Radical Scavenging Mechanisms of Phenolic Compounds: A Quantitative Structure-Property Relationship (QSPR) Study

Abstract

Due to their antioxidant properties, secondary plant metabolites can scavenge free radicals such as reactive oxygen species and protect foods from oxidation processes. Our aim was to study structural influences, like basic structure, number of hydroxyl groups and number of Bors criteria on the outcome of the oxygen radical absorbance capacity (ORAC) assay. Furthermore, similarities and differences to other in vitro antioxidant assays were analyzed by principal component analysis. Our studies confirmed that the antioxidant behavior in the ORAC assay is dominated by the number and types of substituents and not by the Bors criteria, as long as no steric hindrance occurs. For example, morin (MOR) with five hydroxyl groups and two Bors criteria reached an area under the curve of (3.64 ± 0.08) × 105, which was significantly higher than quercetin-7-D-glucoside (QGU7) (P < 0.001), and thus the highest result. Principal component analysis showed different dependencies regarding structural properties of Folin-Ciocalteu (FC)- and 2,2-diphenyl-1-picrylhydrazyl (DPPH)-assays or 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)- and ORAC-assays, respectively. Therefore, we conclude that they are based on different reaction mechanisms. The number of hydroxyl groups showed a stronger influence on the antioxidant activity than the Bors criteria. Due to these differences, the correlation of these rapid tests to specific applications should be validated.

Quantitative Structure-Property Relationship (QSPR) of Plant Phenolic Compounds in Rapeseed Oil and Comparison of Antioxidant Measurement Methods

“…Accordingly, compounds with this group often have a prooxidant effect, which could explain the outcomes of our study [100]. However, this could also be explained by steric hindrance due to the three substituents on the aromatic ring, as shown previously [76,78]. Moreover, compounds with a catechol group reached a higher increase in OIT than compounds with only one hydroxyl group (DBA and CAA higher than HBA, SIA, SRA, PCA, and FEA).…”

“…These solutions were measured in the ABTS, DPPH, FC and ORAC assays. The results were published before and are reproduced here for comparison [76][77][78]. The measurements were performed according to the literature with some modifications, and detailed instructions can be found elsewhere [76][77][78][79][80][81][82].…”

“…By comparison of the two methods, the influence of the structural properties of the phenolic compounds on the oxidative stability was studied in more detail. Furthermore, these findings were compared to the SAR of in vitro assays (the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), Folin-Ciocalteu (FC) and oxygen radical absorbance capacity (ORAC) assays) published previously [76][77][78] to experimentally identify a rapid test method suitable to predict the antioxidant activity of phenolic compounds in oil.…”

“…Table 1. Phenolic compounds analyzed in this study (phenolic acids and subgroups of flavonoids) along with reference standard names, sample codes and substituents (adapted with permission from Table 1 in [76][77][78]).…”

Understanding the Prooxidant Action of Plant Polyphenols in the Cellular Microenvironment of Malignant Cells: Role of Copper and Therapeutic Implications

“…Genistein was discovered to be a more efficient prooxidant and antioxidant than biochanin A. The number of hydroxyl substitutions in a flavonoid’s backbone structure has been shown to affect both its prooxidant and antioxidant properties ( Platzer et al, 2022 ). Modification of the hydroxyl groups has also been found to affect the biological activity of phenolics.…”