Antioxidant Compounds and Activities of Roselle (Hibiscus sabdariffa L.) Decoction Residues from Cordial and Juice Production

Roselle is a popular plant in Malaysia, especially for its use in food and beverage production. The calyces of the roselle plant are commonly decocted to make roselle juice and cordial, resulting in a significant amount of waste in the form of decocted calyces. Surprisingly, these decocted calyces retain their dark red colour and are still intact although soften. However, to date, there is no research on the antioxidant compounds and activities of roselle decoction residues from cordial and juice production have been reported. Therefore, the aim of this study is to determine the phenolic compounds and antioxidant activities of the roselle decoction residues. The roselle decoction residues were evaluated for colour, Delta E (∆E), pH, total anthocyanin content (TAC), total phenolic content (TPC), total flavonoid content (TFC), DPPH radical scavenging assay, ferric reducing ability assay (FRAP), and ferrous ion chelating (FIC). All assays were also correlated and show positive effect among themselves. The decocted residues reported were still in acidic conditions ranged of pH 2 to 4. The decocted cordial residue (DCR) showed similar colour with control or fresh roselle calyx (FRC), and a bit duller in decocted juice residue (DJR). The DCR showed similar and slightly lower antioxidant content and activity of TAC, TPC, TFC, DPPH, FRAP and FIC to FRC but much better than DJR. Therefore, the DCR were still rich in anthocyanin contents and had good antioxidant activity without having colour changes. These residues have the capacity to be converted to wealth and could be an alternative source for natural antioxidants. Further research is needed to explore their potential applications in functional foods, dietary supplements, and pharmaceuticals. By harnessing the potential of roselle decoction residues, we can contribute to a more sustainable and environmentally friendly approach to food and beverage production.