黄原胶流变学特性及其协效性研究

研究了不同浓度的黄原胶溶液的黏度变化以及剪切速率和时间对其流变学特性的影响,此外还对黄原胶与瓜尔豆胶、CMC、果胶的协效性进行了研究.研究结果表明,黄原胶溶液的黏度值随浓度的增加而逐渐增大,对其进行线性回归得方程y=157.8x-182.07,其相关系数达到0.9838.触变性的测定发现,在升速过程中黄原胶的表观黏度随剪切速率的增加而逐渐降低,而在降速过程中,表观黏度有一定的回升,具有很明显的假塑性,并且能够形成触变环,不同浓度黄原胶溶液的黏度值都是随剪切速率的增加而逐渐减小,这些现象表明,黄原胶溶液是一种正触变性流体.此外还发现,黄原胶和瓜尔豆胶具有一定的协效性,当黄原胶同瓜尔豆胶的比例为9 ∶ 1时,表观黏度值达到最大,为768.2mPa.s.黄原胶与CMC、果胶无协效性.     

角蛋白/聚乙烯醇共混溶液流变行为研究

利用AR-1500ex锥板流变仪对角蛋白/聚乙烯醇共混溶液进行了稳态剪切扫描,对比分析了剪切速率、分子量、温度和共混比例对共混溶液流变行为的影响。结果表明,共混溶液的表观黏度随剪切速率的增加而逐渐降低;表观黏度随温度升高而降低,当温度高于50℃后,表观黏度趋于稳定;随着聚乙烯醇分子量的增加,表观黏度有增加的趋势;随着共混比例的增加,表观黏度有下降的趋势。实践表明,温度控制在50℃,剪切速率为100 s-1,共混比例不高于3∶7,共混溶液的可纺性良好。     

常用微胶囊壁材的分子结构及流变学特性研究

本文研究了五种壁材分子结构及其流变学特性。以喷雾干燥制备微胶囊的五种常用壁材变性淀粉、阿拉伯胶、明胶、大豆分离蛋白和羧甲基纤维素为研究对象,采用凝胶渗透色谱法(GPC)测定壁材的分子量分布;傅里叶变换红外光谱法(FT-IR)分析不同壁材的特征基团和蛋白类壁材的二级结构;旋转流变仪研究壁材的表观黏度、动态模量和蠕变柔量。研究结果表明:五种壁材溶液均呈现剪切稀化现象,随着温度的上升壁材溶液的表观黏度逐渐下降;壁材的弹性模量G'和黏性模量G'均随着振荡频率的增大而增大;相同时间下,壁材的蠕变柔量J(t)大小为:变性淀粉阿拉伯胶明胶羧甲基纤维素大豆分离蛋白;壁材分子量越大,表观黏度就越大;同一数量级分子量的壁材,分子量分布越宽,非牛顿"剪切稀化"现象越明显;分子结构越刚性,极性越大,表观黏度也越大。     

豆腐柴叶果胶的流变学性质研究

以混合酸超声微波协同萃取得到的豆腐柴叶果胶为研究对象,研究了果胶溶液的浓度、pH、钙离子浓度、蔗糖含量、不同处理温度、不同热处理时间对果胶溶液流变学性质的影响。结果表明:豆腐柴叶果胶溶液的黏度随剪切速率的增大而降低,表现为典型的非牛顿流体,偏酸或偏碱环境都会导致果胶溶液黏度下降,果胶溶液的黏度随钙离子添加量以及蔗糖含量的增加而增大,热处理一定时间后,果胶溶液表现出理想的牛顿流体性质。     

葛仙米多糖理化性质和流变学特性的研究

为研究葛仙米多糖的流变学特性,以室内培养的葛仙米为原料,通过水提醇沉法得到葛仙米多糖;采用MCR-302型旋转流变仪考察质量浓度、酸碱性、温度、V_C和H₂O₂对多糖溶液表观黏度的影响,探究多糖溶液在扫描频率范围内的动态黏弹性,来反映其流变学特性。结果表明:其多糖含量为96.95%、重均分子量为1.324×105 Da、由阿拉伯糖、半乳糖、葡萄糖、木糖、甘露糖及葡萄糖醛酸组成;葛仙米多糖溶液是假塑性非牛顿流体,具有剪切稀释的特性;溶液黏度随质量浓度的增大而增加;在20~80℃内,溶液黏度随着温度的升高而降低;溶液pH=3.0和pH=11.0时的黏度小于pH=7.0;V_C和H₂O₂可以降低多糖溶液的黏度;在扫描频率0.1~10 Hz内,储能模量(G')和损耗模量(G″)随葛仙米多糖溶液质量浓度的增加而增大。此外,葛仙米多糖与透明质酸具有协效增稠性。     

