两亲性香豆胶衍生物溶液中的缔合行为

以共价酯键方式将长链十二烷基与十六烷基引入羧甲基化香豆胶的大分子骨架上,制得了不同取代度的两亲性香豆胶衍生物(HmCmFG).采用稳态荧光法,通过探针芘的发射光谱与激发光谱研究了HmCmFG在NaCl溶液中的疏水缔合行为.结果表明:增加疏水烷基链长、提高烷基取代度或增大NaCl浓度均有利于疏水缔合作用的增强,使由芘激发谱中荧光响应值显著变化得出的临界缔合浓度降低.在一定HmCmFG浓度(cP)范围内,芘在疏水微区与水相中的浓度比值(cm/cw)与cnp成正比关系(n为幂指数),拟合计算的荧光响应曲线与实验结果相符合,得出芘的分配系数(KP)随疏水烷基取代度增加而增大.     

聚醚型表面活性剂水溶液中胶团的生成

属于ABA型嵌段共聚物(A为聚氧乙烯,B为聚氧丙烯)的聚醚型表面活性剂分子在水中是否生成胶团,文献报道的结果迥异,临界胶团浓度值随测定方法不同出入很大.某些AB型或ABA型嵌段共聚物在选择性有机溶剂中表现出异常胶团化行为,但对于水体系迄今未见报道.本文以多种实验手段研究了典型的聚醚型表面活性剂Pluronic L-64水溶液的胶体与表面性质.结果表明,与通常的表面活性剂不同,随着温度或浓度的变化,L-64溶液中生成单分子胶团或者缔合胶团.在两者的转变间,首次观察到了水体系中的异常胶团化现象.     

多糖类大分子与表面活性剂相互作用的研究进展

多糖类大分子具有天然、无毒、使用安全和可再生及来源丰富等优点. 将多糖类大分子与表面活性剂复配使用, 不仅可利用各自的优势和特性, 而且能发挥二者的协同作用, 大大改善二者的性能. 由于两者之间存在诸如静电作用、疏水作用、偶极相互作用、氢键作用、空间位阻效应等, 水体系中表面活性剂在多糖分子链上的缔合得到调控, 并引起表面活性剂的临界聚集浓度(cac)、临界胶束浓度(cmc)、结合量, 以及体系的表面吸附、界面流变性等呈现各种变化. 本文简要总结了近年来多糖类大分子与表面活性剂复配体系研究方面取得的一些进展, 述及复配体系研究中所采用的方法与手段, 主要讨论复配体系的物理化学性质以及多糖类大分子与表面活性剂相互作用的机制.     

高含水胶

有一种奇特的物质,它不仅不需要通常橡胶那些交联过程,就具有一般大分子弹性体的各种物性,而且含水量高达80—90％。这就是八十年代初日本科学家南部昌生偶尔发现并报道的聚乙烯醇(PVA)水溶胶,又称高含水弹性体或高含水胶。现在,这种高含水胶特殊的制备方法、结构和性质已引起人们的关注。其发现有助于进一步研究高分子的结构与性能,也有希望开发新一代的医用材料。     

钙离子诱导的海藻酸钠/黄原胶凝胶化临界行为研究

研究了海藻酸钠/黄原胶混合体系的相行为及其对海藻酸钠-钙离子凝胶化临界行为的影响.当海藻酸钠浓度为0.5 wt%时,随着黄原胶的添加,混合体系出现相容、相分离及液晶3种不同的相行为.与纯黄原胶溶液相比,海藻酸钠/黄原胶混合溶液在更低的黄原胶浓度下开始形成液晶,这是由于混合体系中相分离的发生导致了黄原胶有效浓度升高.利用葡萄糖酸内酯(GDL)在线酸化Ca-EDTA,释放钙离子,研究了不同钙离子引入量时(f=[Ca2+]/[COO-])混合体系的黏弹性.Winter-Chambon分析发现临界凝胶点(f gel)随黄原胶浓度的增加而降低.当相分离发生时,临界凝胶点急剧降低,当液晶结构形成后,临界凝胶点呈现上升趋势.通过对比Winter-Chambon方法和临界凝胶点模量松弛法所测得的松弛临界指数(nw和nr),发现黄原胶的添加使海藻酸钠临界凝胶失去结构自相似性.相分离的发生导致临界凝胶结构排列更加致密,而液晶的出现使临界凝胶结构排列相对疏松.     

