Effects of drying pretreatments and extraction methods on biochemical activity of Houttuynia cordata Thunb.

Abstract

Houttuynia cordata Thunb. (HCT) consists of various phytochemicals, with flavonoids being the key components. However, their quantity and quality are affected mostly by drying and extraction methods. This study aimed to evaluate the impact of drying and extraction methods on the phytochemical contents such as total phenolic content (TPC), total flavonoid contents (TFC) and the major components of flavonoids. In addition, antioxidant activities were measured using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP). Freeze-drying (FD) and oven-drying (OD) methods were used for drying; aqueous (AE), ethanolic (EE), and ultrasonic assisted extraction (UAE) methods were used for extraction. The results indicated that FD had higher TPC, TFC, DPPH, and FRAP antioxidant activities than OD, irrespective of the extraction methods used. The highest TPC (29.40 ± 0.40 mg gallic acid equivalent (GAE)/ g dry wt.) and TFC (72.80 ± 0.95 mg quercetin equivalent (QE)/g dry wt.) were obtained in UAE. Likewise, UAE had the highest DPPH radical scavenging activity (69.94 ± 0.73%, 1 mg/ml) and FRAP reducing power (314.00 ± 1.51 μmol Fe²⁺/g dry wt.). The HPLC analysis results confirmed the presence of four major flavonoids namely isoquercetin, rutin, quercitrin, and hyperoside. Their content ranges from 0.06 to 1.10 mg QE/g dry wt. of the sample plant. This study showed that both drying, and extraction methods had a substantial impact on the phytochemical contents and antioxidant activities of HCT, with FD and UAE being the best drying and extraction methods, respectively.