Recovery, structure and physicochemical properties of an aggregate-rich fraction from Acacia senegal gum

Acacia senegal gum (Asen) is a natural exudate of Acacia trees species largely used in food as well as other industries. This natural product appears as a continuum of molecular species which shows diverse sugar and protein composition, molar masses and charge density. The presence of larger macromolecules, or aggregates, has been demonstrated to have a great influence on the Acacia gum characteristics. The present work is designed to recover and characterize one protein-rich fraction presenting a high aggregate content. With this fraction we will open the door to future works with the aim to acquire a deeper knowledge about the origin and the role of the aggregates from Asen gum. Our methodology is based on the well-known ion exchange chromatography, using DEAE Sephacel gel as stationary phase. We have separated Asen into two different fractions (fraction IEC-F1 and fraction IEC-F2), being both of them confirmed as arabinogalactan-proteins (AGP) by Yariv detection. Fraction IEC-F1 has been thoroughly characterized (sugar and amino acid composition, molar mass distribution, weight-average molar mass, number-average molar mass, polydispersity index, intrinsic viscosity, radius of gyration, Mark-Houwink-Sakurada analysis, hydrodynamic radius, partial specific volume and partial specific adiabatic compressibility). From amino acid data, we have estimated that fraction IEC-F1 theoretically corresponds to about 70% of HIC-F3 and 30% of HIC-F2, respectively the second and the third fractions separated by hydrophobic interaction chromatography (HIC) and largely described in literature. The obtained information indicates that fraction IEC-F1 appears as a fraction highly rich in aggregates.