Indirect Solar Drying of Mint Using a Hybrid System Under Controlled Air Drying Conditions

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.