Optimization of polyphenolic compounds extraction methods from Okra stem

Abstract

Conventional solvent extraction (CSE), microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) have used to recover phenolic substances from Okra stem (as a related agro-industrial waste). The influences of three extraction methods in terms of total phenolic content (TPC), antioxidant activities (AA) and extraction yield (EY) of Okra stem are investigated and compared. The DPPH, ABTS, FRAP, and β-carotene bleaching methods are used for determining AA. The phenolic compounds’ values existing in Okra stem are determined by High-performance liquid chromatography (HPLC) analysis. The optimized MAE has been compared with both optimized CSE and UAE. The results show that the former method gives the higher TPC (69.99 mg GAE g−1) in the shorter time as compared to CSE and UAE methods by about 89% and 78.17%, respectively. The UAE method shows the best performance in AA (53.06%, 60.10%, 0.94 mM TE g DE, and 69.27% for DPPH, ABTS, FRAP and β-carotene bleaching, respectively) and EY with the content of 19.24%. Regarding the phenolic profile, catechin derivative (9.45 mg g−1) is the main compound which is found in the extracts as well as hydroxycinnamic derivative (9.11 mg g−1) and flavonol (4.99 mg g−1). The obtained results indicate that Okra stems have the capability of being productive sources of phenolic compounds with antioxidant properties.