Chemical Measures of Fish Oil Quality: Oxidation Products and Sensory Correlation

Abstract

Although quality of commercial fish oil is of the upmost importance to both suppliers and consumers, it can be difficult to maintain due to rapid lipid oxidation attributable to the high levels of EPA and DHA. Fish oil quality can be assessed in a number of ways; this paper focuses on ethyl ester (EE) content and oxidation products. Fish oil supplements are sold as both triacylglycerols (TAG) and EE. TAG products are more resistant to oxidation, have better bioavailability and are generally considered to be of higher quality. Here, a method is described to quantify EE in fish oil using solid phase microextraction (SPME) headspace analysis and gas chromatography-mass spectrometry (GCMS). A related aspect of quality is state of oxidation and although the causes of oxidation in fish oil are well known, there is little research on the kinetics of the oxidation process. The work presented here monitors hydroperoxides to model the kinetics of oxidation in two commercially available fish oil supplements by fitting the data to the Arrhenius model. It was determined that the same mechanisms of oxidation hold at temperatures ? 40 °C and thus, this temperature was used in the final stages of this work where accelerated stability testing of fish oil was conducted. Currently, taste panels are the only reliable method to assess the sensory properties of fish oil, but these are costly and subjective. Described here is an alternative method using SPME-GCMS to monitor volatile oxidation products. Two different statistical methods were used to identify oxidative volatiles that correlate with sensory characteristics of fish oil. First, stepwise discriminant function analysis (DFA) was used to identify volatiles that could be used to classify oil as acceptable or unacceptable based on sensory analysis. Principal component analysis (PCA) and linear regression were then applied with greater success. Both techniques identified similar oxidative volatiles as being important to sensory properties. It is anticipated that these methods could be adopted by fish oil manufacturers as measures of quality.