Thin-layer drying of sadabahar (Catharanthus roseus) leaves using different drying techniques and fate of bioactive compounds

Drying of Catharanthus roseus leaves offer easy utilization of its powder for medicinal purposes but is challenging due to temperature sensitivity of its bioactive constituents. In this work, C. roseus leaves were subjected to three economic drying techniques: solar, tray (40, 50, 60 degrees C) and, microwave (450, 600, 900 W) to identify the best drying condition for retention of bioactives of C. roseus leaves. Semi-empirical models that best defined the drying conditions were identified. Results revealed lowest moisture content (similar to 1.2% d.b.), drying time (4-8 min) and activation energy (36.92 kJ/mol) with high moisture diffusivity (similar to 10(-9) m(2)/s) for microwave drying. For retention of bioactives, solar drying in natural convection mode performed well and may serve as a low-cost drying strategy. However, leaves dried at 600 W microwave power showed higher antioxidants (152 mg TE/g), phenols (11.28 mg GAE/g), and flavonoids (59.69 mg/QE g) and is recommended for drying of C. roseus leaves. Practical application: Identification of suitable drying method and conditions for the production of Catharanthus roseus leaf powder can promote its large scale manufacturing while retaining its innate bioactive compounds. Addition of the said powder or its extract in neutraceutical, pharmaceutical formulations, and in oncological ailments can enhance health benefits as these leaves contain essential polyphenols and important dimeric alkaloids like vincristine and vinblastin etc. Optimum C. roseus processing conditions especially for solar and microwave drying can help farmers in producing value added medicinal food products at the field level for generation of additional revenue at lower process cost.