Effect of ultrasound on enzymatic acylation of konjac glucomannan

A comparative study was made of enzymatic acylation of konjac glucomannan with vinyl esters under ultrasonic irradiation and shaking in organic solvent tert-butanol. Among the 13 enzymes selected, Novozym 435 exhibited the highest acylation activity towards KGM whether under ultrasonic irradiation or shaking. The application of ultrasonic irradiation instead of shaking during the acylation led to improvement in the initial reaction rate, yield and degree of substitution of the modified KGM. Appropriate ultrasound power (100 W) and water activity (0.75) were found to accelerate enzymatic reaction. The acceleration effect of ultrasound on Novozym 435-catalyzed acylation decreased with an increase in the chain length of the acyl donors from C2 to C18. Moreover, the acylation of KGM in tert-butanol was proved to be a regioselective one, with C6-OH being acylated. Compared with shaking, ultrasound did not change regioselectivity of Novozym 435 in the acylation.     

Physicochemical characterization of konjac glucomannan

Four commercial konjac glucomannan (KGM) samples and a glucomannan derived from yeast were characterized by aqueous gel permeation chromatography coupled with multi angle laser light scattering (GPC-MALLS). Disaggregation of aqueous glucomannan solutions through controlled use of a microwave bomb facilitated reproducible molar mass distribution determination alleviating the need for derivatization of the polymer or the use of aggressive solvents. Further characterization was undertaken by use of capillary viscometry and photon correlation spectroscopy (PCS). The weight average molecular masses (M(w)) determined were in the region of 9.0 +/- 1.0 x 10(5) g mol(-1) for KGM samples and 1.3 +/- 0.4 x 10(5) g mol(-1) for the yeast glucomannan. The values determined for KGM in aqueous solution are in agreement with those reported for KGM in aqueous cadoxen. The degradation of samples observed upon autoclaving has been quantified by GPC-MALLS and intrinsic viscosity determination, allowing comparison with reported Mark-Houwink parameters. Shear flow experiments were undertaken for a range of KGM solutions of concentration 0.05 to 2.0% using a combination of controlled stress and controlled strain rheometers. The concentration dependence of the zero shear specific viscosity was determined by analysis of the data using the Ellis model. The dependence of the zero shear specific viscosity on the coil overlap parameter was defined and interpretation discussed in terms of the Martin and Tuinier equations.     

魔芋葡甘聚糖的pH触发酶解

利用高效凝胶排阻色谱技术研究并实现了以溶液pH值为简易调节开关,对魔芋葡甘聚糖的酶解反应进行触发调控：结果表明：pH为4时底物分子量不发生变化,而当pH调至7时,酶解被触发进行,底物分子量随之快速下降。分析表明：酶在pH变化过程中发生部分复性的可能原因是pH由7调至4的过程中发生沉淀的酶分子维持了天然构象,当pH反调回7时重新溶解,并对KGM进行剪切。     

Physicochemical properties of extrusion-modified konjac glucomannan

Konjac glucomannan was extruded and subsequently ground under four conditions denoted: KGM1 (33% solids, 90 °C), KGM2 (24% solids, 90 °C), KGM3 (24% solids, 90 °C, die restriction), and KGM4 (24% solids, 110 °C). SEM and particle size analysis showed that extruded KGM had slightly larger and rougher particles. The water absorption index was decreased to 47.92-128.80, as compared to 153.64 for the control (KGMC). The crystallinity index increased to 2.97 and 3.42 for KGM3 and KGM4 samples, as compared to 1.72 for the control. Zero-shear viscosity of 0.5% solutions decreased to 0.36-3.01 Pa s. All samples were shear-thinning and data were best fitted by the Cross model. Based on capillary viscometry, molecular weights were decreased to 2.7 × 10⁵-9.9 × 10⁵, as compared to 1.2 × 10⁶ for the control. In most cases, properties were most altered by higher temperature and shear, and to a lesser extent by lower solids in the feed.     

