Lipids

1. Lipids

2. Class Presentations Will be Discussed at the End of Class Exams back next Monday No class this Wednesday !!!!!

3. Lipids Main functions of lipids in foods • Energy and maintain human health • Influence on food flavor • Fatty acids impart flavor • Lipids carry flavors/nutrients • Influence on food texture • Solids or liquids at room temperature • Change with changing temperature • Participation in emulsions

4. Lipids • Lipids are soluble in many organic solvents • Ethers (n-alkanes) • Alcohols • Benzene • DMSO (dimethyl sulfoxide) • They are generally NOT soluble in water • C, H, O and sometimes P, N, S

5. Lipids • Neutral Lipids • Triacylglycerols • Waxes • Long-chain alcohols (20+ carbons in length) • Cholesterol esters • Vitamin A esters • Vitamin D esters • Conjugated Lipids • Phospholipids, glycolipids, sulfolipids • “Derived” Lipids • Fatty acids, fatty alcohols/aldehydes, hydrocarbons • Fat-soluble vitamins

6. Lipids Structure • Triglycerides or triacylglycerols • Glycerol + 3 fatty acids • >20 different fatty acids

7. Lipids 101 • Fatty acids- the building block of fats • A fat with no double bonds in it’s structure is said to be “saturated” (with hydrogen) • Fats with double bonds are referred to as mono-, di-, or tri- Unsaturated, referring to the number of double bonds. Some fish oils may have 4 or 5 double bonds (polyunsat). • Fats are named based on carbon number and number of double bonds (16:0, 16:1, 18:2 etc)

8. Lipids • Oil- liquid triacylglycerides “Oleins” • Fat- solid or semi-solid mixtures of crystalline and liquid TAG’s “Stearins” • Lipid content, physical properties, and preservation are all highly important areas for food research, analysis, and product development. • Many preservation and packaging schemes are aimed at prevention of lipid oxidation.

9. Nomenclature • The first letter C represents Carbon • The number after C and before the colon indicates the Number of Carbons • The letter after the colon shows the Number of Double Bonds • ·The letter n (or w) and the last number indicate the Position of the Double Bonds

10. Saturated Fatty Acids

11. Saturated Fatty Acids Octanoic Acid

12. Mono-Unsaturated Fatty Acids

13. Poly-Unsaturated Fatty Acids

14. Fatty Acids Melting Points and Solubility in Water Melting Point Response Solubility in H2O z 2 Fatty acid chain length

15. Unsaturated Fatty Acids 3 - Octenoic Acid 3, 6 - Octadienoic Acid

16. Lipids Properties depend on structure • Length of fatty acids (# of carbons) • Position of fatty acids (1st, 2nd, 3rd) • Degree of unsaturation: • Double bonds tend to make them a liquid oil • Significantly lowers the melting point • Hydrogenation: tends to make a solid fat • Significantly increases the melting point • Unsaturated fats oxidize faster • Preventing lipid oxidation is a constant battle in the food industry

17. Fatty Acids Melting Points and Solubility in Water Melting Point Response Solubility in H2O z 2 Fatty acid chain length

18. Fatty Acids M.P.(C) mg/100 ml in H2O C18 70 0.04 Characteristics of Fatty Acids C4 - 8 C6 - 4 970 C8 16 75 C10 31 6 C12 44 0.55 C14 54 0.18 C16 63 0.08

19. O R C OH O R C OH Fatty Acids #1 Carbon Acid Group Polar End - Hydrophilic End Non-polar End - Hydrophobic End (Fat-soluble tail)

20. Lipids 101 • Fatty acid profile- quantitative determination of the amount and type of fatty acids present following hydrolysis. • To help orient ourselves, we start counting the number of carbons starting with “1” at the carboxylic acid end.

21. Lipids 101 • For the “18-series” (18:0, 18:1, 18:2, 18:3) the double bonds are usually located between carbons 9=10 12=13 15=16.

