Total polyphenolic contents and in vitro antioxidant properties of eight Sida species from Western Ghats, India

Sida L., is a medicinally important genus, the species of which are widely used in traditional systems of medicine in India. Pharmacologically, roots are known for anti-tumor, anti-HIV, hepatoprotective, and many other properties. Phenolic antioxidants help in reducing oxidative stress occurring during treatment of such diseases. The study aimed to evaluate and compare polyphenol contents and antioxidant properties of eight selected species of Sida from Western Ghats, India. Methanolic root extracts (10% w/v) of Sida species, viz., S. acuta, S. cordata, S. cordifolia, S. indica, S. mysorensis, S. retusa, S. rhombifolia, and S. spinosa were analyzed. Sida cordifolia possessed highest total phenolic content (TPC: 1.92 ± 0.10 mg Caffeic Acid Equivalent/g and 2.13 ± 0.11 mg Tannic Acid Equivalant/g), total flavonoid content (TF: 2.60 ± 0.13 mg Quercetin Equivalent/g) and also possessed highest antioxidant activities in 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging (51.31 ± 2.57% Radical Scavenging Activity, (RSA); Trolox Equivalent Antioxidant Capacity: 566.25 ± 28.31μM; Ascorbic acid Equivalent Antioxidant Capacity: 477.80 ± 23.89 μM) and Ferric Reducing Antioxidant Power assays (TEAC: 590.67 ± 29.53 μM; AEAC: 600.67 ± 30.03 μM). Unlike DPPH and Ferric Reducing Antioxidant Power (FRAP) activity, 2, 2'-Azinobis (3-ethyl Benzo Thiazoline-6-Sulfonic acid) ABTS(+) antioxidant activity was highest in S. indica (TEAC: 878.44 ± 43.92 μM; AEAC 968.44 ± 48.42 μM). It was significant to note that values of AEAC (μM) for all the antioxidant activities analyzed were higher than that of TEAC. The high contents of phenolic compounds in the root extracts of selected Sida species have direct correlation with their antioxidant properties. Conclusively, roots of S. cordifolia can be considered as the potential source of polyphenols and antioxidants.