Lipids

1. Lipids Chapter 16

2. What are Lipids? • Lipids = are a family of chemical compounds that are a main component in every living cell. They include the following 3 categories: • Triglycerides – largest class of lipids. They include nearly all of the fats and oils people typically eat. (of the lipids 95% are fats and oils) • Phospholipids - these lipids have a structure that enables them to dissolve in both fat and water. – use as an emulsifiers (found in eggs and peanuts) • Sterols – compound, bile acids and certain hormones perform vital functions. Both plant and animal food contain sterols, but food contains cholesterol (a sterol)

3. Triglycerides • Main function is to fuel the body and keep it warm. • Adipose Tissue = pockets of fat-storing cells • Also adipose tissue under each kidney forms a cushion to help protect it from impact. • Natural body oils help keep supple and hair glossy and healthy. • Fat also carries certain vitamins in the body.

4. Structure of Triglycerides • Triglycerides are composed of carbon, hydrogen, and oxygen.

5. Fatty Acids • Organic compounds that contain a carboxyl group at one end are classified as organic acids or fatty acids. • These fatty acids are organic compounds that have a carbon chain with attached hydrogen atoms and carboxyl group at one end. • Carboxyl group = carbon bonded to oxygen by a double covalent bond, and to a hydroxyl group with a single bond. – COOH • Not all fatty acids are the same, the length of the carbon chain makes the different. • To form triglycerides (tri meaning 3), three fatty acids react with the alcohol glycerol • The human body can make all but two fatty acids, linoleic and linolenic. • These are needed for normal growth and development are obtained from foods as vegetables, grains, nuts, seeds, and soybeans.

6. Saturated vs. Unsaturated Fat • Saturated fat – most of the fatty acids are saturated, in other words, the fatty acids contain all their hydrogen atoms their molecular structure can hold, making 4 single bonds. • Single bond – covalent bond in which each atom donates only one electron to form the bond (sharing one pair of electrons between them) • Unsaturated fat – most of the fatty acids are also unsaturated, meaning they’re missing hydrogen • When hydrogen atoms are missing, a single bond cannot form, to make up the difference a double bond forms • Double bond – covalent bond in which each atom donates two electrons to form the bond

7. Unsaturated fat continued • Unsaturated fats are classified by the number of hydrogen atoms that “drop out” and produce double bonds • Monounsaturated fat – lacks two hydrogen's, which creates one double bond between carbons ex oleic acid or avocados, canola and peanut oil • Polyunsaturated fat – has two or more double bonds between carbons ex linoleic acid or nuts, sesame seed and sunflower oils

8. Properties of Triglycerides Energy Value • The structure of triglycerides makes them bundles of energy • Energy is released by oxidation • Triglycerides supply over twice the energy of glucose – 9 kcalories per gram compared to 4 Solubility • Slightly soluble in water Phase Differences • Fats which usually come from animals are saturated – their single bonds allow them a full set of hydrogen's, which makes them solid at room temperature • Most plant oils are unsaturated, the molecule forms a double bond making the oils less compact, so they are liquid at room temperature

9. Properties of Triglycerides Continued Melting Range • Molecular structure has related effect on how fats change • Most substances have a melting point and a freezing point • Fatty acids with more carbon have higher melting point ex olive oil Solidification Point = the temperature at which melted fat regains its original firmness • Ex you put carrots you cooked in butter the night before in your refrigerator, the next day they are coated with firm butter flecks

10. Functions of Fats in Food Tenderizing • One of the most important uses of fats in foods is tenderizing baked goods (fat coast the flour, creating a flaky, delicate, lighter texture) Aeration • Add air or gas to batters and dough's – this decreases viscosity, making the batter flow more easily Emulsions • Lipids play two roles in creating emulsion, they might be part or they might influence one to form. • Ex. adding mayonnaise creates an emulsion between oil and vinegar • Triglycerides can be broken down into monoglycerides, these have one fatty acid attached and are stable enough to emulsify other fats with liquids Flavor • Fats carry flavor, they dissolve aromatic molecules in food and distribute their essence through out the recipe • Ex. bacon is a salty fat, olive oil is mildly flavored

11. Oxidation • The oxidation of fats occur as the surface of foods react with oxygen. • When fatty food oxidize, they lose electron which is a main reason that high-fat foods spoil • Oxidation involves the loss of a hydrogen atom from a single-bonded carbon, this is why unsaturated fats are more prone to oxidation because they have more double bonds • Heat speeds the rate of oxidation, cooling slows but doesn't stop the process • Water prevents slow oxidation as well by preventing contact between substances and elemental oxygen • Rancid = the term that describes the unpleasant flavors that develop as fats oxidize • Rancidity produces a distinctive flavor, but different for each type of food

