1. DISACCHARIDES Disaccharides are two monosaccharide units linked together by acetal or ketal glycosidic linkages. A glycosidic linkage is identified by: the numbers associated with the carbon atoms joined together by the linkage. the configuration of the linkage for any anomeric carbon atom joined by the linkage.

2. IMPORTANT DISACCHARIDES Maltose is: malt sugar. two glucose units joined by  (1→4) glycosidic linkage. formed during the digestion of starch to glucose. found in germinating grain. a hemiacetal, which means maltose is a reducing sugar. hydrolyzed to form two molecules of D-glucose.

3. IMPORTANT DISACCHARIDES (continued) Lactose is: milk sugar (5% cow milk, 7% human milk by weight). composed of galactose and glucose units joined by  (1→4) glycosidic linkage. a hemiacetal, which means lactose is a reducing sugar.

4. IMPORTANT DISACCHARIDES (continued) Sucrose is: common household sugar. composed of fructose and glucose units joined by  1→  2 glycosidic linkage. found in many plants (especially sugar cane and sugar beets). not a reducing sugar. hydrolyzed to produce invert sugar (a mixture of equal amounts glucose and fructose).

5. IMPORTANT DISACCHARIDES (continued) From left to right, four test tubes containing Benedict’s reagent, 2% maltose solution, 2% sucrose solution, and 2% lactose solution. Both maltose and lactose are reducing sugars. The sucrose has remained unreacted.

6. IMPORTANT DISACCHARIDES (continued)

7. POLYSACCHARIDES Polysaccharides are condensation polymers containing thousands of units. They are not water-soluble, but hydroxy groups become hydrated individually when exposed to water. They can form thick colloidal dispersions when heated in water. Starch is used as a thickener in sauces, gravies, pie fillings, and other food preparations.

8. IMPORTANT POLYSACCHARIDES Starch is: a polymer consisting of glucose units. a major storage form of D-glucose in plants. one of two forms, which are: unbranched amylose (10-20%), which is composed of 1000-2000 glucose units with  (1→4) glycosidic linkages;

9. IMPORTANT POLYSACCHARIDES (continued) and branched amylopectin (80-90%) with  (1→4) and  (1→6) glycosidic linkages.

10. IMPORTANT POLYSACCHARIDES (continued) Amylose complexes with iodine to form a dark blue color. The molecular conformation of starch and the starch-iodine complex: (a) the helical conformation of the amylose chain and (b) the starch-iodine complex.

11. IMPORTANT POLYSACCHARIDES (continued) Glycogen (animal starch) is: a polymer of glucose units. used by animals to store glucose, especially in the liver and muscles. structurally similar to amylopectin with  (1→4) and  (1→6) linkages, but more highly branched.

12. IMPORTANT POLYSACCHARIDES (continued) Cellulose is: a polymer of glucose units. the most important structural polysaccharide. the most abundant organic compound on earth. found in plant cell walls. a linear polymer like amylose, but has  (1→4) glycosidic linkages. not easily digested and a constituent of dietary fiber.

13. IMPORTANT POLYSACCHARIDES (continued) Cellulose structure