Yellow mustard mucilage: chemical structure and rheological properties

Abstract

Water-soluble yellow mustard ( Sinapis alba L.) mucilage was found to exhibit pronounced shear thinning behaviour at polymer concentrations between 0.3 and 2.0% at 22.0°C. Isolation and fractionation by hexadecyltrimethylammonium bromide (CTAB) precipitation and ion exchange chromatography produced a number of polysaccharide fractions. This permitted a closer examination of both structural features and rheological properties of yellow mustard polysaccharides. CTAB-precipitated fraction (WSCP) was found to be the major component which contributed more to the weak gel-like properties of the water-soluble yellow mustard polysaccharides than the CTAB soluble fraction (WSCS). Of the ten fractions separated from WSCP and WSCS by ion exchange chromatography, only two fractions from the WSCP (WSCP-I and WSCP-III) and one fraction from WSCS (WSCS-I) appeared responsible for the pronounced shear thinning behaviour of water-soluble yellow mustard mucilage. WSCP-I and WSCS-I were mainly composed of 1, 4-linked β- D-glucans as revealed by methylation analysis and/or NMR spectroscopy. WSCP-III was identified as a pectic polysaccharide containing 1, 6-linked galactose, 1, 2-linked and 1, 2, 4-linked rhamnose, 1, 4-linked galacturonic acid and non-reducing end glucuronic acid. Partial structure of WSCP-III was elucidated by one and two dimensional NMR spectroscopy of the oligosaccharides isolated from the partial hydrolysates.