C9pPHCNa与C10TABr混合水溶液的表面吸附和胶团形成

羧酸盐Gemini表面活性剂C9pPHCNa与季铵盐表面活性剂十烷基三甲基溴化铵(C10TABr)混合水溶液的胶团生成能力、降低水表面张力的能力和效率均出现明显的增效.当C9pPHCNa在溶液中的摩尔分数(α1)为0.33时,cmcT(临界胶团总浓度)、γcmc(临界胶团总浓度对应的表面张力)、c20,T(降低20mN·m-1水表面张力所需的表面活性剂总浓度)这3个指标均达到最低值,分别为0.60mmo·lL-1、23.5mN·m-1和1.58×10-5mol·L-1.在所有考察的溶液比例范围内,二组分在混合胶团和表面吸附层中的组成均接近等摩尔比,表现出强烈的分子间相互作用.     

C12-s-C12•2Br在正庚烷中反胶团形成及增溶水特性

在助表面活性剂正己醇存在下, 季铵盐Gemini表面活性剂C12-s-C12•2Br(s=2、3、4、5、6、8、12)在正庚烷中形成了反胶团. 以水增溶法测定了临界反胶团浓度cmcw, 这些cmcw均分别小于它们在水中生成正胶团的临界浓度cmcaq. cmcw随s的变化规律与cmcaq随s的变化规律类似, 在s=4时出现极大值. 由水增溶法和电导法获得的反胶团饱和增溶水量(mw或mc)约在s=5时出现最大值. 这些现象被归结为联接链构型的变化.     

Triton X-100/CTAB在乙二醇/水混合溶剂中的热力学性质和胶团化行为

利用表面张力法, 研究了非离子表面活性剂Triton X-100和离子表面活性剂十六烷基三甲基溴化铵(CTAB)混合体系在混合极性溶剂乙二醇/水(乙二醇的体积分数分别为5%、10%和20%)中的热力学性质和胶团化行为. 结果表明, 混合体系在乙二醇水溶液中存在协同效应, 临界胶束浓度随乙二醇含量的增加而增大. 利用Rubingh和Maeda模型计算了混合物中各组分在胶团相中的组成、相互作用参数以及自由能的贡献. 在实验研究的乙二醇浓度范围内, 发现该非离子/离子混合体系在离子组分摩尔分数约为0.3时, 协同效应最强.     

浓度对表面活性剂胶团形状影响的分子动力学模拟

表面活性剂的很多行为因多种机制的耦合作用至今还未被理解, 而计算机模拟能方便地使用简化的模型对各种机制分别探索, 日渐受到重视. 文中采用重点描述亲水亲油性质的简化的原子模型对油水混合物中不同浓度十二烷基苯磺酸钠(SDBS)胶团的形状、结构和大小进行了分子动力学(MD)模拟研究. 在临界胶团浓度(cmc)以上, 随浓度的增加, 它们依次自发形成从球形胶团、棒状胶团到层状结构的各种聚集体, 并以胶团转动惯量特征值之比(g₁/g₃, g₂/g₃)定性表明了这种转变过程. 模拟结果表明胶团聚集数与表面活性剂浓度成幂函数关系.     

稳态荧光探针法研究烷基苄基聚氧乙烯醚丙烷磺酸钠的聚集行为

以芘为荧光探针、二苯甲酮为猝灭剂,用稳态荧光探针法测定了合成的3种高纯的烷基苄基聚氧乙烯醚丙烷磺酸钠的临界胶束浓度、不同表面活性剂浓度下的胶团聚集数和胶团微极性.研究了链长变化对烷基苄基聚氧乙烯醚丙烷磺酸钠聚集性质的影响.考察了胶团聚集数的浓度效应,并由胶团聚集数与表面活性剂浓度关系方程外推求得了它们各自的临界胶束聚集数.     

