Solid-liquid extraction of sorrel calyces with ethanol

Abstract

Ethanol extraction of three particle size distributions of sorrel (Hibiscus sabdariffa) calyces was investigated.  Extraction rate was found to increase with reduced particle size, increased temperature and solvent mass (solvent-feed ratio).  At 30^oC, maximum yield or concentration was achieved with 50:1 solvent-feed ratio but no substantial increment occurred in these parameters beyond 20:1 ratio.  No degradation of the extract’s components occurred between 27^oC and 70^oC since linear relation between extraction yield and temperature was sustained.  Peleg equation and a variant of it gave the best fit for extraction kinetics.  The smallest calyx particles (<2 mm) recorded the maximum (saturation) concentration (C_s) of    13.7103 g L^-1, the highest initial extraction rate (B_o) of 1.6510 g L^-1 min^-1  and the fastest time constant (τ_o) of 8.30 minutes while the analogous values for the biggest particles (2.8-5.6 mm) were 7.5162 g L^-1, 0.3401 g L^-1 min^-1 and 22.04 min.

Keywords: extraction kinetics, time constant, extract concentration, extraction yield, medicinal herbs