N-甲基咪唑硫酸氢盐蒸煮麦草浆中木糖和葡萄糖含量的变化

利用N-甲基咪唑硫酸氢盐在离子液体中蒸煮麦草进行制浆,在20 g绝干麦草,离子液体与麦草质量比为6:1的条件下,研究制浆过程中木糖和葡萄糖的变化规律和趋势。结果表明:较短时间和较低温度下戊糖和葡萄糖呈增长趋势,有利于戊糖和葡萄糖溶出;较长时间和较高温度下木糖和葡萄糖呈递减趋势,有利于木糖和葡萄糖进一步水解。     

选择性水解工艺提取蔗髓L-阿拉伯糖的研究

用热水处理蔗髓,通过控制水解温度使L-阿拉伯糖选择性水解以利于L-阿拉伯糖的提取。考察了温度、水解时间及液比对蔗髓水解产出L-阿拉伯糖、木糖及葡萄糖的影响。采用高效液相色谱法对水解液中的单糖含量进行了检测,结果表明:温度对水解液组分的影响最为显著,当温度较低(≤140℃)时,L-阿拉伯糖有明显溶出,而木糖与葡萄糖溶出很少甚至不溶出;当温度超过160℃,木糖产率大于L-阿拉伯糖与葡萄糖;在较低温度下延长保温时间能够使L-阿拉伯糖有较大量溶出,同时木糖及葡萄糖溶出很少。实验得到蔗髓水解提取L-阿拉伯糖的适宜条件为:水解温度140℃,保温时间3h,液比1∶10,此时L-阿拉伯糖的产率为1.40%,木糖、葡萄糖未检出。     

相思木水预水解过程中半纤维素的溶出和解聚

在不同的水解温度和时间下对相思木进行水预水解处理,采用离子色谱分析了水解液中单糖和低聚糖含量以及水解物料中葡萄糖和木糖保留率,以研究水预水解温度和时间对相思木半纤维素水解溶出和解聚行为的影响。结果表明,水预水解温度170℃、水解60 min时,水解液中总低聚糖含量达到最大值17.29 g/L,其中低聚木糖含量为12.45 g/L;水预水解温度170℃、水解80 min时,水解液中总糖含量达到最大值25.86 g/L。水解液中总低聚糖和总糖含量达到最大值后,再提高水解温度和延长水解时间,虽然可提高原料中半纤维素溶出量,但水解液中总低聚糖和总糖含量降低。     

酸催化水解处理甘蔗叶提取木糖的研究

为了从蒸汽爆破预处理后得到的甘蔗叶中提取木糖,采用酸催化水解法处理甘蔗叶研究了提取木糖过程中各因素对木糖溶出量的影响。结果表明,木糖得率随硫酸浓度先增大后减小,随液料比增大而增大,随反应时间延长先增大后减小,随水解温度增高,先增大后减小。最佳酸解工艺条件是,硫酸浓度2%,反应时间2 h,反应温度100℃,液料比是11:1(v/w)。     

麦草热水预水解过程产物分析及木糖生成模型

为了探究麦草热水预水解过程中产物的生成变化规律,分别采用离子色谱和高效液相色谱检测预水解液中糖类(阿拉伯糖、半乳糖、葡萄糖和木糖)和发酵抑制物(甲酸、乙酸、5-羟甲基糠醛和糠醛)的含量,分析了单因素实验中糖类和发酵抑制物的生成变化规律;同时采用响应面法对影响麦草热水预水解液中木糖生成的固液比、水解温度和水解时间进行了优化研究,建立了木糖生成量的二次多项式数学模型。结果表明,在固液比1∶11.67、水解时间57.76 min和水解温度173.96℃的条件下,木糖的生成量达到最高,为83.91 mg/g麦草。     

