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.     

Improved Hypolipidemic Effects of Xanthan Gum-Galactomannan Mixtures in Rats

This study describes the effects of mixtures of xanthan gum and galactomannan, guar gum, or locust bean gum, on the lipids in plasma and liver in non-diabetic and diabetic rats. Non-diabetic rats were fed cholesterol-free diets with 3% guar gum, locust bean gum, or xanthan gum (3G, 3L, and 3X), or a mixture of xanthan gum and guar gum or locust bean gum (1:2, w/w) (2G1X, 2L1X) for 2 weeks. Rats fed diets not containing these polysaccharides were used as controls. The total cholesterol in plasma and the triacylglycerol in liver were significantly lowered in rats fed the 2G1X diet. The 3G, 3X, 3L, and 2L1X diets showed no significant effect on the total cholesterol and triacylglycerol in plasma and liver. In the streptozotocin-induced (STZ) diabetic rats, the total cholesterol in plasma was lowered in rats fed the 3G, 3X or 2G1X diet for 4 weeks, and the 2G1X diet was more effective than the 3G and 3X diets. The triacylglycerol in plasma in STZ diabetic rats was also significantly lowered by the 2G1X diet. These results showed that a mixture of xanthan gum and guar gum has an improved hypolipidemic effect on non-diabetic and STZ diabetic rats. The effects of the 2G1X diet on the diabetic symptoms in STZ diabetic rats, suppression of food and water intakes, decrease in glucose in urine, and lowering of plasma glucose, were also observed.     

Improved hypolipidemic effects of xanthan gum-galactomannan mixtures in rats

This study describes the effects of mixtures of xanthan gum and galactomannan, guar gum, or locust bean gum, on the lipids in plasma and liver in non-diabetic and diabetic rats. Non-diabetic rats were fed cholesterol-free diets with 3% guar gum, locust bean gum, or xanthan gum (3G, 3L, and 3X), or a mixture of xanthan gum and guar gum or locust bean gum (1:2, w/w) (2G1X, 2L1X) for 2 weeks. Rats fed diets not containing these polysaccharides were used as controls. The total cholesterol in plasma and the triacylglycerol in liver were significantly lowered in rats fed the 2G1X diet. The 3G, 3X, 3L, and 2L1X diets showed no significant effect on the total cholesterol and triacylglycerol in plasma and liver. In the streptozotocin-induced (STZ) diabetic rats, the total cholesterol in plasma was lowered in rats fed the 3G, 3X or 2G1X diet for 4 weeks, and the 2G1X diet was more effective than the 3G and 3X diets. The triacylglycerol in plasma in STZ diabetic rats was also significantly lowered by the 2G1X diet. These results showed that a mixture of xanthan gum and guar gum has an improved hypolipidemic effect on non-diabetic and STZ diabetic rats. The effects of the 2G1X diet on the diabetic symptoms in STZ diabetic rats, suppression of food and water intakes, decrease in glucose in urine, and lowering of plasma glucose, were also observed.     

The influence of locust bean gum and dextran on the gelation of κ-carrageenan

The interaction of κ-carrageenan with locust bean gum and dextran has been studied by rheology, differential scanning calorimetry (DSC), and electron spin resonance spectroscopy (ESR). Rheological measurements show that the carrageenan gel characteristics are greatly enhanced in the presence of locust bean gum but not in the presence of dextran. Carrageenan/locust bean gum mixtures show two peaks in the dsc cooling curves. The higher temperature peak corresponds to the temperature of gelation and its intensity increases at the expense of the lower temperature peak as the proportion of locust bean gum in the mixture increases. Furthermore, the DSC heating curves show enhanced broadening when locust bean gum is present, indicating increased aggregation. These results are taken as evidence of carrageenan/locust bean gum association. The gelation process has also been followed by ESR using spin-labeled carrageenan. On cooling carrageenan solutions, an immobile component appears in the ESR spectra signifying a loss of segmental mobility consistent with chain stiffening due to the coil → helix conformational transition and helix aggregation. For carrageenan/locust bean gum mixtures, carrageenan ordering occurs at temperatures corresponding to the higher temperature DSC setting peak and the temperature of gelation. Similar studies using spin-labeled locust bean gum show that its mobility remains virtually unaffected during the gelation process. It is evident, therefore, that carrageenan and locust bean gum interact only weakly. It is proposed that at low carrageenan concentrations the gel network consists of carrageenan helices cross-linked by locust bean gum chains. At high carrageenan concentrations the network is enhanced by the additional self-aggregation of the “excess” carrageenan molecules. For carrageenan/dextran mixtures, only one peak is observed in the dsc cooling curves. The onset of gelation shifts to higher temperatures only at very high (20%) dextran concentrations and this is attributed to volume exclusion effects. Furthermore, there is no enhanced broadening of the peaks in the DSC heating curves as for the carrageenan/locust bean gum systems. It is therefore concluded that carrageenan/dextran association does not occur. The difference in behavior between locust bean gum and dextran is attributed to the greater flexibility of the dextran chains. © 1996 John Wiley & Sons, Inc.     

