ABSTRACT This research aims to study and improve the performance of an indirect solar drying system dedicated to drying mint leaves. The hybrid solar dryer combines a thermal collector for air heating and a photovoltaic panel for electric power generation, ensuring continuous drying even in bad weather conditions such as cloudy weather or at night by supplying hot‐air at temperatures up to 60°C. Experiments were conducted on mint leaves with an initial moisture content of 0.81 kg water/kg w.b.. The results showed that drying at 60°C achieved the highest drying rate of 7.29 × 10 −5 kg water/kg w.b./s, reducing the drying time to 500 min instead of 760 min when operated at 40°C. This hybrid solar dryer showed a high thermal efficiency of 31.3% when operating at 60°C, followed by 50°C (25.7%) and 40°C (20.0%). Experimental results also demonstrated that indirect drying better preserved the color and natural appearance of mint leaves. The drying at 40°C exhibited a distinctive biochemical profile, with a total phenolic content of 441.0 ± 0.3 mg Eq AG/g, a total flavonoid content of 0.276 ± 0.01 mg Eq Q/g and an antioxidant activity (DPPH assy) of 282.79 ± 0.01 μg/mL. These results indicate that this temperature can be considered optimal to preserve bioactive compounds and minimize degradation.
Rabah et al. (Sun,) studied this question.