Roselle Precision Drying: Comparative Performance of Smart Rotary Drum and Solar Dryers

Roselle calyces are regarded as a source of anthocyanins and many nutrients. Despite their high therapeutic and nutritional value, fresh calyces are highly perishable, necessitating efficient preservation methods. Traditional drying, although cost-effective, often degrades heat-sensitive nutrients due to uncontrolled conditions. This study evaluates the efficiency of two precision drying technologies, specifically a hybrid smart solar dryer (HSSD) and a smart hot air rotary drum dryer (DD), at temperatures of 30°C, 40°C, and 50°C. The investigation focuses on drying kinetics and energy consumption while examining the calyces' physicochemical properties. Findings revealed that the hybrid smart solar dryer consumed 19.61, 21.57, and 24.38 kWh/batch of total energy, whereas the smart hot air rotary DD recorded 19.93, 21.52, and 16.3 kWh/batch at 30°C, 40°C, and 50°C. Notably, microstructural analysis showed that the DD produced less cellular collapse than the hybrid smart solar dryer. The highest total anthocyanin (303.09 mg/100 g) and furfural content (43.90%) were preserved in calyces dried at 30°C and 40°C with the DD, respectively. Conversely, the hybrid smart solar dryer at 50°C was more effective in preserving total phenols and vitamin C. Overall, this research emphasizes that the smart hot air rotary drum dryer operated at 40°C can be considered a blueprint for balancing efficient drying kinetics with the retention of valuable quality measurements, especially the anthocyanin. Future studies should focus on longitudinal economic viability, carbon credit potential, and the scalability of these technologies for other industrial medicinal and aromatic plants.