Kinetic Study on the Physicochemical of Ulam Raja (Cosmos caudatus) Leaves Powder

Ulam raja (Cosmos caudatus) is a popular medicinal herb due to its high content of bioactive compounds. However, the leaves must be dried prior to use to extend the shelf life of C. caudatus leaf powder. The main objective of this study was to determine the effects of different oven drying times and temperatures on the physicochemical properties and antioxidant activity of C. caudatus leaf powder. The leaves were dried at 60 °C, 80 °C, and 100 °C, and the moisture reduction kinetics were modelled using zero‑, first‑, and second‑order reaction equations to determine the drying rate constants. Proximate analysis was conducted and the aqueous leaf extracts were prepared for antioxidant evaluation, including total phenolic content via the Folin–Ciocalteu assay and radical scavenging activity using the DPPH assay. Color (L, a, b*) were also measured to assess extract quality. The second‑order kinetic model was identified as the most suitable for describing the drying rate of C. caudatus leaves. Both nutrient and phenolic contents were significantly reduced at higher drying temperatures (80 °C to 100 °C), as excessive heat compromised leaf quality. While higher drying temperatures shortened drying time, 60 °C yielded the highest activation energy (25.508 kJ/mol) without compromising energy consumption, drying efficiency, or nutritional quality.