Temperature–air velocity association, experimental and modeling study of stevia leaves solar drying

Sugar is a natural high-calorie sweetener. Its excessive consumption is associated with health problems such as obesity, diabetes, heart disease, and degenerative issues. The stevia plant is a great natural substitute. It provides no calories and has medicinal properties such as oral antibacterial, hypoglycemic, and anti-hypertensive with a high nutritional value. In this work, the effects of temperature and air velocity in drying kinetics of stevia leaves were studied using a convective drier operating with air velocities (2, 3, and 4 m/s) and temperatures controlled (45 °C, 55 °C, and 65 °C). The highest drying rate was obtained at 65 °C and 4 m/s air velocity at 0.05 kg water/kg dry matter min. The experimental data were fitted to theoretical drying models to determine the best approach. It is found that the Page model gives a good fit for all experiments, with correlation coefficients (R2) > 0.9994. The equations to correlate this model's variables with air and temperature were determined. The results show that ΔE and glucoside values increase when temperature and air velocity increase.