Gas chromatographic determination of polysaccharide gums in foods after hydrolysis and derivatization

A gas chromatographic method was evaluated for the determination of food grade gums in dairy products, salad dressings and meat sauces. The gums studied were tragacanth, karaya, ghatti, carob, guar, arabic and xanthan gum. The extraction method included removal of fat followed by starch degradation then precipitation of protein. The isolated gums were hydrolysed with trifluoroacetic acid and the resulting neutral monosaccharides converted to their aldonitrile acetate derivatives for determination by gas chromatography. Recoveries from thirteen different commodities averaged 85%. However, the recovery of guar gum from ice cream and cold pack cheese was 42 and 50%, respectively. In a comparison of enzyme hydrolysis and iodine complexation for the removal of starch the former was simpler and provided cleaner extracts than the iodine treatment. Both gave similar results.     

Unique properties of high viscosity gums

Guar gum, a galactomannan from the seed endosperm of the legume, Cyamopsis tetragonolobus, is an important food stabilizer used in a variety of food products ranging from sauces to ice cream. Two guars having viscosities 13-250% higher than conventional guars were studied. Viscosity, effect of shear rate on viscosity, synergy with xanthan gum, granulation, galactomannan content, molecular weight, and scanning electron microscopy of the guar types were evaluated. At equal usage levels of guar, the high viscosity type showed a higher viscosity alone and in combination with xanthan gum under all conditions tested. The high viscosity products have electron microscopic morphology that is more elongated and molecular weights which are greater than normal guars. These factors are discussed in light of the viscosity differences which exist between these products.     

N,N-二乙基胺乙基取代瓜尔胶的合成及结构表征

在碱催化条件下,利用N,N-二乙基氯乙胺盐酸盐与瓜尔胶和羟丙基瓜尔胶一步法合成得到N,N-二乙基胺乙基瓜尔胶和N,N-二乙基胺乙基羟丙基瓜尔胶。结果显示合成过程中温度、反应时间、羟丙基取代度及溶剂等因素对产品分子量和N,N-二乙基胺乙基取代度有影响。通过红外光谱和核磁法对N,N-二乙基胺乙基瓜尔胶和羟丙基N,N-二乙基胺乙基瓜尔胶的分子结构进行了分析,并通过碳谱对N,N-二乙基胺乙基在瓜尔胶分子链中糖环上的取代分布进行了分析。     

羟丙基瓜尔胶中羟丙基摩尔取代度以及取代位置的表征

本文探索了表征羟丙基瓜尔胶(HPG)中羟丙基摩尔取代度(MS)以及取代位置的化学方法.当反应温度为110℃、反应时间为14h以及HPG中羟基与对甲苯磺酸-乙酸酐摩尔比为1:3.5时,用对甲苯磺酸-乙酸酐化学法和气相色谱法可准确测定HPG的羟丙基MS,与1H-NMR测定结果相对误差小于10%.在pH=10.30和0℃的条件下,瓜尔胶的伯羟基被2,2,6,6-四甲基哌啶氮--氧化物(TEMPO)-NaClO-NaBr体系选择性氧化成羧基,由此可表征羟丙基链段的取代位置.     

羟丙基瓜尔胶在离子液体中的制备

本文以离子液体1-烯丙基-3-甲基咪唑氯盐(AmimCl)为反应介质,以氢氧化钠为催化剂合成了羟丙基瓜尔胶(HPG),并通过1H NMR确定了产品的摩尔取代度。探讨了水的用量、环氧丙烷的用量、反应温度和反应时间对摩尔取代度的影响。在水与瓜尔胶的质量比为1.7、氢氧化钠与瓜尔胶的质量比为5%、环氧丙烷与瓜尔胶的质量比为3.5、反应温度为60℃和反应时间为12h的条件下,摩尔取代度(MS)可以达到0.76。同时发现在不加催化剂NaOH的情况下,瓜尔胶在AmimCl中的羟丙基化反应同样可以发生,只是得到的HPG的MS相对较小。     

Hydrophobic guar gum derivatives prepared by controlled grafting processes

Introduction of polyalkoxyalkyleneamide grafts to guar gum produces a new water soluble guar derivative. Modification of either guar gum or hydroxyopropyl guar is achieved in a three‐step process: carboxymethylation with sodium chloroacetate, esterification with dimethyl sulfate (DMS) and amidation with a series of polyalkoxyalkyleneamines. The process was followed using infrared spectroscopy; the grafted guar derivatives were characterized using ¹H NMR. A series of hydroxypropyl guar (HPR) derivatives with degrees of carboxymethylations ranging from 0.2–0.3 were modified with polyalkoxyalkyleneamines with molecular weights ranging from 300 to 3000. The ratio of oxypropylene to oxoethylene units in the polyalkoxyalkyleneamines was varied from 9/1 to 8/58 to adjust the hydrophobicity of the grafts. Aqueous solutions of the graft copolymers exhibit viscosities one to two orders of magnitude lower than the corresponding solutions of the parent guar gum. Copyright © 2007 John Wiley & Sons, Ltd.     

