白地霉脂肪酶固定化及其催化光皮树油合成生物柴油的研究

本文采用响应面分析法对树脂NKA-Ⅱ固定脂肪酶的条件进行优化,并对其酶学性质和在催化光皮树油合成生物柴油中的操作稳定性进行了简单的探讨。首先通过单因素试验研究酶液/载体比、温度、缓冲液pH值等条件对固定化脂肪酶酶活力的影响,在此基础上,利用响应面试验设计对树脂NKA-Ⅱ固定化脂肪酶的条件进行优化,用制备的固定脂肪酶催化光皮树油和甲醇反应合成生物柴油。结果表明：酶液/载体比、温度和缓冲液pH值对固定化酶的活力都有影响,树脂NKA-Ⅱ固定化脂肪酶的最佳固定条件是：酶液/载体比为4∶1、温度为39℃、缓冲液pH值为7.5,固定化脂肪酶湿重活力高达216.2±4.5U/g,生物柴油转化率达90%以上。将响应面法应用于树脂NKA-Ⅱ固定化脂肪酶条件的优化是可行的,制备的固定脂肪酶具有工业化生产的潜力。     

催化大豆油脱臭馏出物甲酯化的脂肪酶固定化研究

大豆油脱臭馏出物酶法酯化提取天然VE技术绿色经济,具有理想应用前景。为此,开展了针对催化脱臭馏出物脂肪酸酯化的国产树脂吸附固定化脂肪酶的研究。选用弱极性大孔树脂AB-8作为载体,固定的脂肪酶具有较强的酯化活性与较低的水解活性。在固定化条件单因素试验的基础上,应用Plackett-Burman试验筛选出缓冲液pH值、固定化温度和时间为显著影响因素,通过响应面法优化,AB-8树脂固定化脂肪酶的适宜工艺为：缓冲液pH 7.3、固定化温度25 ℃、时间4 h、酶量50 mg/g树脂、吸附振荡速率150 r/min,得到的固定化酶水解活力为112.4 U/g。应用于催化大豆油脱臭馏出物脂肪酸甲酯化试验,固定化酶催化效果优于游离酶,游离脂肪酸酸值降低88.3%,重复利用3次,酸值降低仍达85%以上,具有实际应用价值。     

用于丁酸香叶酯合成的褶皱假丝酵母脂肪酶固定化

对褶皱假丝酵母脂肪酶（Candida rugosa lipase,CRL）固定化进行研究,采用吸附法将CRL固定在4种不同树脂上,采用考马斯亮蓝法测定酶蛋白在树脂上的固定化率,GC测定催化合成丁酸香叶酯的酯化率,筛选出固定化效果最好的弱酸性大孔阳离子交换树脂D151。采用单因素实验考察酶液浓度、磷酸盐缓冲液pH值以及固定化温度对固定化效果的影响,以固定化酶催化合成丁酸香叶酯的酯化率为指标,优化固定化过程。结果表明,CRL经树脂D151固定后,在酶液质量浓度15 mg/mL,磷酸盐缓冲液pH 6.5,固定化温度45 ℃条件下,吸附8 h,固定化酶具有最高的催化性能,丁酸香叶酯的酯化率可达84%。     

脂肪酶固定化工艺优化及其酶学性质研究

以D-101、AB-8和S-8三种大孔树脂为载体,进行黑曲霉脂肪酶的固定化研究。根据脂肪酶的固定化率及活力回收率,确定D-101为固定化载体。经响应曲面法优化得脂肪酶的固定化工艺:以5 g经预处理的D-101为载体,加入9.0 m L酶液(20 mg/m L),p H 7.6,39℃下吸附4.3 h,脂肪酶固定化率为95.11%,固定化脂肪酶活力回收率为101.36%。固定化酶最适反应温度升高2℃,最适p H不变,固定化脂肪酶的酸碱稳定性和热稳定性均优于游离酶。     