22. Lipids 101 • The biomedical field started using the OMEGA (w) system (or “n” fatty acids). • With this system, you count just the opposite. • Begin counting with the methyl end • Now the 15=16 double bond is a 3=4 double bond or as the medical folks call it….an w-3 fatty acid

23. Tuning Fork Analogy-TAG’s • Envision a Triacylglyceride as a loosely-jointed E • Now, pick up the compound by the middle chain, allowing the bottom chain to hang downward in a straight line. • The top chain will then curve forward and form an h • Thus the “tuning fork” shape • Fats will tilt and twist to the lowest free energy level

24. Lipids • Lipids are categorized into two broad classes. • The first, simple lipids, upon hydrolysis, yield up to two types of primary products, i.e., a glycerol molecule and fatty acid(s). • The other, complex lipids, yields three or more primary hydrolysis products. • Most complex lipids are either glycerophospholipids, or simply phospholipids • contain a polar phosphorus moiety and a glycerol backbone • or glycolipids, which contain a polar carbohydrate moiety instead of phosphorus.

25. Lipids

26. Other types of lipids Phospholipids • Structure similar to triacylglycerol • High in vegetable oil • Egg yolks • Act as emulsifiers

27. Where Do We Get Fats and Oils? • “Crude” fats and oils are derived from plant and animal sources • Several commercial processes exist to extract food grade oils • Most can not be used without first “refining” before they reach consumers • During oil refining, water, carbohydrates, proteins, pigments, phospholipids, and free fatty acids are removed.  • Crude fats and oils can therefore be converted into high quality edible oils • In general, fat and oil undergo four processing steps: • Extraction • Neutralization • Bleaching • Deodorization • Oilseeds, nuts, olives, beef tallow, fish skins, etc. • Rendering, mechanical pressing, and solvent extraction.

28. Fats and Oils: Processing Peanut Extraction • Rendering • Pressing oilseeds • Solvent extraction Rape Seed Safflower Sesame Soybean

29. Fats and OilsFurther Processing • Degumming • Remove phospholipids with water • Refining • Remove free fatty acids (alkali + water) • Bleaching • Remove pigments (charcoal filters) • Deodorization • Remove off-odors (steam, vacuum)

30. Where Do We Get Fats and Oils? • Rendering • Primarily for extracting oils from animal tissues.  • Oil-bearing tissues are chopped into small pieces and boiled in water.  • The oil floats to the surface of the water and skimmed.  • Water, carbohydrates, proteins, and phospholipids remain in the aqueous phase and are removed from the oil.  • Degumming may be performed to remove excess phospholipids. • Remaining proteins are often used as animal feeds or fertilizers.

31. Where Do We Get Fats and Oils? • Mechanical Pressing • Mechanical pressing is often used to extract oil from seeds and nuts with oil >50%.  • Prior to pressing, seed kernels or meats are ground into small sized to rupture cellular structures.  • The coarse meal is then heated (optional) and pressed in hydraulic or screw presses to extract the oil. • Olive oils is commonly cold pressed to get extra virgin or virgin olive oil. It contains the least amount of impurities and is often edible without further processing. • Some oilseeds are first pressed or placed into a screw-press to remove a large proportion of the oil before solvent extraction.

32. Where Do We Get Fats and Oils? Solvent Extraction • Organic solvents such as petroleum ether, hexane, and 2-propanol can be added to ground or flaked oilseeds to recover oil.  • The solvent is separated from the meal, and evaporated from the oil. Neutralization • Free fatty acids, phospholipids, pigments, and waxes exist in the crude oil • These promote lipid oxidation and off-flavors (in due time) • Removed by heating fats and adding caustic soda (sodium hydroxide) or soda ash (sodium carbonate).  • Impurities settle to the bottom and are drawn off.  • The refined oils are lighter in color, less viscous, and more susceptible to oxidation (without protection). Bleaching • The removal of colored materials in the oil. • Heated oil can be treated with diatomaceous earth, activated carbon, or activated clays. • Colored impurities include chlorophyll and carotenoids • Bleaching can promote lipid oxidation since some natural antioxidants are removed.

