Determination of antioxidant activities of some phenolic compounds

Plants synthesize a wide variety of organic compounds called secondary metabolites. Phenolic compounds, which make up a significant portion of these compounds, are intensively purified from plants and their structures are elucidated due to their many biological functions and antioxidant activities. Phenolic compounds are valuable compounds that can replace synthetic antioxidant compounds in the food industry and many other sectors (medicine, pharmacy, etc.).In this study, antioxidant capacity of 18 phenolic compounds (gallic acid, p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, salicylic acid, genticic acid, caffeic acid, p-coumaric acid, ferulic acid, chlorogenic acid, neochlorogenic acid, resveratrol, naringenin, catechin, isoorientin, quercetin, rutin, biochanin A) were compared with three standard antioxidant compounds (BHT, BHA and Trolox). Antioxidant activity of these compounds were determined by free radical scavenging activity (DPPH•), cation radical scavenging activity (ABTS•+), reducing power activity (FRAP), Cu2+ ion reducing capacity (CUPRAC) and metal chelation activity methods. The IC50 values of DPPH radical scavenging activity of the compounds ranged from 5.32 ± 0.18 to 728.14 ± 9.49 µg / mL, while the ABTS method varied from 0.83 ± 0.011 to 6.60 ± 0.07 µg / mL.The first five compounds with the highest activity according to the DPPH method consist of gallic acid, catechin, protocatechuic acid, quercetin, and genticic acid, whereas in ABTS method, gallic acid, naringenin, resveratrol, protocolatechic acid and isoorientine, respectively.FRAP activity of the compounds ranged from 0.14 ± 0.09 to 11.13 ± 0.84 µmol TE / mg, while CUPRAC activity ranged from 2.01 ± 0.37 to 23.66 ± 0.12 µmol TE / mg. According to CUPRAC and FRAP method, the first five compounds with the highest antioxidant activity were found to be gallic acid, protocolatechic acid, caffeic acid, genticic acid and quercetin. Among the phenolic compounds analyzed, the highest metal chelating activity was determined in naringenin, catechin, chlorogenic acid and protocolatechic acid, respectively.As a result of all these analyzes, protocatechuic acid was among the first 4 phenolic compounds having the highest activity according to all antioxidant methods.Gallic acid was found to have the highest activity according to 4 antioxidant methods except metal chelating activity.