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

Abstract

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.

Introduction

Marine and freshwater two-part shell mollusks, in which both valves are typically symmetrical along the hinge line, belong to the class Bivalves (they are also under names Pelecypoda, and/or Lamellibranchia). The words “clams, mussels, scallops and oysters” have no real taxonomic significance in biology, but in cookery these words have absolutely definite significance, and are associated with savoury food (Fernandez, Garcia, Asensio, Rodriguez, & Lobo, 2001). Edible bivalves, clams and mussels are mainly marine species with a few well-known freshwater representatives. They are widely used as nutriment around the world (Ackman, 2000), and they are present at food market for about 100 years.

It is well-known that smell and savour of food results from aldehydes, which are liberated from plasmalogens (both neutral and polar lipids) and/or free ones (usually rare) under cooking conditions of any animals and/or invertebrates (Le Cloirec, 2006). Plasmalogens of marine Bivalvia species have been well studied (Berdyshev, 1989, Dembitsky, 1979, Dembitsky and Vaskovsky, 1976, Kraffe et al., 2004, Kraffe et al., 2006), and a few papers also investigated plasmalogens isolated from freshwater (Dembitsky et al., 1992, Dembitsky et al., 1993a), as well as from brackish (Dembitsky, Rezanka, & Kashin, 1993b) Bivalvia.

Plasmalogen lipids are particular phospholipids characterised by the presence of vinyl ether bond at the C1 position of glycerol skeleton. Serving as structural component of mammalian and invertebrate cell membrane, plasmalogen is widely distributed in excitable tissues, like heart and brain. Plasmalogens mediate dynamics of cell membrane, they provide storage of polyunsaturated fatty acids and can contribute to endogenous antioxidant activity (Brosche, Brueckmann, Haase, Sieber, & Bertsch, 2007). Plasmalogen phospholipids are also suggested to be involved in signal transduction (Latorre, Collado, Fernandez, Aragones, & Catalan, 2003).

Taking into account the growing interest for food plasmalogens and an insufficient data concerning Bivalvia lipids, fatty aldehydes, and fatty acids, we characterised the plasmalogenic phospholipids, and other lipid profiles in edible Bivalvia species from the Mediterranean Sea, Red Sea, and Sea of Galilee.

The benefits of including omega-3 fatty acids in the diets of humans are well documented. Fatty acids play a major role in the functioning of the immune system and the maintenance of all hormonal systems of the organism. Marine and freshwater clams and mussels are an excellent source of both docosahexaenoic, and eicosapentaenoic acids. Bivalves are one of the most popular treats in East as well as in West Mediterranean couisine.