Gum Arabic that is Enzymatically Modified with Arabidopsis Beta-Glucuronosyltransferase Can Make Smaller and more Stable Oil-in-Water Emulsions

A plant glycosyltransferase was utilized to modify the properties of gum arabic as an oil-in-water emulsifier. We previously reported that recombinant beta-glucuronosyltransferase (AtGlcAT14A) from Arabidopsis thaliana produced in Pichia pastoris possesses glucuronosyltransferase activity to transfer glucuronic acid (GlcA) from UDP-GlcA to beta-1,3-galactan main chain and beta-1,6-galactan side chains of type II arabinogalactan. In this paper, we report that AtGlcAT14A can also transfer GlcA from UDP-GlcA to gum arabic at the optimal pH value of 5 in the absence of dicationic ion. In the modified gum Arabic, GlcA was primarily incorporated into the beta-1,6-galactans. The oil-in-water emulsions created by the modified gum arabic were smaller, less flocculated and threefold more stable than that produced by the unmodified gum arabic. It is conceivable that the additional GlcA on the surface of gum arabic prevents flocculation by increasing surface electrostatic repulsion, which leads to more stable oil-in-water emulsions. Our study implicates the structure-function relationship and provides a potential method for the enzyme-based manipulation of gum arabic.