Influence of ultrasonic pretreatment on the convective drying kinetics and quality of cocoa (Theobroma cacao L.)

Background: Convective drying of cocoa (Theobroma cacao L.) is a critical stage in its processing, and ultrasound (US) application may represent an innovative technology to optimize this process. Objectives: To evaluate the effect of ultrasound pretreatment (40 kHz/130 W for 10, 20 and 30 minutes) on the convective drying of cocoa (60 °C, 2 m/s), through the description of the drying kinetics, the determination of the effective diffusion and activation energy, as well as the identification of the most appropriate mathematical model to represent the process. Methods: Five thin-layer mathematical models based on Fick's second law for long periods were used, employing the moisture ratio as an independent variable. Experimental data were adjusted to these models to determine drying kinetics and mass transfer coefficients. Results: US significantly increased (p>0.05) the drying speed in all treated samples, reducing drying time by an average of 52% compared to the control. The Page model was the most appropriate for predicting experimental drying curves, explaining between 98.1% and 99.2% of the variance. The US application increased both the effective diffusivity and the mass transfer coefficient, achieving a 92% weight loss compared to the initial weight. Conclusions: The US is a cost-effective technology for the cocoa industry, improving production times and achieving significant energy savings while maintaining product quality.