Reduced aggregation and sedimentation of zero-valent iron nanoparticles in the presence of guar gum

Injection of nanoscale zero-valent iron (NZVI) is potentially a promising technology for remediation of contaminated groundwaters. However, the efficiency of this process is significantly hindered by the rapid aggregation of the iron nanoparticles. The aim of this study was to enhance the colloidal stability of the nanoparticles through the addition of the "green" polymer guar gum. We evaluated the properties of guar gum and its influence on the surface properties, particle size, aggregation, and sedimentation of iron nanoparticles. Commercial iron nanoparticles were dispersed in guar gum solutions, and their aggregation and sedimentation behaviors were compared to those of bare iron nanoparticles and commercial nanoparticles modified with a biodegradable polymer (polyaspartate). High performance size exclusion chromatography, charge titration, and viscosity assessment showed that guar gum is a high molecular weight polymer which is nearly neutrally charged, rendering it suitable for steric stabilization of the iron nanoparticles. Electrophoretic mobility measurements demonstrated the ability of guar gum to adsorb on the nanoparticles, forming a slightly negatively charged layer. Dynamic light scattering experiments were conducted to estimate the particle size of the different nanoparticle suspensions and to determine the aggregation behavior at different ionic strengths. Guar gum effectively reduced the hydrodynamic radius of the bare nanoparticles from 500 nm to less than 200 nm and prevented aggregation of the nanoparticles even at very high salt concentrations (0.5 M NaCl and 3 mM CaCl(2)). Sedimentation profiles of the different nanoparticle suspensions confirmed the improved stability of the iron nanoparticles in the presence of guar gum. The results strongly suggest that guar gum can be used to effectively deliver stabilized zero-valent iron nanoparticles for remediation of contaminated groundwater aquifers.     

Preparation and characterization of cross-linked guar gum microspheres: optimization using factorial design

In the present work cross-linked guar gum microspheres were prepared for colon specific delivery of ornidazole. Development and optimization of guar gum microspheres for colonic drug delivery was carried out using a 2(4) factorial design based on four independent variables. Microspheres were prepared by emulsification method using glutaraldehyde as cross-linking agent. Morphology and surface characteristics of the formulations were determined by scanning electron microscopy. Particle size of the guar gum microspheres was determined by particle size analyzer. In vitro drug-release studies were performed in conditions simulating stomach-to-colon transit in the presence and absence of rat cecal contents. Only a small fraction of drug was released at acidic pH; however, the release of drug was found to be higher in the presence of rat cecal contents, indicating the susceptibility of guar gum matrix to colonic enzymes released from rat cecal contents. The significance of differences was evaluated by analysis of variance (ANOVA). Differences were considered statistically significant at p<0.05.     

Adsorption of guar gum onto quartz from dilute mixed electrolyte solutions

The effect of potassium, sodium, calcium, magnesium, and hydrogen cations on adsorption of guar gum onto quartz was investigated at natural pH. The role of the background ions was analyzed in terms of their water-structure making or breaking capabilities. In dilute solutions (0.01 mol/L) of structure-makers (NaCl, HCl, CaCl2, and MgCl2), the guar gum adsorption density did not change compared to the adsorption densities obtained in distilled water. Potassium, the only structure-breaking ion (chaotrope) among the tested cations, significantly enhanced guar gum adsorption. The results obtained in mixed electrolytes demonstrate that the strong structure-breaking properties of K+ overcome any contributions from weak structure making ions (kosmotropes), and guar gum adsorption remains at the levels observed in KCl alone. Only when strongly hydrated Mg2+ ions are mixed with KCl, the overall effect becomes additive and the influence of potassium is proportionally reduced by increasing concentrations of magnesium cations. In this approach, guar gum adsorption on quartz is viewed as a competition between polysaccharide and water molecules for silanol surface sites. The hydration of the quartz surface inhibits the adsorption process but the competition equilibrium, and hence polysaccharide adsorption, can be affected by the presence of chaotropes or kosmotropes.     

