Chemical modification of Cassia occidentalis seed gum: carbamoylethylation

The seeds of Cassia occidentalis, an annual weed occurring throughout India, is a rich source of galactomannan gum. The gum derived from seed endosperm can be potentially utilized in a number of industries to replace the conventional gums. With a view to utilize the gum for broader applications, carbamoylethylation of C. occidentalis seed gum was carried out with acrylamide in presence of sodium hydroxide under different reaction conditions. Variables studied were concentration of sodium hydroxide, acrylamide, gum–solvent ratio, reaction time and temperature. The nitrogen content, carboxyl content and total ether content were determined. The optimum condition for preparing carbamoylethyl C. occidentalis seed gum (%N=2.57) comprised concentration of acrylamide (0.070 mol), sodium hydroxide (0.125 mol), C. occidentalis seed gum (0.03 mol) at 30 °C for 3 h. Rheological properties of carbamoylethyl C. occidentalis seed gum solution showed non-Newtonian pseudo-plastic behavior, relatively high viscosity, cold water solubility and solution clarity vis-à-vis unmodified C. occidentalis seed gum.     

Synthesis of oxidized guar gum by dry method and its application in reactive dye printing

The aim of this study was to prepare oxidized guar gum with a simple dry method, basing on guar gum, hydrogen peroxide and a small amount of solvent. To obtain a product with suitable viscosity for reactive dye printing, the effects of various factors such as the amount of oxidant and solvent, reaction temperature and time were studied with respect to the viscosity of reaction products. The product was characterized by Fourier transform infrared spectroscopy, size exclusion chromatography, scanning electron microscopy and differential scanning calorimetry. The hydrated rate of guar gum and oxidized guar gum was estimated through measuring the required time when their solutions (1%, w/v) reached the maximum viscosity. The effects of the salt concentration and pH on viscosity of the resultant product were studied. The mixed paste containing oxidized guar gum and carboxymethyl starch was prepared and its viscosity was determined by the viscometer. The rheological property of the mixed paste was appraised by the printing viscosity index. In addition, the applied effect of mixed paste in reactive dye printing was examined by assessing the fabric stiffness, color yield and sharp edge to the printed image in comparison with sodium alginate. And the results indicated that the mixed paste could partially replace sodium alginate as thickener in reactive dye printing. The study also showed that the method was low cost and eco-friendly and the product would have an extensive application in reactive dye printing.     

Rheological study of interactions between non-ionic surfactants and polysaccharide thickeners used in textile printing

The influence of four non-ionic surfactants (isododecyl and cetyl polyoxyethylene ethers) on aqueous polysaccharide solutions (sodium alginate, guar gum, and sodium carboxymethyl guar), applicable for textile printing pastes, were studied via rheological measurements.

Rheology of polysaccharide–surfactant solutions in aqueous matrices is primarily governed by polymer content, which imparts marked shear-thinning and viscoelastic character to the system. Such properties are modulated in moderate but sensible way by changes in surfactant concentration or type. Above 3% surfactants addition to non-substituted guar gum solutions results in a significant impact leading to phase separation and a particular strongly associated phase is formed due to hydrogen bonds between ethylene oxy units from the surfactant and primary hydroxyl groups in guar.

A satisfactory fitting of viscosity data is obtained with both the Cross equation and the Roberts–Barnes–Carew model. The experimental results of mechanical spectra can be described quite satisfactory with both the Friedrich–Braun and the generalized Maxwell models.     

Modification of hydroxypropyl guar gum with ethanolamine

A new guar gum derivative containing amino group was synthesized through nucleophilic substitution of p-toluenesulfonate activated hydroxypropyl guar gum with ethanolamine. For the preparation of p-toluenesulfonate esters hydroxypropyl guar gum, the results showed that the reaction rate was optimal at 25°C and the reaction could reach equilibrium state when it was carried out for 10h at 25°C. For the nucleophilic substitution of tosyl group with ethanolamine, the reaction was completed after 10h reaction at 50°C. The structures of products were characterized by NMR and FT-IR spectroscopy. The results showed that the p-toluenesulfonate esters can be effectively substituted by ethanolamine to form the hydroxyethyl amino hydroxypropyl guar gum (EAHPG). The content of nitrogen of EAHPG was determined by acid-base titration and element analysis.     

