Effect of brewing conditions of herbal teas from flower and leaf extracts of Sesbania javanica Miq. on total phenolic content, vitamin C content and antioxidant activity

Abstract

Importance of the work: Brewing conditions can reveal major factors for improvement of the components and antioxidant activity of herbal tea. Objectives: To determine the effect of brewing conditions of herbal tea from Sesbania javanica Miq. flowers and leaves on antioxidant properties, vitamin C content and total phenolic content (TPC) and to identify phytochemicals. Materials and Methods: The TPC, vitamin C content and antioxidant activity were determined using methods based on Folin-Ciocalteu’s phenol reagent, radical scavenging and meta-phosphoric acid, respectively. Chemical components were detected using gas chromatography-mass spectrometry. Results: The flower water extract produced the highest TPC (70.55 ±1 4.71 µg gallic acid/mg extract) and antioxidant activity (1/EC50 = 0.0294 ± 0.0093), while the leaf water extract had the highest vitamin C content (14.22 ± 4.13 µg vitamin C/mg extarct). Flower- and leaf-based teas differed significantly (p < 0.05) in TPC, antioxidant activity and vitamin C content. Optimal brewing conditions were flower tea at 70°C for the highest TPC for 10 min (46.73 ± 1.00 µg gallic acid/ mg dried weight) and at 80 °C for 6 min for the highest antioxidant activity (1/EC50 = 0.04±0.01), while leaf tea at 90°C for 6 min produced the highest vitamin C content (190.15 ± 4.93 µg vitamin C/mg dried weight). Temperature was weakly negatively associated with TPC (β = - 0.44, p < 0.05). GC–MS analysis of the flower and leaf ethanol extracts identified several volatile constituents, including 3-methylbutanal, 2-furanmethanol, cyclohexanol, dodecanoic acid, and hexadecanoic acid ethyl ester, while the leaf part contained 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one and dodecanoic acid. Main finding: The bioactive compounds, vitamin C content and antioxidant potential in herbal tea brewed from S. javanica flowers and leaves could be favorable for people wishing to follow a healthy lifestyle.