Combined Multi-assay Evaluation of the Antioxidant Properties of Tree Bark

Abstract Wood logging generates considerable amounts of bark by-product, which are a potential antioxidant source well worth extracting and using. The present work compares the antioxidant properties of the bark of the following selected Hungarian forest tree species: white poplar (Populus alba L.), black locust (Robinia pseudoacacia L.), sessile oak (Quercus petraea Liebl.), black poplar (Populus nigra L.), silver birch (Betula pendula Roth), European larch (Larix decidua Mill.), scots pine (Pinus sylvestris L.), wild cherry (Prunus avium L.), European hornbeam (Carpinus betulus L.) and sweet chestnut (Castanea sativa Mill.). Inner and outer bark were investigated separately. Total polyphenol content (TPC) was determined by the Folin-Ciocâlteu method, whereas antioxidant capacity was assayed using the ferric reducing ability of plasma (FRAP), 2.2-diphenyl-1-picrylhydrazyl (DPPH), and ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) methods. The overall antioxidant power of the samples was evaluated using a scoring system that combined the FRAP, DPPH, and ABTS assay results. The TPC levels did not always follow the FRAP, DPPH, and ABTS assay values. Differing reaction mechanisms and sample compositions are possible reasons for this. The presented scoring evaluation was suitable for the assessment and comparison of complex antioxidant properties of tree bark samples. According to the scores, inner bark showed higher scores compared to outer bark for most species with the exceptions of black poplar, black locust, white poplar, sweet chestnut, and European larch. The highest overall antioxidant capacities were determined in the inner bark of wild cherry and the outer bark of sweet chestnut. The species with the overall lowest scores were black locust and black poplar.