Potential of convective drying in valorization of broccoli leaves: kinetic study, bioaccessibility of phenolic compounds and structural characteristics

Agricultural residues have a high potential to be transformed and utilized into new products through convective drying. In this study, the effects of drying temperature (50, 60, and 70 °C) on kinetic monitoring and mathematical modeling, physical properties, total phenolic compounds, antioxidant activity (ABTS, DPPH, and FRAP), in vitro digestibility, and structural properties of broccoli residues (leaves) were investigated. The analyzed data revealed that the Midilli model adequately fitted the drying data with maximum R² values (99.74%), minimum mean square error (MSE) (< 0.0020) and chi-square ( \(\chi^{2}\) ${\chi }^2$ ) (< 0.0001). Additionally, increasing the drying temperature (50–70 °C) reduced the drying time to 240 min and increased the effective diffusivity (7.25 × 10^–10 m² s⁻¹). The activation energy was estimated at 27.06 kJ mol⁻¹ and thermodynamic properties indicated that the process did not occur spontaneously. Temperature also had a significant effect (p < 0.05) on the physical properties of broccoli leaf powder (BLP), as well as on the total phenolic compound content (185.69–273.81 mg GAE/100 g), antioxidant activity (6.29–12.72 µM TE/g), and bioaccessibility (8.42–14.10%), with the highest contents observed at 50 °C. Finally, structural properties classified BLP as amorphous with preserved primary structures. These findings help to understand the drying behavior of broccoli leaves while promoting practices for recycling agro-food residues.