Comparative analysis of γ-aminobutyric acid, antioxidant capacity, and total phenolic content in common edible leafy plants of Sri Lanka

Abstract

The γ-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the central nervous system, regulating neuronal excitability and reducing anxiety. Antioxidants protect cells from oxidative stress by neutralising free radicals, lowering the risk of chronic diseases. This study evaluated the GABA content and antioxidant properties of six edible leaves: 𝘔𝘶𝘳𝘳𝘢𝘺𝘢 𝘬𝘰𝘦𝘯𝘪𝘨𝘪𝘪 (Karapincha), 𝘈𝘴𝘱𝘢𝘳𝘢𝘨𝘶𝘴 𝘳𝘢𝘤𝘦𝘮𝘰𝘴𝘶𝘴 (Hathawariya), 𝘐𝘱𝘰𝘮𝘰𝘦𝘢 𝘢𝘲𝘶𝘢𝘵𝘪𝘤𝘢 (Kankun), 𝘊𝘦𝘯𝘵𝘦𝘭𝘭𝘢 𝘢𝘴𝘪𝘢𝘵𝘪𝘤𝘢 (Gotu Kola), 𝘔𝘰𝘳𝘪𝘯𝘨𝘢 𝘰𝘭𝘦𝘪𝘧𝘦𝘳𝘢 (Murunga), and 𝘗𝘪𝘯𝘢𝘤𝘪𝘢 𝘰𝘭𝘦𝘳𝘢𝘤𝘦𝘢 (Nivithi). GABA content was determined using the Kitaoka and Nakano spectroscopic method. Antioxidant capacity was assessed using the 2,2-diphenyl-1- picrylhydrazyl (DPPH) assay and the ferric reducing antioxidant power (FRAP) assay. Total phenolic content (TPC) was measured using the Folin-Ciocalteu method. Methanol extracts (0.156 to 5.00 mg mL⁻¹) were prepared for all assays, and the activity at 1 mg mL⁻¹ was extrapolated from the dose-response curves. 𝘔. 𝘬𝘰𝘦𝘯𝘪𝘨𝘪𝘪 had the highest GABA content (0.175 mg mL⁻¹), followed by 𝘈. 𝘳𝘢𝘤𝘦𝘮𝘰𝘴𝘶𝘴 (0.124 mg mL⁻¹), 𝘐. 𝘢𝘲𝘶𝘢𝘵𝘪𝘤𝘢 (0.065 mg mL⁻¹), 𝘗. 𝘰𝘭𝘦𝘳𝘢𝘤𝘦𝘢 (0.051mg mL⁻¹) 𝘔. 𝘰𝘭𝘦𝘪𝘧𝘦𝘳𝘢 (0.043 mg mL⁻¹) and 𝘊. 𝘢𝘴𝘪𝘢𝘵𝘪𝘤𝘢 (0.022 mg mL⁻¹). The highest radical scavenging activity as measured by DPPH assay, was observed in 𝘔. 𝘬𝘰𝘦𝘯𝘪𝘨𝘪𝘪 (IC₅₀ = 1.49), while 𝘐. 𝘢𝘲𝘶𝘢𝘵𝘪𝘤, 𝘔. 𝘰𝘭𝘦𝘪𝘧𝘦𝘳𝘢, 𝘊. 𝘢𝘴𝘪𝘢𝘵𝘪𝘤𝘢, 𝘈. 𝘳𝘢𝘤𝘦𝘮𝘰𝘴𝘶𝘴 and 𝘗. 𝘰𝘭𝘦𝘳𝘢𝘤𝘦𝘢 exhibited IC₅₀ values 4.80, 4.92, 6.32, 19.46 and 80.50 mg mL⁻¹, respectively compared to vitamin C (IC₅₀ = 0.16mg mL⁻¹). The highest FRAP value of 2.08 µmol trolox equivalents mL⁻¹ was recorded for 𝘊. 𝘢𝘴𝘪𝘢𝘵𝘪𝘤𝘢 followed by of 𝘔. 𝘬𝘰𝘦𝘯𝘪𝘨𝘪𝘪 (1.66 µmol mL⁻¹) and 𝘔. 𝘰𝘭𝘦𝘪𝘧𝘦𝘳𝘢 (0.48µmol mL⁻¹). 𝘔. 𝘬𝘰𝘦𝘯𝘪𝘨𝘪𝘪 also showed the highest TPC (0.20 mg mL⁻¹ of gallic acid equivalents) followed by 𝘔. 𝘰𝘭𝘦𝘪𝘧𝘦𝘳𝘢 (0.09 mg mL⁻¹). Among the tested edible leaves, 𝘔. 𝘬𝘰𝘦𝘯𝘪𝘨𝘪𝘪 demonstrated the highest levels of GABA, antioxidant activity, and total phenolic content, indicating its strong potential as a functional food with neuroprotective and antioxidant properties.