A new arabinogalactan is described that is produced in large quantity from the cut stems of the North American grape species Vitis riparia (Frost grape). The sugar composition consists of l-arabinofuranose (l-Araf, 55.2%) and d-galactopyranose (d-Galp 30.1%), with smaller components of d-xylose (11.2%), d-mannose (3.5%), and glucuronic acid (GlcA, ∼2%), the latter linked via a galactosyl residue. Permethylation identified 3-linked Galp residues, some substituted at the 2-position with Galp or Manp, terminal Araf and Xylp, and an internal 3-substituted Araf. NMR (HSQC, TOCSY, HMBC, DOSY) identified βGalp and three αAraf spin systems, in an Araf-α1,3-Araf-α1,2-Araf-α1,2-Galp structural motif. Diffusion-ordered NMR showed that the FGP has a molecular weight of 1-10 MDa. Unlike gum arabic, the FGP does not contain a hydroxyproline-rich protein (HPRP). FGP forms stable gels at >15% w/v and at 1-12% solutions are viscous and are excellent emulsifiers of flavoring oils (grapefruit, clove, and lemongrass), giving stable emulsions for ≥72 h. Lower concentrations (0.1% w/v) were less viscous, yet still gave stable grapefruit oil/water emulsions. Hence, FGP is a β1,3-linked arabinogalactan with potential as a gum arabic replacement in the food and beverage industries.
Keywords: Vitis riparia; arabinogalactan; beverage emulsifier; frost grape polysaccharide; gum arabic.