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.

Comparative Study Regarding the Chemical Composition and Biological Activity of Pine (Pinus nigra and P. sylvestris) Bark Extracts

“…Studies regarding the AOA of P. sylvestris bark extracts evaluated by the ABTS assay were found, but the results were expressed as mg Trolox equivalents/g vegetal material, thus the results could not be compared with the experimental variants [ 49 , 50 ].…”

In vitro antioxidant and antibacterial activities with polyphenolic profiling of wild cherry, the European larch and sweet chestnut tree bark

“…Interestingly, chestnut leaves and burs showed lower phenolic contents of 115.4 ± 1.8 and 93.3 ± 2.4 mg GAE/g dw, respectively, compared to the bark [28]; while cherry fruits showed TPC of 284.48 ± 3.07 GAE mg/100 g of fresh cherries [14]. One of the earlier studies evaluated the phenolic content of the bark extracts after separating the outer bark from the inner bark [10]; although for practical reasons and from a commercialization point of view, we chose to study the whole bark of the tree trunks. Other studies have evaluated the TPC values of bark of Quercus rubra (276.50 ± 3.23 mg GAE/g dw extract), Betula celtiberica (432.02 ± 3.00 mg GAE/g dw extract) [27], Larix laricina (34 ± 2 g GAE/100 g extract) [29], as well as Fagus sylvatica L. (65.22 ± 5.57 mg GAE/g dw) [30].…”

“…It should be pointed out that both inner bark and outer bark of the tree trunk influence the antioxidant properties of the bark. A study found that the inner bark showed higher antioxidant capacity compared to the outer bark for most species [10]. The variations in genetic factors (cultivars) or geographic locations may also affect the metabolite profile [38].…”

“…), which are common in Hungarian forests were chosen. Earlier studies have shown that these species have exceptionally high antioxidant capacity in their bark as well as antimicrobial effects [10][11][12]. Moreover, in Europe, these trees are abundant and easily accessible (Fig.…”

Parameter Optimization and Potential Bioactivity Evaluation of a Betulin Extract from White Birch Bark

“…The FRAP activity of the betulin extract was investigated according to the method detailed by Tálos-Nebehaj and co-workers [22]. Briefly, a fresh working solution was prepared by mixing acetate buffer, 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ), and FeCl 3 •6H 2 O, and then kept at 37 • C until use.…”