[Stability of fatty acids in stored oyster]

The contents of twenty-three kinds of fatty acids in the lyophilized oyster that stored for 0, 15, 30, 45, 60, 75, 90 days were studied. Oyster fat was extracted from the powder by means of SFE. The extraction was performed for 40 min at a pressure of 37 MPa and a temperature of 50 degrees C with supercritical carbon dioxide containing 8% (V/V) ethanol at a flow-rate of 2 mL/min as liquid carbon dioxide, and the recovery of oyster fat by extraction was over 99%. After being extracted, fat was esterified with potassium hydroxide and methanol. Methyl esters of fatty acid were separated and determined by 30 m x 0.25 mm i.d. x 0.25 micron HP-INNOWax capillary column and MS detector. The injector temperature was 220 degrees C. The column temperature was programmed from 150 degrees C (1 min) to 200 degrees C at 10 degrees C/min and then from 200 degrees C to 250 degrees C at 2 degrees C/min. Twenty-three peaks were identified with gas chromatography/mass spectrometry, and quantified with area normalization method. The variations of contents of them were shown. During storage, the contents of saturated fatty acids and mono-unsaturated fatty acids were getting higher, and those of polyunsaturated fatty acids were getting lower. The decrease of them was gradual, and there was no special period of stability. And the stability of fatty acids in oyster related to the degree of unsaturation of them. The higher the unsaturation the lower the stable it was. After being stored for 90 days, the content of EPA decreased from 16.94% to 5.43% and that of DHA from 9.25% to 2.86%.