Antioxidant Hydrophobicity and Emulsifier type Influences the Partitioning of Antioxidants in the Interface Improving Oxidative Stability in O/W Emulsions rich in n-3 fatty acids

Abstract

Emulsions with oils rich in n-3 long chain fatty acids, undergo rapid oxidation reactions that may have adverse effects. Therefore, protection against oxidation is necessary. The efficacy of antioxidants with different hydrophobicities (gallic acid, GA; propyl gallate, PG; ascorbyl palmitate, AP; and α-tocopherol, TC) was evaluated in a 79% oil-in-water emulsion model rich in n-3 long chain fatty acids stabilized with either Tween 65 or Tween 80. Antioxidants efficacy was compared to their partitioning in the phases of the emulsion. The order of the antioxidant protection against peroxides and secondary oxidation products was the same as for the antioxidant partitioning in the water-oil interface: AP > GA > PG > TC. The antioxidant efficacy was influenced by antioxidant (p < 0.001), emulsifier (p < 0.001) and interactions of both factors (p < 0.001). AP was the most active antioxidant, while TC was the least active; it was apparently due to a cut-off effect because of its poor partitioning in the interface. The correlation analysis indicated a negative dependency between the oxidation and the partitioning of the antioxidants at the interface; "R" values of -0.66 and -0.75 were obtained for the peroxide and p-anisidine values, respectively. These results showed that the antioxidant activity is determined by the antioxidant partitioning at the interface, the hydrophobicity of the antioxidant, and the emulsifier.

Practical applications: The understanding of the efficacy of antioxidants in high-fat oil-in-water emulsions, such as mayonnaise enriched with n-3 fatty acids, but stabilized with emulsifiers other than phospholipids (i.e., lecithin or egg yolk) has been subject of growing interest in nutrition and the food industry. Here, the effects of molecular properties of antioxidants (hydrophobicity) and of emulsifier (size and number of hydrophobic groups) were studied, in order to try to elucidate the better alternatives. This study showed that the antioxidant activity is greatly determined by the antioxidant partitioning at the interface, which in turn, depends of molecular properties of both, antioxidant and emulsifier. It is clear that the affinity amongst such molecules is based uporn the amphiphilic properties of both types of molecules. These results seem to support the nonlinear or cut-off theory, recently proposed. We identified some key factors to describe such activity..

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