Environmentally Friendly Extraction from Picea Abies Bark as an Approach to Accessing Valuable Antioxidants in Biorefineries

Abstract

Every year, the pulp and wood-processing industry produces large side streams of bark, the valorisation of which is desirable for both economic and environmental reasons. We investigated organosolv extraction of antioxidants from Picea abies bark using various ratios of ethanol/water with the goal of obtaining high yields of these desirable compounds. The resulting extracts were analysed (I) for their total contents of phenols (TPC), flavonoids (TFC) and tannins (TTC), and (II) for their antioxidant activity using the DPPH radical scavenging method. The highest total yield of bark extract (14.78%) and the highest concentrations of dry extracts of TPC (324.80 mg g−1), TFC (62.55 mg g−1) and TTC (83.63 mg g−1) were obtained under mild conditions (100 °C extraction temperature and an ethanol/water solvent ratio of 50%, v/v). DPPH antioxidant activity index (AAI) ranged from 0.68 (pure water extract) to 1.31. This antioxidant effect was increased to 1.59 by adding oligolignin from the organosolv process. In the extracts, gas chromatography–mass spectrometry (GC–MS) found nine aromatic carboxylic acids, including phenolic acids and the flavonoid compounds quercetin and (+)-catechin. Our environmentally friendly approach will form the basis for pilot plant and industrial applications.