5.2: The Chemist's View of Phospholipids and Sterols

• phospholipids and sterols only make up 5% of the lipids in the diet

Phospholipids

• best known phospholipid is lecithin

• chemical structure E-

  • 1 glycerol

  • 2/3 attachments are occupied by fatty acids

  • 1/3 attachment is occupied by a phosphate group and a molecule of choline

• hydrophobic fatty acids make phospholipids soluble in fat

• hydrophilic phosphate group allows phospholipids to dissolve in water

• used as emulsifiers to mix fats with water so they don’t separate into layers

Lecithin

Phospholipids in Foods

• used in the food industry as emulsifiers

• found naturally in foods

• richests sources of lecithin-

  • eggs, liver, soybeans, wheat germ, peanuts

Roles of Phospholipids

• parts of cell membranes

• help fat-soluble substances (vitamins and hormones) to pass easily in and out of cells

• emulsifiers in the body

  • keeps fats suspended in the blood and body fluids

Sterols

• compounds with a multiple-ring structure

• cholesterol is the most well-known sterol

  • vitamin D (fat soluble) is synthesized from cholesterol

Sterols in Foods

• found in foods derived from plants and animals

• only foods from animals contain significant amounts of sterol

  • meats, eggs, seafood, poultry, and dairy products

• “good” cholesterol-

  • refers to the way the body transports cholesterol in the blood

• sterols other than cholesterol are naturally found in plants

• plant sterols-

  • structurally similar to cholesterol

  • interfere with cholesterol absorption

  • limiting cholesterol absorption lowers blood cholesterol levels

• fortified foods such as margarine with plant sterols helps reduce blood cholesterol

Roles of Sterols

• important body compounds are sterols-

  • bile acids, sex hormones (testerone, androgen, and estrogen), adrenal hormones (cortisol, cortisone, aldosterone), vitamin D, and cholesterol

• cholesterol-

  • serves as a starting material for the synthesis of body compounds as a structural component of cell membranes

  • 90%+ of all the body’s cholesterol is found in the cells

  • cannot be used for energy

  • endogenous: cholesterol that is made in the body

  • exogenous: cholesterol from outside the body

  • liver-

    • manufactures cholesterol from fragments of carbohydrate, protein, and fat

    • makes about 800-1500 mg of cholesterol per day

    • contributes much more to the body’s total cholesterol than the diet does

  • harmful effects on the body-

    • when cholesterol accumulates in the artery walls and contributes to the formation of plaque, leading to atherosclerosis (disease that causes heart attacks and strokes)