Studies on the molecular chain morphology of konjac glucomannan

The chain geometry and parameters of konjac glucomannan were studied by using laser light scatter (LLS), gel permeation chromatography (GPC) and viscosimetry. The weight-average molecular weight (M_w), root-mean-square ratio of gyration (S^21/2), second viral coefficient (A₂) and polydispersity index (M_w/M_n) were 1.036×10⁶, 105±0.9 nm, (−1.587±0.283)×10⁻³  mol ml g⁻² and 1.015±0.003 respectively. Mark-Houwink equation was established as , and the molecular chain parameters were as follows: M_L=982.82 nm⁻¹, q=27.93 nm, d=0.74 nm, h=0.26 nm, L=1054.11 nm. To confirm the above results, konjac glucomannan was observed by using atomic force microscopy (AFM) and transmission electron microscope (TEM). The physical image showed directly that the konjac glucomannan molecule was an extending semi-flexible linear chain without branches, and than the molecular dimension also conformed to the parameters above. Therefore the image of molecular chain geometry confirmed the deduction drawn by Mark-Houwink equation and molecular chain parameters magnificently.     

Gelation of konjac glucomannan crosslinked by organic borate

A series of thermoreversible konjac glucomannan gels crosslinked by organic borate were prepared. The gel network was formed through the crosslinking reaction between borate ions dissociated from organic borate and the cis-diol hydroxyl groups on the mannose units of polysaccharide chains. The rheological properties of the complex gels were studied by dynamic viscoelastic measurement. The gelation kinetics of the gels were studied and the critical gelation points of the gels were exactly determined by the Winter–Chambon criterion. The effects of temperature and composite ratio on the shear storage modulus (G^′), the loss modulus (G^″), and the sol-gel transition points were investigated. The critical gel-sol temperatures of the complex gels were successfully elucidated by Winter–Chambon criterion. The effect of crosslinking density on the critical gelation temperature and the elasticity of the gels were discussed.     

Gelation behavior of native and acetylated konjac glucomannan

Gelation kinetics of native and acetylated konjac glucomannan (KGM) samples in the presence of alkali (sodium carbonate) was studied by dynamic viscoelastic measurements. Molecular weight and other molecular parameters of KGM were determined by static light scattering and viscosity measurements. It was found that KGM molecules were degraded during acetylation treatment, but the molecular weights of acetylated samples were almost independent of the degree of acetylation (DA) and were about a half of that of a native sample. At a fixed alkaline concentration, increasing concentration of KGM or temperature shortened the gelation time, but increasing DA delayed it. The deacetylation reaction and subsequent aggregation process of acetylated samples needed longer time than that of native sample, and acetylated samples formed finally more elastic gels. It implied that the presence of acetyl groups exerts a strong influence on gelation behavior of KGM. It was suggested that the gelation rate of acetylated KGM and native KGM, which depends on the alkaline concentration and temperature, is an important factor that determines the elastic modulus of gels. This was supported by the experimental finding that the saturated elastic modulus tends to the same value when the ratio of alkali concentration to acetylated groups was kept constant. In slower gelation processes, junction zones are more homogeneously distributed and more numerous, leading to the more elastic gels.     

Effect of γ-irradiation on some physiochemical properties of konjac glucomannan

Konjac glucomannan (KGM) was irradiated at 5, 20, 50 and 100 kGy and the effects of γ-irradiation on some physiochemical properties of KGM were studied by using viscosimeter, colorimeter, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV) spectroscopy, thermal gravimetric (TG) analysis and scanning electron microscopy (SEM). γ-irradiation led to significant degradation of KGM according to the significant reduction of the weight-average molecular weight (M_w). The apparent viscosity of KGM decreased with increasing dose, while the viscosity stability was improved after irradiation. The colour of KGM became more intense brown with increasing dose up to 20 kGy. FT-IR spectra indicated that γ-irradiation introduced no significant changes into the structure but UV spectra showed a distinct absorption peak at about 265 nm, increasing with irradiation dose, which was attributed to the formation of carbonyl groups or double bond. High irradiation dose (100 kGy) caused a small decrease of thermal stability but presented no visible fissures or splitting of KGM granules according to the TG analysis and SEM microphotographs.     

Gelation behaviour of konjac glucomannan with different molecular weights

The deacetylation and gelation of konjac glucomannan (KGM) following alkali addition was investigated by Fourier transform infrared, while the rheological properties of KGM with different molecular weights were studied by dynamic viscoelastic measurements in shear mode and penetration force tests. It was found that gelation occurred after significant deacetylation had taken place. Rheometrical studies revealed that KGM with different molecular weights exhibited different gelation characteristics in small amplitude oscillatory shear flow. For the samples of fractionated KGM with lower molecular weights, a decrease in both the storage shear modulus (G') and loss shear modulus (G") was observed during gelation at temperatures above 75 degrees C. It is suggested that the decrease results from the wall slip between sample and measuring geometry owing to a rapid gelation process with syneresis and/or disentanglement of molecular chains adsorbed on the surface of parallel plates from those located in the bulk. Penetration force tests were employed to confirm the occurrence of slippage and thereby no decreases in rigidity of samples were observed during gelation. For the native KGM samples decreases in G' and G" during gelation were not observed, and it is suggested that this is due to the effect of the higher molecular weight and increased solution viscosity of these samples on the gelation kinetics.     

