Structure characterization of an arabinogalactan from green tea and its anti-diabetic effect

A water-soluble polysaccharide, 7WA, with an average molecular mass of 7.1 × 104 Da, was isolated from the leaves of green tea. Monosaccharide composition analysis indicated that 7WA mainly contained Arabinose and Galactose in the molar ratio of 1.0:0.96. By using the methods of methylation analysis, partial hydrolysis, and NMR, 7WA was characterized to possess a backbone consisting of 1,3- and 1,6-linked galactopyranosyl residues, with branches attached to O-3 of 1,6-linked galactose residues, and O-4 and O-6 of 1,3-linked galactose residues. The results of glucose-stimulated insulin secretion (GSIS) showed that 7WA significantly augmented insulin secretion at high glucose level (25 mM), however, such effect was not seen at low glucose level (5 mM). The mechanism study results indicated 7WA, a type II arabinogalactan from Green Tea, enhances GSIS through cAMP-PKA pathway.