1. Unit 9: Organic Composition of Food
CH.10 Lipids

2. 3 general types of lipids:
Lipids: organic compounds that are insoluble in water and have a greasy feel.
Examples: Fats, oils, shortening, phospholipids, sterols, and cholesterol
3 general types of lipids:
Triglycerides
Phospholipids
Sterols

3. Chemical Structure of Lipids
Most lipids are composed of two parts:
Glycerol: have 3 hydroxyl groups that will react easily with other compounds
Fatty acids: consist of a carbon chain with a carboxyl group at one end.

4. Chemical Structure of Lipids Continued…
The carboxyl end of the fatty acids readily reacts with the hydroxyl of glycerol forming a lipid and water.

5. 1. Glycerides Glycerides: molecules that have a glycerol base.
Monoglyceride: glycerol with one fatty acid attached at the site of a hydroxyl group

6. 1. Glycerides Continued…
Diglyceride: glycerol with 2 fatty acids attached
Triglyceride: glycerol with a fatty acid joined at each of the 3 hydroxyl sites

7. 1. Glycerides Continued…
These differences cause differences in cooking performance, shelf life, and nutritional value
Fat molecules are nonpolar, meaning they will not dissolve in water.

8. 1. Glycerides Continued…
Mono- & Diglycerides are partially soluble in water because of their hydroxyl groups, making them very important in the food industry.
They are often added to processed foods to keep mixtures of fats and water stable. Examples) butter & margarine

9. 2. Phospholipids
Phospholipid: glycerol base with 2 fatty acids and a phosphorus-containing acid attached.
The phosphorus end is attracted to water (hydrophilic), while the fatty acid end is repelled by water (hydrophobic).

10. 2. Phospholipids Continued…
Important roles:
In the body, it makes up cell membranes & helps carry fats back and forth across the cell membrane
In food, it helps fats stay mixed in water based solution. Keeping foods like mayonnaise from separating.

11. 3. Sterols Sterols - Molecules derived or made from lipids.
Examples) Cholesterol, Vitamin D, Steroid Hormones (including sex hormones)
Cholesterol in found in all cells of the body. Is used to stabilize the cell membrane.

12. Categories of Lipids
Lipids are categorized according to 1) molecular structure, 2) physical state, and 3) dietary sources.

13. 1. Molecular Structure of Lipids
Carbon is capable of forming 4 bonds
Carbon will bind with another element as a single or double bond in lipids

14. 1. Molecular Structure Continued…
If the fatty acid chain has no double bonds, then it has the maximum amount of bonds to hydrogen – saturated.
If there are double bonds between carbon in the fatty acid, it reduces the number of hydrogen bonds – unsaturated.

15. 1. Molecular Structure Continued…
Saturated fatty acids are typically found in animal sources, such as butyric acid in butter and stearic acid in beef fat.
Saturated lipids= solid at room temperature
Unsaturated Lipids= liquid at room temp. because of double bond. Double bond causes bend, preventing fatty acids to lay flat on each other. This makes the unsaturated fatty acids liquid.

16. 1. Molecular Structure Continued…
Unsaturated fatty acids are categorized based on how many double bonds they have.
Monounsaturated: one double bond. Examples) olive oil, almonds, walnuts, and canola oil.
Polyunsaturated: two or more double bonds. Examples) Sunflower and corn oils.

17. 1. Molecular Structure Continued…
Most lipids contain a combination of fatty acids. The type of fatty acid found in the greatest amount has the largest affect on the characteristics.

18. 2. Physical State of Lipids
Fats – Solid at room temperature. Usually from animal sources.
Oils – Liquid at room temperature. Usually from plant sources.

19. 2. Physical State Continued…
Melting point of lipids = temperature at which all the different fats and oils it contains are completely liquid. (Although oils are liquid at room temperature, they will solidify when frozen.)
Fats have more hydrogen bonds than oils, which makes them more dense. Since fats are more dense, the melting point of fats is higher than the melting point of oils.
With this in mind… Which would have a lower melting point, polyunsaturated or monounsaturated fatty acids?

