THE EFFECT OF LYOPHILIZATION ON THE SOLVENT-EXTRACTION OF LIPID CLASSES, FATTY-ACIDS AND STEROLS FROM THE OYSTER CRASSOSTREA-GIGAS

The lipid class compositions of adult Pacific oysters [Crassostrea gig as (Thunberg)] were examined using latroscan thin-layer chromatography /flame-ionization detection (TLC/FID), and fatty acid compositions det ermined by capillary gas chromatography and gas chromatography/mass sp ectrometry (GC/MS). The fatty acid methyl esters were separated using argentation TLC and also analyzed as their 4,4-dimethyloxazoline deriv atives using GC/MS. Major esterified fatty acids in C. gigas were 16:0 , 20:5n-3, and 22.6n-3. C20 and C22 nonmethylene interrupted (NMI) fat ty acids comprised 4.5 to 5.9% of the total fatty acids. The NMI trien oic fatty acid 22:3(7,13,16) was also identified. Very little differen ce was found in the proportions of the various lipid classes, fatty ac ids or sterols between samples of adult oysters of two different sizes . However, significant differences in some of the lipid components wer e evident according to the method of sample preparation used prior to lipid extraction with solvents. Lyophilization (freeze drying) of samp les led to a significant reduction in the amounts of triacylglycerols (TG) extracted by solvents in two separate experiments (7.0 and 52.5% extracted). Extracts from lyophilized samples had less 16:0, C18 unsat urated fatty acids, and 24-ethylcholest-5-en-3beta-ol, while C20 and C 22 unsaturated fatty acids comprised a higher proportion of the total fatty acids. There was no significant change in the amounts of polar l ipids, total sterols, free fatty acids or hydrocarbons observed in ext racts from lyophilized samples relative to extracts from nonlyophilize d samples. Addition of water to the freeze-dried samples prior to lipi d extraction greatly improved lipid yields and resulted in most of the TG being extracted.