Chemical Compositional Changes in Over-Oxidized Fish Oils.

Austin S Phung,Giulio G Muccioli,Selina C Wang,Adam Ismail,Guillaume Reversat,Thierry Durand,Camille Oger,Claire Vigor,Gerard Bannenberg,Jean-Marie Galano,Martin Roumain

doi:10.3390/foods9101501

Abstract

A recent study has reported that the administration during gestation of a highly rancid hoki liver oil, obtained by oxidation through sustained exposure to oxygen gas and incident light for 30 days, causes newborn mortality in rats. This effect was attributed to lipid hydroperoxides formed in the omega-3 long-chain polyunsaturated fatty acid-rich oil, while other chemical changes in the damaged oil were overlooked. In the present study, the oxidation condition employed to damage the hoki liver oil was replicated, and the extreme rancidity was confirmed. A detailed analysis of temporal chemical changes resulting from the sustained oxidative challenge involved measures of eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) omega-3 oil oxidative quality (peroxide value, para-anisidine value, total oxidation number, acid value, oligomers, antioxidant content, and induction time) as well as changes in fatty acid content, volatiles, isoprostanoids, and oxysterols. The chemical description was extended to refined anchovy oil, which is a more representative ingredient oil used in omega-3 finished products. The present study also analyzed the effects of a different oxidation method involving thermal exposure in the dark in contact with air, which is an oxidation condition that is more relevant to retail products. The two oils had different susceptibility to the oxidation conditions, resulting in distinct chemical oxidation signatures that were determined primarily by antioxidant protection as well as specific methodological aspects of the applied oxidative conditions. Unique isoprostanoids and oxysterols were formed in the over-oxidized fish oils, which are discussed in light of their potential biological activities.

Highlights

Fish oils are a good source of the omega-3 long chain polyunsaturated fatty acids (PUFAs)(omega-3 LCPUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)
In addition to volatiles, we evaluated the presence in the over-oxidized hoki liver oil and anchovy oil of two other families of secondary oxidation products that have been uncovered in recent years, namely isoprostanoids and structurally similar isofuranoids, and oxysterols
Since the present study looked at two different conditions, it was possible to appreciate that the continuous exposure of hoki liver oil to oxygen gas at room temperature under light conditions led to a much stronger formation of primary oxidation products than at elevated temperature

Summary

Introduction

Fish oils are a good source of the omega-3 long chain polyunsaturated fatty acids (PUFAs)(omega-3 LCPUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). The intake of fish oil can impart antioxidant effects though the increased expression of antioxidant enzymes, and components in fish oil are associated with antimicrobial effects [9,10]. Given their relatively high content of polyunsaturated fatty acids, fish oils and other EPA/DHA omega-3-containing oils are susceptible to oxidation [11,12]. Antioxidant concentrations, oxidative condition(s) (for example temperature and light), and specific compositional aspects such as trace metal ions and moisture all affect the oxidation rate of edible LCPUFA-rich oils [13,14,15,16]. It is expected that widely dissimilar and unique profiles of oxidation products will be present in distinct fish oils exposed to different oxidizing conditions

Objectives

Methods

Results

Discussion

Conclusion