Abstract: This study aimed to establish a method for identifying adulterated cod liver oils by analyzing the percentages of fatty acids in pure cod liver oil and the change of the characteristic fatty acids. The fatty acids in samples were methyl esterified by precolumn derivatization before being analyzed by gas chromatography (GC), and the percentage of each fatty acid in the total fatty acids was calculated by peak area normalization method. According to the results of multiplesample analysis, the ratio of docosahexaenoic acid (DHA) to eicosapentaenoic acid (EPA) and the content of cetoleic acid were identified as the characteristic indexes for authentication, which were in the range from 1.40 to 1.68 and from 7.0% to 9.4% in pure cod liver oil. Adulteration of fish oil in cod liver oil samples could be determined when the characteristic indexes exceeded the ranges. A quantitative model for the level of adulteration of cod liver oil was established based on these characteristic indexes, and discriminant analysis was performed for different levels of adulteration. Out of 46 batches of samples examined, 2 were suspected to be adulterated with fish oil at about 25%. This method is accurate, reliable, simple and feasible and can be used for the rapid identification of adulterated cod liver oil.

Key words: cod liver oil, fish oil, adulteration identification, relative content, docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA), cetoleic acid, characteristic indices