Assessment of the Intrinsic and Stability Properties of the Freeze-Dried and Formulated Extract of Hibiscus Sabdariffa Linn. (Malvaceae)

Abstract

Water extract of the calyces of Hibiscus sabdariffa Linn (Malvaceae) is used widely as a food additive and refreshing drink with proven medicinal benefits, which are attributed to its phytochemical constituents. Relevant physicochemical and stability studies have been carried out on the freeze-dried and formulated samples of aqueous extract of the calyces of H. sabdariffa. The phytochemical constituents, moisture sorption characteristics and the effect of extract concentration, light and pH on the color of the extract were determined. The stability of the anthocyanins contained in the extract and the thermal characteristics of the freeze-dried extract were also evaluated. The dye solution which has hot-pink color and a pH of 2.1 ± 0.6 contained flavonoids, glycosides, sterols, balsams, phenols, monosaccharides, free reducing and combined reducing sugars. The extract solution also showed colour and light transmittance responsiveness to changes in pH. Fourier transform infrared (FTIR) spectra and the diffraction scanning thermograms show the degradation effect of light on the extract. The dry samples of the extract showed higher photo-stability relative to the solutions. The isothermal moisture sorption profile of the powdered freeze-dried extract and the formulated granules showed characteristic sigmoidal curves corresponding to Type 2 and 5 isotherms respectively. The aqueous extract of the calyces of H. sabdariffa generally showed high light and pH sensitivity and positive tests for the presence of some active secondary plant metabolites that are probably responsible for its claimed health benefits.