Use of hydrogen-rich water as a green solvent for the extraction of phytochemicals: Case of olive leaves

Olive leaves are a rich source of phytochemicals such as phenolic compounds. ‎Extraction of phytochemicals is the best strategy for valorizing ‎by-products. Any extraction method is chosen based on its economic feasibility, safety, and environmental friendliness. In the present study, the extraction of phenolic compounds (TPC), flavonoids (TFC), and antioxidants (DPPH and ABTS) from the olive leaf was assayed using two types of hydrogen-rich water: hydrogen bubbling (HRW) and magnesium incorporation (Mg water)‎. The highest extraction yield was found for HRW at 34.42% and the lowest one was for pure water at 19.27%. The highest values of TPC, TFC, and antioxidant activity (DPPH and ABTS) were shown for HRW water ‎followed by Mg water/ethanol (50/50) samples, whereas the lowest ones were observed for pure water samples‎. ‎The incorporation of hydrogen into water increased TPC, TFC, DPPH, and ABTS by ‎‎95.63, ‎290.62, ‎‎60.78‎, and ‎118.94%, respectively; whereas the incorporation of Mg increased them by ‎‎7.55, ‎16.49, ‎‎14.23, and ‎8.35%, respectively.‎ Trans-ferulic acid, rosmarinic acid, p-‎coumaric acid, and rutin increased by 1.3, 5.5, 20, and 23 folds when hydrogen was ‎incorporated ‎into water, whereas catechin appeared only ‎in HRW.‎ HRW can be suggested as a green and eco-friendly solvent for improving the extraction of phytochemicals.