白芨多糖胶-瓜尔胶复配溶液的流变性

考察了瓜尔胶溶液和白芨多糖胶-瓜尔胶复配溶液的流变特性。两组溶液呈现典型的假塑性,不同浓度下两组溶液表观黏度(ηa)随剪切速率(τ)的变化可以用Ostwald-Dewaele方程描述。白芨多糖胶和瓜尔胶复配产生协同增效作用,复配溶液的ηa大于单一组分的白芨多糖胶溶液或瓜尔胶溶液的ηa。复配溶液中白芨多糖胶与瓜尔胶的最佳配比是质量比为9∶1。     

Rheological properties of guar gum and hydroxyethyl guar gum in aqueous solution

The rheological properties of aqueous solutions of guar gum (GG) and hydroxyethyl guar gum (HEG) have been investigated. The flow properties of these polysaccharide solutions were studied at the shear rate in the range 1.5–1310s⁻¹ using a Rheotest-2 viscometer. The flow of these polysaccharide solutions was described by equation of state based on Cross model. The basic rheological parameters, like zero shear rate viscosity (η_o), elasticity modulus (G_o) and relaxation time (gl_o) were calculated using simple and established relations. Master viscosity curves indicated that the molecular weight distribution of native guar gum has been changed by hydroxyethylation under specified reaction conditions. The effect of concentration and temperature on η_o and λ_o has been studied, and the relations among these were established by simple equations.     

Effect of polysaccharide structure on mechanical and thermal properties of galactomannan-based films

Films were prepared from guar gum and locust bean gum galactomannans. In addition, enzymatic modification was applied to guar gum to obtain structurally different galactomannans. Cohesive and flexible films were formed from galactomannans plasticized with 20-60% (w/w of polymer) glycerol or sorbitol. Galactomannans with lower galactose content (locust bean gum, modified guar gum) produced films with higher elongation at break and tensile strength. The mechanical properties of films were improved statistically significantly by decreasing the degree of polymerization of guar gum with mannanase treatments (4 h) of 2 and 10 nkat/g, whereas 50 nkat/g produced films with low elongation at break and tensile strength. Galactomannans with approximately 6 galactose units per 10 mannose backbone units resulted in films with 2 peaks in loss modulus spectra, whereas films from galactomannans with approximately 2 galactose groups per 10 mannose units behaved as a single phase in dynamic mechanical analysis.     

Preparation and characterization of hemicellulosic derivatives containing carbamoylethyl and carboxyethyl groups

A series of novel water-soluble hemicellulosic derivatives, containing carbamoylethyl and carboxyethyl groups, were heterogeneously synthesized from wheat-straw hemicelluloses with acrylamide (AA) under alkaline conditions. The factors such as reaction temperature, reaction time, molar ratio of catalysis to xylose unit in hemicelluloses and molar ratio of acrylamide to xylose unit in hemicelluloses, were investigated. The average degree of substitution (DS) was calculated by ¹H NMR spectroscopy. DS values up to 0.23 in a one-step synthesis of hemicelluloses derivatives were obtained. Under optimum conditions (60 °C, NaOH to xylose unit in hemicelluloses molar ratio of 0.8, AA to xylose unit in hemicelluloses molar ratio of 8.0, reaction time of 1 h) an expected ratio of carbamoylethyl group to carboxyethyl group of 4.8 in the hemicellulosic derivatives was obtained. The structural features of the hemicellulosic derivatives were characterized by FTIR, NMR spectroscopy, and by elemental analysis. The current work provides a facile method for the synthesis of hemicellulose derivatives with bifunctional groups, which could be used as wet-end additives in the papermaking industry.     

