A Specific Membranous-Phase Enzyme Exists for the Digestion of Each Type of Polysaccharide

The membranous-phase enzymes of carbohydrate digestion have as their substrates dietary complex carbohydrates, such as sucrose and lactose, as well as the polysaccharide products of luminal-phase starch digestion, including maltose and isomaltose. The specific membranous-phase enzymes are named according to their substrates and include maltase, isomaltase, sucrase, and lactase. The sole product of maltose and isomaltose digestion is glucose, whereas in addition to glucose, fructose and galactose are produced from the digestion of sucrose and lactose, respectively. All polysaccharides are digested to monosaccharides before absorption (Figure 30-10).