Effect of different extraction solvents on phenolic compounds and antioxidant capacity of hop flowers (Humulus lupulus L.)
We investigated the potential of wild hop and determined the effects of different solvent extractions on quality and quantity of hop extracts. Three different solvents - aqueous-ethanol (75%), methanol and acetone - were applied to elicit the secondary metabolites of Humulus lupulus L. cones by automatic Soxhlet system, and extraction yield, total phenolic content, total flavonoid content and antioxidant capacity were compared. The antioxidant activity tests, DPPH, ABTS and FRAP, were used to analyze the antioxidant capacity of extracts. The crude extract obtained by aqueous-ethanol, methanol and acetone extraction were 98.65±5.2, 61.39±3.25, 69.28±4.1 mg g‑1 dry matter, respectively. The total phenolic content (TPC) as well as the total flavonoid content (TFC) of aqueous extracts exhibited the highest values. Also the antioxidant activity of extracts was different: the acetone extract had the highest value of IC50 in the DPPH test, while the methanol extract has the highest antioxidant activity (1.79±0.25 mM Fe2+ g‑1) in the FRAP test, and the best result of percent inhibitors of ABTS (58.12±0.48) was observed for the aqueous-ethanol extract. In addition, ABTS value in aqueous-ethanol extract was 6.45±0.33 mmol Trolox equivalent g‑1 sample, significantly higher than others. No significant correlation was found among antioxidant measurement methods. Overall, 75% ethanol is suggested for the extraction of phenolic compounds from hop flowers due to its polarization diversity. Finally, the wild hop flowers have high antioxidant activity and a remarkable amount of phenolic compounds. They could be applied in food industries as a rich source of antioxidant activity. Characterization of the genetic diversity of wild hops is underway.
Mafakheri, M. and Hamidoghli, Y. (2019). Effect of different extraction solvents on phenolic compounds and antioxidant capacity of hop flowers (Humulus lupulus L.). Acta Hortic. 1236, 1-6
extract, antioxidant capacity, hops, solvent, ethanol, polarity