Structure elucidation of an immunoenhancing pectic polysaccharide isolated from aqueous extract of pods of green bean (Phaseolus vulgaris L.)

A water-soluble pectic polysaccharide (PS-I) isolated from the hot water extract of the pods of green bean (Phaseolus vulgaris L.) by successive purification through dialysis, centrifugation and Sepharose-6B gel filtration was found to consist of methyl ester of d-galacturonic acid, d-galactose, and l-arabinose in a molar ratio of nearly 2:2:1. This molecule showed splenocyte, thymocyte activation as well as antioxidant properties. Structural studies of PS-I was performed using acid hydrolysis, methylation analysis, periodate oxidation studies along with NMR analysis (1H, 13C, TOCSY, DQF-COSY, NOESY, ROESY, HMQC, and HMBC) and the repeating unit of PS-I was established as: