Gel formation and low-temperature intramolecular conformation transition of a triple-helical polysaccharide lentinan in water
✍ Scribed by Yangyang Zhang; Xiaojuan Xu; Lina Zhang
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2008
- Tongue
- English
- Weight
- 293 KB
- Volume
- 89
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
The gelation behavior of the triple‐helical polysaccharide lentinan fractions having different molecular weights in water at 25°C were studied by using a rheometer. The analysis of concentration and molecular weight dependence of shear stress and shear viscosity showed that aqueous lentinan is a typical shear‐thinning fluid, possessing potential as a viscosity control agent, and that a weak gel with entangled network structure formed. The dynamic oscillatory behavior of lentinan in the temperature range of 1–15°C was also investigated by rheologic method. The storage modulus G′ and complex viscosity η* increased first with decreasing temperature, and underwent a maximum centered at 7–9°C, and then decreased with further decreasing temperature. This abnormal phenomenon was ascribed to formation of rigid structure in the gel state, which was confirmed by the experimental results from micro‐DSC. The micro‐DSC curves showed that an endothermic peak appeared at 7–9°C for lentinan in water upon heating, which was attributable to the intramolecular order–disorder structure transition similar to triple‐helical polysaccharide schizophyllan. Namely, at lower temperature, the side glucose residues of lentinan (triplix II) formed a well‐organized triple‐helical structure (triplix I) through hydrogen‐bonding with the surrounding water molecules. Moreover, this conformation transition was proved to be thermally reversible. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 852–861, 2008.
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