Thermal degradation kinetics and physicochemical analysis of the freeze-dried hibiscus flower extract (Hibiscus sabdariffa)

Abstract

The goal of this research was to evaluate the kinetics of thermal degradation of the hibiscus extracts powder at different temperatures and to characterize physicochemically the freeze-dried aqueous extract of the hibiscus flower (Hibiscus sabdariffa) with different concentrations of maltodextrin (0, 5, 10 and 15%). The analyzed parameters were: water content, total soluble solids, titratable acidity, pH, ash, solubility, hygroscopicity, bulk and tapped density, the flowability (Carr index) and cohesiveness (Hausner ratio), lightness (L*) and intensity of red (a*) and yellow (b*). The degradation kinetics was analyzed by the determination of bioactive compounds of flavonoids, anthocyanins and color appearance parameters (lightness, intensity of red and yellow, chroma and hue angle). The increase in maltodextrin concentration resulted in increases of solubility, soluble solids content, pH and color appearance parameters; as the parameters of bulk and tapped density, hygroscopicity, water content, ash and acidity presented decreases as the proportion of additive increased, showing good flowability and low to medium cohesion. Regarding the degradation kinetics, the maltodextrin was effective in the preservation of anthocyanins and flavonoids of the freeze-dried hibiscus flower up to the temperature of 50 °C. Therefore, this work resulted in the preparation of a product derived from the freeze-drying process with and without additives and with preserved sensory attributes of high quality.