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- Anthonsen, M.W., et al.
(author)
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Aggregates in acidic solutions of chitosans detected by static laser light scattering
- 1994
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 25:1, s. 13-23
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Journal article (peer-reviewed)abstract
- Chitosans having degrees of N-acetylation, FA, ranging from 0 to 0·6, were randomly degraded to different molecular weights and studied by multi angle static laser light scattering (LLS). Under the given experimental conditions, negative second virial coefficients of the solutions, A?2, revealed the presence of concentration dependent aggregates. Attempts to remove the aggregates, or to influence the aggregation behavior, were made by ultracentrifugation and extensive filtering of the solutions. Modification of the solvent conditions such as pH, ionic strength and temperature were carried out, and chitosan solutions were digested with an acidic proteinase. Non-degraded samples and chitosans prepared by both heterogeneous and homogeneous N-deacetylation of chitin were also studied. In all cases, the negative A?2 remained. However, it was observed that ultracentrifugation and filtering of the solutions decreased the measured molecular weights and radii of gyration, indicating that some of the material of high molecular weight and size could be removed by ultracentrifugation and filtration. The chemical nature of the physical basis of the molecular association was not revealed. Nevertheless, by the use of gel permeation chromatography coupled to an on-line low angle laser light scattering instrument and a differential refractive index concentration detector (HPSEC-LALLS-RI), a bimodal molecular weight distribution was observed in which about 5% of the sample had a very high molecular weight. These results coupled with the positive virial coefficients obtained earlier from osmotic pressure measurements suggest that a small fraction of the chitosan is aggregated to high molecular weight material, probably following a closed association model. Electron microscopy revealed the presence of some supramolecular structures. The positive second virial coefficients obtained earlier from osmometry are in harmony with these findings. The results demonstrate the occurrence of reversible aggregation in chitosan solutions. Static laser light scattering therefore cannot readily be used to determine molecular weights and sizes of chitosans under these conditions. It was not possible to correlate the extent of aggregation with the chemical composition of the chitosans. © 1994.
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| 4. |
- Hermansson, Ann-Marie
(author)
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Proteiner.
- 1990
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In: Livsmedelsteknik. ; 32:10, s. 25-26
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Journal article (other academic/artistic)
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| 5. |
- Hermansson, Ann-Marie
(author)
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Shear induced changes in the viscoelastic behaviour of heat treated potato starch dispersions
- 1990
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In: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 13:1, s. 29-45
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Journal article (peer-reviewed)abstract
- The viscoelastic behaviour of native potato starch dispersions was studied using dynamic viscoelastic measurements. The influence of various shear and heat treatments of gelatinized starch pastes were compared in the concentration range 4-10%. Heating had a minor effect compared to the effect of shear treatment. The complex modulus (G*) decreased to about 5% of its maximum value when the starch pastes were sheared during the heating cycle, whereas heating alone resulted in a decrease to about 60% of the maximum G* value. Shear also caused an increase in the phase angle and characteristic changes were observed with regard to frequency and strain dependencies. When samples were prepared in a Brabender viscograph, the shear induced changes took place early in the pasting cycle. The characteristics of the concentration dependence differed due to the shear history of the sample. Peculiar concentration dependencies, some even negative, could be obtained from samples with different shear histories. The results imply that even moderate shear treatment gives rise to structure changes which are reflected by a transition in the type of the viscoelastic behaviour. © 1990.
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