Effect of accelerated extraction and sonication on the antioxidant capacity of wood and bark extracts of wet-hearted silver fir (Abies alba Mill.)

Abstract

The aim of this study was to compare the antioxidant capacity of hydrophilic extracts of different tissues of wet-hearted silver fir (Abies alba Mill.) logs. Wet heart is a wood defect of silver fir and lowers the value of wood. The exploitation of extractives could increase utilization and financial returns. The bark, sapwood, heartwood and knotwood were investigated by using two green extraction methods: ultrasound assisted extraction (US) and accelerated solvent extraction (ASE), with aqueous ethanol as solvent. Total extractive content (TEC), total polyphenol content (TPC) and antioxidant capacities (FRAP, DPPH, ABTS) from the extracts were determined and compared. The highest contents of total hydrophilic extractives were measured in knotwood (23.07%, ASE) and bark (10.31%, ASE), and the lowest values were determined for sapwood (2.00%, ASE) and heartwood (3.56%, ASE). The ASE method resulted in significantly higher TPC (0.65–10.58%) than the US (0.46–9.19%) method. Nevertheless, the simplicity of instrumentation and costs can make US also a potential candidate for future extraction and utilization. The highest antioxidant capacities were measured in knotwood (FRAP: 159.75 mg AAE/g, ABTS: 316.15 mg TE/g, DPPH: 189.23 mg TE/g) and bark (FRAP: 159.75 mg AAE/g, ABTS: 126.81 mg TE/g, DPPH: 74.52 mg TE/ g) extracts, prepared with ASE, which complements well the existing literature data on silver fir extractives. The knotwood and bark of wet-hearted silver fir is an abundant source of antioxidant polyphenols, whereas sapwood and heartwood are poor in these extractives and potentially unsuitable for the valorization by the extraction of natural antioxidants.