Irradiation depolymerized guar gum as partial replacement of gum Arabic for microencapsulation of mint oil

Spray dried microcapsules of mint oil were prepared using gum Arabic alone and its blends with radiation or enzymatically depolymerized guar gum as wall materials. Microcapsules were evaluated for retention of mint oil during 8-week storage during which qualitative changes in encapsulated mint oil was monitored using principal component analysis. The microcapsules with radiation depolymerized guar gum as wall material component could better retain major mint oil compounds such as menthol and isomenthol. The t(1/2) calculated for mint oil in microcapsules of gum Arabic, gum Arabic:radiation depolymerized guar gum (90:10), gum Arabic:enzyme depolymerized guar gum (90:10) was 25.66, 38.50, and 17.11 weeks, respectively. The results suggested a combination of radiation depolymerized guar gum and gum Arabic to show better retention of encapsulated flavour than gum Arabic alone as wall material.     

Rheology of hydroxyethyl guar gum derivatives

The rheological properties of aqueous solutions of hydroxyethyl guar gum, a synthetic derivative of guar gum, have been studied under continuous and oscillatory shear flow conditions. Data obtained from both experimental techniques were satisfactorily fitted according to Cross-type models. The effect of polymer concentration, molecular weight and temperature on the rheological behavior of hydroxyethyl guar gum systems have been investigated and discussed in terms of rheological parameters like the zero-shear viscosity η₀ and the characteristic times λ and λ′.     

Guar gum: a cheap substitute for agar in microbial culture media

AIMS: To determine the possibility of using guar gum, a colloidal polysaccharide, as a cheap alternative to agar for gelling microbial culture media. METHODS AND RESULTS: As illustrative examples, 12 fungi and 11 bacteria were cultured on media solidified with either guar gum or agar. All fungi and bacteria exhibited normal growth and differentiation on the media gelled with guar gum. Microscopic examination of the fungi and bacteria grown on agar or guar gum gelled media did not reveal any structural differences. However, growth of most of the fungi was better on guar gum media than agar, and correspondingly, sporulation was also more advanced on the former. Bacterial enumeration studies carried out for Serratia sp. and Pseudomonas sp. by serial dilution and pour-plate method yielded similar counts on both agar and guar gum. Likewise, a selective medium, succinate medium used for growth of Pseudomonas sp. did not support growth of Bacillus sp. when inoculated along with Pseudomonas on both agar or guar gum supplemented medium. CONCLUSIONS: Guar gum, a galactomannan, which is 50 times cheaper than Difco-bacto agar, can be used as a gelling agent in place of agar in microbial culture media. SIGNIFICANCE AND IMPACT OF THE STUDY: As the media gelled with guar gum do not melt at temperature as high as 70 degrees C, these can be used for isolation and maintenance of thermophiles.     

Thermal, Mechanical, and Molecular Relaxation Properties of Frozen Sucrose and Fructose Solutions Containing Hydrocolloids

Model frozen systems formulated with 20wt% sucrose or fructose and with the addition of 0.3 or 0.5wt% of xanthan gum (XG), guar gum (GG), locust bean gum (LBG), or a 50wt% mixture of XG and LBG were studied by differential scanning calorimetry, dynamic mechanical analysis, and ¹H-pulsed nuclear magnetic resonance. Melting onset of either the sucrose or fructose model systems was not affected by the addition of hydrocolloids. As expected, ice content was lower in fructose than in sucrose systems. Addition of hydrocolloids had no effect on ice content, except when the blend of XG and LBG was added to the fructose system, where ice content was significantly diminished. Hydrocolloids decreased molecular mobility for both frozen sucrose or fructose solutions, especially for the addition of XG/LBG blend. Relaxation times and storage modulus of the frozen systems with added hydrocolloids were significantly lower than the control frozen sugar solutions.     

Analysis of proteins associated with growth of Bacteroides ovatus on the branched galactomannan guar gum.