12. Commercial Uses of Fats • Commercially important fats fall into two main groups: animal fats and plant oils • Animal Fats • Butter is a natural emulsion, 80% fat and 18% water, remaining 2% is the protein that binds the other two ingredients • Lard or rendered hog fat is popular in baking • Beef fat is usually combined with vegetable fats for uses in food • Plant Fats • Plant lipids are derived from certain oil-rich seeds, in liquid form they are often called vegetable oil ex corn, olive, canola and oil blends • Hydrogenated Oils • Ex. vegetable shortening • Hydrogenation = a chemical process in which hydrogen is added to unsaturated fat molecules, breaking some double bonds and replacing them with single bonds • Partial hydrogenation changes liquid oil to spreadable, semisolid fat • Hydrogenation adds stability by eliminating some of the double bonds in fatty acids • Hydrogenated oil resists rancidity better than liquid oil because it doesn't develop a stale flavor and odor as quickly

13. Cooking with Fat Effects on Fats • Repeated exposure to intense heat causes a decomposition similar to oxidation • Also foods release some of their own fat, water and other substances into the frying oil, which deteriorates the fat, a process called cracking • Cracking can discolor oil and produce off flavors and odors • Smoke point = the temperature at which a fat produces smoke • Reaching a smoked point is part of a cycle of fat breakdown: smoking makes the fat less stable • Vegetable oils generally have a higher smoke point than animal fats, making them more useful for frying Frying Safety • Safe frying starts with the correct equipment (a deep-fat fryer or a frying pan with heavy-duty metal sides) • Food needs to be dry – WHY • Using the correct amount of oil, if oil spills out of the pan you need to shut off heat IMEDIATELY • How do you put out a grease fire?

14. Triglycerides in the Diet • Fats in food are broken down into fatty acids and glycerol, then absorbed by villi in the small intestine • Some of these fatty acids are stored in the liver, remaining fats end up as adipose tissue (tissue designed to store fat) • A typical American diet gets 45% of its calories from fat, well over the 30% recommended (Recommended daily value limit is 65g for fat and 20g saturated fat) Low-Fat Options • According to a recent survey, as many as 56% of American adults are trying to limit their fat intake • You have to be careful, because often low-fat and fat-free foods are often high in calories

15. Triglycerides in the Diet Continued • Fat Replacers • Fat replacers are loosely grouped as either fat, protein, or carbohydrate based • Fat-based replacers are manufacture from, very short and long carbon-chain acids, which supply fewer kcalories • Protein-based replacers use milk or protein particles to stabilize and texturize dairy products and some baked goods, sauces, and soups • Carbohydrate fat replacers include cellulose, gums, and modified food starch • Trans Fat (also known as trans fatty acids) • Is a manmade type of fat formed when a liquid vegetable oil is made into solid fat, like margarine • Trans fat is made when hydrogen is added to vegetable oil in a process called hydrogenation • Hydrogenation is popular because it increases the stability and shelf life of foods • Partial hydrogenation – is when some of the double bonds and the hydrogen atoms end up on different sides of the chain • Trans fat behaves in the human body much like a saturated fat • It raises the LDL or bad cholesterol • Found in foods like vegetable shortening, some margarines, cookies, snack foods, fried foods, baked goods, and other processed foods made with partially hydrogenated veg. oils

16. Cholesterol • Cholesterol = is not a triglyceride, but a sterol, a fatty alcohol made from glucose or saturated fatty acids • Formula is C27H45OH • Cholesterol is vitamin in producing vitamin D and some hormones • The liver makes all the cholesterol you need • Cholesterol in the blood is though to contribute to the manufacture of plaque = a mound of lipid material mixed with calcium and smooth muscle cells • Atherosclerosis (hardening of the arteries) = buildup of plaque along the inner walls of the arteries

17. LDL and HDL Cholesterol • Lipoproteins = large, complex molecules of lipids and protein that carry lipids in the blood • LDL – low-density lipoproteins, they carry about 75% of cholesterol in the blood • Bad cholesterol (want a low number) • HDL –high-density lipoproteins – they return cholesterol to the liver for breakdown and disposal • Good cholesterol ( want a high number)

18. Omega 3 Fatty Acids • Scientists believe that omega-3 fatty acids, found in some fish, promote heart heath in two ways: • First they make it more difficult for plaque to form or clump • They also make plaque less sticky and less likely to collect in the arteries • Sardines, salmon, tuna, herring, and other ocean fish are highest in omega-3 fatty acids or cod liver oil capsules and marine oils

19. Questions • Describe the tree categories of lipids. • What functions do triglycerides serve in the body? • Describe the structure of triglycerides. • Why does the body need to obtain linoleic and linolenic acids from plant sources? • How are unsaturated fats classified? Give examples. • How do fats compare to carbohydrates as an energy source?

20. Questions Continued • How does carbon bonding affect the phase of a fat? • Why do fats have a melting range rather than a melting point? • From a chemical standpoint, why might stale potato chips become rancid? • How does hydrogenation affect oils? • If you fried chicken in a restaurant, what signs might tell you the frying oil needed changing? • Compare low-and high-density lipoproteins. • How do marine oils differ from animal fats?