Extraction of polyphenols from Eucalyptus nitens and Eucalyptus globulus: Experimental kinetics, modeling and evaluation of their antioxidant and antifungical activities

Abstract The species Eucalyptus globulus and Eucalyptus nitens have become of great importance in Chile and the world, due to their rapid growth and because compounds with greater added-value can be obtained from their waste. This study aimed at obtaining extracts rich in phenolic compounds from the bark of E. globulus and E. nitens and at evaluating the extraction kinetics and the resistance provided by these extracts to the degradation of pine wood attacked by decay fungi. For this purpose, bark samples were taken from E. nitens and E. globulus at a commercial site and then dried and ground. The extraction of the hydrophilic components was optimized by using a Box-Behnken design that considered the influence of temperature, solid/liquid ratio and methanol concentration on the maximization of the following responses: extraction yield, total phenols (Folin-Ciocalteu) and antioxidant capacity (DPPH). Under optimum conditions, the reaction kinetics of phenolic compounds at three temperatures were modeled and determined. Two antifungal assays were performed with the extracts: determination of the minimum inhibitory concentration (MIC) and a mass loss test for three decay fungi. The optimum was obtained at a solid/liquid ratio (1:60) at a 51% concentration of methanol and water for both species and at a temperature of 319 K and 326 K for E. globulus and E. nitens , respectively. The Fick diffusion model of two extractive phases successfully represented the extraction kinetics of the phenolic compounds from the eucalyptus bark at different temperatures. Bark extractions from both species were validated as possible antifungals against the fungal species. In future studies the technical-economic feasibility of replacing commercial antifungals with solutions of the extracts obtained in this study will be analyzed, taking the extraction process to a pilot scale.