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  • Polyphenols: can their antioxidant properties be boosted by lipophilization?

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The lipid-water interface as a structuring element in micellar systems (A), emulsified systems (B), lamellar systems (C), lipoprotein systems (D), liposome systems (E) and cellular systems (F). In bue: the aqueous phase; in yellow, hydrophobic phases of varying compositions (surfactants, triglycerides, phospholipids, galactolipids, cholesterol esters, cardiolipins, lipoproteins, etc)

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Exemple d’une série homologue de phénolipides formés par estérification de l’acide chlorogénique avec des alcools de différentes longueurs de chaîne.

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For further information

Laguerre M., Bayrasy C., Lecomte J., Chabi B., Decker E.A., Wrutniak-Cabello C., Cabello G., Villeneuve P., 2013. How to boost antioxidants by lipophilization? Biochimie, 95: 20-26. Doi: 10.1016/j.biochi.2012.07.018

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Pierre Villeneuve
Jérôme Lecomte
Montpellier, France
Agropolymer Engineering and Emerging Technologies (UMR IATE)

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Polyphenols: can their antioxidant properties be boosted by lipophilization?

10/2013

Non-enzymatic antioxidants have the capacity to neutralize free radicals and protect biological systems. However, for the most part, they are hydrophilic phenolic compounds that are difficult to use in food or non-food lipid matrices. Researchers from CIRAD and their peers have thus grafted lipids onto them, to produce more easily usable molecules. But what becomes of the anti-radical properties of these "lipophilized" molecules? By assessing the anti-oxidant activity of two anti-oxidants and their lipophilized derivatives, the researchers realized that grafting a medium carbon chain would produce much more powerful anti-oxidants than the original molecules.

Non-enzymatic anti-oxidants are subject to particular scrutiny as a result of their capacity to neutralize free radicals and protect biological systems against oxidation. Numerous epidemiological studies have shown that in man, anti-oxidants have a preventive effect against various diseases.

Anti-oxidants help preserve the nutritional and organoleptic properties of foodstuffs by slowing fat and protein oxidation. However, as non-enzymatic anti-oxidants are mostly relatively hydrophilic phenolic compounds, they are difficult to use in food lipid matrices (oils, emulsions, etc) or other products (systems with controlled release of active ingredients, cosmetic formulas, etc), which considerably restricts their applications.

Phenolic anti-oxidant lipophilization

To overcome this difficulty, researchers from CIRAD and their peers have been looking, for some ten years or so, into grafting lipids onto phenolic anti-oxidants, be they pure molecules or plant extracts of tropical or Mediterranean origin (green coffee, olive leaves, rosemary, etc).

This modification, which is known as lipophilization, can be done either chemically or enzymatically using lipases, serves to adjust the hydrophilic/hydrophobic balance of the anti-oxidant. The subsequent lipophilized molecules, known as "phenolipids", have new self-assembly properties and affinity for lipid-water interfaces. But what about their anti-oxidant properties?

Anti-oxidant properties of phenolipids

After the synthesis stage, the researchers assessed the anti-oxidant activity of the modified molecules or extracts in systems of increasing complexity (emulsions, membranes, living cells), using methods developed in the laboratory? In particular, they worked on chlorogenic and rosmarinic acid (two representatives of the large phenolic acid family) and their two lipophilized derivatives.

Irrespective of the system studied, it was found that grafting a medium carbon chain (eight to twelve carbon atoms) resulted in anti-oxidants that were two to five times more powerful than the original molecules. More surprisingly, grafting longer chains (14 to 20 carbon atoms) resulted in a drastic fall in, if not a total loss of activity.

The anti-oxidant activity of lipophilized derivatives is thus not proportional to the length of the grafted chain. Consequently, lipophilization cannot be done at random, given that there is an optimum chain length, known as the critical chain length, with which activity is markedly improved.

Rationalizing lipophilization

In other words, if the lipid chain is too short or too long, the activity of the molecule will be much poorer than hoped for. For a given anti-oxidant, the most effective lipophilization strategy is thus to determine the critical chain length. This work will serve to rationalize the lipophilization concept, which was previously applied empirically.

Based on this experience, the researchers are now looking into direct lipophilization of plant phenolic extracts, particularly the rich and abundant biodiversity found in southern and Mediterranean countries. The aim is to make optimum use of largely or totally unexploited resources, such as reject green coffee beans, olive leaves and rosemary, and eventually develop powerful anti-oxidant cocktails, that are both inexpensive and suited to a wide range of applications: food, cosmetics, medicines and materials. Access to medium-chain lipids (eight to twelve carbon atoms), such as those in palm kernel and copra oil, should be an additional asset.


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