Electron spin resonance estimation of hydroxyl radical scavenging capacity for lipophilic antioxidants.

Hydroxyl radical scavenging capacity estimation for lipophilic antioxidants is a challenge due to their poor solubility in aqueous radical generating and measuring systems. In this study, an electron spin resonance (ESR) method was developed and validated for its application in estimating the relative hydroxyl radical (HO*) scavenging capacity for lipophilic antioxidants under physiological pH using a Fenton Fe2+/H2O2 system for radical generation and acetonitrile as a solvent. The Fenton Fe2+/H2O2 system generates a constant flux of pure HO* under the assay conditions. The method was validated by linearity, precision, and reproducibility using selected known lipophilic antioxidants including alpha-tocopherol, lutein, beta-carotene, and BHT. The potential effects of commonly used water-miscible and water-immiscible organic solvents on the Fenton Fe2+/H2O2 HO* generating system as well as their possible interactions with the fluorescent and spectroscopic probes were also reported. In addition, the limitation of the ESR assay was described.