Low-frequency, green sonoextraction of antioxidants from tree barks of Hungarian woodlands for potential food applications

Highlights

• Low-frequency ultrasound was used for intensification of the bark extraction process.

• Antioxidant capacity of whole barks was evaluated using various biochemical assays.

• Aqueous ethanol performed better than aqueous acetone as an extraction solvent.

• Pedunculate oak, black locust, European ash had the highest antioxidant potential.

• Polyphenolic composition of selected bark extracts revealed by HPLC-MS/MS.

Abstract

The present work evaluates and compares the antioxidant capacities of bioactive constituents in the barks of ten common wood species from Hungary (Quercus rubra, Prunus serotina, Quercus robur, Betula pendula, Fraxinus excelsior, Robinia pseudoacacia, Carpinus betulus, Picea abies, Alnus glutinosa, Pinus sylvestris). Low-frequency ultrasound was used for intensification of extraction from the bark to obtain extracts rich in polyphenolic antioxidants with potential applications in the food industry. The extractions were carried out in different aqueous organic solvents- ethanol 80 % and acetone 80 % at optimized conditions. The overall antioxidant capacity of the extracts was estimated by the combined evaluation of Folin-Ciocâlteu total phenol content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and ferric reducing ability of plasma (FRAP) assays using a scoring system. Aqueous ethanol had better extraction efficiency than aqueous acetone as a solvent medium. Of all the investigated species, Quercus robur showed the maximum antioxidant capacity with TPC of 105.88 ± 17.75 mg GAE/g dw, DPPH (IC₅₀) of 1.90 ± 0.10 μg/mL, ABTS of 437.09 ± 36.22 mg TE/g dw and FRAP of 102.62 ± 8.69 mg AAE/g dw. The polyphenolic characterization of Quercus robur, Robinia pseudoacacia and Fraxinus excelsior was done by liquid chromatography/tandem mass spectrometry.