Effects of pretreatment and drying methods on drying characteristics and quality attributes of Andrographis paniculata

The appropriate stage of maturity of Andrographis paniculata (AP) was selected based on the level of phytochemicals. Prior to drying, samples were blanched in boiling water. The Modified Halsey and Modified Henderson models offered the best fit of desorption isotherms for fresh and blanched AP, respectively. AP was dried in a tray dryer (TD) and heat pump-dehumidified dryer (HPD) at 40–60 °C; microwave dryer (MWD) at 270–720 W and freeze dryer (FD). Five mathematical models were fitted into the experimental data. The three-parameter model gave the best fit. The drying rate constant was related to the drying temperature using the Arrhenius model. Effective moisture diffusivity was increased with increase in drying temperature and microwave power. HPD and blanching increased antioxidant activity, total phenolics, andrographolide, and neoandrographolide by 1.45, 11.16, 6.31, and 23.57%, respectively. The blanching pretreatment followed by HPD should be considered for drying AP for its further utilization. Practical applications Andrographis paniculata (Burm.f.) Nees has been used in a traditional herbal medicine to treat the common cold, fever, and diarrhea. The active components of A. paniculata are very bitter diterpene lactones known as andrographolide and neoandrographolide found in the aerial parts but contained the maximum contents in leaf. The pretreatment followed by drying process may greatly influence the quality of A. paniculata leaves. Heat pump-dehumidified dryer (HPD) was adopted for dried A. paniculata in order to obtain dehydrated herb with high drying quality. The knowledge of drying kinetics was used to find the optimum point of the drying process for A. paniculata. The results of this study revealed that blanching followed by HPD could reduce drying time and increase phytochemical contents compared with commercial product and will be useful in the pharmaceutical products with good chemical properties.