Effect of drying techniques, conditions and feed types on the quality of dried curry leaf powder

Curry leaf (Murraya koenigii L.) is valued for its characteristic flavor and is used in varied cuisines and formulations. In this work, the effect of three different drying techniques: tray drying (TD), conductive hydro drying (CHD), and freeze drying (FD), at varying temperatures (40 °C, 60 °C, 80 °C) on the phytochemical and physical properties of curry leaf dried as leaf or as pulp was evaluated. Drying behavior was studied using the Page model and effective diffusivity was found to increase with temperature. CHD at 40 °C resulted in the lowest moisture content (4.98 ± 0.03 %) while FD resulted in the lowest water activity (0.54 ± 0.04). Excellent flow properties were observed in TD 60 °C and CHD 80 °C. However, CHD at 40 °C exhibited superior color retention. TD 80 °C and CHD 80 °C, with reduced drying duration resulted in higher phenolics, flavonoids and alkaloid contents. On the contrary, CHD 40 °C sample showed better antioxidant activity and flavor retention through GC-MS. Similarly, SEM analysis showed intact cell structures in samples dried at lower temperatures. Overall, considering drying time, product quality, and process costs, CHD, often regarded as a nonthermal approach, is an excellent approach for the production of curry leaf powder.