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Molecular weight, tertiary structure, water binding and colon behaviour of ispaghula husk fibre

Published online by Cambridge University Press:  05 March 2007

Saphwan Al-Assaf ,
Glyn O. Phillips ,
Peter A. Williams ,
Shoji Takigami ,
Peter Dettmar  and
Michael Havler
Saphwan Al-Assaf
Affiliation:
The North East Wales Institute, Plus Coch, Mold Road, Wrexham, LL1 2AW, UK
Glyn O. Phillips*
Affiliation:
The North East Wales Institute, Plus Coch, Mold Road, Wrexham, LL1 2AW, UK
Peter A. Williams
Affiliation:
The North East Wales Institute, Plus Coch, Mold Road, Wrexham, LL1 2AW, UK
Shoji Takigami
Affiliation:
University of Gunma, Kiryu, Gunma-ken, Japan
Peter Dettmar
Affiliation:
University of Gunma, Kiryu, Gunma-ken, Japan
Michael Havler
Affiliation:
Reckitt Benckiser pic, Dansom Lane, Kingston upon Hull, HU8 7DS, UK
*
*Corresponding author: Professor Glyn O. Phillips, Present address: Research Transfer Ltd, 2 Plymouth Drive, Radyr, CardiffCF15 8BL, fax +44 29 20 843145, [email protected]
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Abstract

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Molecular variables, using aqueous and alkaline extracts, of the polysaccharide from ispaghula husk (IH) were examined using gel-permeation chromatography linked to multi-angle laser light scattering. Progressive extraction can yield a component with a molecular weight (MW) value up to about 7×106 Da, and gels, which accompany the extraction, have MW ranging from 10–20× 106 Da. To mimic the polysaccharide degradation, particularly in the colon, the solid IH was degraded progressively using ionising radiation. A chain break occurs every 7.5 kGy in NaOH and every 15 kGy in water. The solid-state matrix is opened by the radiation to yield increased visco-elasticity of the aqueous extracts at critical radiation doses, before further degradation occurs after about 12 kGy. Differential scanning calorimetry is used to study the mechanism of interaction of water with IH. The first water to be taken up is non-freezing water and represents about twelve water molecules/disaccharide unit of the polysaccharide. As the water content is increased, the water becomes bound to the polysaccharide and freezes and melts at a temperature different from free water. This water is thermodynamically distinguishable from free water. It forms amorphous ice on cooling which crystallises exothermically and subsequently melts endothermically. Saturation occurs at a water content of 2–3 g water/g polymer, showing that about 60% of the water in the system is ‘bound’. The most surprising conclusion is that despite the fact that the IH swells in water to form a solid and stiff gel, the greater part of that water in the gel is still free and behaves like liquid water.

Keywords

Non-starch polysaccharidesIspaghula huskColonGel permeation chromatographyMulti-angle laser light scattering
Type
Session: Physiological aspects of fibre
Information
Proceedings of the Nutrition Society , Volume 62 , Issue 1 , February 2003 , pp. 211 - 216
Copyright
Copyright © The Nutrition Society 2003

References

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