A comparative study on the phenolic composition, antioxidant and enzyme inhibition activities of two endemic Onosma species

Abstract

The studies on bioactivities of plant extracts are a fundamental requirement for future pharmacological research. Therefore, the present study extracted the phytochemicals from the two endemic species such as Onosma isaurica and O. bracteosa and tested their antioxidant, reducing power and enzyme inhibitory activities followed by scanning of the phytochemicals in the extracts by using liquid chromatography–electrospray tandem mass spectrometry (LC–ESI–MS/MS). The results revealed that the antioxidant activity in terms of 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging and ferrous ion chelating was not statistically significant between the species but 2,2-azino-bis (3-ethylbenzothiazloine-6-sulphonic acid) (ABTS) radical scavenging was significant between the two species. Reducing power in terms of ferric reducing antioxidant power (FRAP) reducing did not exhibit the significance while cupric ion (CUPRAC) reducing and phosphomolybdenum displayed significance between the two species. In case of the enzyme inhibitory assay, the α-amylase inhibitory activity was significant but tyrosinase inhibitory was not significant between the species. The bioactivities of the extracts were compared with standard positive controls as trolox for ABTS radical, DPPH radical, FRAP reducing, CUPRAC reducing and phosphomolybdenum; Ethylenediaminetetraacetic acid (EDTA) for ferrous ion chelating; acarbose for α-amylase inhibition; and kojic acid for tyrosinase inhibition. Both of the species showed significantly higher bioactivity than their respective positive controls. Interestingly the bioactivity was found promising with O. bracteosa over O. isaurica due to the high presence of the phenolics. The richness of the phytochemicals in O. bracteosa was evidenced by LC–ESI–MS/MS analysis. In conclusion, the two endemic species - O. isaurica and O. bracteosa – which are rich in bioactivity deserve for conservation and sustainable utilization towards developing pharmaceutically valid natural products in the future.