Optimisation of the microwave-assisted extraction process of bioactive compounds with antioxidant activity from cocoa pod husk (Theobroma cacao L.)

Abstract

Cocoa pod husk (CPH), the main by-product of cocoa production, represents up to 80% of the fresh weight of the fruit and is often discarded, despite being a rich source of bioactive compounds such as polyphenols, flavonoids and saponins. The objective of this study was to optimise the microwave-assisted extraction (MAE) of bioactive compounds with the highest antioxidant activity from CPH using the Box–Behnken design (BBD) and Response Surface Methodology (RSM). The effects of microwave power (285, 570, and 855 W), extraction time (2, 3, and 4 min) and liquid/solid ratio (30, 40, and 50 mL g⁻¹) on the Total Phenol Content (TPC), Total Saponin Content (TSC) and antioxidant activity—DPPH Radical Scavenging Capacity (DRSC), ABTS Radical Scavenging Capacity (ARSC) and Ferric Reducing Antioxidant Power (FRAP)—of bioactive compounds were evaluated. The globally optimised conditions (855 W, 3.06 min, and 50 mL g⁻¹) achieved high extraction efficiencies, and yielded a TPC of 2.724 mg_GAE g⁻¹, TSC of 0.241 mg_EE g⁻¹, and DRSC, ARSC, and FRAP of 81.966, 99.680, and 90.890 µmol_TE g⁻¹, respectively, with a desirability index of 0.84. Microwave power emerged as the main factor influencing bioactive recovery, while extraction time and liquid/solid ratio modulated diffusion and prevented thermal degradation. Notably, the protocol was implemented using a modified domestic microwave oven, offering a cost-effective and sustainable alternative to conventional MAE systems. Comprehensive UHPLC-Q-Orbitrap-MS/MS profiling revealed a diverse metabolomic signature, including malic, citric, tartaric, and gluconic acids, and the phenolic compound clovamide, confirming the chemical complexity and functional potential of the extract. The integrated optimisation and profiling framework reinforces the sustainable nature and methodological novelty of MAE in enhancing the value of CPH, supporting its role as a clean-label candidate for functional nutrition, health-promoting products, and circular bioeconomy initiatives.