Abstract
Halimodendron halodendron has been used as forage in northwestern China for a long time. Its young leaves and flowers are edible and favored by indigenous people. In this study, eleven phenolic compounds were bioassay-guided and isolated from the aerial parts of H. halodendron for the first time. They were identified by means of physicochemical and spectrometric analysis as quercetin (1), 3,5,7,8,4′-pentahydroxy-3′-methoxy flavone (2), 3-O-methylquercetin (3), 3,3′-di-O-methylquercetin (4), 3,3′-di-O-methylquercetin-7-O-β-d-glucopyranoside (5), isorhamentin-3-O-β-d-rutinoside (6), 8-O-methylretusin (7), 8-O-methylretusin-7-O-β-d-glucopyranoside (8), salicylic acid (9), p-hydroxybenzoic acid (ferulic acid) (10), and 4-hydroxy-3-methoxy cinnamic acid (11). They were sorted as flavonols (1–6), soflavones (7 and 8), and phenolic acids (9–11). Among the compounds, flanools 1–4 revealed a strong antibacterial activity with minimum inhibitory concentration (MIC) values of 50–150 μg/mL, and median inhibitory concentration (IC50) values of 26.8–125.1 μg/mL. The two isoflavones (7 and 8) showed moderate inhibitory activity on the test bacteria. Three phenolic acids (9, 10 and 11) showed strong antibacterial activity with IC50 values of 28.1–149.7 μg/mL. Antifungal activities of the compounds were similar to their antibacterial activities. All these phenolic compounds showed significant antimicrobial activity with a broad spectrum as well as antioxidant activity based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and β-carotene-linoleic acid bleaching assays. In general, the flavonol aglycones with relatively low polarity exhibited stronger activities than the glycosides. The results suggest the potential of this plant as a source of functional food ingredients and provide support data for its utilization as forage as well.
Highlights
Antioxidants play important roles in scavenging free radicals and/or chain breaking the oxidation reactions both in vitro and in vivo to minimize oxidative damages to the cells [1]
H. halodendron and characterized based on the physicochemical properties and spectral data. Their chemical structures were elucidated based on the spectral data and comparison of the properties and spectral characteristics with those in the literature, which were all known compounds and confirmed as quercetin (1) [21], 3,5,7,8,4'-pentahydroxy-3'-methoxy flavone (2) [22], 3-O-methylquercetin (3) [23], 3,3'-di-O-methylquercetin (4) [24], 3,3'-di-O-methylquercetin-7-O-β-Dglucopyranoside (5) [25], isorhamentin-3-O-β-D-rutinoside (6) [26], 8-O-methylretusin (7) [27], 8-O-methylretusin-7-O-β-D-glucopyranoside
The antifungal activity of the phenolic compounds with their minimum inhibitory concentration (MIC) and IC50 values shown in Figure 3 was similar to the antibacterial activity
Summary
Antioxidants play important roles in scavenging free radicals and/or chain breaking the oxidation reactions both in vitro and in vivo to minimize oxidative damages to the cells [1]. The application of synthetic antioxidants, such as butylated hydroxytoluene (BHT), butylated hydroxylanisole (BHA), and propyl gallate in foods has led to notable adverse effects in consumer health [2,3] Microbial contamination is another common problem in the food, cosmetic and pharmaceutical industries and the resistance to existing antimicrobial agents creates the need for new antimicrobial compounds. To the best of our knowledge, there is little information of its chemical composition and bioactivity except for our previous studies about the preparative separation of the main phenolic compounds by high-speed countercurrent chromatography (HSCCC) [17] and bioactivities of the flower essential oil [18] Other investigations into this plant included a few phylogenic and cytological studies [19,20].
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