Computational Models for the Determination of Antioxidant Capacity and Phenolics in Dietary Supplements Using Real-Time Proton Transfer Kinetics Data

Hydrogen atom transfer (HAT) underlies free-radical chain-breaking by phenolic compounds. Using linear free energy relationship (LFER) analysis, proton transfer kinetics was hypothesized as a surrogate rate process for HAT. Phenol red is a probe that is easily oxidized to highly absorbing specie by hydroxyl ion. Absorbance decay of oxidized phenol red was induced by incremental proton transfer from a model phenolic (resorcinol). Global best-fit kinetics profile of resorcinol approximates a mono-exponential decay model (R2 = 0.991) as a limiting law. Proton transfer rate constant (Kptt) versus concentration reveal the utility of the slope (?aoc) of the linear plot (r2= 0.990) as a sensitive predictor of phenolic antioxidant capacity. Superior antioxidant capacity profile of a polyphenol-rich dietary supplement: Garcinia kola seed extract, optimally obeyed a mixed linear/mono-exponential decay equation. Model robustness and selectivity for phenolics was achieved by specifying mathematical constraints as acceptance criteria. The method is more biologically relevant for chain-breaking antioxidants than free-radical-based assays because it captures antioxidant structure-function relationships. Further validation studies, using structurally diverse polyphenols, are warranted to ascertain general utility of the kinetic assay for achieving quality by design (QbD) in phenolic dietary supplement products.