20. 2. Physical State Continued…
Hydrogenation - process of adding hydrogen atoms to an unsaturated lipid. Used to make some oils solid at room temperature.
Examples: Margarine made from 100% corn oil. Solid vegetable shortening.

21. 2. Physical State Continued…
Process: oil is heated, breaking the double bonds. In the presence of a catalyst the oil picks up hydrogen atoms, causing the oil to solidify.
Industry Importance: Longer shelf life than lard, greater stability than lard, lower production costs than lard, faster dissolving and setting properties in chocolate production

23. 3. Dietary Sources
Triglycerides come from 7 main groups of dietary sources
Milkfats: from milk of cows, goats etc. Milkfats differ from lard because they have shorter fatty acid chains.
Lauric Acids: found in oils of fruits and seeds from tropical palm trees. Has a low melting point.
Vegetable butters: from seeds of tropical plants. Most important example is cocoa butter, which is used in candies.

24. 3. Dietary Sources
Triglycerides come from 7 main groups of dietary sources
Oleic-linoleic acids: from corn, peanuts, sunflowers, olives, cotton seeds, and sesame seeds. Largest group of triglycerides.
Linolenic Acid: found in soybean and wheat germ. Must be refrigerated after opening.
Animal Fats: found in meats and poultry. High melting points.
Marine Oils: from fish. Spoil quickly, which is why fish must be eaten or frozen within 24 hours.

25. 3 Physical Characteristics of Lipids
These impact the way lipids perform in food products.
Melting and solidification point
Nonpolar nature
Tendency to react with oxygen

26. 1. Melting and Solidification Points
Solidification point: temperature in which all the lipids in a mixture are in a solid state. Lower than the melting point.
Unlike water, lipids do not have a specific melting/solidification point because they are made up of a mix of different fatty acids. Causes vegetable oil to become cloudy when refrigerated.

27. 1. Melting and Solidification Points Continued…
Lower melting points: unsaturated fatty acids, shorter fatty acid chains (and vice versa)
Which would have a lower melting point, butyric acid or steric acid?

28. 2. Nonpolar Nature Nonpolar: an equal sharing of electrons.
Properties:
readily dissolve/mix in other nonpolar substances,
repel polar substances (causing lipids to be less dense than water)
Salad dressings are a mixture of vinegar and oil. To keep them together an emulsifier must be added

29. 3. Reaction to Oxygen
Auto-oxidation: reaction when lipids are exposed to oxygen. Causes lipids to deteriorate.
Unsaturated oils are more susceptible to auto- oxidation than saturated fats due to their double bonds.

30. 3. Reaction to Oxygen
Deterioration of lipids causes them to be rancid – food spoilage that causes unappetizing color and flavor changes.
Hydrolysis (when large molecules are broken down) also causes deterioration of lipids. The shorter the fatty acid chains, the more likely the lipid will become rancid.

31. Functions of Lipids in Food Preparation
Structures and characteristics of lipids affects how they perform in food products
6 main functions in cooking
Heat Mediums
Tenderizers
Aerators
Flavor Enhancers
Lubricants
Liquids in Emulsions

32. 1. Heat Medium
Unlike water, the temperature of lipids will continue to increase as heat is added. Allows lipids to get hot enough to brown food.
All lipids have a temperature when they begin to break apart and produce smoke – smoke point.
Never reuse oil after breakdown occurs, since an undesirable flavor and color will occur.

33. 1. Heat Medium Continued…
Flash point – temperature at which lipids will flame. You must be diligent when cooking with oil to avoid fires.
Example) Deep Frying
Requires a hot enough temperature to cook the food all the way through without burning the surface. Electric Fryers are easier and safer because it automatically turns off the heat when the oil reaches the set temperature to prevent fires.
Other tips for frying: cut all pieces equally to decrease cooking time. Remove excess fluid to prevent spattering. Cook a small amount of food at a time to keep the temperature stable. Let coat of batter sit for 20 min to help it stick and prevent spattering. Add salt afterwards, since it pulls water to the surface and would cause spattering.

