Comparison of in-vitro antioxidant activity of two varieties of Clitoria ternatea flowers in Sri Lanka

Introduction: Clitoria ternatea, commonly known as “butterfly pea” in English and “Nil Katarolu" in Sinhala, is widely distributed in tropical regions. Due to its distinctive deep blue colour, it is now widely used in herbal teas, herbal juices, and cosmetic items. Additionally, flowers, seeds, roots, and leaves of this plant have been used for ages in traditional medicine to treat various diseases. As the antioxidant mechanism is crucial in many diseases, this study aimed to evaluate the antioxidant potential of boiled aqueous extracts of fresh flowers of C. ternatea i.e. normal keel blue petals (AEFCN) and enlarged keel blue petals (AEFCL). Methods: The in-vitro antioxidant activity of both crude extracts was evaluated by following a 2-2-diphenyl-1-picrylhydrazyl (DPPH) assay. Further, the total phenolic and flavonoid contents were determined using the Folin-Ciocalteu method and AlCl3 method respectively. The data was analyzed using SPSS software and p<0.05 was considered as statistically significant. Results: The results showed that the AEFCN and AEFCL exhibited dose-dependent DPPH scavenging activity with an IC50 value of 20.09 mg/mL and 26.8 mg/mL respectively whereas, 26.61 µg /mL for ascorbic acid. Further, total phenolic present (p>0.05) in AEFCN and AEFCL were 3.651 ± 0.05 mg GAE/g fresh flower of C. ternatea and 3.47 ± 0 mg GAE/g fresh flower weight of C. ternatea respectively, while total flavanoids (p<0.05) present were 63.58 ± 0.58 mg QE/g fresh flower of C. ternatea and 50.42 ± 0.29 mg QE/g fresh flower weight of C. ternatea respectively. Conclusion: The presence of a significantly (p<0.05) low IC50 value of AEFCN in DPPH assay provided scientific evidence for the high antioxidant activity of normal keel petals compared to the enlarged petals. Although there was no significant difference between phenol amounts, the AEFCN showed higher flavonoid amounts than AEFCL (p<0.05). In addition, AEFCN showed higher total phenols and flavonoid amounts than AEFCL. As phenolic compounds and flavonoids are well-known bioactive compounds with antioxidant properties, a comparatively higher amount of total phenols and flavonoids supports the relatively high antioxidant activity of AEFCN.