Conveyor-belt drying of Eugenia uniflora L. leaves: Influence of drying conditions on the yield, composition, antioxidant activity and total phenolic content of supercritical CO2 extracts

Abstract

Eugenia uniflora L. leaves were dried in a conveyor-belt dryer to assess the influence of drying conditions (air temperature and number of passes/residence time in the dryer) on the yield, composition, antioxidant activity and concentration of phenolic compounds found in the extracts obtained from supercritical extraction. An analysis of leaf drying in the conveyor belt was carried out by investigation of sorption isotherms and drying curves obtained under air temperatures of 50, 60 and 70°C. The sorption curves were fitted to the GAB thermodynamic model and the drying curves to a one-parameter empirical equation. The fitted equations were effective to predict the discharge moisture as function of the residence time under different temperatures. The samples for extraction were dried under 50°C/120min, 60°C/60min and 70°C/60min and their moisture levels were reduced respectively to 15wt.%, 10wt.% and 6wt.%. The extractions were carried out at 80°C and 250bar using as solvents either the pure supercritical CO2 or a mixture of ethanol and supercritical CO2 at a mass ratio of 0.5:1. The higher extraction yields (9.9±0.1wt.%), phenolic content (85±2mg GAE/g extract) were found in the extracts from samples dried under 60°C/60min using ethanol as a co-solvent in extraction.