Microwave-assisted drying kinetics of cocoa pod husk (Theobroma cacao L.): physicochemical, techno-functional and phytochemical analysis

Abstract

Cocoa pod husk (CPH), the principal by-product of cocoa processing, constitutes up to 80% of the fresh weight of the fruit and remains underutilized despite its richness in dietary fibres and bioactive compounds with antioxidant and antiinflammatory potential. This study investigated the microwave-assisted drying (MAD) kinetics of CPH using grams per watt (g/W) as a control parameter and, evaluate its impact on the effective diffusivity (Deff), activation energy (Ea), and preexponential factor (D0), as well physicochemical, techno-functional, and phytochemical changes in the resulting flour. A Fickbased model quantified moisture transfer, revealing a clear exponential rise in Deff (3.74 × 10⁻⁷ to 7.44 × 10⁻⁷ m²/s) with decreasing g/W. The Arrhenius fit (R²= 0.9383) yielded a low Ea (14.94 kJ/mol) and high D0 (9.23 × 10⁷ m²/s), confirming efficient volumetric heating. Page's model best describes the kinetics, indicating diffusion-driven drying. Physicochemical parameters remained stable, whereas water absorption decreased and solubility increased at higher powers, intensified by ultrafine particle size (<53 µm). Colour shifts included reddish tones at intermediate power and yellow hues at high powers.All treatments enhanced phenolic and antioxidant levels relative to fresh CPH, with 0.52 g/W preserving bioactivity most effectively. These findings support MAD as a viable strategy for sustainable valorisation of CPH into functional food ingredients.