Phase transition of locust bean gum-, tara gum- and guar gum-water systems

Phase transition behaviour of neutral galactomannans, i.e., locust bean gum (LBG), tara gum (Tara-G) and guar gum (GG)-water systems is investigated. In this study, water content {W_c=(gram of water)/(gram of dry sample)} of these systems was varied from 0.2 to 3.6 g g^-1. In the DSC heating curves, glass transition (T_g), cold crystallization (T_cc) and melting (T_m) were observed in all three samples. In addition, liquid crystal transition (T*) was observed in GG-water systems at a temperature higher than Tm. Using T_g, T_cc, Tm and T*, phase diagrams of each system were established. From the melting enthalpy of ice in the systems, three types of water, non-freezing water (W_nf), freezing bound water (W_fb) and free water were calculated. The maximum amount of Wnf was observed at Wc=0.7 g g-1, where Tg showed the lowest temperature. The amount of Wnf in LBG and GG is higher than that of Tara-G, whereas the highest amount of Wfb is found in GG. T* was only observed in GG-water systems. It is concluded that frequency of the side chains in the repeating unit of the main chains of these three galactomannan affects the frozen structure of the glassy state in the presence of water. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wettability of commercial starches and galactomannans

This paper describes the wettability of basic commercial polysaccharides: starches (potato PS, wheat WS, corn CS, tapioca TS, kuzu KS) and galactomannans (fenugreek gum FG, guar gum GG, tara gum TG, locust bean gum LBG). The study was conducted using the Washburn capillary rise method and thermal drying. This allowed one to determine the material constant C, contact angle θ, surface free energy of solid SFE, and initial moisture content M. The measured values of contact angle θ and surface free energy SFE indicated that potato starch (70.9°, 41.1?mN?·?m^?1) and wheat starch (88.4°, 30.2?mN?·?m^?1) were characterized by the highest and lowest wettability among the examined starches, respectively. In turn, the galactomannans were poorly wettable substances. Their contact angles θ were approximately equal to 90°, showing a slight increase with increasing substitution degree. The observed decrease in surface free energy SFE from 30 to 29.6?mN?·?m^?1 indicated a very minor hydrophobization of their surfaces. Material constant C was practically independent of temperature, and an increase in initial moisture content M in the examined starches and galactomannans proceeded according to the following schemes: CS?相似文献   

Locust Bean Gum Hydrogels Formed by Freezing and Thawing

Locust bean gum (LBG) hydrogels were prepared by freezing and thawing. It was found that the junction zone of LBG hydrogels is tightly formed by repeating freezing and thawing. During this process, LBG molecules not connected with the junction zone are excluded from the gel portion and the remaining molecules gradually form densely packed hydrogels. Molecular conformation in the sol state affects the rate of the junction formation. Obtained LBG hydrogels are thermally stable and no gel-sol transition was observed in temperatures from 40 to 100 °C by the observation of differential scanning calorimetry (DSC). Non-freezing water content calculated from the DSC melting peak of water in the gel indicates that the junction zone became dense with increasing freezing and thawing.     

Study of galactomannose interaction with solids using AFM, IR and allied techniques