Photo-induced Synthesis and Characterization of Poly（methyl methacrylate） Grafted Sodium Salt of Partially Carboxymethylated Guar Gum

Photo-induced graft copolymerization of methyl methacrylate（MMA） onto sodium salt of partially carboxymethylated guar gum（Na-PCMGG, DS = 0.291） was carried out in an aqueous medium using ceric ammonium nitrate（CAN） as photoinitiator to synthesize a novel graft copolymer, Na-PCMGG-g-PMMA, which may find its potential application as a metal adsorbent. The influences of synthesis variables such as concentrations of photoinitiator（CAN）, nitric acid and monomer（MMA） as well as reaction time, temperature and amount of substrate on the grafting yields were studied and the reaction conditions for optimum photo-grafting were evaluated. At optimum concentration, the maximum values of the grafting yields achieved were G = 271.61% and GE = 63.89%. The experimental results were found to be in very good agreement with the proposed kinetic scheme. The photo-graft copolymerization of MMA onto Na-PCMGG（ DS = 0.291） was also carried out in the presence and absence of ultraviolet radiation for studying the efficiency of the photoinitiator. The influence of carboxymethyl groups introduced onto the guar gum molecules with regard to its behavior towards ultra-violet radiation induced grafting with MMA was also investigated. Photo-grafting process was confirmed and the products were characterized with the help of the spectroscopic（1H-NMR and FTIR） and SEM techniques.     

Effect of alkali metal cations on adsorption of guar gum onto quartz

The effect of cesium, potassium, sodium, and lithium cations on the adsorption of natural guar gum onto quartz was investigated. The role of these ions was analyzed in terms of their water structure-making or -breaking capabilities. In the presence of structure makers (Na+, Li+) the polymer adsorption density did not change compared to the adsorption levels observed in distilled water. However, in dilute solutions (0.01 N) of structure-breaking cations (Cs+, K+) the adsorption density of guar gum significantly increased, with potassium and cesium producing the same adsorption densities of the polymer. The resulting colloidal aggregation/dispersion equilibria in the quartz-guar gum system were discussed and mechanisms of guar gum-quartz interactions were also suggested. Assuming hydrogen bonding to be the driving adsorption mechanism, it was proposed that guar gum molecules compete with water for silanol surface sites. Structure-breaking cations disturb the interfacial water structure around the quartz particles thus allowing the polymer to more closely approach the quartz surface and interact with the surface groups.     

Syntheses and properties of superabsorbent composites based on natural guar gum and attapulgite

Utilization of raw materials available in nature and their application to derive other useful products without any adverse impact on the environment has long been a desired goal. In this work, guar gum (GG) and attapulgite (APT) clay were used as raw materials for preparing guar gum‐g‐poly(acrylic acid)/attapulgite (GG‐g‐PAA/APT) superabsorbent composites through the graft copolymerization of GG, partially neutralized acrylic acid (AA) and APT in aqueous solution. The effects of reaction conditions such as concentrations of the initiator and crosslinker, APT content, etc. on water absorbency were investigated. The composite prepared under optimal conditions gave the best absorption of 529 g/g sample in distilled water and 61 g/g sample in 0.9 wt% NaCl solution. Swelling behaviors revealed that the superabsorbent composites retained a high water absorbency over a wide pH range of 4–11, and the developed composites also exhibited improved reswelling and water‐retention capabilities. The superabsorbent composites can be utilized as eco‐friendly water‐manageable materials for agricultural and horticultural applications. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

凝胶压井液用阴离子改性胍胶的制备及其流变性能

以环氧氯丙烷和NaHSO_3为原料,Na_2SO_3为引发剂,乙二胺四乙酸二钠(EDTA-2Na)为络合增效剂,经酸催化开环反应合成了磺酸型两性表面活性剂中间体3-氯-2-羟基丙磺酸钠,然后在弱酸性条件下与胍胶通过醚化反应制备了磺酸基羟丙基胍胶,其结构经IR表征。通过正交实验确定了合成配方和条件的最优结果,研究了反应温度、pH、改性胍胶浓度对成胶后凝胶的表观粘度影响,并测试了最佳条件下制备的凝胶和对应稀溶液的流变性能。结果表明:氧氯化锆可有效交联改性胍胶,在pH为6、温度为70℃、改性胍胶浓度为0.6%的条件下制备的凝胶具有剪切变稀性质以及较好的粘弹性。     

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.     

Preparation and Performance of Thickened Liquids for Patients with Konjac Glucomannan-Mediated Dysphagia

The present study sought to characterize the rheological and thickening properties of Konjac glucomannan (KGM) and prepare thickening components for special medical purposes using KGM and maltodextrin as the primary raw materials and guar gum (GG), xanthan gum (XG), locust bean gum (LBG), and carrageenan (KC) as the supplemented materials. The formulation and preparation processes were optimized through single factor experiments taking sensory evaluation as an indicator. The results confirm that KGM had excellent thickening performance, reaching about 90 times its own mass. The optimal formulation process of the thickening components based on KGM was as follows: the mass concentration of the compound thickener (KGM/GG/XG/LBG/KC = 13:2:2:2:1) was 5.0–7.0 mg/mL; the maltodextrin concentration was 10.0 mg/mL; the brewing temperature of the thickening component was 60 °C with no restriction on consumption time. The rheology test results revealed that the thickening components had shear thinning characteristics, which could provide three different thickening effects of nectar-thick level (350 mPa·s), honey-thick level (1250 mPa·s), and pudding-thick level (1810 mPa·s) suitable for people with different degrees of chewing disorders. Overall, this study provides a theoretical basis and technical reference for KGM as a dietary nutrition support for patients with dysphagia.     

