Effects of drying conditions on physical properties, bioactive compounds and antioxidant activity of Andrographis paniculata leaves

Abstract

Andrographis paniculata (Burm. f.) Wall. ex Nees (AP) is a medicinal plant widely used in the tropical area of Asia. The effects of drying temperature and time on the andrographolide (AG) content, total phenolic content (TPC), 2,2-diphenyl-1- picrylhydrazyl (DPPH) radical scavenging activity and ferric ion reducing antioxidant power (FRAP) activity were investigated. A 3×4 factorial completely randomized design was performed. Sun drying and hot-air drying at different temperatures (50℃, 60℃ and 70℃) and different drying times (5 hrs, 6 hrs and 7 hrs) were investigated. The results demonstrated that a higher drying temperature and a longer time decreased the AG content, the TPC, the DPPH radical scavenging activity and the FRAP activity. Dried AP leaves at 50℃ for 5 hrs had the highest AG content. However, sun drying for 5 hrs resulted in the greatest TPC, DPPH radical scavenging activity and FRAP activity. Therefore, the recommended options for the optimum drying of AP to maintain active ingredients were 50℃ for 5 hrs, while sun drying was recommended to maintain antioxidant activity. These results provided the basis for further development of dried Andrographis paniculata leaf products containing high contents of bioactive and antioxidant activity as functional or nutraceutical foods in the future.