亚硫酸盐预处理对麦草组分分离和糖化的影响

通过正交实验设计,研究了亚硫酸盐预处理对麦草组分分离和糖化的影响,所考虑的主要因素是预处理温度、保温时间、亚硫酸氢钠用量及硫酸用量,极差分析结果表明这四个因素均影响麦草的糖化效率。升高温度、增加亚硫酸氢钠用量和硫酸用量、延长保温时间均能增加麦草的糖化效率,同时促进原料中木素和戊聚糖的溶出,但也会使戊糖发生进一步的转化。从原料中溶出戊聚糖和木素是麦草糖化效率提高的重要原因。在预处理温度180℃、亚硫酸氢钠用量3%、硫酸用量1.48%和保温时间20min条件下,酶水解后纤维素转化率为90.9%。     

热水预处理过程中P因子对杨木半纤维素溶出效果的影响

制浆前对生物质原料进行热水预处理,可以有效地提取半纤维素,这对于生物质高值化利用具有重要意义。本实验研究了不同工艺条件下杨木热水预处理过程中半纤维素糖类组分的溶出规律以及酸溶木素、乙酸和醛类物质随预水解因子(P因子)的变化规律。结果表明,在热水预处理过程中,P因子较适宜的范围是685~1225,此范围内杨木中的半纤维素糖类能够较好地溶出,总木糖溶出率高达51.8%,预水解液中木糖、酸溶木素、乙酸、糠醛等含量与P因子的增加成正比,而低聚合度聚木糖(聚合度2~25)含量随P因子的增加先增加后降低。当P因子在717时,水解液中低聚合度聚木糖含量达最大值10.24 g/L,此P因子下原料中总木糖溶出率为44.2%,而且酸溶木素、乙酸、糠醛等非糖类物质含量较低,这有利于后续低聚合度聚木糖和木糖的分离提取生产功能性低聚木糖产品。     

超声波处理玉米芯制备低聚木糖的条件优化

考察了试验室规模下超声波处理玉米芯提取木聚糖经酶水解制备低聚木糖的影响因素,通过单因素试验和正交试验,优化了提取和水解条件。结果表明:以质量分数5%Na OH溶液为提取剂,超声功率为180 W,超声温度为60℃的条件下提取45 min,木聚糖产率可达到33.18%。所得提取液经脱色,调p H,调木聚糖底物浓度后酶水解制备低聚木糖。最佳酶解条件为:木聚糖底物质量浓度10 mg/m L,加酶量质量分数1.5%(相对于玉米芯干物料),酶水解时间为8 h的条件下,水解液中还原糖的质量浓度达到6.89 mg/m L。     

毛竹渣中提取木糖的水解工艺研究

对从毛竹渣中提取木糖的水解工艺进行了研究,在单因素实验和正交实验的基础上,得到最佳水解条件:水解温度120℃,水解硫酸浓度1.2%,水解时间3h,水解料液比1∶6,木糖收率21.56%。     

粉单竹热水预抽提过程碳水化合物的变化规律

本文以粉单竹为原料,在水解温度90~150℃、时间40~100min、液比1∶4~1∶7范围内研究了热水预抽提过程碳水化合物的变化规律。结果表明:当水解温度为150℃、保温时间为100min、液比为1∶4时,水解液中木糖的溶出率为0.471%、葡萄糖的溶出率为1.315%、阿拉伯糖的溶出率为0.224%、半乳糖的溶出率为0.150%、甘露糖的溶出率为0.023%。热水预抽提过程中粉单竹的半纤维素容易溶出,主要单糖是木糖,还有相当含量的葡萄糖、阿拉伯糖,其次是半乳糖和甘露糖。温度的变化是影响主要糖组分溶出率的主要因素,其中对葡萄糖的影响最大,极差达到0.956;而固液比对糖溶出率的影响最小,特别是甘露糖,极差只有0.002。因此在热水预抽提过程中应该严格控制预抽提温度,以达到在短时间、小液比内半纤维素溶出、减少纤维素降解的目的。     

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.