The Lipids: Triglycerides, Phospholipids and Sterols

Lipids Objectives 1. Understand the chemical composition and differences between fats 2. Explain the structural and functional processes of triglycerides, phospholipids, and sterols 3. Describe the process of fat digestion and absorption 4. Discuss the different types of lipoproteins in the body 5. Clarify the recommended intakes of fat and essential fatty acid requirements to meet daily nutritive needs 6. Describe the health-risk factors with over consumption of lipids in the diet

Triacylglycerol Triglycerides R-COO-CH 2 R-COO-CH R-COO-CH 2 Triglycerides found in seeds and animal adipose. Diglycerides found in plant leaves, one fatty acid is replaced by sugar (galactose).

Most Common Fatty Acids in Di- and Triglycerides Fatty acidCarbon:Double bondsDouble bonds Myristic14:0 Palmitic16:0 Palmitoleic16:1 Cis-9 Stearic18:0 Oleic18:1 Cis-9 Linoleic18:2 Cis-9,12 Linolenic18:3 Cis-9,12,15 Arachidonic20:4 Cis-5,8,11,14 Eicosapentaenoic20:5 Cis-5,8,11,14,17 Docosahexaenoic22:6 Cis-4,7,10,13,16,19 CH 3 (CH 2 ) n COOH

Triglyceride Containing Linoleic Acid Omega-6

Linolenic Acid Omega-3

Fatty Acid Isomers

Fatty Acids The Length of the Carbon Chain –long-chain, medium-chain, short-chain The Degree of Unsaturation –saturated, unsaturated, monounsaturated, polyunsaturated The Location of Double Bonds –omega-3 fatty acid, omega-6 fatty acid

Lipid Content of Feeds Forages Fat content is low: 1 to 4% of dry matter High proportion of linolenic acid (18:3) Diglycerides in fats of leaves Grains Fat content variable: 4 to 20% of dry matter High proportion of linoleic acid (18:2) Triglycerides in oils of seeds

The Length of the Carbon Chain Short-chain Fatty Acid (less than 6 carbons) Medium-chain Fatty Acid (6-10 carbons) Long-chain Fatty Acid (12 or more carbons)

Fatty Acids are Key Building Blocks Saturated Fatty Acid All single bonds between carbons

Monounsaturated Fatty Acid (MUFA) One carbon-carbon double bond

Polyunsaturated Fatty Acid (PUFA) More than one carbon-carbon double bond

Location of Double Bonds PUFA are identified by position of the double bond nearest the methyl end (CH 3 ) of the carbon chain; this is described as a omega number; If PUFA has first double bond 3 carbons away from the methyl end=omega 3 FA 6 carbons from methyl end=omega 6 FA

Degree of Unsaturation Firmness –saturated vs. unsaturated Stability –oxidation, antioxidants Hydrogenation –advantages, disadvantages Trans-Fatty Acids –from hydrogenation

Hydrogenation

Cis-fatty acid : H’s on same side of the double bond; fold into a U-like formation; naturally occurring; Trans-fatty acid : H’s on opposite side of double bond; more linear; occur in partially hydrogenated foods;

Essential Fatty Acids (EFA) Omega-3: –Eicosopentaenoic acid (EPA) –Docosahexaenoic acid (DHA) –Alpha-linolenic acid (ALA) flaxseed--most, canola (rapeseed), soybean, walnut, wheat germ body can make some EPA and DHA from ALA Omega-6 –corn, safflower, cottonseed, sesame, sunflower –Linoleic acid FISH

Omega-3 Omega-6

Omega-3 Fatty Acids Associated with: –anti-inflammatory, antithrombotic, antiarrhythmic, hypolipidemic, vasodilatory properties Inflammatory conditions Ulcerative colitis, Crohn’s Cardiovascular disease Type 2 diabetes* Mental function Renal disease* Growth and development

Essential Fatty Acid Deficiency Classical symptoms include: –growth retardation, reproductive failure, skin lesions, kidney and liver disorders, subtle neurological and visual problems People with chronic intestinal diseases Depression--omega-3 –?inadequate intake alters brain activity or depression alters fatty acid metabolism? Attention Deficit Hyperactivity Disorder –lower levels of omega-3--more behavioral problems

Eicosanoids: made from EFA --derivatives of 20-carbon fatty acids; --affect cells where they are made; --have different effects in different cells --cause muscles to contract and muscles to relax; -- help regulate blood pressure, blood clot formation, blood lipids, and immune response; --participate in immune response to injury and infection, producing fever, inflammation, and pain; --include:prostaglandins, thromboxanes, leukotrienes

Triglycerides Structure –Glycerol + 3 fatty acids Functions –Energy source 9 kcals per gram Form of stored energy in adipose tissue –Insulation and protection –Carrier of fat-soluble vitamins –Sensory properties in food

Triglycerides: lipids composed of three fatty acids attached to a glycerol

Triglycerides Food sources –fats and oils butter, margarine, meat, baked goods, snack foods, salad dressings, dairy products, nuts, seeds –Sources of omega-3 fatty acids Soybean, canola, walnut, flaxseed oils Salmon, tuna, mackerel –Sources of omega-6 fatty acids Vegetable oils

Fatty Acids in Common Food Fats

Phospholipids Structure –Glycerol + 2 fatty acids + phosphate group Functions –Component of cell membranes –Lipid transport as part of lipoproteins –Emulsifiers –Phosphatidylcholine Food sources –Egg yolks, liver, soybeans, peanuts

Cell membranes are phospholipid bilayers

Sterols: Cholesterol Functions –Component of cell membranes –Precursor to other substances Sterol hormones Vitamin D Bile acids Synthesis –Made mainly in the liver Food sources –Found only in animal foods