沙蒿胶磁性微球固定化脂肪酶及部分理化性质的研究

以沙蒿多糖-壳聚糖复合磁性微球为载体,采用物理吸附法固定化脂肪酶,对固定化过程中对酶活力有影响的各种因素做了研究,同时对固定化酶的部分理化性质、最适pH、最适温度、酶的热稳定性以及表现米氏常数与游离酶做了比较.固定化酶的Km小于游离酶的Km,其最适pH和最适温度分别为8.0和50℃,而且固定化脂肪酶具有良好的热稳定性、可应用性和重复使用性.     

壳聚糖微球固定化葡萄糖氧化酶的研究

以壳聚糖微球为载体,戊二醛为交联剂,固定葡萄糖氧化酶,对葡萄糖氧化酶的固定化条件及固定化酶的各种性质进行了研究,确定了酶固定的最佳条件为0.1g壳聚糖微球与5ml5%戊二醛交联,固定6mg葡萄糖氧化酶,在此条件下酶活力回收可达60%。固定化酶的最适温度为50℃,最适pH为6.0,通过Lineweaver-Burk作图,确定动力学参数Km值为18.3mmol/L,表观米氏常数较游离酶有所降低,固定化酶的热稳定性较游离酶明显提高,该固定化酶具有良好的操作及保存稳定性。     

纳米磁性壳聚糖微球固定化Alcalase碱性蛋白酶的制备及酶学性质研究

以自制磁性壳聚糖微球作固定化酶载体,考察给酶量、pH、戊二醛浓度和交联时间对固定酶酶活和酶活回收率的影响,并研究固定化酶的酶学性质及其微观结构。结果表明:给酶量112 000 u/g载体,pH 8.5,戊二醛体积分数8%,交联时间11 h条件下酶活达最高(86 779±119.26)u/g,酶活回收率达(77.48±0.11)%。固定化酶和游离酶最适pH分别为11和10.5,最适温度皆为60℃,且固定酶pH和温度稳定性明显高于游离酶;重复使用5次固定酶酶活保持(80.89±0.20)%;由米氏常数可知固定酶具有更强的底物亲和力;电镜显示Fe3O4磁核和磁性壳聚糖微球皆为表面光滑球形的纳米粒子,高比表面积能提供更多酶结合位点;红外光谱证明Fe3O4已被壳聚糖包埋,振动样品磁强计检测固定化酶具有良好磁响应性。     

壳聚糖-埃洛石纳米管微球的制备及其对木瓜蛋白酶的固定化

运用交联-吸附法制备壳聚糖-埃洛石纳米管(chitosan-halloysites nanotube,CTS-HNTs)复合微球固定木瓜蛋白酶,并通过傅里叶红外光谱、扫描电子显微镜、荧光标记等方法进行表征。2%CTS+1%HNTs制备的微球对木瓜蛋白酶的固定量最高。固定化条件为木瓜蛋白酶质量浓度1 mg/mL、固定化时间10 h。固定化木瓜蛋白酶最适pH 6.8(游离酶pH 7.2)、最适温度60℃(游离酶50℃),保存30 d该酶相对活性为62%(游离酶27%),使用4次后,木瓜蛋白酶的相对活性仍然保留26.26%。CTS-HNTs微球固定化木瓜蛋白酶耐贮存,操作稳定性强,可以提高酶的利用率,降低酶解的成本,提高生产效率。     

磁性壳聚糖复合微球固定化葡萄糖异构酶制备及性能研究

通过化学共沉淀法合成纳米级Fe3O4粒子,并将其作为磁核,采用乳化交联法制备磁性壳聚糖复合微球,用SEM、FT-IR及激光粒度仪对微球结构进行表征。以磁性复合微球为载体,对葡萄糖异构酶进行固定化,并对固定化酶的参数、性质以及动力学参数进行研究。试验结果表明:磁性复合微球呈圆球形,具有较好的磁性。在加酶量12 mg/mL、戊二醛体积分数2%、交联时间2 h、振荡时间6 h条件下可以得到较佳的固定化效果,其酶活回收率达84.7%。对固定化酶性质的测定结果显示,最适Mg2+浓度0.01 mol/L,最适Co2+浓度0.003 mol/L,最适pH 7.2,最适温度75℃。通过计算其半衰期为40 d。对动力学参数的测定结果是:固定化酶的米氏常数为9.720,游离酶的米氏常数为8.190。     

