Analysis of the Products of Extraction and Water-Alkaline Hydrolysis of Technical Birch Bark under Microwave EMF Exposure

Research was carried out on the isolation of betulin and suberin from the debarking waste of the Arkhangelsk Pulp and Paper Mill pulpwood, ground on an abrasive crusher. Betulin was extracted from various fractions of technical bark with 86% ethanol under exposure to microwave electromagnetic field (EMF) (microwave extraction). Suberin was isolated from the extracted bark by hydrolysis with an aqueous KOH solution under microwave heating conditions as well. The maximum yields of betulin and suberin were achieved when using coarse bark fractions (3-4.5 mm), which were essentially crushed birch bark. The resulting products were identified by IR and NMR spectroscopy and by gas chromatography combined with mass spectrometry (GC/MS). The contents of the components in the bark extracts were determined by HPLC analysis. The extractives were dominated by triterpenoid betulinol (70-72%), with betulinic acid, lupeol, and erythrodiol being present less abundantly. Fatty, dibasic carboxylic acids, and hydroxy acids, dominated by 2-hydroxydecanedioic (2-hydroxysebacic) acid, were identified among the suberin monomers. The content of ferulic acid, a natural antioxidant, was determined in the product from different fractions of the bark (from 2.65 to 11.27 g/kg). The suberin obtained from fine bark fractions differs in the composition from that obtained from coarse fractions. Ribofuranose and xylose were detected in the product obtained from the 1-2 mm bark fraction but were absent in that from the 2-3 mm fraction; lanosterol was present in the suberin from fine fraction of the bark, and cycloartenol, in that from coarse fraction.