Extraction of oleanolic acid from wine pomace using betaine-based deep eutectic solvents

Oleanolic acid is the main component of wine pomace and has anti-caries properties, antitumor effects, anti-obesity effects, and protects hepatic function. However, the majority of pomace has only been used for compost despite the production of thousands of tons per year of wine pomace in Japan. The present study describes the use of low-toxicity solvents called betaine-based deep eutectic solvents (DESs) for efficient extraction of oleanolic acid. H₂O and 1,3-butanediol were used as control solvents to evaluate the extraction. Quantitative analysis using reversed phase high-performance liquid chromatography (RP-HPLC) indicated that extraction of pomace using betaine/xylitol (molar ratio 3:2) afforded the highest yield of oleanolic acid among the deep eutectic solvents. Scanning electron microscope observations and antioxidant assays of extracted samples were also conducted. The results demonstrated effective extraction of pomace under milder conditions than those needed for conventional methods. The less toxic and environmentally benign DESs for extraction would be applicable to the food and cosmetic industries.