Rheology and synergy of κ-carrageenan/locust bean gum/konjac glucomannan gels

The rheology and melting of mixed polysaccharide gels containing konjac glucomannan (KGM), locust bean gum (LBG) and κ-carrageenan (KC) were studied. Synergy-type peaks in the Young's modulus at optimal mixing ratios were found for both KC/LBG and KC/KGM binary gels at a fixed total polysaccharide content (1:5.5 for LBG:KC and 1:7 for KGM:KC). The Young's modulus peak for KC/KGM was higher than for KC/LBG gels. The same stoichiometric mixing ratios were found when either LBG or KGM was added to KC at a fixed KC concentration, where the Young's modulus increased up to additions at the stoichiometric ratio, but leveled off at higher LBG or KGM additions. Addition of KGM or LBG to the 2-component gels beyond the stoichiometric (optimal) mixing ratio at a fixed total polysaccharide content led to a decrease in the Young's modulus and an increase in the rupture strain and stress in extension, and both trends were stronger for KGM than for LBG.     

Studies on κ-carrageenan/locust bean gum mixtures in the presence of sodium chloride and sodium iodide

The solution properties of κ-carrageenan and κ-carrageenan/locust bean gum mixtures have been studied by small deformation oscillation measurements and differential scanning calorimetry (DSC) in the presence of sodium chloride and sodium iodide. Both salts induced the κ-carrageenan to undergo a coil-helix conformational change as noted by an increase in the storage and loss moduli (G′, G′) and by an exothermic peak in the DSC cooling curves. The enthalpy ΔH_c-h and temperature of the conformational transition T_c-h were higher in Nal compared to NaCl and T_c-h increased with increasing the concentration of both electrolytes. Gelation was not observed for carrageenan or carrageenan/locust bean gum mixtures in the presence of up to 200 mM Nal. Although carrageenan alone did not gel in the presence of 100 mM NaCl, a weak gel was obtained for a mixture containing 0.9%/0.1% carrageenan/locust bean gum. Furthermore, the mixture showed hysteresis in both the rheological and DSC cooling and heating curves. A strong gel was produced for carrageenan alone in the presence of 200 mM NaCl and the gel strength increased on adding a small proportion of locust bean gum (0.9%/0.1%). © 1997 John Wiley & Sons, Inc. Biopoly 41: 657–671, 1997     

Microscopy of xanthan/galactomannan mixtures

Polarization microscopy has been used to investigate the structure of 50/50 xanthan/galactomannan (guar gum or locust bean gum) mixtures in aqueous solution, the total concentration ranging from 0.5 to 4%. By the use of polarized light microscopy birefringent areas resulting from the formation of cholesteric mesophases in xanthan gum was clearly seen as has previously been reported by several authors. In xanthan/galactomannan mixtures, we also observed birefringent areas. Moreover, these zones in the blend appeared more anisotropic than with xanthan gum alone. This suggests that xanthan molecules organize themselves as liquid crystalline mesophases in definite enriched xanthan areas resulting from a concentration of xanthan inside these birefringent zones. Upon heating, this anisotropy disappears at a temperature well below the helix-coil transition temperature of xanthan molecules. In fact, this loss of order of the mixed system occurs at the same temperature as the melting temperature of the gel, as assessed by the use of rheological measurements. Since the ordered helical structure of the xanthan molecules still exists beyond the melting temperature while anisotropy disappears, this suggests that the xanthan molecules are no longer concentrated in specific areas but more evenly distributed in the medium. Gel melting would, therefore, be the result of the disappearance of these xanthan enriched areas.     

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.     

