Gum Arabic : same but different : comparative analysis of structural characteristics and emulsifying properties of 20 Acacia senegal samples of various qualities

Abstract

Gum Arabic, an exudate from Acacia senegal, is very commonly used for the stabilization of aroma oil and beverage emulsions due to its high emulsifying capacity. However, differences in gum Arabic quality and its relation to the molecular structure are not yet fully understood. In this study, we analyzed the structural characteristics and functional properties of 20 gum Arabic samples of various qualities to investigate the relation between molecular structure and functionality. First, an improved hydrolysis protocol for a valid determination of the monosaccharide composition of gum Arabic by HPAEC-PAD was established. The application of this method showed that previous monosaccharide compositions potentially underestimated neutral sugars and overestimated uronic acids. The gum samples were subsequently analyzed for their monosaccharide composition, protein content, molecular weight, and molecular weight distribution as well as the radius of gyration and hydrodynamic radius. O/W emulsions with weighted orange oil were prepared from all samples and their initial droplet size distribution and viscosity were determined. By using Pearson correlation tests, we were able to demonstrate that rhamnose content and the rhamnose/galactose ratio positively correlate with the molecular mass MW. The molecular weight MW itself correlated with the viscosity of the emulsion, while the protein content anticorrelated with the droplet size distribution x90,3. Altogether, we provide a comprehensive and detailed data set on various gum Arabic samples which establishes correlations between individual structural parameters and emulsion properties. However, explaining quality and long-term stability requires a deeper understanding of the molecular structure, emulsion formation, and stabilization processes.