Bacteroides ovatus, a gram-negative obligate anaerobe from the human colon, can ferment the branched galactomannan guar gum. Previously, three enzymes involved in guar gum breakdown were characterized. The expression of these enzymes appeared to be regulated; i.e., specific activities were higher in extracts from bacteria grown on guar gum than in extracts from bacteria grown on the monosaccharide constituents of guar gum, mannose and galactose. In the present study, we used two-dimensional gel analysis to determine the total number of B. ovatus proteins enhanced during growth on guar gum. Twelve soluble proteins and 20 membrane proteins were expressed at higher levels in guar gum-grown cells than in galactose-grown cells. An unexpected finding was that the expression of the two galactomannanases was induced by glucose as well as guar gum. Three other proteins, one membrane protein and two soluble proteins, had this same expression pattern. The remainder of the guar gum-associated proteins seen on two-dimensional gels and the guar gum-associated alpha-galactosidase were induced in cells grown on guar gum but not in cells grown on glucose. Two transposon-generated mutants (M-5 and M-7) that could not grow on guar gum were isolated. Both mutants still expressed the galactomannanases and the alpha-galactosidase. They also still expressed all of the guar gum-associated proteins that could be detected in two-dimensional gels of glucose-grown or galactose-grown cells. A second transposon insertion that suppressed the guar gum-negative phenotype of M-5 was isolated and characterized. The characteristics of this suppressor mutant indicated that the original transposon insertion was probably in a regulatory locus.     

基于闪爆-超声波联合作用的红麻精干麻制备

针对红麻脱胶困难且传统脱胶方法污染严重的问题,提出一种新的脱胶方法,即闪爆-超声波联合脱胶。首先对红麻进行闪爆预处理,进而结合红麻超声波脱胶单因子试验和正交试验,以红麻精干麻纤维残胶率为考核指标,探讨了不同超声波频率、氢氧化钠介质浓度以及超声波处理时间对脱胶效果的影响。结果表明,在闪爆预处理后,采用频率为28 kHz的超声波在氢氧化钠浓度为2%的溶液中处理红麻试样60 min,可以使红麻精干麻纤维残胶率降低到9.72%,细度达到139.45 Nm。闪爆-超声波处理可有效去除红麻胶质成分,提高红麻精干麻的分散性,以利于后续纺织加工。     

改性瓜尔胶的研究进展

瓜尔胶是一种天然的半乳甘露聚糖,广泛用于食品、日化、医药等行业.改性瓜尔胶的性能具有较大改善,近年来瓜尔胶的改性研究成为热点.论述了瓜尔胶结构和性质以及改性瓜尔胶的研究进展,为瓜尔胶进一步开发研究提供参考.     

Analysis of proteins associated with growth of Bacteroides ovatus on the branched galactomannan guar gum.

Bacteroides ovatus, a gram-negative obligate anaerobe from the human colon, can ferment the branched galactomannan guar gum. Previously, three enzymes involved in guar gum breakdown were characterized. The expression of these enzymes appeared to be regulated; i.e., specific activities were higher in extracts from bacteria grown on guar gum than in extracts from bacteria grown on the monosaccharide constituents of guar gum, mannose and galactose. In the present study, we used two-dimensional gel analysis to determine the total number of B. ovatus proteins enhanced during growth on guar gum. Twelve soluble proteins and 20 membrane proteins were expressed at higher levels in guar gum-grown cells than in galactose-grown cells. An unexpected finding was that the expression of the two galactomannanases was induced by glucose as well as guar gum. Three other proteins, one membrane protein and two soluble proteins, had this same expression pattern. The remainder of the guar gum-associated proteins seen on two-dimensional gels and the guar gum-associated alpha-galactosidase were induced in cells grown on guar gum but not in cells grown on glucose. Two transposon-generated mutants (M-5 and M-7) that could not grow on guar gum were isolated. Both mutants still expressed the galactomannanases and the alpha-galactosidase. They also still expressed all of the guar gum-associated proteins that could be detected in two-dimensional gels of glucose-grown or galactose-grown cells. A second transposon insertion that suppressed the guar gum-negative phenotype of M-5 was isolated and characterized. The characteristics of this suppressor mutant indicated that the original transposon insertion was probably in a regulatory locus.     

