Extraction of Sorrel Calyces Using Water

Abstract

Extract of the calyces of sorrel (Hibiscus sabdariffa) is a popular refreshing juice drink in tropical countries and is known to possess medicinal value. In this work, two particle size ranges (<5.6 and 5.6–11.2 mm) of the calyx were extracted with water under varying conditions. The purpose was to obtain extraction parameters for the design, optimization and operation of a leaching plant. A linear increase in extraction yield and extract concentration with temperature was obtained between 27 and 100°C with the smaller particles recording higher yield and concentration. Solvent volume (solvent-to-feed ratio) of 50 ml g⁻¹ solid gave saturated capacity at 90°C, but the maximum yield/concentration gradient was noticed between 15 and 20 ml g⁻¹ solid. The kinetics of the extraction process is adequately described by the Peleg equation and another variant of this equation that gives maximum capacity (yield/concentration) and time constant (time required for optimum yield or concentration) directly. The smaller particles gave maximum concentration, initial extraction rate and time constant as 5.6119 g l⁻¹, 0.3194 g l⁻¹ min⁻¹ and 17.57 min, respectively. The analogous values for the bigger calyx particles were 5.5386 g l⁻¹, 0.2708 g l⁻¹ min⁻¹ and 20.45 min.

Keywords:

• Hibiscus sabdariffa
• solid–liquid extraction
• Peleg equation
• extraction parameters
• extract kinetic models