Extraction, Partial Characterization, and Studies of Some Spectroscopic Properties of the Anionic Polysaccharide from Colocasia Antiquorum

Abstract

The natural anionic polysaccharide (Ps-A) isolated from arum (Colocasia antiquorum) tubers contains 56% neutral sugars as galactose, mannose, rhamnose, and arabinose, and 40% anionic components as galacturonic acid and mannuronic acid. The equivalent weight of Ps-A estimated by conductometric and spectrophotometric titrations is rather high, 1510 ± 5, which on saponification is reduced to 479. This indicates that about two-thirds of the carboxylic groups of Ps-A exist in the esterified form. Ps-A and its saponified product (Ps-B) induce strong metachromasia in the dyes 1,9-dimethyl methylene blue and pinacyanol chloride (PCYN). Ps-A, with its lower charge density, induces relatively sharp and single banded metachrotnatic spectra, but the spectra induced by Ps-B, with its higher charge density, is broad and multiple banded. Ps-A induces weak dichroism in PCYN, indicating a bit of helical asymmetry in its conformation; Ps-B does not induce dichroism in this dye. The failure of Ps-B to induce dichroism presumably indicates that Ps-B has a nonhelical conformation.