Guar gum (GG) and locust bean gum (LBG) are two galactomannose polysaccharides with different mannose/galactose ratio which is widely used in many industrial sectors including food, textiles, paper, adhesive, paint, pharmaceuticals, cosmetics and mineral processing. They are natural nonionic polymers that are non-toxic and biodegradable. These properties make them ideal for industrial applications. However, a general lack of understanding of the interactions between the polysaccharides and solid surfaces has hindered wider application of these polymers. In this work, adsorption of locust bean gum and guar gum at the solid-liquid interface was investigated using adsorption tests, electrophoretic mobility measurements, FTIR, fluorescence spectroscopy, AFM and molecular modeling. Electrokinetic studies showed that the adsorption of GG and LBG on talc do not change its isoelectric point. In addition, GG and LBG adsorption on talc was found not to be affected by changes in solution conditions such as pH and ionic strength, which suggests a minor role of electrostatic force in adsorption. On the other hand, fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene probe showed no evidence of the formation of hydrophobic domains at talc-aqueous interface. Moreover, urea, a hydrogen bond breaker, markedly reduced the adsorption of LBG and GG on talc, supporting hydrogen bonding as an important role. In FTIR study, the changes in the infrared bands, associated with the CO stretch coupled to the CC stretch and OH deformation, were significant and therefore also supporting hydrogen bonding of GG and LBG to the solid surface. In addition, Langmuir modeling of adsorption isotherm further suggested that hydrogen bonding is the dominant force for polysaccharide adsorption since the adsorption free energy of these polymers is close to that for hydrogen bond formation. From molecular modeling, different helical structures are observed for LBG and GG because of their different galactose/mannose ratio and these polymers were found to adsorb flat on solid to let more of its OH groups in contact with the surface. All of the above results suggest that the main driving force for adsorption both of GG and LBG on talc is hydrogen bonding rather than hydrophobic force even though there is difference in G/M ratio between them.     

Effects of enzymes and hydrocolloids on physical, sensory, and shelf-life properties of wheat bread

This study compares two types of enzymes: maltogenic amylase (Novamyl 10000 BG) and lipase (Lipopan F BG, Lipopan Xtra BG), both separately and in combination, and seven hydrocolloids (guar gum, xanthan gum, carrageenan, β-glucan, carob gum, and carboxymethyl cellulose (CMC)) on the physical and sensory properties of a bakery product (white wheat bread). Their effect was observed on the baking characteristics of volume, specific volume, shape, mass, shelf-life (penetration and water activity test), and overall taste. The best results in shelf-life extension from the hydrocolloids were shown by β-glucan, a combination of xanthan gum + carrageenan and guar gum. From the enzymes, the best results were achieved with Lipopan Xtra BG and Novamyl 10000 BG + Lipopan F BG combination. The sensory properties (e.g. taste, colour, shape, aroma, elasticity, hardness) were evaluated by ten trained panellists, holding certification in sensory analysis. β-Glucan and Novamyl 10000 BG + Lipopan F BG combination increased the bread volume significantly and also were deemed to afford the most favourable taste.     

Hydrocolloid gels of polysaccharides and proteins

Recent developments from 1997 to 2000 in hydrocolloid gels which consist of dispersed phase (polysaccharide or protein) and dispersing medium (water) are reviewed in the present paper. Gels and gelling processes of polysaccharides such as gellan gum, methylcellulose, xyloglucan, curdlan, konjac glucomannan and starch are described. Fluid gels and galactomannan gels prepared by freeze-thaw cycling are also described. Effects of pH and ionic strength on the gelation of proteins such as casein and β-lactoglobulin are described. Fractal treatment is introduced to study the structure–property relationship for globular protein gels. Gels formed by different hydrocolloids are also described briefly.     

Synthesis of a New Hydrogel,Based on Guar Gum,for Controlled Drug Release

Summary: Guar gum (GG) polymer was crosslinked in order to obtain a new hydrogel. The GG hydrogel has been characterized by means of FT-IR spectroscopy, the determination of the water content, at different pH values, rheological measurements and in vitro release studies. The GG hydrogel shows a maximum water uptake at acid and basic pH values. The mechanical properties are investigated in order to verify the thixotropic behaviour of the material. In vitro release studies are conducted to evaluate the application of the GG hydrogel as a matrix for controlled drug release.     

