木质素模型化合物在Co-salen型仿酶降解体系中的结构变化

用由Co-8alen、吡啶、H2O2、O2组成的Co-salen型仿酶体系对β-O-4型木质素模型化合物--愈创木基丙三醇-β-愈创木基醚进行仿酶降解,并用GC-MS等方法分析β-O-4型木质素模型化合物在降解过程中的结构变化,并在此基础上初步探讨了Co-salen型仿酶体系对木质素的降解机理.结果表明:Co-saJen型仿酶体系埘β-O-4型木质索模型化合物有较强的降觯能力,降解后产生一系列含羟基、醛基和羧基的芳香族低分子化合物,根据反应产物的结构可以说明β-O-4型木质素模型化合物的主要降解途径为β-O-4醚键、Cα-Cβ键、烷基-芳基键的断裂和苯环开环反应等.     

玉米秸秆酶解木质素及麦草甲酸木质素在钙钛矿催化体系下催化活性比较

考察了玉米秸秆高温爆破法制浆酶解木质素(EL)以及麦草甲酸木质素(SL)在LaMn0.8Cu0.2O3催化体系下催化湿法氧化为芳香醛反应中的活性差异。结果表明:该催化剂对麦草甲酸木质素的对羟基苯甲醛、香草醛、紫丁香醛的最大得率分别提高33%、65%、48%,最大得率分别达到0.56%、2.97%、4.91%;而玉米秸秆酶解木质素分别相应提高85%、57%、208%,最大得率分别达到2.90%、5.07%、14.6%。同时发现麦草甲酸木质素无论在无催化反应还是该催化体系下各芳香醛的得率均远低于玉米秸秆酶解木质素,其原因是麦草甲酸木质素发生了严重缩合,而玉米秸秆酶解木质素接近原始木质素,未发生缩合反应。     

麦草甲酸法制浆木素结构及分子质量变化

本研究采用甲酸法蒸煮麦草,首先对蒸煮废液的物理化学性质进行检测,分别对残余木素及溶出木素进行红外谱图分析,探讨木素在蒸煮过程中的结构变化通过凝胶渗透色谱(GPC)得出木素的分子质量分布及变化,并对其进行分析对比结果表明:25℃下废液黏度1.25mPa·s,有机物含量19.30g·L~(-1),占总固形物的82.8%,无机物含量4.18g·L~(-1);蒸煮过程中由于α-醚键或β-醚键断裂产生了较多的共轭和非共轭C=O基团,溶出木素含有较多的伯醇-OH和仲醇-OH,有利于木素的进一步加工利用;溶出木素的平均分子质量大于残余木素的平均分子质量,为甲酸法制浆的最佳工艺条件的确定提供理论参考,同时为未来麦草甲酸制浆法工业化提供借鉴     

有机溶剂法麦草木质素的化学特性研究

用不同浓度的乙酸-水、甲酸-乙酸-水、甲醇-水及乙醇-水溶液处理脱蜡的麦草,获得的木质素采用FT-IR、~1H-NMR、~(13)C-NMR及化学法研究其化学特性,结果表明,有机酸溶液比有机醇溶液脱木素作用更加广泛,能选择性降解麦草中的纤维素、木质素及半纤维素。甲酸对木质素的溶解有显著影响。随着乙酸或甲酸浓度的增加,愈创木基结构单元增加,木质素缩合。有机醇处理获得的木质素中,含有几乎等量的非缩合型愈创木基和紫丁香基结构单元及少量的对羟苯基结构单元。     

愈创木基型和紫丁香基型木素小分子的漆酶生物改性

从松柏醇、紫丁香醇模型物的角度人手,通过气相色谱-质谱联用(GC-MS)、凝胶渗透色谱(GPC)、红外光谱和颗粒电荷等测试手段,综合考察了漆酶对松柏醇、紫丁香醇生物改性的机理.松柏醇、紫丁香醇经漆酶处理后,GC-MS检测不到小分子单体的存在,推测两者都参与了化学反应.GPC分析证明,松柏醇和紫丁香醇漆酶处理后分子质量变大,发生了聚合.红外光谱确定了松柏醇漆酶处理过程中反应位点,主要是酚羟基、苯环上的甲氧基、苯环侧链上的双键,β碳、γ碳也有可能参与了反应,紫丁香醇反应位点是酚羟基、苯环上的甲氧基.产物苯环相应吸收峰强度和面积增加,有新的芳基醚键产生,说明苯环以醚键方式连接而聚合.漆酶处理后松柏醇、紫丁香醇阳离子需求量分别下降了88.4%,87.4%.     