橙皮果胶流变学性质的影响因素

以采用离子交换树脂法从橙皮中提取的果胶为研究对象,研究浓度、温度、pH、金属离子Ca2+、糖、盐等对果胶流变性质的影响.结果表明:橙皮果胶溶液的黏度随剪切速率的增加而降低,为典型的非牛顿流体.这种剪切稀化现象受果胶溶液黏度的影响.随着果胶浓度的增大,浓度对果胶溶液流变学性质的影响增强.当热处理一定时间后果胶溶液黏度急剧下降直至表现出理想的牛顿流体性质;偏酸或偏碱环境下都导致果胶溶液黏度下降且碱性条件下降低更显著;果胶分子间疏水作用的增强使果胶溶液的黏度降低,共聚物之间氢键的形成受到抑制会使果胶溶液的黏度降低,较强的静电作用可以增强果胶网络结构的强度,使果胶溶液黏度升高.     

微波降解果胶对其流变性质的影响及动力学

对不同质量浓度(0.5、1.0、1.5、2.0 g/100 m L)的果胶溶液微波处理不同时间(0、1、3、5、8、15、20、30 min)后的流变性质及动力学进行考察。结果表明,随着果胶溶液质量浓度降低、微波处理时间延长、剪切速率增大,样品的表观黏度和特性黏度[η]均降低。用牛顿幂律方程描述溶液的流体行为,果胶溶液是剪切稀化的假塑性非牛顿流体,在低质量浓度时,微波处理对溶液的流体行为影响最大。根据特性黏度对样品进行反应动力学拟合,发现果胶的微波降解遵循反应一级动力学,在质量浓度0.5 g/100 m L时降解速率最快,质量浓度1.5 g/100 m L时降解速率最慢。经与沸水浴无微波的空白组对比,发现微波降解果胶的过程还存在非热效应。     

马铃薯果胶流变特性的研究

以马铃薯果胶(potato pectin extracted by chelating agent,PPCH)为研究对象,研究果胶溶液质量分数、剪切速率、温度、pH、金属离子等因素对马铃薯果胶流变学特性的影响。研究表明,PPCH溶液的黏度随溶液质量分数上升而增加。随着剪切速率的增大,PPCH溶液黏度下降,剪切变稀现象随着果胶质量分数的增加而更加明显,属于非牛顿流体。PPCH溶液流体行为受温度的影响。在剪切速率为50 s^-1时,温度10~47℃为时,PPCH溶液黏度随着温度升高而急速下降;温度为47~65℃时PPCH溶液黏度随着温度升高而缓慢波动,较难以用Arrhenius方程加以解释;温度为65~80℃时,PPCH溶液黏度随着温度升高而缓慢下降。在剪切速率为100、500 s^-1时,PPCH溶液黏度随着温度升高而缓慢下降。温度为10~47℃时,PPCH溶液活化能与剪切速率有较大的相关性,而温度为47~80℃时,活化能与剪切速率相关性较小。pH值对PPCH溶液流动性能有较大的影响。随着pH的升高,果胶溶液的黏度呈先增加后减小的趋势,在pH 4.0时,果胶溶液黏度最低,流动性最差。二价金属离子(Ca^2+、Mg^2+)可提高PPCH溶液的黏度,Ca^2+对于PPCH溶液黏度的增加幅度明显高于Mg^2+。     

红枣多糖黏度特性的研究

为研究红枣多糖的黏度特性,将红枣多糖配制成多糖溶液,采用布氏旋转黏度计测定多糖浓度、温度、剪切速率、NaCl浓度和pH对红枣多糖溶液黏度的影响。结果表明,红枣多糖溶液的浓度越大,其黏度也越大;多糖溶液的温度越高,其黏度越小;剪切速率提高,多糖溶液的黏度下降;NaCl浓度增加,多糖溶液黏度下降;酸碱均使其多糖溶液的黏度下降。因此,加工条件会对红枣多糖溶液的性质产生影响。     

草鱼鱼鳞胶原蛋白的流变学性能研究

以草鱼鱼鳞为原料,在低于蛋白变性温度的条件下提取酸溶性胶原蛋白(acid-soluble collagens,ASC)和酶溶性胶原蛋白(pepsin-soluble collagens,PSC),并对其溶液流变学性能进行系统测定。实验结果表明,在实验选择的剪切速率范围内,ASC 和PSC 溶液均表现为典型非牛顿流体的假塑性流动行为,即溶液黏度随剪切速率的增加而减小;在相同浓度条件下,溶液黏度的大小依次为ASC ＞ PSC ＞明胶;剪切速率、温度、pH 值等因素对ASC 和PSC 溶液流体性能均有显著影响;在0.6% 浓度条件下,ASC 和PSC 溶液主要表现为流体行为,基本不具备凝胶的弹性行为;胶原蛋白发生热变性后,其流体的弹性行为增强而黏性行为下降。     

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.     

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.     

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.     

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.