Abstract
A kinetic approach was used to determine the radical scavenging activities of sinapic acid and its derivatives: sinapine, 4-vinylsyringol, syringic acid, syringaldehyde, and ethyl, propyl and butyl sinapate. The responses were expressed as rates of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) scavenging (RS), superoxide radical (O2˙−) scavenging (RFF), and β-carotene bleaching in the emulsion system (RB). For RS and RB, the esters of sinapic acid showed the highest responses while, for RFF, this was seen for syringic acid. The effectiveness of the selected compounds for scavenging these free radicals was also determined at a fixed endpoint. The early response parameters were demonstrated to be good discriminators in assessing differences for antioxidants with comparable fixed endpoint activity. The primary feature that ranks the kinetic data and the endpoint determinations is interpreted in terms of the mechanisms of the reactions involved in each of the assays conducted.
Highlights
Phenolic compounds are considered to be great contributors to the health effects of plant-based diets mostly due to their ability to scavenge free radicals
To determine the early responses of the hydrogen from an antioxidant, and the effects of the investigated antioxidant can be estimated by selected antioxidants towardsinDPPHradicals, at the change indetermine absorbance
A higher Chromatographic partition values (CPV) indicates higher content of acetonitrile in the mobile phase and slower elution of the analyte from the column, and lower polarity of the compound. In this investigation a kinetic approach was used in combination with standard fixed endpoint radical scavenging analysis to examine the scavenging activities and reaction mechanisms of sinapic acid and its derivatives against DPPH·, O2 ·− and lipid radicals
Summary
Phenolic compounds are considered to be great contributors to the health effects of plant-based diets mostly due to their ability to scavenge free radicals. For that reason they are extensively investigated for their antioxidant activity. A significant aspect in the determination of antioxidant activity of phenolic compounds would be the reactivity in terms of the response of an antioxidant at the early steps of the process [3], which is related to the kinetics of the free radical quenching [4] and is conditioned by the reaction mechanism. The scavenging of free radicals by antioxidants can occur by two major mechanisms: hydrogen atom transfer (HAT) and electron transfer (ET). Which mechanism is going to be Molecules 2017, 22, 375; doi:10.3390/molecules22030375 www.mdpi.com/journal/molecules
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