34. 2. Tenderizers
Process: Flour is the bulk of structure in baked goods. The protein in flour forms long strands. Fat is added to shorten these strands – this is why solid white fat is called shortening.
Fat-to-Flour ratio of a dough will determine how flaky a baked product is as a result of the fat separating but not soaking into the flour.
Don’t overwork the dough or the fat can melt causing toughness, or a greasy ball of dough.

35. 3. Aerators Aeration – the addition of air into batter
Saturated fats are able to hold its shape around the air pockets; oils cannot be substituted because they cannot provide the structure to trap air.
Used in baking cakes and making whipped margarines/butters

36. 4. Flavor Enhancers Some fats can be used as seasoning.
Buttering bread
Bacon fat to beans, soups, and sauces
Fat dissolves and disperses the flavor from foods, which increases the flavor.
Sometimes you do not want to taste the fat in the dish. Use oils that have little to no flavor – cottonseed, soybean, and canola oil

37. 5. Lubricant As the fat increases, meat is easier to chew.
Example) Marbled meats have fat evenly distributed throughout the meat. As the meat cooks the fat melts, which keeps the meat tender and adds flavor.

38. 6. Liquids in Emulsions
Emulsion – mixture that contains a nonpolar lipid and a polar liquid. The mixture does not stay mixed unless a compound is added to stabilize the nonpolar and polar ends.
Example) Phospholipid Lecithin: found in mayo that prevents the egg yolk, oil, and water from separating.
Other fat based emulsions: butter, milk, bottled salad dressings

39. Functions of Lipids in the Body
Energy – lipids deliver 9 Calories per gram. More than 2x the energy given from carbohydrates.
Adipose tissue stores lipids in the body for future use. Helps with insulation (to maintain body temp. and protect organs), and energy when glycogen stores are depleted.
Make cell membranes.

40. Functions of Lipids in the Body Continued…
Transport vitamins. Vitamins A, D, E, and K are fat soluble, so they must combine with fat to be transported.
Production of hormones
Provide the body with essential fatty acids

41. Essential Fatty Acids
Essential fatty acids – fatty acids that cannot be produced by the body
The only 2 fatty acids that cannot be made by the body are Linoleic acid and Linolenic acid. Found in most plant and fish oils.
Needed for growth and development.

42. Omega-3 Fatty Acids Found in high amounts in fish.
Recommended to eat 8 ounces or more of fish/seafood per week

43. Omega-3 Fatty Acids Continued…
Benefits
Reduce heart disease by lowering the triglyceride level in the blood and preventing plaque to form in the arteries
Strengthen brain-cell membranes, and cell-cell communication.
Reduce joint inflammation
Prevent heartbeat abnormalities
Prevents mental decline

44. Role of Cholesterol Used to produce hormones and build cell membranes
Found only in animal sources – meats, dairy, egg yolks
Plaque hardens and narrows artery walls.

45. Role of Cholesterol
Too much cholesterol in the blood results in deposits on artery walls called plaque. Plaque causes heart disease that can lead to a stroke or heart attack.
Cholesterol levels are controlled through diet (by decreasing overall fat intake because the body can convert fat to cholesterol) and exercise
Plaque hardens and narrows artery walls.

46. Unsaturated Oils
Olive oil and canola oil can help control cholesterol levels.
Olive oil has 2 disadvantages
Has a distinctive flavor not suitable in all foods
Has a low smoke point, so it would be a poor choice for frying.

47. Dietary Recommendations
Recommended that 20-35% of calories come from fat
Fats should mainly come from polyunsaturated and monounsaturated fatty acids
A fat-free diet does not provide essential fatty acids, so moderation is key!