Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2015
Publication Date: 8/11/2015
Publication URL: http://handle.nal.usda.gov/10113/5642486
Citation: Price, N.P.J., Vermillion, K.E., Eller, F.J., Vaughn, S.F. 2015. Frost grape polysaccharide (FGP), an emulsion-forming arabinogalactan gum from the stems of native North American grape species Vitis riparia Michx. Journal of Agricultural and Food Chemistry. 63(32):7286-7293. doi: 10.1021/acs.jafc.5b02316.
Interpretive Summary: A new polysaccharide is described that is isolated from the North American frost grape species, Vitis riperia. This is a wild grape that is typically found in woodland across the United States, and grows up to 50 feet in length. Because it is resistant to the phylloxera pathogenic aphid the frost grape is used agriculturally as a root stock for grafting of commercial edible grapes. We found that the cut stems of frost grape produce large amounts of a viscous, transparent polysaccharide gum. We have chemically characterized this gum, and shown it to consist of arabinose and galactose sugars, plus smaller but significant amounts of mannose, xylose, and glucuronate. Using mass spectrometer and various nuclear magnetic resonance (NMR) methods we show that the frost grape polysaccharide (FGP) is a high molecular weight arabinogalactan, similar in structure to gum arabic, a food emulsifying agent. Like gum arabic the FGP forms viscous solutions and gels, and is also an excellent non-oily emulsifier of various food-grade oils. We anticipate that this research will be of interest to the US food and beverage industries.
Technical Abstract: 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 identified ßGalp and three aAraf spin systems, in a Araf-a1,3-Araf-a1,2-Araf-a1,2-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 (AGP). 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 hours. Lower concentrations (0.1% w/v) were less viscous, yet still gave stable grapefruit oil/water emulsions. Hence, FGP is a ß1,3-linked arabinogalactan with potential as a gum arabic replacement in the food and beverage industries.