New coacervates and crosslinkers from Araucaria heterophylla and Commiphora pedunculata exudates for microencapsulation of essential oils

Abstract

Araucaria heterophylla (Ah) and Commiphora pedunculata (Cp) are plant exudate gums from the flora of Benin composed mainly of carbohydrate polymers and a considerable amount of essential oils. The aim of this work is to evaluate the functional properties of these polysaccharide extracts such as the ability to coacervation and cross-linking with gelatin, in order to formulate polymeric materials as microcapsules for essential oils produced exclusively from local resources without toxic products. Their physicochemical and chemical characterics were analysed. The polysaccharide extracts of Ah and Cp plants are water-soluble, amorphous, thermally stable polymers (Td ≈ 300°C) with a number-average molar mass of 21300 and 362600 g.mol^-1. The composition of the monosaccharide was determined by HPLC after acid hydrolysis. Galactose, arabinose, rhamnose and glucuronic acid are present in both plants. Galactose is predominant in Ah, while arabinose dominates in Cp. Their aqueous solutions, with mass fractions between 0.5 and 1 %, are slightly acidic and surface-active. At 25°C, in a range of higher concentrations (10-60 %), their aqueous solutions are shear thinning. The presence of glucuronic acid gives the polysaccharides in aqueous solution sufficiently stable negative charges (ζ= -17.0±2.4 mV) to behave like an anionic polymer. These properties allow microencapsulation of the essential oils by complex coacervation between extracted polysaccharides and gelatin for an antioxidant and antibacterial activity. In addition, the polysaccharides were oxidized to be used as crosslinkers for gelatin and their non-cytotoxicity was demonstrated. This work closely follows the guidelines of green chemistry and contributes to a circular economy.