Preparation of konjac glucomannan hydrogels as DNA-controlled release matrix

In this study, hydrogels for DNA-controlled release was prepared with konjac glucomannan (KGM), a water-soluble non-ionic polysaccharide, by means of deacetylated reaction and physically cross-linking method under mild conditions. The properties of the KGM hydrogels were analyzed by FTIR spectra and scanning electron microscopy (SEM). The integrality of the released DNA was investigated by circular dichroism (CD). The DNA release kinetics was performed using the DNA-loaded KGM gels in buffer solutions of pH 7.4 at 37+/-0.5 degrees C. Peppas model and Higuchi model were used to analysis the DNA release mechanism; the data indicated that the DNA release can be controlled by changing the preparation conditions and the structure parameters of the gels. This study suggested that the KGM hydrogels have a potential use for advanced controlled release.     

Xanthan and glucomannan mixtures: synergistic interactions and gelation

The synergistic interaction between xanthan and glucomannan in solution and in the gel phase has been studied by circular dichroism spectroscopy and differential scanning calorimetry. The study in solution of the polysaccharidic mixture indicates a preferred stoichiometry of the interaction corresponding to a weight fraction of xanthan around 0.55. This finding is in reasonable agreement with the differential scanning calorimetry measurements carried out on the gel phase. Models from conformational analysis based on these results were formulated in terms of 1:1 and 2:1 Konjac glucomannan/xanthan molecular assemblies. The experimental and calculation results clearly indicate the involvement of the side chains of xanthan and suggest that the ordered portions of the macromolecular complex in solution act in the gel phase as junction zones.     

Structural characterization and properties of starch/konjac glucomannan blend films

In this work, a series of glycerol-plasticized pea starch/konjac glucomannan (ST/KGM) blend films was prepared by a casting and solvent evaporation method. The structure, thermal behavior, and mechanical properties of the films were investigated by means of Fourier Transform Infrared Spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and tensile testing. The results indicated that strong hydrogen bonding formed between macromolecules of starch (ST) and konjac glucomannan (KGM), resulting in a good miscibility between ST and KGM in the blends. Compared with the neat ST, the tensile strength of the blend films were enhanced significantly from 7.4 to 68.1 MPa with an increase of KGM content from 0 to 70 wt%. The value of elongation at break of the blend films was higher than that of ST and reached a maximum value of 59.0% when the KGM content was 70 wt% and 20% of glycerol as plasticizer. The incorporation of KGM into the ST matrix also led to an increase of moisture uptake for the ST-based materials. The structure and properties of pea starch-based films were modified and improved by blending with KGM.     

Condensed state structure and biocompatibility of the konjac glucomannan/chitosan blend films

Specialised blend films have been prepared by blending 1% w/v konjac glucomannan aqueous with 1% w/v chitosan solution in acetate solution and drying at room temperature for 24 h. The condensed state structure and miscibility of the blend films were studied by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. The results indicated that the blend film obtained from an 80/20 mixing ratio of konjac glucomannan and chitosan derivate showed the highest miscibility and blend homogeneity, and that strong intermolecular hydrogen bonds took place between the amino groups of chitosan and the hydroxyl groups of konjac glucomannan; thus the tensile strength also achieved its maximum in this ratio. The cell morphologies on the pure and blend films were examined by light microscopy and cell viability was studied by using MTT assay. The results showed that the particular blend film was more suitable for the cell culture than the pure konjac glucomannan film, and that the cells cultured on this blend film had greater spreading coefficients than that of the pure konjac glucomannan film. As a result of the good mechanical properties, miscibility and biocompatibility, the blend film is a promising biomaterial matrix.     

