Antioxidant capacity and total phenol content of beech (Fagus sylvatica L.) bark extracts

• Beech bark is an abundant by-product, but also a source of antioxidant compounds.
• Utilization possibilities of bark extracts in food industry and wood technology.
• Complex assessment of antioxidant properties by multiple methods for the first time.
• Comparison of different extraction techniques and solvents.
• Pure water can be an efficient solvent, supporting the concept of green extraction.

Tree bark is mostly regarded as a by-product of log processing but it can be a rich source of antioxidant compounds which are worthwhile to extract and use for industrial purposes (e.g., nutrition supplements, food conservants, wood preservatives). Beech (Fagus sylvatica L.) is a common industrial wood species and the antioxidant properties of its bark have not yet been studied in detail. The main objective of the current study was the assessment of the total phenol content and the comprehensive antioxidant properties of beech bark extracts prepared with different extraction techniques to obtain maximum yield of the active compounds. Three extraction methods were used: sonication, stirring and a microwave assisted technique. For each method we used water, methanol:water 80:20 v/v, and ethanol:water 80:20 v/v solutions. The antioxidant capacity of the extracts was determined with the DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)) and FRAP (ferric reducing ability of plasma) assays. Total phenol content was measured using the Folin–Ciocâlteu assay. Different antioxidant capacity assays give comprehensive results on the antioxidant properties of the extracts basing on their different selectivity. Ethanol-containing solutions are more efficient for extraction than the respective mixtures with methanol especially at ambient conditions. Under pressurized high temperature conditions, pure water can be as effective as alcohol containing mixtures. Results show that the antioxidant compounds of beech bark can be extracted efficiently using eco-friendly solvents which opens up possibilities for the utilization of beech bark extracts in the future for food industry and wood technology.