Plasmalogens, fatty acids and alkyl glyceryl ethers of marine and freshwater clams and mussels

Shelled molluscs constitute an excellent source of protein, sugars and lipids, and the demand for various mollusks species is increasing. We analysed lipid composition of different bivalves, quite important in the diet of East Mediterranean inhabitants. Plasmamlogens, glyceryl ethers, and diacyl phospholipid forms as well as their fatty aldehydes, fatty alcohols, and fatty acid derivatives were examined. PE of clams and mussels, containing aldehydes C16 (variations from 4% to 31%), C18 (29-46%), C9-18:1(6-32%), C11-20:1 (3-19%), and several minor aldehydes, were detected. The major saturated 1-O-alkyl glycerol ethers C16 and C18. Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in both PE and PS plasmalogens were dominated acids. The sum of these acids in PE varied from 33% to 43%, and in PS, from 45% to 66%. EPA levels in PE (30-37%) and PS (39-57%) of marine species were higher than those in freshwater species (PE, 13-16%; PS, 23-29%), and levels of DHA were higher in freshwater than in marine mollusks. A series of saturated fatty aldehydes C12-C24, with major C18:0 in all studied species (over 40%) and C16:0 (10-25%), as well as of unsaturated C16:1 (1-7%) and 18:1 (18-36%) species were isolated from neutral plasmalogens. Predominant fatty acids in neutral plasmalogens were found to be 16:0 (12-17%), 20:5n-3 (9-27%), and 22:6n-6 (9-18%). Distribution of plasmalogens, alkyl glyceryl ethers, and their fatty aldehydes and fatty alcohols in mollusks and other invertebrates is discussed.