Structural analysis and characterization of a mucopolysaccharide isolated from roots of cassava (Manihot esculenta Crantz L.)

A mucopolysaccharide, referred to as cassava tuber mucilage (CTM), was isolated from the roots of sweet cassava and studied for its characteristic physical, molecular, and structural properties. Sugar composition and molecular properties of purified samples were analyzed using high-performance liquid (HPLC), anion exchange (HPAEC-) and size exclusion (HPSEC- MALLS-RI) chromatographic techniques. Structural properties of crude and purified samples were analyzed and compared using Fourier transformation infrared (FT-IR) and nuclear magnetic resonance spectroscopy. CTM is mainly composed of the major neutral sugars sucrose, fructose, glucose, galactose, and arabinose. It has a molecular average weight of 3.6×105, number average molecular mass (Mn) of 2.4×106, and a polydispersity index (Mw/Mn) of 1.5. FT-IR spectroscopy revealed high protein content in the crude fractions, whereas purified fractions were mainly carbohydrate. 1H NMR and 13CNMR showed that the mucilage consists of 1, 3-linked glucan chains with 1, 6-linked galactan side chains attached to position 6. The mucilage is purely hemicellulosic and possibly an arabinogalactan, confirmed by SDS gel electrophoresis of crude CTM samples, containing a (1, 3)-linked β-glucan backbone having side chain branching with non-reducing terminal residues mostly of (1, 6)-linked galactose and some arabinose and glucosyl moieties.