鹰嘴豆蛋白酶解动力学研究

从酶解反应机理出发,应用数学推导的方法,以鹰嘴豆蛋白为原料,考察底物浓度、酶浓度对鹰嘴豆蛋白水解度（DH）的影 响,将水解试验结果用推导的动力学模型方程进行拟合,建立酶解动力学模型。 结果表明：鹰嘴豆蛋白水解度随着初始底物浓度（S0） 的上升而下降,随着初始蛋白酶浓度（E0）的增加而上升,碱性蛋白酶水解鹰嘴豆蛋白的速率动力学模型：R=(39.522E0-0.080 4S0)exp [-0.148(DH)],水解度-水解时间的动力学模型：DH=6.76ln[1+(5.85E0/S0-0.011 9)t],酶解反应速率常数k2为39.522 min-1,酶失活常数为 6.371 min-1,该动力学模型对试验结果有很好的拟合度,对实际酶解过程具有一定的指导作用。     

碱性蛋白酶酶解梭子蟹蛋白动力学模型研究

对梭子蟹蛋白的酶解动力学机制进行研究,建立碱性蛋白酶酶解梭子蟹蛋白的动力学模型。结果表明：在温度55℃、pH8.5 条件下,水解度随着初始酶浓度的增加而上升,随着初始底物浓度的上升而下降;水解动力学模型为：水解度(DH)＝ 3.558ln[1 ＋(2.553E0/S0+0.116)t],验证实验证明,模型得到的理论DH 值与实际DH 值基本吻合,该动力学模型具有一定的实用价值。     

荞麦蛋白的碱性蛋白酶酶解动力学研究

为掌握碱性蛋白酶对荞麦蛋白的酶解特性,实现对荞麦蛋白的深加工利用及生物活性肽的开发.采用pH-stat法,系统分析了底物浓度、酶浓度、pH及温度对荞麦蛋白水解度的影响,并运用对数函数对水解动力学过程进行描述和拟合.结果表明:在碱性蛋白酶水解荞麦蛋白的过程中,水解度随水解时间的变化呈现对数函数关系,可用公式h=(1/b)ln(1+abt)对其水解动力学过程进行描述;底物具有促进水解反应速度和抑制酶活性的双重作用,在低底物浓度条件下,荞麦蛋白的水解度较高;当底物浓度增加到6%时,蛋白水解度与底物浓度的关系曲线出现转折,水解度较低且趋于平缓;在酶浓度为0.002 g/mL时,水解反应的临界底物浓度为12.27%;在pH9.8、水解温度为50℃、水解时间30 min的条件下,碱性蛋白酶催化水解荞麦蛋白的动力学方程为h=1.218 2 ln(1+12.6([E]/[S]+0.58)t)     

碱性蛋白酶酶解青稞蛋白质的动力学研究

为深入了解与调控碱性蛋白酶水解青稞蛋白过程,准确控制其水解程度,获得定向肽组成的酶解产物。采用碱性蛋白酶在温度55℃、pH10.0条件下酶解青稞蛋白,分析酶浓度、底物浓度对青稞蛋白水解度的影响,并建立可控酶解动力学方程。结果表明:青稞蛋白水解度随着初始底物浓度S_0的上升而下降,随着初始蛋白酶浓度E_0的增加而上升,水解速率随着水解时间的延长而下降。模型的验证结果显示,预测值与实测值基本吻合,通过对E_0/S_0、反应时间的调节可有效控制水解程度,为利用酶解制备青稞活性肽的产业化实践提供指导。     

碱性蛋白酶Alcalase酶解大米蛋白制备小分子肽的动力学研究

以大米蛋白为原料,用碱性蛋白酶Alcalase2.4 L酶解大米蛋白制备小分子多肽。采用单因素试验方法优化酶解条件,考察酶解过程中pH、加酶量、底物浓度和温度酶解初速度的影响,并建立了酶解动力学方程。研究了最优酶解条件下酶解过程中酶解产物的分子量分布状态。结果表明,Alcalase2.4 L酶解大米蛋白的最优pH 8.5、温度65℃、酶底比0.096 AU/g(底物),在酶解过程中存在产物抑制,在研究的底物浓度范围内(90 g/kg)不存在底物抑制。主要动力学参数为:Km为5.76(g·min)/mmol,Vmax为0.67mmol/(kg·min),k2为0.28 mmol/(AU·min)。酶解动力学方程为:1/V0=56.29/[S0][E0]+1/0.28[E0]。酶解至3 h时水解度达到16%,酶解产物的分子量在264~584 u之间的组分达到94%,酶解3 h后酶解产物的分子量分布基本保持不变。本研究结果为制备大米蛋白小分子活性肽奠定基础。     