TEXTURE OF SWEET ORANGE GELS BY FREE-CHOICE PROFILING

Texture of orange gels prepared with 15% fruit pulp, sucrose up to 55° Brix and five different gelling agents — kappa-carrageenan, kappa-carrageenan plus locust bean gum, alginate, gellan gum, and gellan, xanthan and locust bean gums — was studied by Free-Choice Profile (FCP) analysis. Maximum rupture force and deformation at rupture were also determined by uniaxial compression in an Instron texturometer. Generalized Procrustes Analysis applied to FCP data permitted differentiation between samples and informed on the textural attributes responsible for the observed differences. Sensory differences were in general in accordance with mechanical differences. However, carrageenan and gellan gum gels were differentiated with the sensory method applied but not with mechanical tests.     

Associative phenomena in galactomannan-deacetylated xanthan systems

The interaction between mesquite seed galactomannan (MSG; D-mannose to D-galactose ratio (M/G) approximately 1.1) and deacetylated xanthan (DX) in 5 mM NaCl leading to synergistic gel formation at 25 degrees C was investigated and compared with the far more studied system made of xanthan and locust bean gum (LBG; M/G approximately 3.5). Rheology and differential scanning calorimetry were used to measure temperatures of gel formation and transition enthalpy as a function of polymer composition, while circular dichroism was used to probe the conformation of DX in the LBG-DX system. MSG and DX associate at 25 degrees C with a well defined stoichiometry of 0.6:1.0 (w/w) at low ionic strength favouring the disordered coil state of DX. When LBG was used in place of MSG in water or 5 mM NaCl, two types of mechanisms of interpolymeric association are envisaged.     

Anti-juvenile Hormone Effects of an Imidazole Compound (KK-42) in Different Larval Instars of Bombyx mori

The non-Newtonian behavior and dynamic viscoelasticity of solutions of the Ca salt of xanthan were measured with a rheogoniometer. The Ca salt of xanthan showed pseudoplastic behavior < 0.1 % but was plastic >0.3%. Compared with native, Na, and K salts of xanthan, the Ca salt had higher dynamic viscoelasticity at high concentrations. The apparent viscosity of Ca salt of xanthan was very large at low temperatures and decreased with increasing temperature. These suggest very strong intermolecular association of the xanthan (Ca salt) molecules, probably due to the formation of ionic force between adjacent charged trisaccharide side-chains via Ca²⁺ on different molecules. Possible structures for quaternary association including intramolecular association of xanthan molecules (Ca and K salts) in aqueous solution were proposed.     

Incorporation of galactomannans in the diet of newly weaned piglets: Effect on bacteriological and some morphological characteristics of the small intestine

In search of substances replacing antibiotics as growth promoters for farm animals, non-digestible oligosaccharides (NDO) or non-starch polysaccharides (NSP) have been proposed as possible alternatives. In this context, the influence of galactomannans on bacteriological and morphological aspects of the gastrointestinal tract in weanling pigs was investigated. Four groups of five newly weaned piglets received one of the following diets: control feed (C), C supplemented with guar gum (1%), C supplemented with locust bean gum (1%) and C supplemented with 10% of carob tree seeds meal as source of locust bean gum. The animals were euthanized after 11?–?12 days and digesta were sampled in stomach, jejunum (proximal and distal) and caecum, while mucosal scrapings and ring shaped tissue samples were taken of proximal and distal jejunum. On these samples bacteriological, biochemical and morphological determinations were carried out. Total count of bacteria in digesta and mucosal scrapings was not influenced by the different diets, with the exception of the proximal jejunum where a small decrease (0.5 log₁₀ CFU) was noted with the guar gum and carob tree seeds diet. The number of E. coli increased by feeding both gums and carob tree seeds. With the latter diet, higher counts of streptococci were observed. In agreement with the lower concentration of lactic acid in jejunal contents, guar gum decreased the number of lactobacilli. Locust bean gum decreased the molar proportion of acetate in caecal contents while butyrate and valerate were augmented. Feeding the carob tree seeds resulted in shorter villi and a lower villus height/crypt depth ratio in the jejunum mucosa, which was an indication for a faster renewal rate of the epithelium. Both locust bean gum feeds significantly lowered the mitotic index in the crypts of the small intestine. Only with the carob tree seeds diet, viscosity of jejunal contents was increased. In conclusion, the effects of the addition of 1% of pure guar gum or locust bean gum were inconsistent and not very outspoken, whereas 10% of carob tree seeds meal in the diet resulted in influences on intestinal characteristics at the bacteriological and morphological level.     

