Role of hydrophobicity on antioxidant activity in lipid dispersions, From the polar paradox to the cut-off theory

This chapter focuses on the versatile role of hydrophobicity on antioxidant capacity in lipid dispersions. This crucial parameter affects both the location and the diffusivity of antioxidants in dispersed lipid systems, which, in turn, impacts their antioxidant capacity. Until recently, the polar paradox was the only theory available to explain how hydrophobicity impacts antioxidant capacity in oil-in-water emulsions, micelles, liposomes, and membranes.

However, one cannot but notice the great number of discrepancies and contradictions to the polar paradox when scrutinizing data accumulated for more than 20 years in this field. An alternative hypothesis—the cut-off theory—accounts for the polar paradox's limitations. The chapter presents an overview of the latest experimental and theoretical advances in the field.

It re-examines the polar paradox assumption wherein fewer polar antioxidants tend to be more effective than their polar counterparts in lipid dispersions, reviews the experimental data supporting the cut-off theory, and addresses the physicochemistry behind antioxidant action by developing two new, complementary approaches based on location and diffusion.

While the polar paradox is founded exclusively on the prominent influence of the antioxidant location, it is seen that the cut-off theory tries to account for both the impact of diffusion and location of the antioxidant on its activity..