The aim of this study was to analyze the equilibrium and dynamic periods for mass transfer during the antioxidant solid-liquid extraction of dry roselle flower (Hibiscus sabdariffa). Extraction kinetics for total phenolic compounds (TPC), total flavonoids (TFL) and total antioxidant capacity (TAC) were obtained at different temperatures (50, 60, 70 or 80 °C) and solvent-to-product mass ratios (100:1, 200:1 or 300:1 g/g) under stirring (220-230 rpm). An analytical solution for unsteady-state mass transfer based on Fick's second law of diffusion was used to mathematically describe solid-liquid extraction curves and for the simultaneous estimation of diffusion coefficients and the final amount of extracted bioactive compounds, which were further related to experimental conditions by a second order model. The amount of extracted bioactive compounds at equilibrium were in the ranges of 30.8-89.8 g GAE/kg d.m. for TPC (0.154-0.373 g GAE/L extract), 40.0-131.6 g catechin/kg d.m. for TFC (0.269-0.559 g catechin/L extract) and 37.5-227.0 g trolox/kg d.m. for TAC (0.346-0.865 g trolox/L extract). On the other hand, diffusion coefficients for TPC, TFC and TAC were in the ranges of 0.72-2.66 × 10-11, 0.25-2.37 × 10-11 and 1.19-5.79 × 10-11 m2/s, respectively.
Keywords: Bioactive compounds; Diffusion coefficient; Equilibrium point; Solid–liquid extraction.