Rheology and microstructure of Ca- and Na-K-carrageenan and locust bean gum gels

The viscoelastic and microstructural influences of 0.1-0.6% locust bean gum on 0.5 or 1.0% κ-carrageenan gels, in different ionic environments, have been studied using small deformation oscillatory measurements and transmission electron microscopy (TEM). The results from the Theological measurements showed synergistic effects in the storage modulus, G', as locust bean gum, of two different mannose to galactose ratios (3 and 5), was mixed with ion-exchanged Na- and Ca-κ-carrageenan, in 0.25 M NaCl and 0.030 M CaC1₂, respectively. The increase in G' was dependent on the mannose to galactose ratio, polymer concentrations, and ionic environment.

At the supermolecular level, the microstructure of dilute samples has been visualised using low angle rotary metal shadowing for TEM. In the presence of sodium and calcium ions, the self-association of κ-carrageenan helices is moderate to low. Locust bean gum did not influence the supermolecular structure of κ-carrageenan to any large extent. The microstructure of the gels at the network level was studied using plastic embedding and thin sectioning for TEM. In both sodium and calcium ionic environments, the mixed gels showed a more homogeneous and connective network structure.     

Pretreatment of Cells of Klebsiella pneumoniae with 50% (v/v) Dimethylsulfoxide Yields Purified Deoxyribonucleic Acid of Low Polysaccharide Content

The flow behavior and dynamic viscoelasticity of welan gum solutions were measured with a rheogoniometer. The welan gum showed shear-thinning behavior at a concentration of 0.1%, but plastic behavior above 0.3% at 25°C. The dynamic viscoelasticity increased with increasing concentration, and was scarcely changeable with increasing temperature even at 80°C. Gelation did not occur even in a polysaccharide concentration of 1.0% at low temperature (0°C). An increase of the dynamic modulus was not observed on the addition of CaCl₂ (6.8 mm). The dynamic viscoelasticity of welan gum solution was scarcely changeable in a wide range of pH from 2 to 12. The dynamic modulus was also scarcely changeable on addition of urea (4.0 m). Possible mode of intramolecular associations between the OH-4 of the d-glucosyl residue and the adjacent hemiacetal oxygen atom of the l-rhamnosyl residue, and between the methyl group of the l-rhamnosyl residue and the adjacent hemiacetal oxygen atom of the d-glucosyl residue were proposed.     

Incorporation of galactomannans in the diet of newly weaned piglets: effect on bacteriological and some morphological characteristics of the small intestine

In search of substances replacing antibiotics as growth promoters for farm animals, non-digestible oligosaccharides (NDO) or non-starch polysaccharides (NSP) have been proposed as possible alternatives. In this context, the influence of galactomannans on bacteriological and morphological aspects of the gastrointestinal tract in weanling pigs was investigated. Four groups of five newly weaned piglets received one of the following diets: control feed (C), C supplemented with guar gum (1%), C supplemented with locust bean gum (1%) and C supplemented with 10% of carob tree seeds meal as source of locust bean gum. The animals were euthanized after 11-12 days and digesta were sampled in stomach, jejunum (proximal and distal) and caecum, while mucosal scrapings and ring shaped tissue samples were taken of proximal and distal jejunum. On these samples bacteriological, biochemical and morphological determinations were carried out. Total count of bacteria in digesta and mucosal scrapings was not influenced by the different diets, with the exception of the proximal jejunum where a small decrease (0.5 log10 CFU) was noted with the guar gum and carob tree seeds diet. The number of E. coli increased by feeding both gums and carob tree seeds. With the latter diet, higher counts of streptococci were observed. In agreement with the lower concentration of lactic acid in jejunal contents, guar gum decreased the number of lactobacilli. Locust bean gum decreased the molar proportion of acetate in caecal contents while butyrate and valerate were augmented. Feeding the carob tree seeds resulted in shorter villi and a lower villus height/crypt depth ratio in the jejunum mucosa, which was an indication for a faster renewal rate of the epithelium. Both locust bean gum feeds significantly lowered the mitotic index in the crypts of the small intestine. Only with the carob tree seeds diet, viscosity of jejunal contents was increased. In conclusion, the effects of the addition of 1% of pure guar gum or locust bean gum were inconsistent and not very outspoken, whereas 10% of carob tree seeds meal in the diet resulted in influences on intestinal characteristics at the bacteriological and morphological level.     

