Nutritional and Phytochemical Characterization of Hibiscus sabdariffa L. Calyces and Antioxidant Potential of Hydroethanolic Extracts

Abstract

Hibiscus sabdariffa L. (roselle) calyces are a potential source of nutrients and bioactive compounds, but their recovery depends on extraction conditions. This study aimed to characterize the nutritional and phytochemical composition of H. sabdariffa L. calyces and evaluate the influence of ethanol concentration on the phytochemical profile and antioxidant potential of hydroethanolic extracts. Dried and milled calyces were extracted by maceration with 50%, 70%, and 90% ethanol at a 1:20 (w/v) solid-to-solvent ratio for 120 min under agitation. Proximate composition was determined according to AOAC methods, while minerals were assessed on a dry-weight basis. Total phenolics, flavonoids, and anthocyanins were quantified using spectrophotometric and chromatographic methods, and individual phenolic compounds and phytohormones were characterized by UPLC-MS/MS using an Agilent 1200 Infinity liquid chromatograph coupled to a 6430 triple-quadrupole mass spectrometer. Antioxidant activity was evaluated using DPPH, ABTS, and FRAP assays. Data were analyzed by one-way ANOVA followed by Tukey’s test (p < 0.05). The calyces contained 68.76% carbohydrates, 15.72% lipids, 9.21% protein, and 6.31% ash, with potassium as the predominant mineral (12 g/kg). Ethanol concentration significantly influenced phytochemical recovery. The 70% extract showed the highest total phenolic content (1717 mg GAE/100 g) and anthocyanin content (315.5 mg/100 g), whereas total flavonoids did not differ significantly among extracts. UPLC-MS/MS revealed distinct solvent-dependent profiles of individual phenolic compounds and related metabolites, demonstrating selective extraction of chemically diverse constituents. Antioxidant activity was assay-dependent: the 70% extract showed the highest ABTS activity (5119 µmol TE/g), while the 50% extract exhibited the highest FRAP activity (2604 µmol Fe²⁺/g); DPPH activity did not differ significantly among extracts. These findings indicate that 70% ethanol favored the recovery of phenolic and anthocyanin compounds and enhanced ABTS activity, whereas the superior FRAP response of the 50% extract demonstrates that antioxidant capacity cannot be predicted solely from total phenolic content. Overall, 70% hydroethanolic extraction provided the most favorable integrated phytochemical and antioxidant profile under the conditions investigated and was selected for subsequent biological investigations.

Keywords: Hibiscus sabdariffa L.; Roselle calyces; Hydroethanolic extraction; Phenolic compounds; Antioxidant activity.

Acknowledgments: The authors acknowledge the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support.