What Makes Good Antioxidants in Lipid-Based Systems? The Next Theories Beyond the Polar Paradox

Abstract

The polar paradox states that polar antioxidants are more active in bulk lipids than their nonpolar counterparts, whereas nonpolar antioxidants are more effective in oil-in-water emulsion than their polar homologs. However, recent results, showing that not all antioxidants behave in a manner proposed by this hypothesis in oil and emulsion, lead us to revisit the polar paradox and to put forward new concepts, hypotheses, and theories. In bulk oil, new evidences have been brought to demonstrate that the crucial site of oxidation is not the air-oil interface, as postulated by the polar paradox, but association colloids formed with traces of water and surface active molecules such as phospholipids. The role of these association colloids on lipid oxidation and its inhibition by antioxidant is also addressed as well as the complex influence of the hydrophobicity on the ability of antioxidants to protect lipids from oxidation. In oil-in water emulsion, we have covered the recently discovered non linear (or cut-off) influence of the hydrophobicity on antioxidant capacity. For the first time, different mechanisms of action are formulated in details to try to account for this nonlinear effect. As suggested by the great amount of biological studies showing a cut-off effect, this phenomenon could be widespread in dispersed lipid systems including emulsions and liposomes as well as in living systems such as cultured cells. Works on the cut-off effect paves the way for the determination of the critical chain length which corresponds to the threshold beyond which antioxidant capacity suddenly collapses. The systematic search for this new physico-chemical parameter will allow designing novel phenolipids and other amphiphilic antioxidants in a rational fashion. Finally, in both bulk oils and emulsions, we feel that it is now time for a paradigm shift from the polar paradox to the next theories.

Mass Transport Phenomena in Lipid Oxidation and Antioxidation

“…For CTAB micelles, the deeper the phenolic is in the micelle, the less active it is toward a free radical that is supposed to be located within the same micelle core. This sheds doubts on the validity of the so-called internalization hypothesis (Laguerre et al 2015) (Figure 5c). If only location matters, octyl gallate would have been a better reducer of galvinoxyl radicals than short-chain gallate alkyl esters.…”

“…), far from the interface (Figure 5c). In other words, the current model of the cut-off effect implies that a too-short or a too-long hydrophobic chain in a homologous series of antioxidants does not ensure a proper interfacial location, which, in turn, does not lead to an optimal activity (Laguerre et al , 2015.…”

“…Literally speaking, an antioxidant needs to be at the right place at the right time, which should prompt researchers to study them in a space-and time-resolved manner. A recent illustration of this approach is given by the observation of the so-called cut-off effect in homologous series of antioxidants in lipid dispersions and cultured cells showing that an optimal hydrophobicity exists, for which the activity of an antioxidant is maximal (Laguerre et al 2015). Although the activity in such systems seems to be governed by this effect, no clear explanation has yet been provided to account for the sudden drop in activity when a hydrophobicity threshold is surpassed.…”

Investigation of Distribution of Antioxidant Compounds from Natural Sources and Study of Lipid Protection in Oil-in-Water Emulsions

“…4,[10][11][12] However, the results of other studies are not in accordance with this theory. [13][14][15] As such, some authors have attempted to improve the polar paradox theory, [16][17][18] employing esters from phenolic acids, such as esters of the acids p-hydroxybenzoic, caffeic and vanillic. 16,19,20 However, some of these compounds (e.g., esters of p-hydroxybenzoic acid) are related to serious health problems, such as mammary tumors in humans and reproductive problems in animals, 21 limiting the future extrapolation of these results to other food sources, as well their application in industrialized foods.…”

Aplicação de planejamento fatorial na oxidação de óleos contendo diferentes tipos de ácidos graxos ômega 3

“…products that lower food quality and safety 2,[6][7][8][9][10][11] . The autoxidation of oils depends on the temperature, …”