山楂多酚氧化酶的酶学特性研究

研究山楂多酚氧化酶(PPO)的酶学特性。采用分光光度法测定PPO的酶活性,考察底物特异性、p H值、温度、热稳定性、底物浓度、金属离子以及抑制剂对PPO酶活性的影响。实验结果表明,山楂PPO的最适底物为邻苯二酚;最适p H值为6.5;最适温度为40℃;90℃热处理1.0 min或85℃处理1.5 min PPO酶活基本完全丧失;山楂PPO最适底物浓度为0.10 mol/L,PPO酶促褐变反应动力学符合米氏方程,相应的动力学参数Km=55.83 mmol/L,Vmax=98.04 U/min;Al3+对PPO酶活的抑制作用较强,Mn2+、Ca2+和Zn2+次之,Cu2+和Mg2+对PPO酶活抑制作用不明显,Fe3+对PPO酶活有一定的促进作用;四种抑制剂对山楂PPO酶活均有一定的抑制作用,且抑制效果与抑制剂浓度呈量效关系,相同浓度下抑制效果由强到弱顺序为:抗坏血酸L-半胱氨酸亚硫酸氢钠柠檬酸,抗坏血酸的抑制效果最为显著。     

杏鲍菇多酚氧化酶的酶学特性研究

以杏鲍菇中多酚氧化酶(PPO)为研究对象,采用分光光度法在420nm处对其酶学特性进行研究.结果表明,杏鲍菇PPO的最适底物为邻苯二酚;最适pH为6.0;最适温度为35℃;90℃处理2min,可使酶完全失活;PPO催化的酶促褐变反应动力学符合米氏方程,动力学参数为Km=0.0207mol/L,Vmax=41.32U/min;7种金属离子对PPO酶活性的影响效果各不相同,Al3+、Mn2+对PPO酶活性有一定的抑制作用,Mg2+、Zn2+、Ca2+和Cu2+对PPO酶活性的抑制作用不明显,Fe3+对PPO酶活性有激活作用;抗坏血酸、柠檬酸、L-半胱氨酸和亚硫酸钠对PPO酶活性的抑制作用均随浓度的增大而加强,抑制能力由强到弱依次为:抗坏血酸＞亚硫酸氢钠＞L-半胱氨酸＞柠檬酸.     

八角莲多酚氧化酶的酶学性质

以邻苯二酚为底物,研究八角莲多酚氧化酶（polyphenol oxidase,PPO）粗提液的酶学特性。结果表明,底物邻苯二酚最适浓度为1.0 mol/L,八角莲PPO的最适pH值为7.0,最适温度为30 ℃,90 ℃高温处理10 min,八角莲PPO酶活力仅剩11.92%。PPO催化的酶促褐变反应符合米氏动力学方程,相应动力学参数Km和vmax分别为0.230 7 mol/L和769.23 U/min。抗坏血酸、甘氨酸、乙二胺四乙酸、柠檬酸对酶活性具有抑制作用,十二烷基硫酸钠表现出激活作用,亚硫酸氢钠对酶活性的抑制作用强于硫代硫酸钠,Al3+和Cu2+对酶活性具有一定的激活作用,Ca2+对酶活性有一定的抑制作用,Mg2+、Fe2+和Fe3+对酶活性影响不显著。     

银杏外种皮多酚氧化酶的研究

采用不同条件抽提银杏外种皮多酚氧化酶(简称PPO),比较抽提条件对PPO活性的影响;利用乙醇分级法对PPO进行初步分离纯化,比活力从49.8u/mg提高到292u/mg;研究pH、温度、金属离子对乙醇分级提纯后的PPO的影响,发现其最适温度为30℃,最适pH=7.6,Mg2+对酶有明显的激活作用。而Na+、K+、Fe2+则对酶有抑制作用。     

曹州木瓜多酚氧化酶的酶学特性

以邻苯二酚为底物,采用分光光度法对曹州木瓜多酚氧化酶(PPO)的酶学特性进行了研究。结果表明:曹州木瓜PPO的最适pH为5.0,最适温度为30℃;PPO在60⁹0℃内的热失活曲线具有双相特征,活化能Ea=112.95 kJ/mol;PPO催化的酶促褐变反应动力学符合米氏方程,且相应动力学参数为K m=6.92 mmol/L,V max=769.23 U;5种抑制剂对PPO的抑制效果从大到小依次为:亚硫酸氢钠>抗坏血酸(Vc)>L-半胱氨酸(Lcys)>柠檬酸>EDTA-2Na;Na+和K+对PPO活性的影响不明显,Al3+、Ba2+、Cu2+对PPO具有抑制作用,Mg2+、Mn2+、Ca2+在低浓度(1 mmol/L)时对PPO具有激活作用,高浓度(10 mmol/L)时具有抑制作用。     

