Green subcritical extraction of lipophilic compounds from cocoa bean shells using hydrofluoroolefin as solvent

Cocoa bean shell (CBS), a by-product of cocoa processing, is a promising source of lipids and bioactive compounds, including theobromine. This study explores the use of hydrofluoroolefin R1234ze as a green solvent for subcritical extraction of fats and theobromine from CBS, with a focus on the effects of particle size on extraction efficiency. The process was optimized using different particle size fractions (0–1000 μm, 1000–2000 μm, 2000–6000 μm) and solvent-to-feed mass ratio (7.3–3.7 g solvent/g CBS). Results indicate that smaller particle sizes led to higher extraction efficiencies, with the best fat recovery (78.71%) achieved from the smallest fraction with a ratio of 4.9 g R1234ze/g CBS. Theobromine was co-extracted, demonstrating the feasibility of simultaneous recovery of lipids and methylxanthines. Kinetic modelling identified pseudo-second order kinetics for fat extraction and the Power Law model for theobromine extraction, highlighting mass transfer limitations. Overall, R1234ze proves to be a promising solvent for CBS valorisation, offering an eco-friendly alternative to conventional methods due to its mild temperature and pressure conditions (30 °C and 5–7 bar).