Kinetic investigations on the alkaline hydrolysis of tris-(1,10-phenenthroline)Fe(II) with guar gum–surfactant interactions

The kinetic investigations on the alkaline hydrolysis of tris-(1,10–phenanthroline)iron(II) has been explored spectrophotometrically in microheterogeneous environment at 301?K and ionic strength of 0.13?mol?L^?1. Guar gum, cationic amphiphiles, and their mixtures are used as the reaction environments to carry out the reaction. Guar gum decreases the rate of reaction, which indicates that Fe(II) complex may be trapped in the hydrophobic region of gum. Cationic amphiphile decreases the rate in the presence of guar gum. The extent of interaction between guar gum and amphiphile increases with the hydrophobic carbon chain length. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of the amphiphiles (cetyl trimenthyl ammonium bromide (CTAB), tetradecyl trimenthyl ammonium bromide (TTAB), dodecyl trimenthyl ammonium bromide (DTAB)) in the presence of guar gum have been determined with conductometry and tensiometry. All observations support either weak or strong interaction of cationic amphiphiles with guar gum. Activation parameters of the reaction in different environments have been determined which corroborate the rate data.     

Preparation,Characterization and Anticoagulant Activity of Guar Gum Sulphate

Guar gum was chemically modified by sulphonation using chlorosulphonic acid (ClSO₃H) as a reagent. Effects of molar ratio of ClSO₃H to glucopyranosic unit (ClSO₃H/GU), reaction time and reaction temperature on the degree of sulphonation (DS) and molecular weight (Mw) of products were studied. The structures of guar gum sulphate were investigated by GPC, FT‐IR and UV‐Visible spectroscopy. Activated partial thromboplastin time (APTT) assay showed that the guar gum sulphate could inhibit the intrinsic coagulant pathway. The anticoagulant activity strongly depended on the DS and Mw of polysaccharides. DS>0.56 was essential for anticoagulant activity. The guar gum sulphate with the DS of 0.85 and the Mw of 3.40×10⁴ had the best blood anticoagulant activity.     

Preparation of cross-linked guar gum nanospheres containing tamoxifen citrate by single step emulsion in situ polymer cross-linking method

In the present work, guar gum nanospheres containing tamoxifen citrate (TC) were prepared and characterized for using it as a carrier for targeted drug delivery. Tamoxifen is a non steroidal drug used in the treatment of breast cancer. The compound administered to patients is the citrate salt of the trans isomer, tamoxifen citrate. Single step emulsion in situ polymer crosslinking technique was employed to prepare polymer coated drug nanoparticles. Model polymer used in this study was guar gum, which is commonly used for colon specific drug delivery in the pharmaceutical industry. During preparation four-different drug loading solvents were tried and dichloromethane provided the best drug loading result. Briefly, 5 mg drug was dissolved in dichloromethane and emulsified with an aqueous solution of guar gum using span 80 as emulsifier. Cross-linking was made by the use of cross linker glutaraldehyde during the process. A core shell type particles were observed. Drug load was confirmed by FT-IR and quantitated by HPLC. Nanoparticles were further characterized for particle size and morphology. Particle size between 200 and 300 nm were obtained. Influence of process variables on the size of nanoparticles were studied. It was observed that the concentration of polymer and stabilizer determined the size of nanoparticles.     

Rheological behavior and particle suspension capability of guar gum: sodium tetraborate decahydrate gels containing cellulose nanofibrils

Guar gum (GG) fracturing fluids were studied by incorporating cellulose nanofibrils (CNFs) in anhydrous borax crosslinked guar gum gels. To fully understand the impact of CNF on the proppant suspension capability of developed fracturing fluids, their shear rate-dependent viscosity and viscoelasticity were investigated. The shear rate dependencies of fluids was fitted to the Carreau model. The zero shear rate viscosity and elasticity of fracturing fluids increased significantly by incorporating CNF in guar gum gels. On the other hand, the viscosity at high shear rates (>100 s^?1) decreased as desired. The proppant settling velocities through fracturing fluids were evaluated by modeling the terminal falling velocity of proppants moving through a Carreau model fluid. The experimental results of the rheological behavior and the modeling results of the proppant settling rate indicated that the fracturing fluids containing CNF had better suspension capabilities. In addition, the lower viscosities of CNF formulated GG gels at higher shear rates will make them more pumpable.