An amendment to the fine structure of galactoxyloglucan from Tamarind (Tamarindus indica L.) seed.

A polysaccharide from tamarind seeds (TSP) was characterized in terms of backbone and side chain structural features, as well as conformational property using methylation and GC-MS analysis, 2D NMR, MALDI-TOF MS, and high performance size exclusion chromatography (HPSEC). Results showed that TSP was a galactoxyloglucan (GXG) consisting of glucose, xylose, and galactose in a molar ratio of 3.1: 1.7: 1.0. The Mw was determined to be 524.0 kDa with radius of gyration (Rg) of 55.6 nm. The chemical structure was confirmed as a classical β-(1 → 4)-glucan with short side chains of T-β-Galp-(1 → 2)-α-Xylp-(1 → and T-α-Xylp-(1 → attached to O-6 position of glucose. MALDI-TOF MS analysis indicated that TSP mainly composed of nonasaccharide (XLLG) and octasaccharide (XLXG or XXLG) blocks in periodic or interrupted sequence in a ratio of 3: 2, occasionally interrupted by heptasaccharide (XXXG), hexasaccharide (XLG or XXGG), or even hendesaccharide blocks. Conformational study indicated that TSP was in a random-coil shape with relative extended stiff chain in aqueous solution. This study provided more evidences to make an amendment to the fine structure of tamarind GXG.