Immobilization of derivatized dextran nanoparticles on konjac glucomannan/chitosan film as a novel wound dressing

The aim of this study was to prepare konjac glucomannan (KGM)/chitosan (CS) film containing glycidyl methacrylate derivatized dextran (dex-GMA)/acrylic acid(AAc) nanoparticles loaded with antibacterial agent. In this study, An optimized procedure chosen from three methods was used to prepare Erythromycin (EM)-loaded poly(dex-GMA/AAc) nanoparticles and obtained nanoparticles ranged from 50-200 nm. Film was found to have equilibrium water content (EWC) 99.3% which could prevent exudates on wound bed from accumulating and also have excellent water adsorption 2362.3 +/- 55.2%; the water vapor transmission rate (WVTR) was 2335 +/- 36 gm(-2) day(-1) and evaporative water loss from the film (EWL) was approximately 10% after 1 h and within 6 h it increased to 90%. Drug release of film containing nanoparticles or absent was determined, within 22 h accumulative release was 40.3%, 72.5% respectively. In conclusion, KGM/CS film containing nanoparticles could not only maintain a moist environment over wound bed in moderate to heavily exuding wound but also provide a continuous and sustained release of the antibacterial agent on the wound surface, which could be potential wound dressing.     

Molecular and crystal structure of konjac glucomannan in the mannan II polymorphic form.

A probable crystal structure of konjac glucomannan (mannose:glucose ratio = 1.6) is proposed based on X-ray data and constrained linked-atom least-squares model refinement. The structure crystallizes in the mannan II polymorphic form, in an orthorhombic unit-cell with a = 9.01 A, b = 16.73 A, c (fiber axis) = 10.40 A, and a probable space group I222. The backbone conformation of the chain is a two-fold helix stabilized by intramolecular O-3-O-5' hydrogen bonds, with the O-6 rotational position gt. The unit cell contains four chains with antiparallel packing polarity and eight water molecules which reside in crystallographic positions. Intermolecular hydrogen bonds occur exclusively between chains and water molecules, establishing a three-dimensional hydrogen-bond network in the crystal structure. The glucose residues replace mannoses in the structure in isomorphous fashion, although some disorder appears possible. A structure having alternating gg-gt O-6 rotational positions and conforming to space group P222 appears to describe the disorder regions of the crystal. The reliability of the structure analysis is indicated by the X-ray residuals R = 0.276 and R" = 0.223.     

Effect of locust bean gum and konjac glucomannan oh the conformation and rheology of agarose and κ-carrageenan

Mixing with locust bean gum (LBG) induces obvious gel-like character in very dilute solutions of K⁺ κ-carrageenan (< 0.01% w/w in 100 mM KCl). At higher concentration (0.085%), addition of LBG (0.036%) gives a shoulder on the high-temperature side of the DSC (differential scanning calorimetry) exotherm associated with the carrageenan disorder-order transition, with an accompanying increase in gelation temperature and enhancement in gel strength (storage modulus, G′). On substitution of LBG by konjac glucomannan (KM) the shoulder in DSC cornverts to a discernable peak. Van't Hoff analysis of optical rotation data indicates that the high-temperature thermal processes could arise from association of LBG or KM chains to the carrageenan double helix as it forms, with the main transition at lower temperature corresponding to ordering of surplus carrageenan. With K -carrageenan in the nongelling tetra-methylaminonium salt form, addition of LBG causes no delectable change in DSC; rheological enhancement at high concentration (1% w/w) is limited to development of a very tenuous network, and in dilute solution a decrease in viscosity is observed. Agarose shows only a very slight increase in the disorder-order transition temperature on addition of KM, and it shows no detectable change with LBG. These observations are interpreted as showing that efficient binding of mannan or glucomannan chains requires some aggregation of the algal polysaccharide helices, but that extensive aggregation restricts synergistic interaction by competition with heterotypic association. © 1995 John Wiley & Sons, Inc.     

Preparation and characterization of konjac glucomannan/poly(diallydimethylammonium chloride) antibacterial blend films

A novel antibacterial film was prepared by blending konjac glucomannan (KGM) and poly(diallydimethylammonium chloride) (PDADMAC) in an aqueous system. The antibacterial activity of the films against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Saccharomyces were measured by the halo zone test and the double plate method. The films exhibited an excellent antibacterial activity against B. subtilis and S. aureus but not against E. coli, P. aeruginosa or Saccharomyces. The miscibility, morphology, thermal stability, water vapour permeability and mechanical properties of the blend films were investigated by density determination, SEM, ATR-IR, XRD, DSC, TGA, WVA and tensile tests. The results of density determination predicted that the blends of KGM and PDADMAC were miscible when the PDADMAC content was less than 70 wt%. Moreover, SEM and XRD confirmed the result. ATR-IR showed that strong intermolecular hydrogen bonds and electrostatic interactions occurred between KGM and PDADMAC in the blends. The tensile strength and the break elongation of the blends were improved largely to 106.5 MPa and 32.04% and the water vapour permeability decreased when the PDADMAC content was 20 wt%. The thermal stability of the blends was higher than pure KGM. The blends should be good antibacterial materials.     

