Quantification of cholesterol oxidation products in commercial fish meals and their formation during storage

Twenty-two samples of commercial fish meals from Norway, Chile and Peru were analysed for cholesterol and oxysterols using gas chromatography. Cholesterol content ranged from 25.2 to 64.8 g kg(-1) total lipids. Detectable levels of the oxysterols 7 beta-hydroxycholesterol and 7-ketocholesterol were found and their identity was confirmed by gas chromatography-mass spectrometry. Samples of fish meal exhibited wide variability in oxysterols content, 7 beta-hydroxycholesterol ranging from 3.9 to 105.6 mg kg(-1) total lipids (0.4-9.4 mg kg(-1) dry matter) and 7-ketocholesterol from 2.0 to 56.2 mg kg(-1) total lipids (0.2-5.0 mg kg(-1) dry matter). The formation of 7 beta-hydroxycholesterol and 7-ketocholesterol in one sample of Norse LT94 fish meal stored at room temperature was also studied. Oxysterol content increased during the first 42 days of storage by about 350% and then decreased with further storage. The low amount of oxysterols measured indicates a limited degree of cholesterol oxidation in commercially available fish meals.