On-site characterization of humic-rich hydrocolloids and their metal loading by means of mobile size-fractionation and exchange techniques

Humic-rich hydrocolloids and their metal loading in selected German bog-waters have been characterized by a novel on-site approach. By use of an on-line multistage ultrafiltration (MST-UF) unit equipped with conventional polyethersulfone (PES)-based flat membranes (nominal cut-off 0.45, 0.22, and 0.1 microm, or 100, 50, 10, 5, 3 kDa) the hydrocolloids could be fractionated on-site in both sub-particulate and macromolecular size ranges. Characterization (dissolved organic carbon (DOC), metals) of the colloid fractions obtained this way was performed off-site by use of conventional instrumental methods (carbon analyzer, AAS, ICP-OES, and TXRF (total reflection X-ray fluorescence)). Major DOC fractions of the hydrocolloids studied were found to be in the size range <5 kDa. The assessed metals (Al, Cu, Fe, Mn, Pb, and Zn) were, however, predominantly enriched in the macromolecular and sub-particulate range, depending on the metal and the sample, respectively. In addition, metal species bound to these hydrocolloids were kinetically characterized on-site by use of competitive ligand (EDTA (ethylenediaminetetraacetate)) and metal (Cu(II)) exchange; the EDTA complexes formed and the metal ions exchanged were separated by means of a small time-controlled tangential-flow UF unit (cut-off 1 kDa). Bound metal fractions, in particular Al and Fe, reacted only slowly (500 to 1000 min) with EDTA; the conditional availability was 60-99%, depending on the hydrocolloid. In contrast, the Cu(II) exchange of colloid-bound metal species approached equilibrium within 5-10 min, with characteristic exchange constants, Kex, of the order of 0.01 to 90 for the metals (Fe相似文献   

Functional and preliminary characterisation of hydrocolloid from tamarillo (Solanum betaceum Cav.) puree

Hydrocolloid from tamarillo (Solanum betaceum Cav.) puree was extracted using water and characterised for the first time. Proximate compositions of the extracted hydrocolloid were also determined. Functional characteristics such as water-holding capacity, oil-holding capacity, emulsifying activity, emulsion stability, foaming capacity and stability of the hydrocolloid were evaluated in comparison to that of commercial hydrocolloids. Its functional groups and degree of esterification were determined using Fourier Transform Infrared (FT-IR) spectroscopy. Monosaccharide profiling was done using reverse-phase high pressure liquid chromatography (RP-HPLC). Screening of various fruits for high hydrocolloid yield after water extraction resulted in tamarillo giving the highest yield. The yield on dry weight basis was 8.30%. The hydrocolloid constituted of 0.83% starch, 21.18% protein and 66.48% dietary fibre with 49.47% degree of esterification and the monosaccharides identified were mannose, ribose, rhamnose, galacturonic acid, glucose, galactose, xylose and arabinose. Higher oil-holding capacity, emulsifying activity and emulsion stability compared to commercial hydrocolloids propose its possible application as a food emulsifier and bile acid binder. Foaming capacity of 32.19% and good foam stabilisation (79.36% of initial foam volume after 2 h of foam formation) suggest its promising application in frothy beverages and other foam based food products. These findings suggest that water-extracted tamarillo hydrocolloid can be utilised as an alternative to low methoxyl pectin.     

Determination of locust bean gum and guar gum by polymerase chain reaction and restriction fragment length polymorphism analysis

A polymerase chain reaction (PCR) was developed to differentiate the thickening agents locust bean gum (LBG) and the cheaper guar gum in finished food products. Universal primers for amplification of the intergenic spacer region between trnL 3' (UAA) exon and trnF (GAA) gene in the chloroplast (cp) genome and subsequent restriction analysis were applied to differentiate guar gum and LBG. The presence of <5% (w/w) guar gum powder added to LBG powder was detectable. Based on data obtained from sequencing this intergenic spacer region, a second PCR method for the specific detection of guar gum DNA was also developed. This assay detected guar gum powder in LBG in amounts as low as 1% (w/w). Both methods successfully detected guar gum and/or LBG in ice cream stabilizers and in foodstuffs, such as dairy products, ice cream, dry seasoning mixes, a finished roasting sauce, and a fruit jelly product, but not in products with highly degraded DNA, such as tomato ketchup and sterilized chocolate cream. Both methods detected guar gum and LBG in ice cream and fresh cheese at levels <0.1%.