Extraction, purification and characterization of an arabinogalactan from frost (riverbank) grape (Vitis riparia michx.) stems

Authors: Eller, Fred; Vaughn, Steven; Price, Neil; Kenar, James - Jim; Jackson, Michael - Mike; Berhow, Mark; BROWNSTEIN, KOREY - Orise Fellow; Selling, Gordon

Submitted to: BioResources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2023
Publication Date: 5/17/2023
Citation: Eller, F.J., Vaughn, S.F., Price, N.P., Kenar, J.A., Jackson, M.A., Berhow, M.A., Brownstein, K.J., Selling, G.W. 2023. Extraction, purification and characterization of an arabinogalactan from frost (riverbank) grape (Vitis riparia michx.) stems. BioResources. 18(3): 4610-4635. https://doi.org/10.15376/biores.18.3.4610-4635.
DOI: https://doi.org/10.15376/biores.18.3.4610-4635

Interpretive Summary: Gum Arabic is an imported natural plant gum commonly used to thicken and emulsify foods. However, it also contains a protein known to cause allergic reactions. Therefore, a quality domestic alternative to gum Arabic is preferred. Domestic frost grapes have been shown to produce a polysaccharide which is very similar to gum Arabic with excellent thickening and emulsification properties but without its allergenic proteins. This study investigated the development of an extraction and purification method for the frost grape polysaccharide (FGP). The amount of FGP collected from living grape vines varied with the time of year. A ratio of water to grape chips of about 40 to 1 gave an excellent yield of FGP. The optimal size of grape chips for extraction was found to be between 1.8 and 3.8 mm. Passing the extraction water through a non-polar filter removed co-extracted colored contaminants from the extract leading to higher quality FGP. Pre-extracting the frost grape chips with methanol also removed a large amount of colored materials from the FGP. The FGP had better emulsification activity than gum Arabic, however it was not quite as stable. Sugars such as glucose and fructose present in crude FGP extracts could be separated from the FGP using ultrafiltration or ethanol precipitation. This purification step leads to a more stable product. These results provide means to obtain purified FGP suitable for food applications.

Technical Abstract: Gum Arabic (GA) is a common natural plant arabinogalactan gum used as an emulsifier and thickening agent. However, its quality can vary greatly, and it also contains a antigenic protein. Therefore, an alternative to GA is desirable. A similar arabinogalactan polysaccharide from frost grape stems (FGP) has been identified and some of its chemical and physical properties previously reported. This study sought to determine yields and further investigate the physical and chemical properties of this arabinogalactan. The effects of 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. A scaled-up extraction was also run. Properties such as 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 living stems were very thick with a high percent solids and FGP content, while those made in May were watery with low percent solids and little FGP. For lab extractions, frost grape stems were collected in the field, cleaned, chipped and classified by size. The chips were extracted with water using a system that extracted the chips either under pressure or vacuum to increase the contact between the FGP and extracting water. A S:F ratio of ca. 24 gave 92% of the yield of a 38.6 S:F ratio. Chips between 1.8 and 3.8 mm gave the highest mass yields. Filtration of the frost grape stem extract through a C-18 filter removed colored material from the extract and gave a lighter product. The EAI for the FGP was higher than that for GA, however, its ESI was lower. Methanol pre-extraction of the frost grape chips yielded ca. 5% of the original chip mass and this extract was found to contain resveratrol and viniferin. FGP samples containing glucose, fructose and sucrose were found to adsorb water and become darker.