GC-HRTOF-MS metabolite profiling and antioxidant activity of methanolic extracts of Tulbaghia violacea Harv

Abstract

Tulbaghia violacea is a bulbous herb that is used extensively in traditional medicine to alleviate various illnesses. The current study aimed to evaluate the total phenolic and flavonoid contents of methanolic extracts of the bulb, leaves, rhizome, and stem of the plant, T. violacea, and to compare the phytochemical profile of these extracts utilizing gas chromatography/high-resolution time-of-flight mass spectrometry (GC-HRTOF-MS). The antioxidant potential of the plant extracts was also determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS). All methanolic T. violacea extracts were rich in terpenoids, flavonoids, and saponins; however, only leaf extract contained tannins. Cardiac glycosides and anthraquinones were not observed in any of the tested extracts. All plant extracts showed weak antioxidant capabilities in both DPPH and ABTS assays with IC50 values from 146.4 ± 1.11 to 303.15 ± 1.98 µg/mL and 136.25 ± 0.03 to 246.09 ± 0.01 µg/mL, respectively. Methanolic bulb extract of T. violacea contained significant phenolic content (22.85 ± 3.15 mg GAE/g), followed by rhizomes (17.46 ± 1.75 mg GAE/g), whereas the leaf (9.47 ± 0.64 mg GAE/g) and stem (5.83 ± 0.77 mg GAE/g) extracts had the least phenolic contents. Similarly, the bulb extracts possessed significant flavonoid content (37.59 ± 1.27 QE/g), followed by rhizome (26.40 ± 0.21 QE/g) and leaves (22.67 ± 1.26 QE/g), and then stems with flavonoid content of 8.65 ± 2.11QE/g. These results were significantly different at P < 0.05. The GC-HRTOF-MS revealed that stem extract is rich in sulphur-containing compounds (51.2 %), followed by fatty acid amides (23.64 %), esters (10.50 %) and flavonoids (10.51 %). The rhizome extract showed the presence of sulphur-containing compounds (40.11 %), fatty acid amides (37.24 %), fatty acid esters (14.33 %), phenol (3.70 %), butyl alcohol (3.04 %) and sterols (0.77 %), while the bulb extract possessed a high quantity of sulphur compounds (93.34 %) with a lesser amount of fatty acid amide (0.29 %), fatty acid esters (2.91 %), flavonoids (0.81 %) and miscellaneous compounds (1.35 %). Additionally, the leaf extract also possessed sulphur compounds (48.37 %), fatty acid esters (15.77 %) and fatty acid amides (21.97 %), vitamins (9 %), terpenoids (1.37 %), sterols (1.63 %) and phenols (0.19 %). The findings from this study indicate that bulb extract of T. violacea holds potential pharmacological properties, which can induce detoxifying enzymes and can protect against reactive oxygen species due to its high number of sulphur-containing compounds.

Keywords

• Tulbaghia violacea
• Phytochemicals
• Antioxidant activity
• Phenolic content
• GC-HRTOF-MS