风味蛋白酶水解菜籽蛋白中2S和12S条件的优化

通过单因素试验和正交试验,研究了风味蛋白酶对菜籽蛋白中2S(RP-2S)和12S(RP-12S)的水解条件。结果表明,水解RP-2S的最佳酶解条件为底物浓度1%,酶与底物浓度比(E/S)95LAPU/g,酶解温度50℃,pH 7.0,酶解时间3 h,此条件下RP-2S的水解度达33.64%;水解RP-12S的最佳酶解条件为底物浓度1%,酶与底物浓度比(E/S)85 LAPU/g,酶解温度50℃,pH 6.6,酶解时间3 h,此条件下RP-12S的水解度达19.97%。     

Bacillus cereus胞外胶原蛋白酶水解牛骨胶原蛋白的动力学

针对从细菌蜡样芽孢杆菌(Bacillus cereus)MBL13中提取得到的胶原蛋白酶酶解牛骨胶原蛋白的动力学性质进行研究。考察底物质量浓度、时间、温度、酶质量浓度、pH值5个因素对酶解水解度的影响,优化酶解的条件;并对酶解过程的动力学进行分析。结果表明:最佳的酶解工艺参数为底物质量浓度30g/L、时间6h、温度45℃、初始酶液质量浓度为0.35g/100mL、pH8.0。在此基础上推导出酶解动力学方程为:V=9.3633[S]/(114.785+[S])。并在波长230nm和570nm处对酶解过程动态变化进行测定,表明胶原多肽含量不断增加的动态变化。     

碱性蛋白酶酶解绿豆蛋白制备低聚肽工艺优化

采用碱性蛋白酶酶解绿豆蛋白,通过单因素试验方法优化酶解条件,经测定水解度考察了酶解过程中p H、温度、底物浓度[S]、酶用量[E/S]、酶解时间等因素对绿豆蛋白酶解效果的影响。通过L_9(3~4)正交试验设计,确定碱性蛋白酶酶水解的最适反应条件为:pH 8.5,温度65℃,底物浓度9%,酶用量5%,水解时间240 min。该条件下绿豆蛋白的水解度可达31.55%。     

碱性蛋白酶水解制备赤豆蛋白肽的工艺研究

本文主要利用碱性蛋白酶水解赤豆蛋白制备赤豆蛋白肽,研究各因素对酶水解反应的影响,并通过正交试验对pH值、酶解时间、酶用量（E/S）、底物浓度等参数进行了优化。确定了适宜反应条件为：E/S为8%,pH值9.0,底物浓度为4%,酶解时间为4h,酶解温度为55℃,在此条件下测得水解度为45.82%。     

核桃蛋白最佳酶解条件研究

以水解度为指标,研究五种蛋白酶对核桃蛋白水解作用;结果表明,AS.1398中性蛋白酶为水解核桃蛋白最佳酶,最佳酶解条件为:底物浓度2.5%,E/S为7%,温度40℃,pH7.5,酶解3h;在该实验条件下,AS.1398中性蛋白酶酶解核桃蛋白水解度可达45.37%,水解液仅微苦。     

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.     

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.     

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.     

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.     

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.     

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.     

Influence des ions sur le pouvoir hydratant de l'ure e: e tude sur peau de porc ex vivo

This study deals with the influence of ions (NaCl and MgSO4) in a W/O emulsion containing 10% urea. Moisturization kinetics are assessed by corneometry on pig skin ex vivo. The formula's influence on urea penetration is measured by infrared spectrometry with an ATR device and the stripping method. Corneometry and spectroscopy were chosen to record simultaneously the hydratation levels and urea localization into superficial cell layers. Urea crystallization after evaporation of emulsions and aqueous solutions is described. Results show that urea does not hydrate nor penetrate when applied to the skin through an aqueous gel. In a W/O emulsion, sodium chloride increases the ability of urea to moisturize without improving penetration. In vitro urea crystallization is disturbed by sodium chloride or magnesium sulphate for solutions and emulsions. This stabilization by ions is correlated with good moisturization values. The stabilization of urea in the solute state provided by ions increases its water epidermal binding capacity without enhancing penetration.     

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.