| 1. |
- Lundqvist, Jon, et al.
(författare)
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Characterization of galactoglucomannan extracted from spruce (Picea abies) by heat-fractionation at different conditions
- 2003
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Ingår i: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 51:2, s. 203-211
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Tidskriftsartikel (refereegranskat)abstract
- Water-soluble hemicelluloses were extracted from spruce chips by microwave heat-fractionation. The galactoglucomannan (GGM) extraction was evaluated on the basis of weight-average molecular weight (MW), yield and carbohydrate composition of the GGM. The MW was determined by size-exclusion chromatography with column calibration using off-line MALDI-MS analysis, and determination of mannan content in the fractions collected. Water impregnated spruce chips were heat-fractionated at three different temperatures (180, 190, and 200oC). The spruce chips were also impregnated in NaOH solutions of different concentrations, and then heat-fractionated at 190oC for 5min. The highest mannan yield (78% based on the amount in the raw material) was obtained from water impregnated spruce chips heat-fractionated at 190oC for 5min (MW of 3800). The highest MW (14,000) was obtained from impregnation with 2% NaOH (190oC, 5min), but the yield of mannan was very low (3%). Impregnation with 0.025% NaOH and heat-fractionation at 190oC for 5min resulted in extraction of GGM with MW of 9500 and a mannan yield of 31%. When the spruce chips were impregnated with =<0.05% NaOH an O-acetyl-galactoglucomannan was extracted, whereas when higher NaOH charges were used in the impregnation, the extracted GGM lacked acetyl groups.
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| 2. |
- Berggren, R., et al.
(författare)
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Alkaline degradation of birch and spruce : influence of degradation conditions on molecular mass distributions and fibre strength
- 2003
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Ingår i: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 51:3, s. 255-264
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Tidskriftsartikel (refereegranskat)abstract
- The alkaline degradation of birch and Norway spruce during kraft pulping was studied on a laboratory scale by two degradation strategies, by varying the pulping time using the same initial alkali level and by varying the initial alkali concentration using a constant time. The degradation at the molecular level was monitored by determining the carbohydrate composition, intrinsic viscosity and-molecular mass distribution (MMD). The influence of the degradation on fibre strength was studied as zero-span tensile index. The alkaline degradation was to a large extent homogeneous on a molecular level. However, some significant differences in degradation patterns were found. In the case of birch, the two different degradation strategies (increased alkali level and increased pulping time) caused differences in MMD and fibre strength (comparisons made at a given intrinsic viscosity or M-w). For spruce pulps, the decrease in fibre strength and the shift in MMD were the same in both series, regardless of degradation strategy.
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| 3. |
- Stading, Mats, et al.
(författare)
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Humidity-induced structural transitions in amylose and amylopectin films
- 2001
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Ingår i: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 45:3, s. 209-217
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Tidskriftsartikel (refereegranskat)abstract
- The effect of humidity on the dynamic mechanical and barrier properties and on the microstructure of amylose and amylopectin films was studied. The films were solution-gel-cast, with and without glycerol as added plasticizer, and dried to equilibrium weight under various relative humidities (RH). The network microstructure of glycerol-plasticized amylose films was shown to change from dense and homogeneous to a more open structure with fluctuations in the pore size when the surrounding RH was increased. The structural change was attributed to plasticization of the amorphous areas by increased water content, leading to higher mobility in the network and subsequent inhomogeneous swelling. This structural change had a direct influence on the oxygen permeability, which drastically increased. The onset of the increase occurred at lower surrounding RH for the films containing glycerol, and these films also had higher oxygen permeability. Glycerol-plasticized amylopectin films with gradually increased crystallinity were prepared by varying the RH during film formation. Dynamic mechanical analysis at both varied temperature and RH showed that the increased crystallinity led to higher glass transition temperature, T g, and a smaller effect of the surrounding humidity on mechanical and barrier properties. The RH during the formation of glycerol-plasticized amylose films did not affect crystallinity or T g. These films formed at 70% RH were shown to have a marked heterogeneous network. © 2001 Elsevier Science Ltd.
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| 4. |
- Richardson, G., et al.