响应面法优化脂肪酶的固定化条件及其水解橄榄油的特性研究

采用Sepharose CL-4B和7种大孔树脂为载体固定Palatase 20000L脂肪酶,对载体进行筛选,以酶活力为指标,采用响应面法优化固定化条件,并考察所制得固定化酶的稳定性和水解橄榄油的酶学性质。结果表明：以大孔树脂HPD-600为载体制得的固定化酶具有较高的活性和良好的稳定性。其最优的固定化条件为：pH3.9,酶与载体比例为9.1mg/g,吸附时间1.8h。在最优条件下制得固定化酶在最适合条件下测得的酶活力达到1440U/g,酶活回收率大于50%。固定化酶最适作用温度为50℃,最适作用pH值为8.0。固定化酶的Km值为0.130g/mL,高于游离酶的Km(0.069g/mL)。固定化酶的热稳定性有一定程度的提高,其重复操作5次后相对酶活力仍保持在58%以上。     

醋酸纤维素-聚四氟乙烯复合膜固定化脂肪酶的研究

以醋酸纤维素(CA)和聚四氟乙烯(PTFE)为材料制备醋酸纤维素-聚四氟乙烯复合膜,采用吸附-交联相结合的固定化方法,用该复合膜固定化脂肪酶。研究温度、吸附时间、酶液质量浓度、交联时间和交联剂体积分数对脂肪酶固定化效率和催化效果的影响,并对固定化酶膜的酶学性质进行研究。得到最佳的固定化条件为：温度25℃、吸附时间2h、酶液质量浓度0.02g/mL、交联时间3h、交联剂(戊二醛)体积分数0.2%,固定化酶最大酶活力为17.2U/cm2。固定化酶膜的酶学性质为：最适温度35℃,比游离酶降低了5℃;最适pH8.5,与游离酶相比pH值向碱性偏移1.0;经10次(10h /次)重复使用后,固定化酶相对酶活力为55.5%。SEM结果显示CA-PTFE复合膜能较好的固定化脂肪酶。     

离子交换树脂固定化α-淀粉酶的研究

选择12种吸附和离子交换树脂对α-淀粉酶进行固定化,筛选出固定效果较好的D380大孔弱碱性丙烯酸系阴离子交换树脂为载体,通过先吸附后交联的方法固定化.通过实验对加酶量、交联剂浓度、吸附时间、吸附pH等能够影响固定化酶活力回收率的因素的研究和优化,得出较优的固定化条件为:戊二醛浓度0.1%、处理时间45min、加酶量3mg/g(蛋白量/载体)、酶液pH5.8、25℃、固定化处理时间为6～10h,获得的固定化酶活力可达80U/g(载体),并进一步对固定化后的酶学性质作了初步研究.     

PVA-SA-活性炭共聚物固定脂肪酶的研究

以聚乙烯醇(PVA)-海藻酸钠(SA)-活性炭共聚物为载体,对脂肪酶进行固定化.研究了活性炭浓度、酶初始浓度、缓冲液pH值、吸附时间及温度对固定化酶的活性及蛋白载量的影响.结果表明:在聚乙烯醇(PVA)-海藻酸钠凝胶中加入1 g/dL活性炭制成复合凝胶球,在25 ℃、pH值5.5的条件下对30 mg/mL的酶液吸附12 h,所得吸附固定化脂肪酶的活性较好.吸附固定的脂肪酶较游离酶的最适作用温度升高10 ℃,最适作用pH范围变宽,且向碱方向偏移0.2个单位.     

离子交换树脂吸附法固定化脂肪酶的研究

以D311离子交换树脂为载体,通过离子交换吸附法对Lipolase100L脂肪酶进行了固定化。采用考马斯亮蓝法测定了酶蛋白在离子交换树脂上的吸附率,考察并得到了酶固定化的最佳条件：在pH10缓冲液下,加酶液量为每克预处理过的树脂加入1.5mL,吸附时间为10h,吸附温度为35℃。所得固定化酶用于催化合成月桂酸月桂醇酯,在反应物质的量比为1∶1时,水质量分数为8%,在50mL异辛烷有机溶剂中固定化酶用量为200mg,反应时间为210min,温度为55℃的最佳条件下,酯化率可达91.3%。     

