Polyelectrolyte complexes from gum arabic and gelatin: Optimal complexation pH as a key parameter to obtain reproducible microcapsules

Herein we report the formation of polyelectrolyte complexes (PECs) based on type-A gelatin and gum arabic. The polysaccharides were extracted from gum exudates of Acacia mearnsii De Wild, grown in Brazil, where they are considered an agro industrial residue. Two polysaccharide fractions were obtained from crude Acacia mearnsii gum exudates, after successive aqueous and alkaline extractions, denoted as GNF and GNA, respectively. Molecular and functional properties differ between samples. Surface behavior of GNF and GNA are mainly associated with their composition and molecular mass distribution profile. The results were compared to a commercial gum (GAC). Targeting optimal complexation conditions, a straightforward and elegant approach was employed, that consists in determining the pK(a) of the macromolecules, which is intrinsically related to their molecular characteristics. Hence, the optimal condition is achieved when the concentration of positively and negatively charged species of gelatin and gum, respectively, are concomitantly maximized. This method proved to be simple and effective in predicting the best pH for obtaining PECs, corroborated by a thorough complexation study at different pHs. Our work demonstrates that the optimal complexation pH is the key parameter to obtain reproducible microcapsules with targeted features, regardless of the origin of the gum. Also, GNF and GNA showed to be promising substituents for GAC, thus extending the range of applications of acacia gum obtained in Brazil, strengthening the interest in this material. (C) 2014 Elsevier Ltd. All rights reserved.