“Melt-in-the-mouth” gels from mixtures of xanthan and konjac glucomannan under acidic conditions: A rheological and calorimetric study of the mechanism of synergistic gelation

The effect of acidification on a typical commercial xanthan and on pyruvate-free xanthan (PFX), alone and in gelling mixtures with konjac glucomannan (KGM), has been studied by differential scanning calorimetry (DSC) and small-deformation oscillatory measurements of storage modulus (G′) and loss modulus (G″). For both xanthan samples, progressive reduction in pH caused a progressive increase in temperature of the disorder–order transition in DSC, and a progressive reduction in gelation temperature with KGM. This inverse correlation is interpreted as showing that synergistic gelation involves disruption of the xanthan 5-fold helix, probably by attachment of KGM to the cellulosic backbone of the xanthan molecule (as proposed previously by a research group in the Institute of Food Research, Norwich, UK). Higher transition temperature accompanied by lower gelation temperature for PFX in comparison with commercial xanthan at neutral pH is explained in the same way. However, an additional postulate from the Norwich group, that attachment of KGM (or galactomannans) can occur only when the xanthan molecule is disordered, is inconsistent with the observation that gelation of acidified mixtures of KGM with PFX can occur at temperatures more than 60 °C below completion of conformational ordering of the PFX component (as characterised by DSC). Increase in G′ on cooling for mixtures of commercial xanthan with KGM at pH values of 4.5 and 4.25 occurred in two discrete steps, the first following the temperature-course observed for the same mixtures at neutral pH and the second occurring over the lower temperatures observed for mixtures of KGM with PFX at the same values of pH. These two “waves” of gel formation are attributed to interaction of KGM with, respectively, xanthan sequences that had retained a high content of pyruvate substituents, and sequences depleted in pyruvate by acid hydrolysis. At pH values of 4.0 and lower, gelation of mixtures of KGM with commercial xanthan followed essentially the same temperature-course as for mixtures with PFX, indicating extensive loss of pyruvate under these more strongly acidic conditions. Mixtures prepared at pH values in the range 4.0–3.5 gave comparable moduli at room temperature (20 °C) to those obtained at neutral pH, but showed substantial softening on heating to body temperature, suggesting possible applications in replacement of gelatin in products where “melt-in-the-mouth” characteristics are important for acceptability to the consumer.     

Dietary pulverized konjac glucomannan prevents the development of allergic rhinitis-like symptoms and IgE response in mice

Konjac is a traditional Japanese food with a peculiar texture, and it has been suggested that its main ingredient, konjac glucomannan (KGM), ameliorates metabolic disorders such as diabetes and hypercholesteremia. We have found that feeding with pulverized KGM (PKGM) prevents skin inflammation in a murine model of atopic dermatitis. Here, we show that dietary PKGM suppresses allergic rhinitis-like symptoms in mice upon immunization and nasal sensitization with ovalbumin (OVA). The PKGM-fed mice showed a much lower frequency of sneezing than in control animals. We also found that PKGM supplementation exclusively suppressed OVA-specific IgE response without affecting IgG1/IgG2a responses as well as systemic Th1/Th2 cytokine production. These results suggest that PKGM can be a beneficial foodstuff in preventing nasal allergy such as seasonal pollinosis.     

Structure of the oligomers obtained by enzymatic hydrolysis of the glucomannan produced by the plant Amorphophallus konjac

Dimers and trimers obtained by enzymatic hydrolysis of the glucomannan produced by the plant Amorphophallus konjac were analysed in order to obtain information on the saccharidic sequences present in the polymer. The polysaccharide was digested with cellulase and beta-mannanase and the oligomers produced were isolated by means of size-exclusion chromatography. They were structurally characterised using electrospray mass spectrometry, capillary electrophoresis, and NMR. The investigation revealed that many possible sequences were present in the polymer backbone suggesting a Bernoulli-type chain.