转谷氨酰胺酶交联酶晶体的制备及其结构表征

采用双功能试剂戊二醛对转谷氨酰胺酶晶体进行化学变联,得到交联条件.对交联酶晶体用电镜扫描以及红外光谱和XPS进行结构表征.交联条件:戊二醛质量分数1％,交联pH 6,交联温度4℃,交联时间40min.红外光谱显示,游离酶在1 651 cm-1出现强峰,而交联酶晶体在1 634、1 281和1 241 cm-1出现峰值,在α-螺旋区域没有检测到峰值.通过X-射线光电子能谱分析证实,交联酶晶体与游离酶相比,在285.1 eV处的C1S的信号峰增强,在400.375 eV处的NlS峰几乎消失,说明酶蛋白表面的游离氨基已经与戊二醛结合,表面蛋白结构发生了变化.     

磁性固定化漆酶在苹果汁除酚中的应用研究

以磁性聚苯乙烯微球为载体,戊二醛为交联刑,制备出了磁性固定化漆酶。研究表明：固定化酶的Km值较游离酶小,最适温度与游离酶相同,最适pH较游离酶下降0．4个单位,热稳定性、pH稳定性和贮存稳定性均较游离酶有所提高。Fe^2 、Hg^2 、Cr^3 对固定化酶有抑制作用,Cu^2 对固定化酶有激活作用。抑制刑EDTA、DMSO对磁性固定化酶的抑制作用明显较游离酶小。固定化漆酶在40℃条件下处理2h后,苹果汁中多酚含量减少20％,而酶活力没有变化。     

TG酶和漆酶对双歧杆菌益生菌酸奶品质的影响

为了比较谷氨酰胺转氨酶(TG酶)和漆酶的添加对双歧杆菌益生菌酸奶感官、蛋白质交联及组织质构变化的影响,测定和分析了两种酶交联益生菌酸奶的游离氨基变化率、感官、质构、表观黏度、蛋白条带及微观结构,并添加阿魏酸改善漆酶酸奶的品质。结果表明:当TG酶用量增加时,TG酶交联酸奶的游离氨基变化率、感官得分和硬度显著增大(p<0.05),胶黏性、粘聚性及表观黏度先增大后减小(p<0.05),内聚性变化不显著(p>0.05),TG酶最佳用量为1.8 U/g;随着漆酶用量的增加,漆酶酸奶游离氨基变化率、感官得分、硬度、内聚性、胶黏性、粘聚性及表观黏度均先增大后减小(p<0.05),漆酶最佳用量为0.3 U/g;添加4.5 mmol/L的阿魏酸明显改善了漆酶交联酸奶的感官、质构及表观黏度;所有待测酸奶中均缺少β-lg条带,TG酶交联酸奶的κ-CN和β-CN条带消失,聚集成了新的蛋白质,而漆酶交联酸奶和阿魏酸+漆酶酸奶与对照及TG酶酸奶相比,分子量在14 kDa的蛋白条带明显变宽;经两种酶交联的酸奶,三维网络结构变得致密,TG酶交联酸奶的胶粒分布更均匀,网络结构更致密,且在漆酶交联酸奶中添加了阿魏酸后,相较于漆酶交联酸奶,蛋白胶束聚集的更紧密,从而得出,不同类型酶对牛奶乳蛋白质交联的催化作用不同,但均可改善酸奶的感官及食用品质。     

交联酶聚集体法制备单宁酶及固定化酶性质研究

交联酶聚集体法(cross-linked enzyme aggregates,CLEAs)是一种新型的无载体酶固定化方法。使用该法固定化黑曲霉产单宁酶,制备无载体固定化单宁酶(Cross-linkedenzyme aggregates-tannase,CLEAs-TA),并对其制备条件、结构特征、酶学性质进行分析。结果表明,最优制备条件为单宁酶游离粗酶液在冰水浴中经80%的硫酸铵沉淀30min后,以1.5%戊二醛水溶液进行酶聚集体交联反应,可获得较高活性、较高稳定性的交联酶聚集体,酶活回收率达47.33%,对酯键水解作用的最适温度、最适pH值分别为50℃、4.5,与游离酶相比,表现更高的pH及温度稳定性,重复使用6次后,活力剩余32.86%,其良好的操作稳定性有利于没食子酸丙酯高效转化为没食子酸及广泛应用于水解茶饮料中单宁的反应。     

交联海藻酸钠固定化柚(皮)苷酶

以海藻酸钠为载体,戊二醛为交联剂,采用交联-包埋-交联法对柚(皮)苷酶进行了固定化。在单因素实验基础上,通过正交实验得到海藻酸钠固定化柚(皮)苷酶的最优工艺条件:海藻酸钠质量浓度3.0%,给酶量为0.01mg/g载体,前交联戊二醛体积分数2.0%,前交联时间1.5h,后交联戊二醛体积分数0.025%,后交联时间2h,制备的固定化酶最高活力5.07U/g。同时,对固定化柚(皮)苷酶的稳定性进行了研究,结果表明:固定化酶的温度耐受性与存储稳定性较游离酶有较大幅度的提高;固定化酶重复使用7次(60℃,pH4.0)后,活力仍然保持在60%。     

