Oxidation of DHA-enriched fish oil and extraction and identification of the volatile oxidation products
H. I. LEE1, Y. Lee2, J. Y. Yang2, S. A. Kizito1, J. S. Weese1, and H. An1. (1) Dept. of Nutrition & Food Science, Auburn University, Auburn, AL 36849-5605, (2) Dept. of Food Sci. & Tech., Pukyoung National University, Pusan, 608-737, South Korea
Docosahexaenoate (DHA) is abundant in fish oil widely applied to infant formula and other foods as a nutritional ingredient. However, DHA is easily oxidized, causing nutritional loss and producing strong off-flavors, and, thus, adversely affect consumer’s acceptance. Because of the problem, shelf-life of DHA-containing food is substantially shortened and its application has been limited.
The objectives were to study the relationship between degradation of DHA and formation of oxidized volatile compounds, to identify the oxidized compounds in fish oil, and to determine optimum extraction condition for headspace volatile compounds during storage of fish oil using solid phase microextraction (SPME).
DHA-enriched fish oil (XO0355TG) was obtained from Ocean Nutrition Canada Ltd (Mulgrave, Nova Scotia, Canada) and stored at –80°C until used. Saturated sodium nitrite was added in serum bottle to control humidity and to activate lipid oxidation, and test tubes containing 0.5 g oil were inserted into the bottle for storage test at 20°C, 40°C and 60°C. For fatty acid analysis, fish oil was methylated and analyzed by gas chromatography (GC). For compound identification, lipid oxidation products were separated by GC and identified by matching data of mass spectrometer (MS) with the reference MS data bank and comparing their retention time indices.
The volatile compounds of 16 aldehydes, 12 alcohols, 3 ketones were identified from the 50 separated compounds. The optimum extraction condition of these oxidation products using SPME fiber (PDMS/DVB, blue, Supelco, Bellefonte, Pennsylvania) was 60 min at 80°C. Appearance of aldehydes and alcohols having two or three double bonds highly correlated with the loss of DHA during storage of fish oil.
The identified compounds having double bonds may be used as the index of DHA degradation. SPME was effective in extracting volatile compounds generated by oxidation of fish oil, showing promises to be effective in extracting compounds generated by oxidation of other foods containing a high amount of lipids.
Session 30A, Food Chemistry: Lipids