Drying of Orthosiphon aristatus leaves: Mathematical modeling, drying characteristics, and quality aspects

ABSTRACT

The stage of maturity for Orthosiphon aritatus (OA) leaves revealed that stage I (young leaves) provided the highest bioactive compounds. Vacuum blanching (VB) for 75 s gave the highest sinensetin (28.4% increment) and eupatorin (21.0% increment) compared with heated water blanching (HWB). The modified Henderson model was the most suitable desorption isotherm model for the OA leaves. The VB and unblanched OA leaves were dried by different drying methods, including convection tray drying (CTD, 40–60°C), heat pump dehumidify drying (HPD, 40–60°C), mixed mode solar drying (64.6°C), and freeze-drying. Three-parameter model (TP) was the best model to explain all drying curves. The drying constant, K in the TP and activation energy were fitted to the Arrhenius model. Effective moisture diffusivities were increased with the VB, drying temperatures, and HPD. The highest specific moisture extraction rate was obtained from the VB and dried in the HPD at 60°C. The quality aspects of sinensetin (10.2% retention), eupatorin (10.7% retention), total phenolics, and antioxidant activity revealed the best quality for the OA leaves pretreated by the VB and dried in the HPD at 60°C and could reduce drying time by 44.8% compared with the CTD. The VB of the OA leaves and dried using the HPD at 60°C were recommended.

KEYWORDS:

• Antioxidant
• blanching
• desorption isotherms
• food drying
• mathematical modeling
• Orthosiphon aristatus

Additional information

Funding

The authors would like to acknowledge the Royal Golden Jubilee Ph.D. scholarship [grant number 2.F.KK/53/B.1], the Thailand Research Fund, and the Office of the Higher Education Commission for their financial support in cooperation between Khon Kaen University and Iowa State University.