Exploiting Kinetic Features of ORAC Assay for Evaluation of Radical Scavenging Capacity

Abstract

The analysis and interpretation of data retrieved from Oxygen Radical Absorbance Capacity (ORAC) assays represent a challenging task. ORAC indexes originate from different mathematical approaches often lacking correct elucidation of kinetic features concerning radical scavenging reactions by antioxidant compounds. In this work, the expression of ORAC values as area under fluorescein (FL) decay curves (AUC) and lag time are critically compared. This multi-parametric analysis showed the extension of radical scavenging reactions beyond the lag time period for caffeic acid, gallic acid, reduced glutathione and quercetin, extending their antioxidant protection of FL. Ethanol delayed the reaction of both FL and antioxidant compounds with free radical species generated from 2,2′-azobis(2-amidinopropane) dihydrochloride thermolysis. Trolox equivalent values, commonly used to express ORAC values, were more affected by the differences in radical scavenging kinetics between the reference and the tested antioxidant compounds when calculated from AUC than from lag time. These findings stressed the importance of choosing calibrator compounds presenting ORAC kinetics similar to samples to prevent biased estimation of the antioxidant capacity. Additionally, the framework proposed here provides a sustainable analytical method for the evaluation of antioxidant capacity, with an AGREE score of 0.73.

Colour characteristics, phenolic content and antioxidant activity of Spirulina platensis soaked in basil (Ocimum basilicum) leaves extract

“…Carvalho et al . (2023) informed that there are two potential mechanisms in which antioxidants can function for chain‐breaking antioxidants. The oxygen radical absorbs a hydrogen from the antioxidant in the first pathway, which results in the production of a stable antioxidant radical.…”

“…The oxygen radical absorbs a hydrogen from the antioxidant in the first pathway, which results in the production of a stable antioxidant radical. Single electron transfer is the second potential mechanism via which antioxidants deactivate free radicals and this mechanism usually is strong‐solvent‐dependent (Carvalho et al ., 2023). However, the ORAC value of S. platensis seemed to follow the first pathway due to its solvent independent.…”

“…The high ORAC values of S. platensis soaked in BLE both extracted in water and ethanol showed that S. platensis can be chain-breaking antioxidants. Carvalho et al (2023) informed that there are two potential mechanisms in which antioxidants can function for chain-breaking antioxidants. The oxygen radical absorbs a hydrogen from the antioxidant in the first pathway, which results in the production of a stable antioxidant radical.…”

Evaluating the total antioxidant capacity of processed milk: utilising applicable antioxidant assays and key antioxidant components

“…ORAC assay followed the description of Carvalho et al . (2023). Samples (20 μL) and fluorescein solutions (120 μL, final concentration at 70 nM) were placed in microplate.…”

“…Samples were mixed with FRAP reagent (1:11, v:v), the supernatant (0.5 mL) was mixed with distilled water (0.5 mL) and FeCl 3 solution (0.1%, w:v), and absorbance was measured at 593 nm. ORAC assay followed the description of Carvalho et al (2023). Samples (20 lL) and fluorescein solutions (120 lL, final concentration at 70 nM) were placed in microplate.…”