Modeling the drying of spent hibiscus flower calyxes (hibiscus sabdariffa l.): evaluation of empirical models at different temperatures

Abstract

This study aimed to model the drying kinetics of spent calyces of roselle (Hibiscus sabdariffa L.) at 50, 60, and 70 °C, in order to select the empirical model that best describes moisture loss and to promote the use of this by-product as a functional ingredient rich in dietary fiber and phenolic compounds. Drying was carried out in a forced convection oven with constant air flow, using trays with a uniform material thickness of 3 mm. Four empirical model: Page, modified Page, Henderson-Pabis, and Midilli-Kucuk, were evaluated using nonlinear regression. Model parameters were calculated, and the goodness of fit was assessed using the adjusted coefficient of determination (R²_adjusted), root mean square error (RMSE), and reduced chi-square (c²_red). Results showed that the drying coefficient (k) increased with temperature across all models, indicating thermal acceleration of the process. The exponent (n) ranged from 1,2 to 1,9, confirm that drying occurred mainly during the falling rate period controlled by internal diffusion. Among the models evaluated, the Midilli-Kucuk model proved to be the most suitable for representing the drying kinetics, serving as a useful tool for process optimization and valorization of this agro-industrial by-product.