Extraction, Purification and Characterization of an Arabinogalactan from Frost (Riverbank) Grape (Vitis riparia Michx.) Stems

This study investigated the extraction and properties of an arabinogalactan polysaccharide from frost grape (FGP) as a potential alternative to gum arabic (GA). Collection date, solvent:feed ratio (S:F), chip size, C-18 filtration, ultrafiltration, freeze drying versus spray drying, methanol pre-extraction, and water absorption were examined. Sugar composition, elemental analysis, dietary fiber content, emulsification activity index (EAI), emulsification stability index (ESI), and viscosity were used to evaluate the extracts. Exudates collected in March from live stems were viscous with high percentage solids and FGP, while May collections were watery with low percentage solids and FGP. Frost grape stems were collected, chipped, and classified by size. The extraction system utilized pressure or vacuum to increase contact between the chips and extraction water. A S:F ratio of ca. 24% gave an excellent yield of FGP. Chips between 1.8 and 3.8 mm gave the highest mass yields. Pre-extracting the chips with methanol and C-18 filtration of the water extract both yielded a lighter product. The EAI for the FGP was higher than that for GA; however, its ESI was lower. Ultrafiltration of the crude extract separated glucose, fructose, and sucrose from the FGP. FGP with glucose, fructose, and sucrose adsorbed water and became darker.