Functionality of gum arabic. Fractionation, characterization and evaluation of gum fractions in citrus oil emulsions and model beverages

Abstract

Gum arabic, the exudate from Acacia Senegal, has been fractionated by size exclusion chromatography (SEC) and by hydrophobic interaction chromatography (HIC). Five SEC fractions and two HIC fractions have been evaluated in orange oil emulsions and also in model beverages. Comparisons were made on an equal nitrogen and/or equal weight basis to controls. Amino acid and other analyses of the whole gum and its fractions have also been performed. While the higher protein, higher mol. wt fractions make the best emulsions, all fractions, except the lowest mol. wt fraction (~5% of the whole gum), make reasonably good emulsions and perform well in model beverage. Although the protein content of this last SEC fraction (lowest mol. wt) is comparable to that of the whole gum, the fraction made a very poor emulsion. Since the zeta potential of the droplets in all these emulsions is the same, the differences in emulsion stability can be attributed to non-electrostatic factors. The data support a picture of gum arabic as a very complex, polydisperse glycoprotein, polydisperse in mol. wt and particularly in protein composition. Gum arabic, an excellent emulsifier, is endowed with a particularly good combination of many molecular species differing in size and composition.