Comprehensive characterization of the overlooked residue generated during roselle calyxes brewing with potential use as functional ingredient

A significant quantity Hibiscus sabdariffa L. calyxes are generated as by-products during the decoction process commonly used for roselle beverage preparation. We conducted an extensive characterization of polyphenols, organic acids, and antioxidant potential in roselle calyxes, decoction, and their by-product. Roselle calyxes were found to be a rich source of diverse polyphenols, including delphinidin sambubioside, caffeoylquinic acids, hibiscus acid, and citric acid as major components. Importantly, we extracted a significant proportion of these bioactive compounds during the decoction process, resulting in a polyphenol-rich beverage. The used calyces (decoction by-product) retained from 23 % to 140 % of the extractable polyphenols and organic acids found in roselle calyxes. Additionally, due to the leaching of hydrophobic components like soluble dietary fiber and extractable polyphenols and organic acids, the roselle by-products were enriched with non-extractable constituents attached to dietary fiber (126 % - 272 %). Therefore, roselle calyxes and their decoction by-products emerge as promising sources of polyphenols with the potential for use in dietary supplements, alongside the commonly consumed roselle decoction.