Assessment of Antioxidant Potential and Related Structural Diversity of Polyphenols in Indian Foliose Lichens

Abstract

Lichens have been used since ancient times to cure various ailments. To study the variation in phytochemical composition and antioxidant activity of n-hexane, acetone and methanol extracts in seven lichen species. Phytochemical study includes total phenolic and flavonoid content and quantitative study by HPLC technique. Furthermore the in vitro antioxidant activities were determined by DPPH and ABTS methods in seven lichen species. The findings revealed the significant (p less then 0.05) variations in phytochemical profiles and antioxidant activity for all the analyzed samples. The Flavoparmelia caperata extracts showed highest antioxidant activity followed by Sticta nylanderiana. The amount of total phenolic and flavonoid contents were highest in methanol extracts of Everniastrum nepalense (95.9±2.62 mg GAE/gm dw) and F. caperata (78.04 ± 2.31 mg QAE/gm dw) respectively. The phenolic acids and flavonoids contents of lichen samples were quantified by RP- HPLC and compared with standard markers, which varied between 0.03- 970.01 and 0.16- 1316.54 μg/gm dry weight, respectively. Gallic acid was present in all the tested extracts of which, highest concentration was found in acetone (970.01± 2.48 μg/gm dw) and methanol (846.86±1.86 μg/gm dw) extracts of F. caperata. Maximum concentration of rutin (1316.54 ± 3.23 μg/gm) was present in acetone extract of Lobaria retigera. The scavenging capacity of methanol fraction of lichens were also compared with individual scavenging capacity of the phenolic compounds. The structure–activity relationship was elucidated and discussed within each class of phenolic substances. The variation in radical scavenging activity of the tested phenolic compounds were attributed to structural differences mainly on number and position of hydroxyl groups.