Effects of Drying Temperature on the Amount of Secondary Metabolites and Antioxidant Activity of Orthosiphon aristatus (Blume) Miq. Tea Extracts

Abstract

Orthosiphon aristatus (Blume) Miq. tea is a traditional herbal tea in Thailand. This herb is used to prevent and treat a wide range of diseases such as diuresis, hypertension, and diabetes. In this study, three different drying temperatures used for herbal tea processing were evaluated (40, 50, and 60 °C) for their secondary metabolites [total phenolic content (TPC), caffeic acid (CA), rosmarinic acid (RA), and total flavonoid content (TFC)] and antioxidant activity. The herbal tea processed at 40 °C showed significantly (P < 0.05) higher TPC [485.26 ± 49.43 mg gallic acid equivalent (GAE)/ 100 g], CA (202.17 ± 1.00 mg/kg), RA (469.99 ± 1.56 mg/kg), TFC [356.86 ± 41.81 mg catechin equivalent (CE)/ 100 g], and 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging activity than those at other drying temperatures. Therefore, a drying temperature of 40 °C was the optimum condition for the Orthosiphon aristatus(Blume) Miq. leaves because it retained the secondary metabolite content with strong antioxidant potential.