Synergistic Interaction between Kappa-Carrageenan and Locust-bean Gum in Aqueous Media

Although neither kappa-carrageenan nor locust-bean gum gelled alone, a mixed aqueous solution of the above gums gave a gel at the concentration of 0.6% total gums in a range of low temperatures. The solution also gelled even at the concentration of 0.4% total gums in the presence of 0.1% KC1. The maximum dynamic modulus was obtained with a series of the samples composed of kappa-carrageenan and locust-bean gum in the mixing ratios of 1:1 and 3:1 at the concentration of 0.6 and 0.8% total gums at 0°C. The dynamic modulus of a mixed solution of kappa-carrageenan and locust-bean gum was not influenced by pH between pH 7.0 to 11.5, but decreased in the acidic range.

We concluded that intermolecular interactions, at low temperature, between kappa-carrageenan and locust-bean gum may take place on the K⁺-bridge of the former and the backbone of the latter molecule at low concentrations, but at high concentration of the gums, self-association of kappa-carrageenan molecules might also occurred.     

A celluloytic complex from <Emphasis Type="Italic">Clostridium cellulovorans</Emphasis> consisting of mannanase B and endoglucanase E has synergistic effects on galactomannan degradation

In our previous study using a fluorescently labeled cohesin biomarker, we detected and identified a putative cellulosomal mannanase belonging to the glycosyl hydrolase family 26 from Clostridium cellulovorans in xylan-containing cultures. In this study, a mannanase gene, manB from C. cellulovorans, was expressed in Escherichia coli. The optimal pH of a purified enzyme was around pH 7.0 and the optimal temperature was 40°C. The purified mannanase B (ManB) showed high hydrolytic activity toward galactomannan. An assembly of ManB with mini-CbpA, which contains a carbohydrate-binding module that provides proximity to insoluble substrates, increased the activity toward galactomannan [locust bean gum (LBG) and guar gum] 1.7- and 2.0-fold over those without mini-CbpA. We tested the synergistic effects on galactomannan (LBG and guar gum) degradation using cellulosomal mannanase ManB with cellulosomal endoglucanase E, which was predicted to have mannanase activity in C. cellulovorans as a cellulolytic complex. When assembled with the mini-CbpA, the mixture of endoglucanase E (EngE) and ManB at a molar ratio of 1:2 showed the highest synergistic effect (2.4-fold) on LBG. The mixture at a ratio of 1:3 showed the highest synergistic effect (2.8-fold) on guar gum. These synergistic actions indicated that ManB assembled with mini-CbpA hydrolyzed insoluble galactomannan, which in turn promoted soluble galactomannan degradation by EngE.     

A novel gene encoding xanthan lyase of Paenibacillus alginolyticus strain XL-1

Xanthan-modifying enzymes are powerful tools in studying structure-function relationships of this polysaccharide. One of these modifying enzymes is xanthan lyase, which removes the terminal side chain residue of xanthan. In this paper, the cloning and sequencing of the first xanthan lyase-encoding gene is described, i. e., the xalA gene, encoding pyruvated mannose-specific xanthan lyase of Paenibacillus alginolyticus XL-1. The xalA gene encoded a 100, 823-Da protein, including a 36-amino-acid signal sequence. The 96, 887-Da mature enzyme could be expressed functionally in Escherichia coli. Like the native enzyme, the recombinant enzyme showed no activity on depyruvated xanthan. Compared to production by P. alginolyticus, a 30-fold increase in volumetric productivity of soluble xanthan lyase was achieved by heterologous production in E. coli. The recombinant xanthan lyase was used to produce modified xanthan, which showed a dramatic loss of the capacity to form gels with locust bean gum.     

A Novel Gene Encoding Xanthan Lyase of Paenibacillus alginolyticus Strain XL-1

Xanthan-modifying enzymes are powerful tools in studying structure-function relationships of this polysaccharide. One of these modifying enzymes is xanthan lyase, which removes the terminal side chain residue of xanthan. In this paper, the cloning and sequencing of the first xanthan lyase-encoding gene is described, i.e., the xalA gene, encoding pyruvated mannose-specific xanthan lyase of Paenibacillus alginolyticus XL-1. The xalA gene encoded a 100,823-Da protein, including a 36-amino-acid signal sequence. The 96,887-Da mature enzyme could be expressed functionally in Escherichia coli. Like the native enzyme, the recombinant enzyme showed no activity on depyruvated xanthan. Compared to production by P. alginolyticus, a 30-fold increase in volumetric productivity of soluble xanthan lyase was achieved by heterologous production in E. coli. The recombinant xanthan lyase was used to produce modified xanthan, which showed a dramatic loss of the capacity to form gels with locust bean gum.