Polyunsaturated fatty acids, seafood

Seafood consumption is a rich source of vitamins, minerals, proteins, and omega-3 polyunsaturated fatty acids that have a wide range of beneficial effects for human health (Sidhu, 2003). However, among food... 

The development of both desirable and undesirable fishy flavors has long-been a concern to the seafood and fishery Industry (1-6). Oxidative processes occurring through enzymic and nonenzymlc mechanisms Initiate hydroperoxide formation In fish lipid systems that are responsible for the formation of the short chain carbonyls and alcohols which exhibit distinct flsh-llke flavors and aromas. Because the generation of fresh fish aroma compounds Involves some of the same polyunsaturated fatty acid precursors and oxidative pathways as autoxldatlon. It has been a tedious task to differentiate the mechanisms and aroma compounds... 

The fat in foods contains a mixture of saturated, monounsaturated and polyunsaturated fatty acids. In foods of animal origin, a large proportion of fatty acids are saturated. In contrast, in foods of plant origin and some seafood, a large proportion of the fatty acids are monounsaturated and polyunsaturated. The structures of saturated and unsaturated chemical bonds are shown below. 

Flavors and aromas commonly associated with seafoods have been intensively investigated in the past forty years ( l-7), but the chemical basis of these flavors has proven elusive and difficult to establish. Oxidized fish oils can be described as painty, rancid or cod-liver-oil like (j ), and certain volatile carbonyls arising from the autoxidation of polyunsaturated fatty acids have emerged as the principal contributors to this type of fish-like aroma ( 3, 5, 9-10). Since oxidized butterfat (9, 11-12) and oxidized soybean and linseed oils (13) also can develop similar painty, fish-like aromas, confusion has arisen over the compounds and processes that lead to fish-like aromas. Some have believed that the aromas of fish simply result from the random autoxidation of the polyunsaturated fatty acids of fish lipids (14-17). This view has often been retained because no single compound appears to exhibit an unmistakable fish aroma. Still, evidence has been developed which indicates that a relatively complex mixture of autoxidatively-derived volatiles, including the 2,4-heptadienals, the 2,4-decadienals, and the 2,4,7-decatrienals together elicit unmistakable, oxidized fish-oil aromas (3, 9, 18). Additionally, reports also suggest that contributions from (Z -4-heptenal may add characteristic notes to the cold-store flavor of certain fish, especially cod (4-5). 

The aromas associated widi very fi esh fish are usually mild, delicate and fi esh (53,54), and generally described as green (hexanal), melon-like ((E,Z)-3,6-nonadienal), iodine-like (bromophenols). Fresh fish and seafood aromas are due to volatile carbonyls and derive fi om lipoxygenase catalyzed oxidation of polyunsaturated fatty acids. The oxidation of Eicosapentaenoic acid (C20 5) leads to C5 to C9 alcohols, aldehydes, ketones and hydrocarbons. The formation of methyl mercaptan, dimethyl sulfide and dimethyl disulfide in fi esh fish at the time of harvest has been reported by Shiomi et al. (55). Although these compounds are usually associated with fish deterioration, they contribute to the fi esh aroma ch cter at low concentrations. For instance, dimethyl sulfide is... 

Salem NJ, Kim H-Y, Yergey JA. Docosahexaenoic acid membrane function and mctabohsm. In Simopoulos AP, Kifer RR, and Martin RE, eds. Health Effects of Polyunsaturated Fatty Acids in Seafoods. Academic, New York, 1986, pp. 319-351. 

Connor WE, Neuringer M, and Reisbick S. Essentiality of to3 fatty acids Evidence from the primate model and implications for human nutrition. In Simopoulos AP, Kifer RR, Martin RE, and Barlow SM, eds. Health effects of 0)3 polyunsaturated fatty acids in seafoods. 1991 66 118-132, Karger Press, Basel, Switzerland. 

Lands WEM. Dose-response relationships for 3/ 6 effects. In Simoupoulos AP et al., eds. Health Effects of 3 Polyunsaturated Fatty Acids in Seafoods. World Review of Nutrition and Dietetics, Vol. 66, pp.177-194. Karger, Basel, 1991. 

Several studies have shown the protective role of dietary (n-3) polyunsaturated fatty acids (PUFA) against cardiovascular diseases [56-57]. Greenland Eskimos and, to a lesser extent, some Japanese, with high dietary intake of (n-3) PUFA from seafood, have a low incidence of cardiovascular diseases compared with Western populations [58]. 

Source Adapted and modified from Weber, P.C., and Leaf, A., in Health Effects of w3 Polyunsaturated Fatty Acids in Seafoods, Simopoulos, A.R et al., Eds., vol. 66 World Rev. Nutr. Diet, Karger, Basei, 1991, 218. 

Lewis, R.A., Lee, T.H., and Austen, K.F, Effects of omega-3 fatty acids on the generation of products of the 5-lipoxygenase pathway, in Health Effects of Polyunsaturated Fatty Acids in Seafoods, Simopoulos, A.R, Kifer, R.R., and Martin, R.E., lids.. Academic Press, Orlando, 1986, 227. 

Although these essential fatty acids are available from both seafood and fresh water fish in Thailand (2), the effects of supplementation were evident in this study. The diversity of dietary intake, the effects of cooking and oxidation on these heat-labile nutrients, as well as high consumption of vegetable oil rich in n-6 polyunsaturated fatty acids, may all play a role in the inadequate intake of n-3 polyunsaturated fetty acids in this study cohort. 

It is noteworthy that research on various species of hairy animals has established that the nutrients which might be helpful in the prevention of excessive hair loss are amino acids, particularly those which contain sulfur (cystine and methionine) the essential, polyunsaturated fatty acids iodine and zinc many members of the vitamin B complex and vitamins A, C, and E. The E)est way to obtain these nutrients is from a wide variety of nutritious foods such tis dairy products, eggs, fish and seafood, fruits and vegetables, meats and poultry, vegetable oils, and whole-grain breads and cereal products. 

The fishy aroma of seafood is incorrectly attributed to trimethyl amine. Flavor formation in fresh and saltwater fish results from complex enzymatic, oxidative, and microbial reactions of n-3 polyunsaturated fatty acid precursors (e.g., eicosapentaenoic acid) (69,70). Hence, fish flavor is mostly composed of non-characterizing planty or melon-like aromas from lipid-derived unsaturated carbonyl compounds. Examples are (Z)-l,5-octadien-3-one ( geranium-like ) in boiled cod (71) and (7i,Z)-2,6-nonadienal ( cucumber-like ) in boiled trout (72). 

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