蛋白反应法改性水解明胶的条件

研究了在木瓜蛋白酶作用下蛋氨酸酯与水解明胶进行类蛋白反应的条件,利用单因素实验并通过主成分分析法对几个评价指标进行综合评定,得出最佳反应条件为:氨基酸酯采用蛋氨酸月桂醇酯、底物浓度为4 0 % ,反应时间为6h ,加酶量为0 1%水解明胶,加酯量为0 0 2 5mol/10 0g水解明胶,反应温度为5 5℃,pH为6 0。     

富硒酵母中硒蛋氨酸的GC-MS/MS测定

建立酵母中硒蛋氨酸含量的气相色谱——串联质谱法(GC-MS/MS)分析方法。比较3种富硒酵母中硒蛋氨酸检测样品的提取方法,优化硒蛋氨酸的酶解提取条件;以氯甲酸乙酯为衍生化试剂,2-氯苯丙氨酸为内标物,采用选择离子模式对衍生物进行GC/MS/MS检测。结果表明,硒蛋氨酸的回收率为90.0%～97.0%,检测限为4μg/L,方法精密度(RSD)为7.8%。该方法简单快捷、定量准确、灵敏度高。     

右旋糖酐酶酶学特性及热失活动力学研究

以右旋糖酐为底物,采用DNS法测定右旋糖酐酶酶活,揭示其酶学特性及热失活动力学性质。考察了温度、pH、离子强度、常见食品添加剂对右旋糖酐酶活性的影响,并建立右旋糖酐酶酶促反应动力学及热失活动力学参数。结果表明,最适温度、pH和离子强度分别为60/65℃,5.5,0.015 mol/L;pH 5.5～9.5或乙醇添加量0%～30%的环境常温保存30 min,酶活性保持相对稳定;酶促反应动力学符合米氏方程所描述的单底物酶促反应动力学,其K_m和V_(max)分别为0.01321 mol/L、0.5153μmol/(min·U);右旋糖酐酶的热失活遵循一级反应动力学规律,在60℃、含蔗糖0,200 g/L的环境下热失活速率常数分别为0.1268,0.1105 min~(-1)。2 mmol/L亚硫酸钠对右旋糖酐酶活性具有抑制作用(P0.05)。该试验为制糖行业和其他行业应用该酶提供了较详细的数据支持。     

蛋氨酸螯合铬营养强化剂的合成工艺

对蛋氨酸铬螯合物的合成工艺条件进行了研究,重点研究了配体摩尔比和pH值对螯合反应的影响,确定合适的配合反应条件为配位体摩尔比3∶1、pH =7 0、反应温度80℃,蛋氨酸铬螯合物产率为4 8 4 1%。     

分光光度法测定牦牛不同脏器中左旋肉碱方法优化及含量分析

对牦牛脏器中左旋肉碱的分光光度法测定进行优化,并对其脏器中左旋肉碱含量进行分析。在单因素实验的基础上,以加酶反应时间、缓冲体系pH、酶反应温度为自变量,以吸光度为响应值,进行响应面分析。确定最优工艺条件为:酶反应温度37℃、缓冲体系pH7.6、加酶反应时间16min,在此条件下,左旋肉碱吸光度值为0.321。通过对牦牛心、肝、肺、肾中左旋肉碱测定值的分析发现,肝脏中左旋肉碱含量最高,为28.35mg/kg;肺脏中左旋肉碱含量为22.75mg/kg;心脏中含左旋肉碱14.61mg/kg;肾脏中左旋肉碱的含量最低,为5.22mg/kg。     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

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

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

Chlorohydrins of bisphenol A diglycidyl ether (BADGE) and of bisphenol F diglycidyl ether (BFDGE) in canned foods and ready-to-drink coffees from the Japanese market

BADGE.2HCl and BFDGE.2HCl were determined in 28 samples of ready-to-drink canned coffee and 18 samples of canned vegetables (10 corn, 5 tomatoes and 3 others), all from the Japanese market. HPLC was used as the principal analytical method and GCMS for confirmation of relevant LC fractions. BADGE.2HCl was found to be present in one canned coffee and five samples of corn, BFDGE.2HCl in four samples of canned tomatoes and in one canned corn. No sample was found which exceeded the 1mg/kg limit of the EU for the BADGE chlorohydrins. However the highest concentration was found for the sum of BFDGE.2HCl and BFDGE.HCl.H₂O at a level of 1.5mg/kg. A Beilstein test confirmed that all cans containing foods contaminated with BADGE.2HCl or BFDGE.2HCl had at lest one part coated with a PVC organosol.     

European priorities for research to support legislation in the area of food contact materials and articles

A strong science base is required to underpin the planning and decision-making process involved in determining future European community legislation on materials and articles in contact with food. Significant progress has been made in the past 5 years in European funded work in this area, with many developments contributing to a much better understanding of the migration process, and better and simpler approaches to food control. In this paper this progress is reviewed against previously identified work-areas (identified in 1994) and conclusions are reached about future requirements for R&D to support legislation on food contact materials and articles over the next 5 or so years.     

Analysis of benzo[a]pyrene in spiked fatty foods by second derivative synchronous spectrofluorimetry after microwave-assisted treatment of samples

A simple, rapid and inexpensive method has been developed for the determination of benzo[a     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. II: Certification study

This paper describes the second part of a project undertaken to develop certified mussel reference materials for paralytic shellfish poisoning toxins. In the first part two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin and decarbamoyl-saxitoxin in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the certification exercise. Fifteen laboratories participated in this certification study and were asked to measure saxitoxin and decarbamoyl-saxitoxin in rehydrated lyophilized mussel material and in a saxitoxin-enriched mussel material. The participants were allowed to use a method of their choice but with an extraction procedure to be strictly followed. The study included extra experiments to verify the detection limits for both saxitoxin and decarbamoyl-saxitoxin. Most participants (13 of 15) were able to meet all the criteria set for the certification study. Results for saxitoxin.2HCl yielded a certified mass fraction of <0.07 mg/kg in the rehydrated lyophilized mussels. Results obtained for decarbamoyl-saxitoxin.2HCl yielded a certified mass fraction of 1.59+/-0.20 mg/kg. The results for saxitoxin.2HCl in enriched blank mussel yielded a certified mass fraction of 0.48 +/- 0.06 mg/kg. These certified reference materials for paralytic shellfish poisoning toxins in lyophilized mussel material are the first available for laboratories to test their method for accuracy and performance.     

Announcing a new international peer-reviewed journal:Food Science and Human Wellness now accepting manuscript submission in English

<正>We are pleased to announce the launch of a new international peer-reviewed journal-Food Science and Human Wellness,ISSN 2213-4530,which is an open access journal,produced and hosted by Elsevier B.V.on behalf of Beijing Academy of Food Sciences.Food Science and Human Wellness is an international peer-reviewed English journal that provides a forum for the dissemination of the