Microwave-assisted solubilization and solution properties of hyperbranched polysaccharide

Abstract

A water-insoluble hyperbranched β- d-glucan (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was treated by microwave exposure to improve its solubility in water. This method led to complete dissolution of the TM3a polysaccharide in 0.02 wt % aqueous NaN 3. Various treatment periods were tested, and optimal conditions corresponded to 35 s at 765 W. The solution properties of TM3a in water were studied systematically by using size-exclusion chromatography combined with laser light scattering, viscometry, and dynamic light scattering at 25 °C. The dependences of intrinsic viscosity ([ η]), radius of gyration ( 〈 S 2 〉 z 1 / 2 ), and hydrodynamic radius ( R h) on weight average molecular weight ( M w) for TM3a in 0.02 wt % aqueous NaN 3 at 25 °C were found to be [ η ] = 3.02 × 10 - 2 M w 0.44 ± 0.1 ( cm 3 g - 1 ) , 〈 S 2 〉 z 1 / 2 = 8.32 × 10 - 2 M w 0.38 ± 0.2 ( nm ) , and R h = 4.37 × 10 - 2 M w 0.46 ± 0.08 ( nm ) in the M w range from 8.20 × 10 5 to 4.88 × 10 6. The fractal dimension, ratio of ρ = 〈 S 2 〉 z 1 / 2 R h , and the < r 2> o/ M w value of TM3a were calculated and discussed. The results indicated that TM3a existed in a sphere-like conformation in 0.02 wt % aqueous NaN 3. Furthermore, by using transmission electron microscopy, we observed directly the spherical molecules of TM3a. This work gave valuable information on improvement of solubility and chain conformation characterization of the water-insoluble polysaccharide in water.