Grey alder (Alnus incana (L.) Moensch) bark valorisation potential: longitudinal variability of chemical composition and antimicrobial, antioxidative, and cytotoxic activity of extractives

Abstract

Grey alder Alnus incana (L.) Moensch bark represents a prospective raw material for acquiring a broad range of high-value green chemicals with various biological activities. Bark, rich in valuable extractives, is considered an important resource for sustainable development because of its abundance, renewability, and availability. Herein, we investigated the longitudinal variability of A. incana bark chemical composition and bark extractives yield for their potential utilization/valorisation. A. incana bark extractives were obtained by Soxhlet extraction using four solvents of different polarities: ethanol, ethyl acetate, petroleum ether, and water, while the bark samples were collected from three trunk heights. Extractive contents (EC) and total phenolic content (TPC) were determined, as well as their antioxidative (AO), antimicrobial, and cytotoxic activity were examined. The results showed that the A. incana bark contains an elevated amount of extractives compared to the other deciduous tree species with the highest content found for water and ethanol extractives. The extractives exhibited high antioxidative activity and antibacterial effects on eight Gram-positive and seven Gram-negative bacterial stains. Furthermore, the A. incana bark extractives showed antiproliferative activity towards two human breast adenocarcinoma cell lines MCF-7 and MDA-MB-231. The ethyl acetate extract showed the best activity on the inhibition of the growth of the MDA-MB-231 cell line (IC50 value 30.9 µg/ml). In contrast, the ethyl acetate extractive showed the best cytotoxic effect on the MCF-7 cell line (IC50 value 15.7 µg/ml).