Roselle (Hibiscus sabdariffa) by-product as functional ingredient: effect of thermal processing and particle size reduction on bioactive constituents and functional, morphological, and structural properties

Food industry is in the search of new functional ingredients, so this study was focused on evaluating the effect of thermal processing used to produce roselle beverages, and the effect of particle size reduction, on the retention of bioactive constituents, and physicochemical, functional, and structural properties of Hibiscus sabdariffa calyces. After decoction process (DP), by-products retained up to 56% of polyphenolic compounds, 54% of flavonoids and 44% of anthocyanins; mainly delphinidin 3,5-O-diglucoside (74.1%); besides presenting an increased content of total dietary fiber (DF) as compared to roselle calyces (26%). Viscosity and hydration properties were improved by the DP, which may be related to an increased porosity as observed in the SEM micrographs. Fourier transform infrared spectroscopy spectrum, reflected the differences in the chemical composition of BP and calyx, whereas the X-ray diffraction analysis showed no effect of DP. Interestingly, samples with a large particle size (250–177 µm) presented increased viscosity, which was the most important change for particle size. Therefore, roselle beverage by-product could be a functional ingredient since is an excellent source of phenolic compounds and dietary fiber with improved functional and physicochemical properties as compared to calyces.