Evaluation of guar gum derivatives as gelling agents for microbial culture media

Guar gum, a galactomannan, has been reported to be an inexpensive substitute of agar for microbial culture media. However, its use is restricted probably because of (1) its highly viscous nature even at high temperatures, making dispensing of the media to Petri plates difficult and (2) lesser clarity of the guar gum gelled media than agar media due to impurities present in guar gum. To overcome these problems, three guar gum derivatives, carboxymethyl guar, carboxymethyl hydroxypropyl guar and hydroxypropyl guar, were tested as gelling agents for microbial growth and differentiation. These were also evaluated for their suitability for other routine microbiological methods, such as, enumeration, use of selective and differential media, and antibiotic sensitivity test. For evaluation purpose, growth and differentiation of eight fungi and eight bacteria grown on the media gelled with agar (1.5%), guar gum (4%) or one of the guar gum derivatives (4%), were compared. All fungi and bacteria exhibited normal growth and differentiation on all these media. Generally, growth of most of the fungi was better on guar gum derivatives gelled medium than on agar medium. The enumeration carried out for Serratia sp. and Pseudomonas aeruginosa by serial dilution and pour plate method yielded similar counts in all the treatments. Likewise, the selective succinate medium, specific for P. aeruginosa, did not allow growth of co-inoculated Bacillus sp. even if gelled with guar gum derivatives. The differential medium, Congo red mannitol agar could not differentiate between Agrobacterium tumefaciens and Rhizobium meliloti on color basis, if gelled with guar gum or any of its derivatives However, for antibiotic sensitivity tests for both Gram-positive and -negative bacteria, guar gum and its derivatives were as effective as agar.     

Cross-linked guar gum microspheres: A viable approach for improved delivery of anticancer drugs for the treatment of colorectal cancer

In the present work, guar gum microspheres containing methotrexate (MTX) were prepared and characterized for local release of drug in the colon, which is a prerequisite for the effective treatment of colorectal cancer. Guar gum microspheres were prepared by the emulsification method using glutaraldehyde as a cross-linking agent. Surface morphological characteristics were investigated using scanning electron microscopy. Particle size, shape, and surface morphology were significantly affected by guar gum concentration, glutaral dehyde concentration, emulsifier concentration (Span 80), stirring rate, stirring time, and operating temperature. MTX-loaded microspheres demonstrated high entrapment efficiency (75.7%). The in vitro drug release was investigated using a US Pharmacopeia paddle type (type II) dissolution rate test apparatus in different media (phosphate-buffered saline [PBS], gastrointestinal fluid of different pH, and rat cecal content release medium), which was found to be affected by a change to the guar gum concentration and glutaraldehyde concentration. The drug release in PBS (pH 7.4) and simulated gastric fluids followed a similar pattern and had a similar release rate, while a significant increase in percent cumulative drug release (91.0%) was observed in the medium containing rat cecal content. In in vivo studies, guar gum microspheres delivered most of their drug load (79.0%) to the colon, whereas plain drug suspensions could deliver only 23% of their total dose to the target site. Guar gum microspheres showed adequate potential in achieving local release of drug in in vitro release studies, and this finding was further endorsed with in vivo studies. Published: September 8, 2006     

Purification of guar gum for biological applications

Commercial guar gum (GG) was purified by four different methods and characterized by gel permeation chromatography (GPC), thermogravimetric analysis and the determination of monosaccharides composition, protein and copper content, turbidity, intrinsic viscosity and rheological parameters. The first method was based on enzymatic hydrolysis with porcine pancreatin. In the second method successive gum dissolution, centrifugation and precipitation with acetone and ethanol were carried out. Precipitation with Fehling solution was employed in the third method. In the fourth method, the gum was purified by method 2 and then by method 3. All methods led to a reduction in protein content, arabinose and glucose residues, considered as sugar contaminants, and also in intrinsic viscosity and molar mass. Total elimination of protein was only achieved by method 4. Using methods 3 and 4, the gum was contaminated with small amounts of Cu(II) from the Fehling solution. Methods 2 and 4 apparently provided purer guar gum. If the amount of protein is a crucial parameter in the biological application and the guar will be taken in low amounts, method 4 is recommended. Taking into account the purity, thermal stability, rheological parameters of the purified gum and also the cost and simplicity of the procedure, method 2 has wider biological application.