Microwave-Assisted Water Extraction of Aspen (<i>Populus tremula</i>) and Pine (<i>Pinus sylvestris</i> L.) Barks as a Tool for Their Valorization

• Published in: Plants
• Main Authors: Matiss Pals, Liga Lauberte, Jevgenija Ponomarenko, Maris Lauberts, Alexander Arshanitsa
• Format: Article
• Language: English
• Published: MDPI AG 2022-06-01
• Subjects: bark; microwave-assisted extraction; salicin derivatives; oligomeric proanthocyanidins
• Online Access: https://www.mdpi.com/2223-7747/11/12/1544

The barks of aspen (<i>Populus tremula</i>) and pine (<i>Pinus sylvestris)</i> are byproducts of wood processing, characterized by their low economic value. In the present study, microwave-assisted one-cycle water extraction was explored as a tool for the valorization of this biomass as a source of biologically active compounds. The microwave extractor of the original construction equipped with a pressurized extraction chamber and a condenser section was used. The microwave-assisted extraction (MAE), specially including dynamic dielectric heating up to 70 °C followed by 30 min of isothermal heating, promoted the isolation of salicin from aspen bark, allowing for the obtention of a two-times-higher free salicin concentration in water extracts (−14% vs. 7%) reached by multi-cycle accelerated solvent extraction (ASE), which is an advanced technique used as a reference. The MAE of pine bark with dynamic heating up to 90–130 °C, avoiding the isothermal heating step, allowed for the obtention of a 1.7-times-higher concentration of proantocyanidin dimers-tetramers, a 1.3-times-higher concentration of catechin and a 1.2-times-higher concentration of quinic acid in water extracts in comparison to a more time- and solvent-consuming ASE performed at the same temperature. The biological activity of the obtained extracts was characterized in terms of their ability to inhibit xahntine oxidase enzyme, which is a validated target for the therapeutic treatment of hyperuricemia.