麦草微波碱法制浆中木质素基团变化趋势研究

通过傅立叶变换红外光谱技术初步研究了碱法麦草蒸煮制浆中木质素的结构变化。通过不同微波辐射功率、温度、时间不同蒸煮制浆,分析黑液中木质素的红外谱图,可看出木质素中羟基溶出量均随着蒸煮温度、时间、功率的增加先增加后减少;随着温度升高,紫丁香基木质素和愈创木基型木质素的溶出量先增加后减少,在较短时间内,二者均大量溶出,而功率对二者溶出量影响较小,且可看出蒸煮温度、功率对木质素甲氧基溶出量在蒸煮过程中影响较小,时间较长时,木质素甲氧基溶出量增加;温度过高,时间过长,功率过大都会使木质素醚键发生断裂。     

蓝花楹磨木木素在硫酸盐法蒸煮过程中的降解及与多糖的缩合

提取蓝花楹磨木木素(MWL),并在木聚糖存在的条件下,模拟硫酸盐法蒸煮MWL。对MWL和蒸煮产物的酸不溶物进行FT-IR和13C-NMR分析,研究蓝花楹MWL的结构变化,探讨在硫酸盐法蒸煮产物中木素-碳水化合物复合体(LCC)的形成情况。研究发现:蒸煮产物中的酸不溶物含有碳水化合物,其中有大量木聚糖。蓝花楹MWL结构单元之间的α-芳基醚键、β-芳基醚键非常容易断裂,有新的LCC结构形成木素和碳水化合物间的连接在蒸煮过程中发生不完全降解。     

Co-salen型仿酶体系降解β-O-4型木素模型化合物的研究

为了研究Co—salen型仿酶体系对木素的降解机理,采用由Co—salen、吡啶、H2O2、O2组成的Co—salen型仿酶体系对β-O-4型木素模型化合物——愈创木基丙三醇-β-愈创木基醚进行仿酶降解的研究,并采用GC—MS等方法分析了该β-O-4型木素模型化合物在降解过程中的结构变化,在此基础上对这种仿酶体系降解的机理进行了初步探讨。研究表明：Co—salen型仿酶体系对β-O-4型木素模型化合物有较强的降解能力,降解后产生一系列含羟基、醛基和羧基的芳香族低分子化合物,根据反应产物的结构可以说明β型木素模型化合物的主要降解途径为：β醚键断裂、Ca—cp键断裂、烷基-芳基键的断裂和苯环开环反应等。本研究为该仿酶降解体系在无污染漂白工业上的应用提供理论依据。     

乙二醇抑制DES预处理过程中木质素缩合程度的研究

利用氯化胆碱/草酸和氯化胆碱/草酸/乙二醇2种低共熔溶剂（DES）体系预处理竹粉以分馏提取木质素,并通过多种表征手段探究木质素的结构变化。结果表明,在110 ℃反应180 min的条件下,氯化胆碱/草酸二元DES体系提取的木质素（二元DES木质素）中β-O-4芳基醚键的相对含量仅为0.26/Ar,氯化胆碱/乙二醇/草酸三元DES体系提取的木质素（三元DES木质素）此值则为0.43/Ar。同时,二元DES木质素中的缩合结构（β-β,β-5=3.11/Ar）及缩合的芳环C—C连接（Aromatic C—C=2.18/Ar）多于三元DES木质素（β-β,β-5=2.02/Ar,Aromatic C—C=1.99/Ar）。利用超声辅助三元DES体系预处理过程,发现反应20 min后木质素脱除率即可达76.0%。采用水相电位滴定法测定不同反应条件下的三元DES木质素的酚羟基和羧基含量;并提出乙二醇在三元DES体系预处理竹粉过程中抑制木质素缩合的机理,证实乙二醇与对香豆酸和阿魏酸反应生成了酯化的木质素结构。     

磨木木素在Cu-salen型仿酶降解体系中的变化

采用由Cu-salen、吡啶等组成的Cu-salen型仿酶体系对β-O-4型木素模型化合物和三倍体毛白杨磨木木素(MWL)进行仿酶降解的研究,并采用GC-MS等方法分析了该β-O-4型木素模型化合物和磨木木素(MWL)在降解过程中的结构变化。研究表明:Cu-salen型仿酶体系对β-O-4型木素模型化合物和磨木木素(MWL)有较强的降解能力,产生一系列含羟基、醛基和羧基的芳香族低分子化合物。根据反应产物的结构可以说明β-O-4型木素模型化合物的主要降解途径为β-O-4醚键断裂、Cα-Cβ键断裂、烷基-芳基键的断裂和苯环开环反应等。还有一部分MWL成为香草醛和香草酸等低分子化合物,这说明木素在侧链上受到氧化作用,使结构单元之间的连接键断裂。     

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.     

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.     

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.     

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.     

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.