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Keywords:

  • Antioxidants;
  • Emulsion;
  • Iron;
  • Marine lipids;
  • Oxidation;
  • Oxygen uptake

Abstract

Addition of antioxidants into food containing fish omega-3 PUFA is an approach to protect the healthy omega-3 lipids from oxidation and to increase the oxidative stability of the food. Low molecular weight (LMW) iron (Fe2+/Fe3+) is a ubiquitous component in emulsified food and a mediator of lipid peroxidation even at trace levels. In this work, the effects of EDTA, citric acid, caffeic acid, propyl gallate, α-tocopherol, ascorbic acid, β-carotene, and astaxanthin on iron-mediated lipid peroxidation in 10% w/v herring oil emulsions stabilized with herring phospholipids (pH 3.5–5.5) were studied by measurement of the dissolved oxygen consumption by unsaturated fatty acids. EDTA and citric acid completely inhibited iron-mediated oxidation when they were added in twice the ratio to iron at pH>3.5. Caffeic acid, ascorbic acid, and α-tocopherol enhanced the oxidation by reducing Fe3+ to the more prooxidatively active Fe2+, while propyl gallate reduced the oxidation by iron chelation. Ascorbic acid was depleted by interactions with iron and decreased the prooxidative activity of α-tocopherol. Astaxanthin and β-carotene showed minor effects on iron-mediated lipid oxidation. This study shows that the interactions between LMW iron and antioxidants have an impact on lipid peroxidation in emulsions in concentration dependent manners. Interactions with metals must therefore be considered when interpreting the activity/behavior of antioxidants in emulsions rich in omega-3 fatty acids. This study also shows that it is possible to screen these interactions by quantification of the dissolved oxygen consumption.

Practical applications: This work investigates the behavior of several food antioxidants in the presence of LMW iron in fish oil emulsions stabilized with marine phospholipids, and shows that interactions with iron can convert some of the anticipated antioxidants into pro-oxidants. Measurements of dissolved oxygen concentration have been used in this study to follow iron-mediated lipid peroxidation in the emulsions. It is shown that by quantification of the dissolved oxygen consumption it is possible to screen and evaluate the interactions between LMW iron and antioxidants in emulsion-type systems.

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This paper studies the impact of interactions between low molecular weight iron and dietary antioxidants on the rate of lipid peroxidation in fish oil emulsions stabilized with marine phospholipids. It is shown that measurement of dissolved oxygen consumption by fatty acids can be used for characterization of these interactions in emulsion-type systems.