Maximizing the freeze-dried extract yield by considering the solvent retention index: Extraction kinetics and characterization of Moringa oleifera leaves extracts

Abstract

A complete chemical characterization of Moringa oleifera leaves was carried out showing a high content of extractives. Extraction kinetics of bioactive compounds present in this fraction were performed by conventional and ultrasound assisted extraction (UAE). A 50% (v/v) hydroalcoholic mixture led to the highest total phenolic compounds yield by conventional solvent extraction, 29.5 ± 0.3 mg per gram of moringa leaves. UAE did not bring any improvement when using hydroalcoholic mixtures probably due to the physical properties of the ethanol aqueous mixtures that affect the UAE performance, such as viscosity and vapor pressure of the mixture. The retention index of the different solvents in the raffinate phase was determined revealing the highest retention index for water, 9.5, and a continuous decrease by increasing ethanol concentration. Retention index is a key parameter in a solvent extraction process since it determines the number of stages in an industrial separation process and it is not usually reported in bioactive compounds extraction. Solvent extraction capacity and the retention index determined the final freeze-dried extract yield.