This is the first report on the extraction of cocoa bean shell (CBS) using deep eutectic solvents (DESs). Screening results with 16 different choline chloride-based DESs showed how choline chloride:oxalic acid DES was the most suitable solvent for the extraction of the bioactive compounds from CBS and that concentrations varied greatly depending on the used solvent. The DES extraction was compared to the DESs coupled with microwave extraction (MAE), and the yields of the extracted compounds were higher for DES/MAE. For theobromine, the obtained yields for DES extraction were 2.145-4.682 mg/g, and for caffeine, were 0.681-1.524 mg/g, whereas for DES/MAE, the same compounds were obtained in 2.502-5.004 mg/g and 0.778-1.599 mg/g. Antioxidant activity was also determined, using DPPH method, obtaining 24.027-74.805% activity for DES extraction and 11.751-55.444% for DES/MAE. Water content significantly influenced the extraction of targeted active compounds from CBS, whereas extraction time and temperature did not show statistically significant influence. The extraction temperature only influenced antioxidant activity. The study demonstrated how extraction using DES and microwaves could be of a great importance in the future trends of green chemistry for the production of CBS extracts rich in bioactive compounds.
Keywords: active compounds; cocoa bean shell; deep eutectic solvents; microwave-assisted extraction; waste.