Optimization and greenness evaluation of extraction methods of bioactive compounds from cocoa bean shells (Theobroma cacao L.)

Abstract

In this study, the efficiency of two green technologies, ultrasound-assisted extraction (CBS-UAE) and microwave-assisted extraction (CBS-MAE), was optimized and compared for the recovery of bioactive compounds from cocoa bean shells (CBSs). Response surface (I-optimal) experimental designs were applied, considering variables such as temperature, time, solid–liquid ratio, particle size, and power. Total phenol content (TPC) and antioxidant capacity (DPPH = 2,2-diphenyl-1-picrylhydrazyl, ABTS = 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid, and FRAP = ferric reducing antioxidant power) were analyzed. CBS-UAE showed higher antioxidant activity, as measured by the ABTS (265.8 ± 5.1 mg TE per g CBS extract b.s.) and FRAP (212.86 ± 4.95 mg TE per g CBS extract b.s.) assays, than CBS-MAE. Optimal conditions obtained for UAE were 65 °C, 45 min, a ratio of 70 mL g⁻¹, and a fine particle size (75–150 µm). While both methods yielded similar TPC and DPPH profiles, UAE achieved the highest antioxidant activity in the ABTS and FRAP assays, whereas MAE drastically reduced the extraction time. UHPLC–HRMS (Q-Exactive–MS/MS) analysis of the optimal CBS-UAE/CBS-MAE extracts mainly identified methylxanthines (theobromine and caffeine), amino acids (L-phenylalanine and arginine), and organic acids (mannitol). The environmental impact of the extraction technique was validated using AGREE metrics, confirming the ecological sustainability of MAE and UAE with AGREE scores of 0.62/1.00 and 0.55/1.00, respectively. These results validate the use of cocoa by-products via clean, sustainable technologies, thereby adding value to these residues.