![]() ![]() They can enhance palatability by absorbing and retaining flavors and by influencing the texture of foods. Triglycerides are the principal lipid component of foods and the most concentrated source of energy among the macrocomponents of the diet (9 kcal/g). The major polyunsaturated fatty acids in fish are eicosapentaenoic acid (EPA), an n-3 fatty acid with 20 carbons and 5 double bonds, and docosahexaenoic acid (DHA), an n-3 fatty acid with 22 carbons and 6 double bonds. The major polyunsaturated fatty acids in plant foods are linoleic acid, an n-6 fatty acid with 18 carbons and two double bonds, and linolenic acid, an n-3 fatty acid with 18 carbons and 3 double bonds. The major monounsaturated fatty acid is oleic acid (18 carbons). The major saturated fatty acids in foods are palmitic acid (16 carbons) and stearic acid (18 carbons). The polyunsaturated fatty acids are subdivided into those whose first double bond occurs either three carbon atoms from the methyl carbon (n-3 or w-3) or six carbon atoms from the methyl carbon (n-6 Fatty acids are also classified as saturated (lacking double bonds), monounsaturated (containing a single double bond), or polyunsaturated (containing more than one double bond). More than 90% of the fatty acids have an even number of carbon atoms. The fatty acid components of lipids are classified as short-chain (less than 6 carbons), medium-chain (6 to 10 carbons), or long-chain (12 or more carbons). The term phospholipids encompasses glycerophosphatides and sphingomyelins. The polar or amphipathic lipids include fatty acids, in which the polar component is a negatively charged carboxyl ion cholesterol, in which the polar component is an alcohol sphingolipids, in which the polar group is phosphorylcholine (sphingomyelin) or a carbohydrate (glycosphingolipid) and glycerophosphatides (mainly lecithins), in which the polar component is a phosphate-containing aminoalcohol or polyalcohol. Cholesteryl esters are composed of a single fatty acid esterified to cholesterol. The triacylglycerols (also called triglycerides or fats) are composed of three fatty acids esterified to glycerol. ![]() The nonpolar lipids occur mainly as esters of fatty acids that are virtually insoluble in water and enter metabolic pathways only after hydrolysis. They are present in biologic systems mainly as energy stores within cells or as components of cell membranes. Lipids are organic compounds with limited solubility in water.
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