(författare)
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Differences in amylose aggregation and starch gel formation with emulsifiers
- 2004
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 58:1, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- The effects of different kinds of emulsifiers, polyglycerol ester and glycerol monostearate, and the surface-active lignosulfonate, on network formation and aggregation of amylose and starch in gels were studied. Pastes with emulsifier and 5% amylose or different starches were heated to between 90 and 150°C, cooled and studied by means of transmission electron microscopy. The fine-stranded amylose network aggregated into thicker strands when emulsifiers were added. At high emulsifier concentrations, spherical aggregates without internal structure formed, and the network disappeared. In wheat starch gels, a lower concentration of emulsifier was needed for amylose aggregation than in pure amylose gels. At high temperatures (> 140°C), aggregation was more ordered, and long, needle-like threads or brush-like aggregates were achieved. The amylose aggregated similarly with the complexing emulsifiers used in this work as with the non-complexing surfactant, which showed that amylose-lipid complex formation was not the primary explanation for aggregation. © 2004 Elsevier Ltd. All rights reserved.
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| 5. |
- Richardson, G., et al.
(författare)
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Effects of Ca- and Na-lignosulfonate on starch gelatinization and network formation
- 2004
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 57:4, s. 369-377
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of lignosulfonates with starches was examined by microscopy and viscosity measurements. 8% starch dispersions with Ca- or Na-lignosulfonate, or with only Ca2+ or Na+, were heated to 97°C and cooled to 50°C in a Brabender Viscograph, the gelatinization was followed by light microscopy and image analysis, and the gel network formed after cooling to 4°C was studied under the transmission electron microscope. The lignosulfonates (2%) delayed the initial granule swelling in all starches (native maize, waxy maize and waxy barley). The presence of ions enhanced amylose leakage resulting in lower peak viscosity. The viscosity during cooling increased more with Ca-LS than with Na-LS. With a low lignosulfonate concentration the network formed after cooling was homogeneous with fine strands. With Na-lignosulfonate, as well as with Na+, the network connectivity deteriorated and spherical aggregates formed. Ca-lignosulfonate induced a network with thick strands, but with Ca2+ the strands became thinner. © 2004 Elsevier Ltd. All rights reserved.
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| 6. |
- Karlson, L, et al.
(författare)
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A rheological investigation of the complex formation between hydrophobically modified ethyl (hydroxy ethyl) cellulose and cyclodextrin
- 2002
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Ingår i: Carbohydrate Polymers. - 0144-8617. ; 50:3, s. 219-226
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Tidskriftsartikel (refereegranskat)abstract
- The thickening effect of a hydrophobically modified polymer in an aqueous solution is dependent on intermolecular hydrophobic associations, and if the polymer concentration is significantly above the overlap concentration also on chain entanglements. In this investigation we have added different cyclodextrins (CD) in order to decouple hydrophobic polymer-polymer associations via inclusion complex formation with the polymer hydrophobic tails. Both size and hydrophobicity of the cavity of the CD-molecules were found to have an effect on the process. In addition, the influence of chemical structure of the polymer hydrophobic tails was investigated. Either a linear C-14-chain or a more bulky nonylphenol group was used. The viscosity as a function of CD-concentration first decreased strongly, and then attained a constant value. At excess CD the viscosity became virtually the same as in a solution of the unmodified parent polymer, provided that complex formation was not sterically bindered. This suggests that all hydrophobic links, originating from the hydrophobic modification process, which influence the theology could be deactivated. On the other hand, with combinations where the complex formation was hindered to a certain degree the initial decrease was less accentuated, and also, the viscosity leveled out at a significantly higher value. In an attempt to rationalize the data a simple model based on the assumption that each complex formed deactivates one theologically active link was used. In combination with the Langmuir adsorption model the number of complexes as a function of CD concentration could be obtained. This model also gave a value of the complex formation constant. Furthermore, in solutions where all hydrophobic links could be deactivated the results from the model suggested that all polymer hydrophobic tails were originally active in forming the network. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 7. |
- Lundqvist, Henrik, et al.
(författare)
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Binding of hexadecyltrimethylammonium bromide to starch polysaccharides. Part 1. Surface tension measurements
- 2002
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Ingår i: Carbohydrate Polymers. - 0144-8617. ; 49:1, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- Surface tension measurements were used to characterise the binding of the cationic surfactant hexadecyltrimethylammonium bromide, CTAB, to three starch polysaccharides, amylose from potato, amylopectin from potato and amylopectin from barley. Surface tension measurements were used according to the axisymmetric drop shape analysis. ADSA, to determine the concentration of free CTAB monomers during consecutive addition of CTAB to the polysaccharide solutions, The interaction between the starch polysaccharides and CTAB was studied at three starch concentrations. 0.1, 0.25 and 0.5% (w/w). Binding isotherms were derived from the concentration of free CTAB and the type of binding was determined with Scatchard plots. The binding capacities of CTAB correlated linearly with the polysaccharide concentration but were independent of the type of starch polysaccharide. All three starch polysaccharides were able to bind 33 mmol CTAB per mole glucose units. The binding of CTAB to amylose was cooperative while the binding of CTAB to amylopectin was of Langmuir type.
