1. Polar Paradox： Development and Challenge
Luna Wang

2. Contents 1 2 3 History Introduction Significance of Polar Paradox
Limitation of Polar Paradox 3
Recent and Future Development
Conclusion

3. History
Before 1995, a relative effectiveness data for antioxidants was generated
During the 1980s, Porter and his collegues reported a lot of studies showing differences of antioxidant behavior as a function of the lipid system used
In 1994, Frankel etal. Postulating that the polar paradox is due to an interfacial phenomenon.

4. Antioxidant Polar Paradox Theory
(Nonpolar)
(polar)

5. Interfacial Phenomenon
(polar)
(nonpolar)
Mickaël Laguerre,2015

6. The significance of Polar Paradox
The polar paradox hypothesis has significance in the food and medicinal applications of antioxidants, especially in developing new antioxidant strategies, such as producing lipophilic derivatives of naturally occurring antioxidants for use in emulsions, liposomes, and other biological media, because there are very few promising lipophilic or low HLB antioxidants from natural sources.
Shahidi, F. et al.

7. Limitations of Polar Paradox Theory
Question of the Lipid-Air Interfacial Oxidation Concept
The Concentration Hypothesis
Structure Difference Hypothesis

8. Question of the Lipid-Air Interfacial Oxidation Concept
In 1995, Koga and Terao postulated that the actual site of oxidation in bulk oil is not the air-oil interface but oil-water interfaces formed with traces of water. They based their interpretation upon the observation that the presence of phospholipids enhanced the antioxidant activity of α-tocopherol in model bulk oil systems containing a trace amount of water (1% v/v).

9. The Concentration Hypothesis
Ying Zhong and Fereidoon Shahidi. Antioxidant Behavior in Bulk Oil: Limitations of Polar Paradox Theory : The polar paradox theory applies only when the concentration of the antioxidant is over a critical value, so that interfacial phenomenon dominates over the solubility parameter.
Zhong,Y. 2012

10. The Concentration Hypothesis: Materials
Four sets of antioxidants (each containing one hydrophilic antioxidant and its hydrophobic counterpart) were tested for their activity in bulk oil (stripped corn oil). The antioxidants tested included Trolox/α- tocopherol, ascorbic acid/ascorbyl palmitate, gallic acid/lauryl gallate, and EGCG/EGCG-tetrastearate.

11. The Concentration Hypothesis: Methods
The four sets of antioxidants were evaluated for their activity in a stripped corn oil over a concentration range. The antioxidants were added to stripped corn oil at a series of concentrations (0.02, 0.04, 0.08, 0.16, and 0.32 μmol/g oil), and the oil was stored under Schaal oven conditions at 60 °C for 7 days. The oxidative status of the oil was indicated by its content of conjugated dienes (CD).
The CD values were determined by measuring the absorbance of the oil dissolved in iso-octane at 234nm.

12. The Concentration Hypothesis: Results

13. The Concentration Hypothesis: Results

14. The Structure Hypothesis
The more polar antioxidants are not necessarily the more active. For instance, it has been shown by Rancimat analysis that the stability of oil increases when the alkyl chain of the protocatechuyl alcohol is lengthened (Torres de Pinedo et al., 2007). Such result can not be anticipated nor explained by the polar paradox hypothesis.

15. The Structure Hypothesis
In the paper“Mickaël Laguerre, Christelle Bayrasy, Atikorn Panya, Jochen Weiss, D. JulianMcClements, Jérôme Lecomte, Eric A. Decker & Pierre Villeneuve (2015) What Makes Good Antioxidants in Lipid-Based Systems?”States“Old studies draw a binary representation instead having the overall picture of the influence of the polarity on antioxidants. Besides these “binary” studies, others confirmed the polar paradox using more than two molecules, but in this case, these molecules were not always structurally related, and thus introduced a lot of new variables (number and location of OH groups, double bonds, side chain substitutions, etc.) which renders difficult the investigation of the sole effect of the polarity.”

16. Developments in Antioxidants
New phenolic antioxidant models have been used with the same active phenolic group, yet with differences in hydrophobicity. Such phenolic molecules with various alkyl chain lengths are known as “phenolipids” a term we adopted in 2010 to describe a phenolic compound conjugated to a lipid moiety.

17. Conclusion
The polar paradox states that polar antioxidants are more active in bulk lipid than their nonpolar counterparts, whereas nonpolar antioxidants are more effective in oil-in-water emulsion than their polar homologs.
Paradox experiences limitations in bulk oil and its validity is also dependent on the concentration of the antioxidants employed.
The recent work done on manufacturing on phenolipids paves the way for systematic investigation of the chain length effect to design new phenolipids and other novel antioxidants in a rational fashion.

18. References
Shahidi, F.; Zhong, Y. U.S. Patent Provisional Application 61/322,004, 2010; patent pending.
Shahidi, F.; Zhong, Y. Novel antioxidants in food quality preservation and health promotion. Eur. J. Lipid Sci. Technol. 2010,112, 930–940.
Ying Zhong and Fereidoon Shahidi. Antioxidant Behavior in Bulk Oil: Limitations of Polar Paradox Theory. dx.doi.org/ /jf204165g | J. Agric.Food Chem. 2012, 60, 4−6.
MICKAE.L LAGUERRE, LUIS J. LoPEZ GIRALDO, JE RO ME LECOMTE, MARIA- CRUZ FIGUEROA-ESPINOZA, BRUNO BAREA, JOCHEN WEISS,)ERIC A. DECKER, AND PIERRE VILLENEUVE, Relationship between Hydrophobicity and Antioxidant Ability of “Phenolipids” in Emulsion: A Parabolic Effect of the Chain Length of Rosmarinate Esters. J. Agric. Food Chem., 2010, 58 (5), pp DOI:  /jf904119v