Valorization of birch bark using a low transition temperature mixture composed of choline chloride and lactic acid

Abstract

This article presents the results obtained in the extraction of birch bark with a green solvent. A low transition temperature mixture (LTTM) consisting of choline chloride (ChCl) and lactic acid in a molar ratio of 1:1 was used as the solvent. Extraction was performed at 60°C and 80°C. At both temperatures, the effect of extraction time on the yield of the extracted substances was monitored. The yields reached were compared with those obtained in studies using common solvents such as ethanol, methanol, d-limonene, ethyl acetate, and others. The extract was quantitatively analyzed by HPLC-UV to determine betulin and betulinic acid (0.491-1.788 mg/g dry bark and 0.106-0.316 mg/g dry bark, respectively). Total phenolic content was determined spectrometrically using Folin-Ciocalteu reagent and expressed as Gallic acid equivalents (GAE; 18.6-56.8 mg GAE/g dry bark). This study has shown that extraction with a green solvent composed of ChCl and lactic acid can be an effective method for extracting polyphenolic compounds from birch bark. The process for extracting triterpenes (betulin and betulinic acid) is less suitable compared to conventional methods using the mentioned organic extractants.