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| 8. |
- Lundqvist, Henrik, et al.
(författare)
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Binding of hexadecyltrimethylammonium bromide to starch polysaccharides. Part II. Calorimetric study
- 2002
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Ingår i: Carbohydrate Polymers. - 0144-8617. ; 49:2, s. 109-120
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Tidskriftsartikel (refereegranskat)abstract
- Isothermal titration calorimetry was used to study the interaction between hexadecyltrimethylammonium bromide, CTAB, and three starch polysaccharides, amylose from potato, amylopectin from potato and amylopectin from barley. The enthalpy change for consecutive additions of CTAB to starch polysaccharide solutions were measured at 27degreesC. The starch-CTAB interaction enthalpies, DeltaH(f), were calculated by subtracting the enthalpy of micelle dissociation and dilution from the observed heat and relating the interaction enthalpy to the amount of interacting CTAB. The interaction was studied at three polysaccharide concentrations, 0.1, 0.25 and 0.5% w/w. The exothermic interaction enthalpy was constant and quite large in the main part of the concentration range studied for all three-starch polysaccharides. Amylose had an interaction enthalpy of -55 kJ/mol CTAB while the amylopectin samples had an interaction enthalpy of -40 kJ/mol CTAB. Amylopectin and amylose seemed to have a similar interaction with CTAB, the small differences were probably due to the differences in structure between the polysaccharides.
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| 9. |
- Lundqvist, Jon, et al.
(författare)
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Isolation and characterization of galactoglucomannan from spruce (Picea abies)
- 2002
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Ingår i: Carbohydrate Polymers. - 0144-8617. ; 48:1, s. 29-39
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Tidskriftsartikel (refereegranskat)abstract
- Water-soluble hemicelluloses were extracted from spruce chips by microwave heat fractionation. The chips were impregnated with water at different pH values. Screening of heat-fractionation conditions, i.e. impregnation medium, temperature and residence time was performed with the aim to extract O-acetyl-galactoglucomannan. The impregnation and heat fractionation conditions were evaluated on the basis of the yield of dissolved mannan (oligo- and polysaccharides), molecular weight of the carbohydrates and amount of dissolved lignin. Increasing temperature and residence time increases the yield of mannan and decreases the molecular weight of dissolved carbohydrates. For a structural study of the extracted carbohydrates the chips were impregnated with water and treated at 200oC for 2min. Oligo- and polysaccharides were fractionated with preparative size-exclusion chromatography from the filtered extract.The structure of the obtained saccharides in two fractions 8 and 9 was determined by 1H NMR spectroscopy. The polysaccharides in the fractions were O-acetyl-galactoglucomannan with a degree of polymerization ~20 and ~11 for fractions 8 and 9, respectively. The molar ratio for galactose:glucose:mannose was approximately 0.1:1:4. About one-third of the d-mannosyl units are substituted by O-acetyl groups almost equally distributed between C-2 and C-3.
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| 10. |
- Nilsson, G. S., et al.
(författare)
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Microdialysis clean-up and sampling in enzyme-based methods for the characterisation of starch
- 2001
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 46:1, s. 59-68
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Tidskriftsartikel (refereegranskat)abstract
- Microdialysis was used for sampling enzyme hydrolysis products of starch hydrolysed with beta -amylase, pullulanase, and/or isoamylase, to obtain information about the molecular structure of starch. Starches from waxy, normal, and high amylose maize, and from normal and genetically modified potato (amylose deficient) were used, and also commercial potato amyloses. The hydrolysis products were analysed using high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Simultaneous sampling and sample clean-up were achieved with microdialysis, thus enabling on-line injection into the liquid chromatographic system. The molecular weight cut-off of the membrane allowed for diffusion of small molecules such as oligosaccharides through the membrane, but hindered large molecules, e.g. enzymes and large polysaccharides, from entering the chromatographic system. With microdialysis sampling, it was possible to investigate the short chain fractions of debranched starch in the presence of amylose without pre-fractionation. The microdialysis-HPAEC-PAD system was also used for determination of the A:B chain ratio and the P-limit value. After P-amylolysis, only liberated maltose diffused through the dialysis membrane, which resulted in on-line sample clean-up from branched P-limit dextrin as well as from the enzyme. The proposed method is fast and easy to handle since clean-up of the hydrolysate is achieved on-line with the chromatographic system. (C) 2001 Elsevier Science Ltd. All rights reserved.
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