Kinetics, thermodynamics and antioxidant activities of water and ethanol extract of stem bark of <i>Anacardium occidentale</i>.

Abstract

Extraction is a required process for the utilization of bioactive compounds from their natural sources as ingredients and additives in food, pharmaceutical and cosmetic industries. Extracts from various parts of A. occidentale have received massive investigations especially in the management and treatment of various ailments which include diabetes, malaria, yellow fever as well as diarrhoea. In this study, the stem bark of A. occidentale was extracted with water and ethanol. Antioxidant activities of the extracts were determined using DPPH, hydrogen peroxide free radical scavenging and ferrous ion chelating activities. To explain the solid–liquid extraction processes of A. occidentale in water and ethanol, the kinetic of extraction in ethanol was best fitted with pseudo first order while that in water fitted best with the second order kinetic models. The isotherm fitted well with Power law models for ethanol and water extraction process. The transition rate theory was used to estimate the   thermodynamic parameters, the ΔH^# values of 49.67 and 47.37 kJ mol^-1 obtained for the ethanol and water extraction processes respectively showed that water extraction process is endothermic while ethanol extraction   is an exothermic process. The ΔS^# values of -0.09 and -0.42 kJ mol^-1 K^-1 obtained for the ethanol and water extraction processes respectively suggest a higher entropy in ethanol than in the water extraction processes.

Keywords: Extraction; Pseudo first order; second order; Isotherm; Thermodynamic;