固定化脂肪酶的制备及其酶学性质的研究

以大孔树脂为载体进行脂肪酶的固定化,通过优化固定化条件得到高活性固定化脂肪酶并对其酶学性质进行研究。结果表明:弱碱性大孔阴离子交换树脂D301R是最佳的固定化载体;最优固定化条件为加酶量10%(以大孔树脂质量计),加水量30%(以大孔树脂质量计),4℃下在异辛烷中固定5 h。与游离脂肪酶相比,固定化脂肪酶具有良好的热稳定性、储存稳定性、吸附稳定性和对有机溶剂的抗逆性,循环使用6次,水解橄榄油的酶活回收率仍可达到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.     

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.     

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.     

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.     

Contribution of European research to risk analysis

The European Commission's, Quality of Life Research Programme, Key Action 1—Health, Food & Nutrition is mission-oriented and aims, amongst other things, at providing a healthy, safe and high-quality food supply leading to reinforced consumer confidence in the safety of European food. Its objectives also include the enhancing of the competitiveness of the European food supply. Key Action 1 is currently supporting a number of different types of European collaborative projects in the area of risk analysis. The objectives of these projects range from the development and validation of prevention strategies including the reduction of consumers risks; development and validation of new modelling approaches; harmonization of risk assessment principles, methodologies, and terminology; standardization of methods and systems used for the safety evaluation of transgenic food; providing of tools for the evaluation of human viral contamination of shellfish and quality control; new methodologies for assessing the potential of unintended effects of genetically modified (genetically modified) foods; development of a risk assessment model for Cryptosporidium parvum related to the food and water industries; to the development of a communication platform for genetically modified organism, producers, retailers, regulatory authorities and consumer groups to improve safety assessment procedures, risk management strategies and risk communication; development and validation of new methods for safety testing of transgenic food; evaluation of the safety and efficacy of iron supplementation in pregnant women; evaluation of the potential cancer-preventing activity of pro- and pre-biotic ('synbiotic') combinations in human volunteers. An overview of these projects is presented here.     

低温带皮菜籽粕微粉的不同粒级部分的功能特性

为研究低温带皮菜籽粕微粉的不同粒级部分的功能特性,以经低温脱脂的带皮菜籽粕为原料,经微粉碎后筛分成212~425μm、150~212μm和106~150μm的3个不同粒级的微粉样品,检测这些样品的吸水性、吸油性、乳化性和乳化稳定性、蛋白质体外消化率。结果表明:1 3个不同粒级的微粉样品之间的粗纤维含量存在显著差异,表明三者的结构组成成分有一定差异。23个微粉样品的乳化活性和乳化稳定性随粒度级别的减小而显著增加(P0.01)。33个微粉样品的蛋白质体外消化率随粒度级别的减小而显著增加(P0.01)。4不同粒级带皮菜籽粕微粉样品的吸水性与吸油性受其结构组成物质不同和粒度的双重影响,与粒度的相关性不明显。     

Microbiology of food taints

Fresh and processed foods are often spoilt by the presence of undesirable flavours and odours caused by microbial action. The aim of this paper is to review the current knowledge of microbiologically induced taints that occur in a wide range of foodstuffs, including meats, poultry, fish, crustaceans, milk, dairy products, fruits, vegetables, cereals and cereal products. Examples have been chosen where the compounds responsible for the taint have been identified and sufficient data obtained to demonstrate the involvement of microorganisms. However, in some cases the full identity of the causative organism may not have been elucidated. The types of microorganisms covered by this review include bacteria, fungi, yeasts, actinomycetes and cyanobacteria. Although cyanobacteria do not in general infect foods, their presence in aqueous systems and water supplies can lead to off-flavours in aquatic organisms and processed foodstuffs. Several examples of each of these processes are discussed. Wherever possible, the likely biosynthetic pathway used by the microorganism to produce the offending compound in a foodstuff is indicated.