Comparative Study on the Antioxidant and Antimicrobial Activities of Stem-Bark Extract of Litchi chinensis and its Organic Fractions

Abstract

Aqueous-methanolic (20:80) extract of stem-bark of Litchi chinensis Sonn. was fractionated with diethyl ether, ethyl acetate and n-butanol using solvent extraction technique, and then total phenols (TP), total flavonoides (TF) and total condensed tannins (TCT) were calculated for this extract and its organic fractions. Total phenolic compounds ranged from 145.2±1.3 – 680.3±1.2 mg GAE/g of sample, while total flavonoides and total condensed tannins ranged from 101.5±1.4 – 210.4±2.0 mg equivalent to catechin /g of sample and 95.7±1.2 – 324.5±0.8 mg equivalent to catechin/g of sample respectively. Antioxidant potential of the extract and its fractions was evaluated using DPPH radical scavenging and phosphomolybdate assays. Ethyl acetate fraction scavenged maximum DPPH radical (78%, IC₅₀= 15.3 µg/ml), close to BHT (80%, IC₅₀ = 12.4 µg/ml) while aqueous-methanolic extract showed the highest total antioxidant activity (1.09) as compared to its fractions relative to gallic acid. Agar well diffusion assay was also carried out to check the antibacterial activity against six different bacterial strains (Proteus mirabilis, Micrococcus luteus, Bacillus licheniformis, Nocardia asteroids, Salmonella typhimorium and Bacillus subtilis). The aqueous-methanolic extract showed the maximum growth inhibition (19.7±0.9 mm, MIC = 1.2 mg/ml) against Bacillus subtilis. These results suggested the potential use of Litchi extracts as an antioxidant as well as antibacterial agent.