一种复合酶的固定化及应用研究

以壳聚糖为原料制备了壳聚糖微球,并通过扫描电镜对微球的形态和结构进行了表征。以自制的壳聚糖微球为载体固定化复合酶,分别通过单因素试验和正交试验,对影响酶固定化效果的因素及固定化酶的酶学性质进行了考察,并采用HPLC对其应用于催化京尼平苷制备京尼平的效果行了研究。结果表明:壳聚糖微球平均粒径约为2 mm,表面呈多孔结构。酶固定化最优化条件为:吸附时间4 h,交联时间1 h,交联剂质量分数0.2%。固定化酶的最适温度为60℃,游离酶最适温度55℃,且固定化酶温度稳定性比游离酶高;固定化酶与游离态酶的最适pH5.0,且固定化酶pH稳定性比游离酶高;固定化酶在使用8次以后剩余酶活力仍在50%以上;固定化酶湿态储存适合短期内使用和储存,干态储存适合长期储存。采用此固定化方法制得的固定化酶催化京尼平苷水解制备京尼平效果良好。     

表面复合修饰纳米超顺磁性材料固定化α-淀粉酶性能研究

以复合修饰的纳米超顺磁性Fe3O4颗粒聚集体为载体固定化α-淀粉酶,比较分析固定化α-淀粉酶及游离α-淀粉酶的酶学性能。研究固定化及游离α-淀粉酶的最适温度、最适p H、操作稳定性及基本动力学等。结果表明,固定化α-淀粉酶最适p H为7,最适温度为60℃。固定化α-淀粉酶与游离α-淀粉酶相比,具有更好的温度和酸碱的耐受性。固定化α-淀粉酶重复催化反应10次,相对酶活力仍剩余72.09%,重复操作的半衰期为18.97次,具有良好的操作稳定性。固定化α-淀粉酶的米氏常数Km值为45.31 mg/m L,亲和性弱于游离α-淀粉酶。      

固定化木聚糖酶的比较研究

以海藻酸钠和壳聚糖两种载体对木聚糖酶进行固定化,研究游离酶和固定化酶的性质.结果表明,游离酶的Km=0.546mg/L,以海藻酸钠和壳聚糖为载体的固定化酶的Km分别为38mg/L和0.342mg/L.尽管以壳聚糖固定的酶的最适pH与游离酶相同(都为5.0),但前者的适宜pH范围明显变宽;而经海藻酸钠固定的酶,最适pH向酸性范围移动0.5个pH;两种载体固定的酶最适温度与游离酶相比,都从40℃提高到50℃.实验还表明,固定化酶提高了游离酶的贮藏稳定性.     

表面复合修饰纳米超顺磁性材料固定化α-淀粉酶性能研究

以复合修饰的纳米超顺磁性Fe3O4颗粒聚集体为载体固定化α-淀粉酶,比较分析固定化α-淀粉酶及游离α-淀粉酶的酶学性能。研究固定化及游离α-淀粉酶的最适温度、最适p H、操作稳定性及基本动力学等。结果表明,固定化α-淀粉酶最适p H为7,最适温度为60℃。固定化α-淀粉酶与游离α-淀粉酶相比,具有更好的温度和酸碱的耐受性。固定化α-淀粉酶重复催化反应10次,相对酶活力仍剩余72.09%,重复操作的半衰期为18.97次,具有良好的操作稳定性。固定化α-淀粉酶的米氏常数Km值为45.31 mg/m L,亲和性弱于游离α-淀粉酶。     

固定化亚油酸异构酶制备及其性质

以海藻酸钠、壳聚糖为载体,分别采用直接包埋、交联-包埋法制备固定化亚油酸异构酶;研究酶的固定化条件和固定化酶的部分性质。结果表明：以海藻酸钠为载体,采用交联-包埋法以戊二醛为交联剂时固定化效果较好;最佳固定化条件为：海藻酸钠质量浓度为3g/100mL,戊二醛质量浓度为0.3g/100mL,CaCl2质量浓度为2g/100mL;固定化酶的最适反应温度为50℃,最适反应pH值为5.0;与游离酶相比,固定化酶的热稳定性显著提高,温度在20～60℃之间较稳定,pH值在2～8之间表现出较好的酸碱耐受性;固定化亚油酸异构酶的Km为0.36mg/mL。连续操作6次固定化相对酶活力仍保持70.6%,与游离酶相比,固定化亚油酸异构酶催化效率约提高了50%。     

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