33. Where Do We Get Fats and Oils? Deodorization • The final step in the refining of oils. • Steam distillation under reduced pressure (vacuum). • Conducted at high temperatures of 235 - 250ºC. • Volatile compounds with undesirable odors and tastes can be removed. • The resultant oil is referred to as "refined" and is ready to be consumed. • About 0.01% citric acid may be added to inactivate pro-oxidant metals.

34. Fats and OilsFurther Processing Hydrogenation • Add hydrogen to an oil to “saturate” the fatty acid double bonds • Conducted with heated oil • Often under pressure • In the presence of a catalyst (usually nickel) • Converts liquid oils to solid fats • Raises melting point

35. Hydrogenating Vegetable oils can produce trans-fats Cis- Trans-

36. The cis- and trans- forms of a fatty acid

38. Fats and Oils in Foods • SOLID FATS are made up of microscopic fat crystals. Many fats are considered semi-solid, or “plastic”. • PLASTICITY is a term to describe a fat’s softness or the temperature range over which it remains a solid. Even a fat that appears liquid at room temperature contains a small number of microscopic solid fat crystals suspended in the oil…..and vice versa • PLASTIC FATS are a 2 phase system: • Solid phase (the fat crystals) • Liquid phase (the oil surrounding the crystals). • Plasticity is a result of the ratio of solid to liquid components. • Plasticity ratio = volume of crystals / volume of oil • Measured by a ‘solid fat index’ or amount of solid fat or liquid oil in a lipid • As the temperature of a plastic fat increases the fat crystals melt and the fat will soften and eventually turn to a liquid.

39. Fat and Oil: Further Processing • Winterizing (oil) • Cooling a lipid to precipitate solid fat crystals • DIFFERENT from hydrogenation • Plasticizing (fat) • Modifying fats by melting (heating) and solidifying (cooling) • Tempering (fat) • Holding the fat at a low temperature for several hours to several days to alter fat crystal properties (Fat will hold more air, emulsify better, and have a more consistent melting point)

40. Lipid Oxidation

41. Oleic acid Radical Damage, Hydrogen Abstraction Formation of a Peroxyl Radical

42. Simplified scheme of lipoxidation + Catalyst + Oxygen

43. Primary Drivers • Temperature-basic rxn kinetics • Water Activity • Both high and low Aw • At low Aw, peroxides decompose faster and metal ions are better catalysts in a dry environment • MetalIons-catalysts • Light-energy source • SingletOxygen- ROS, highly electrophilic • Reacts 1,500 times faster at C=C than ground state O2 • Enzymes ie. Lipoxygenase (LOX)

44. Initiation of Lipid Oxidation • There must be a catalytic event that causes the initiation of the oxidative process • Enzyme catalyzed • “Auto-oxidation” • Excited oxygen states (i.e singlet oxygen): 1O2 • Triplet oxygen (ground state) has 2 unpaired electrons in the same spin in different orbitals. • Singlet oxygen (excited state) has 2 unpaired electrons of opposite spin in the same orbital. • Metal ion induced (iron, copper, etc) • Light • Heat • Free radicals • Pro-oxidants • Chlorophyll • Water activity

45. Considerations for Lipid Oxidation • Which hydrogen will be lost from an unsaturated fatty acid? • The longer the chain and the more double bonds….the lower the energy needed.

46. Bond Strength 103 kCal 65 kCal 65 kCal 85 kCal Fatty acid .OH or other Free radicals . . .

47. Propagation Reactions Peroxyl radical Ground state oxygen Initiation Hydroperoxide New Radical Alkoxyl radical Hydroxyl radical!! Hydroperoxide decomposition Start all over again…

48. Mechanism of Photooxidation Chlorophyll Chlorophyll 3O2 1O2 or

49. Singlet Oxygen Oxidation

50. Autoxidation + +