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18.4 Chemical properties of fats and oils
1. Hydrolysis Reverse of esterification Forms carboxylic acids (FAs) and alcohol (glycerol) Catalyst = acid or enzyme (lipase)
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Chemical reactions of TAGs
2. Saponification (hydrolysis in base) Forms carboxylic acid salts (soaps) Na+ = hard soap; K+ = liquid soap
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Chemical reactions of TAGs
3. Hydrogenation Unsaturated chains add H2 (become “hydrogenated”) Increase the melting point (become semi-solid) Side effect = production of trans fats
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Olestra Artificial, noncaloric fat substitute (indigestible)
FDA warning “This Product Contains Olestra. Olestra may cause abdominal cramping and loose stools. Olestra inhibits the absorption of some vitamins and other nutrients. Vitamins A, D, E, and K have been added.”
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Reaction map for triglycerides
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18.5 Waxes Esters of fatty acids Alcohol has long chain
Insoluble in water Not easily hydrolyzed Natural protective coatings on plants, fruit, skin, fur, feathers Commercially used as candles, cosmetics
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Membrane/structural lipids
18.6 Phospholipids (phosphoglycerides) 18.7 Sphingolipids (sphingomyelins and glycolipids)
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18.8 Biological membranes Separate contents of cells from external fluids Semipermeable Nutrients enter, waste products leave Lipid bilayer = structural lipids and cholesterol
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Fluid-mosaic model
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18.9 Steroids Ex: Cholesterol, hormones 4 ring structure
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Cholesterol Contains –OH Produced by liver Supplied by diet
Precursor for hormones, vitamin D Component of cell membranes Provide rigidity High levels Gallstones Deposits on arteries
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18.10 Steroid hormones Chemical messengers carried through the blood
Same 4-ring structure as cholesterol Examples: Cortisol: increase glucose concentration in the body Cortisone: anti-inflammatory (arthritis, asthma) Testosterone, estradiol, estrone, progesterone: sex hormones
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18.11 Prostaglandins Hormones involved in production of pain, fever, inflammatory reactions Synthesized from arachidonic acid (a polyunsaturated FA) Synthesis inhibited by NSAIDs e.g. acetylsalicylic acid (aspirin)
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Summary of lipids
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