多酚氧化酶的固定化及其酶学性质研究

游离多酚氧化酶在使用过程中容易流失,无法重复利用。文章主要研究了低成本、高效率的两种固定化方法:海藻酸钠包埋法和戊二醛交联法,确定了其最优固定化条件,分别为海藻酸钠包埋法:2.5%CaCl2,2.5%海藻酸钠,固定化时间2h;戊二醛交联法:1.25%戊二醛,振荡固定pH 4.5,酶与载体质量比75(mg/g),固定化反应时间6.5h。同时对游离多酚氧化酶及固定化多酚氧化酶的酶学性质进行了研究。结果表明:游离酶、海藻酸钠包埋法固定多酚氧化酶(polyphenol oxidase immobilized by sodium alginate,A-PPO)和戊二醛交联法固定多酚氧化酶(polyphenol oxidase immobilized by glutaraldehyde crosslinking,C-PPO)的比活力分别为864,490,371U/mg,A-PPO和C-PPO的酶活回收率分别为18.6%和24.0%。同时,固定化酶在pH稳定性、热稳定性上优于游离酶,戊二醛交联法固定酶的效果优于海藻酸钠包埋法。     

MJL交联酶聚体的制备及性质研究

本实验制备MJL交联酶聚体并对其性质进行研究。运用交联酶聚体技术制备MJL交联酶聚体;测定游离MJL和CLEAs的酶活,最适pH和温度;比较MJL交联酶和游离酶在室温下的稳定性。方法:利用戊二醛做交联剂制备MJL交联酶聚体;α-乙酸萘酯法测定游离MJL及MJL交联酶聚体的最适pH和温度。实验结果显示,交联后酶适应温度范围变宽,最适pH较游离酶(pH7.0)向酸性偏移。结论:交联后脂肪酶聚活性变化较低,对温度、pH的耐受性提高,稳定性也有所提高。     

壳聚糖固定化α-葡萄糖苷酶的研究

以粉末状壳聚糖为载体 ,采用吸附 交联的方法将α 葡萄糖苷酶固定化。在最适固定化条件下 ,室温吸附 6h ,然后与 3 5%的戊二醛在 4 5℃交联 6h ,可得到固定化酶的活力为1430 0U ,酶活力回收率为 59 6 %。通过实验发现 ,与游离酶相比 ,固定化酶的最适 pH向酸性方向移动 0 5pH单位 ,为 pH 4 5;最适作用温度达到 70℃ ,比游离α 葡萄糖苷酶提高 5℃ ;酸碱稳定性、热稳定性及贮存稳定性均有较大提高 ;在 6 0℃操作半衰期为 16 8h     

脂环酸芽孢杆菌α-葡萄糖苷酶固定化及酶学性质研究

以戊二醛为交联剂,壳聚糖为载体,优化脂环酸芽孢杆菌α-葡萄糖苷酶的固定化条件,探讨固定化对酶性质的影响。结果表明:当戊二醛浓度0.2mol/L、戊二醛交联时间12h、交联pH7.5和交联温度15℃时,酶的固定化效果最佳。此时,固定化酶的最适pH4.5,最适反应温度55℃,在pH4.5～8.0范围酶的活性不受损失。当温度为65℃时,固定化酶的活力接近100%。酶储存3周以上,可以保持80%以上的活力。重复使用6次后,酶活保持在80%左右,说明固定化酶优化了游离酶的部分酶学性质,具有一定的应用价值。     

交联壳聚糖固定化β-葡萄糖苷酶的稳定性研究

以戊二醛交联壳聚糖微球为载体通过共价连接反应固定化β-葡萄糖苷酶,研究固定化β-葡萄苷酶的稳定性。结果表明:固定化和游离β-葡萄糖苷酶的最适温度分别为706、5℃,最适pH分别为4.0、4.5。固定化β-葡萄苷酶贮存11周以后仍保持75.0%以上的相对活力,连续使用6批次后其相对活力仍保持在65.0%以上。固定化β-葡萄糖苷酶的高温、pH、贮存、操作稳定性明显高于游离酶。     

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.     

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     

Chinese CTP Market

According to Printing and Printing Equipment Industries Association of China（PEIAC）＇s statistics to the plate manufucturer in China, in 2013, the actual offset plate production has reached 346 million square meters in China. Among them, the CTP production volume was 245 million square meters, up by 11% than that of last year; the total sales of the CTP plate was 239 million square meters, up by 13%.     

Preparatory Work of Print China 2015 is Going Smoothly

正Held at Guangdong Modern International Exhibition Center,Print China 2015 will cover 7exhibition halls,besides the original Hall No.3,4,5,6,7,the newly built F zone of Hall 3 will be used too.The total area will be140,000 square meters.Hall 3:Offset and large printing equipment,package printing equipment,post press