槟榔芋多酚氧化酶的酶学特性研究

以邻苯二酚为底物,采用分光光度法研究p H、温度、底物浓度对槟榔芋多酚氧化酶(PPO)活性的影响,建立相应的酶促褐变反应动力学方程,并探讨抗坏血酸、L-半胱氨酸、甘氨酸、尿素、Cu Cl2对PPO活性的影响。研究结果表明,槟榔芋PPO的最适p H为6.5;最适温度为35℃;在20℃和30℃时在60 min之内槟榔芋PPO保持较稳定的活性,30℃~60℃处理破坏PPO部分活性,70℃加热10 min PPO活性接近零;在最适作用条件下,槟榔芋PPO的酶促褐变反应动力学符合米氏方程,且相应动力学参数为Km=54.05 mmol·L-1,Vmax=588.24 U·min-1。抗坏血酸、L-半胱氨酸可抑制槟榔芋PPO活性,当它们浓度分别为2.5 mmol/L和6 mmol/L时,可有效抑制槟榔芋PPO活性,而甘氨酸对槟榔芋PPO活性无抑制作用;尿素、Cu Cl2可增强槟榔芋PPO活性,当它们浓度分别为150 mmol/L和1 mmol/L时,可明显提高槟榔芋PPO活性。     

莲子多酚氧化酶的酶学性质

以新鲜莲子为原料制备莲子多酚氧化酶(Polyphenol Oxidase,PPO)粗酶液,探讨莲子PPO酶学性质。结果表明:莲子PPO的活性最适温度范围为45~50℃、活性最适pH范围为6.5~7.0,即中性时PPO的稳定性最高;而金属离子对其活性的影响显示出Ca2+、Mn2+、Fe3对莲子PPO酶活性具有一定的促进作用,铜离子则表现出较强的抑制作用;还原剂亚硫酸氢钠和亚硫酸钠对莲子PPO酶活性都有抑制作用。本研究旨在为有效抑制鲜莲褐变提供理论依据。     

“黑美人”马铃薯多酚氧化酶的特性研究

以邻苯二酚为底物,在413nm处测定黑美人马铃薯多酚氧化酶(PPO)的活性,研究了温度、pH、底物浓度对其活性的影响,并建立了酶促褐变反应动力学方程,探讨了L-半胱氨酸、抗坏血酸、柠檬酸、EDTA及亚硫酸氢钠五种抑制剂对酶促褐变的抑制效果。结果表明:黑美人马铃薯多酚氧化酶最适反应pH为6.3;最适反应温度为35℃;酶促褐变反应动力学符合米氏方程描述的单底物酶促反应动力学,以邻苯二酚为底物,Km=0.0011mol/L,Vmax=142.23U/min.g;动力学方程为V=142.23[S]/(0.0011+[S]);五种抑制剂均对PPO酶促褐变具有抑制作用,其强弱依次为亚硫酸氢钠>L-半胱氨酸>抗坏血酸>EDTA>柠檬酸。     

毛酸浆多酚氧化酶的酶学特性研究

以毛酸浆中多酚氧化酶(PPO)为研究对象,采用分光光度法在420nm处对其酶学特性进行研究。结果表明,毛酸浆PPO的底物邻苯二酚的最适质量分数为0.04%;最适pH为7.0;最适温度为35℃;100℃处理2min,可使酶完全失活;PPO催化的酶促褐变反应动力学符合米氏方程,动力学参数为Km=0.025mol/L,Vmax=125U/min;抗坏血酸、柠檬酸、L-半胱氨酸和亚硫酸钠对PPO酶活性的抑制作用均随浓度的增大而加强,抑制能力由强到弱依次为:抗坏血酸柠檬酸L-半胱氨酸EDTA亚硫酸氢钠。     

粗糙脉孢菌木聚糖酶酶学性质的研究

对粗糙脉孢菌木聚糖酶粗酶的酶学性质进行了研究,结果表明:该木聚糖酶的最适反应温度50℃、pH值为5.8,温度低于50%、pH 4.6～7.4时该酶稳定性较好;金属离子Ca2+、Mg2+、Mn2+、Fe2+对该酶的活性有促进作用,K+、Na+、Pb2+、Cu2+、Fe3+、Al3+对酶的活性有抑制作用;EDTA、SDS、DMSO对该酶活性的抑制作用较小;以木聚糖为底物的酶动力学常数Km和Vmax值分别为1.30g/L和1.35μmol/(min·mL).     

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