Q.How are polysaccharides and disaccharides digested?

Polysaccharides, chiefly starch, are digested in two stages:

1. In the mouth, salivary amylase (ptyalin) acts on starch, partially breaking it down into the disaccharide maltose (and some limit dextrins), though the short time food spends in the mouth means this is only a partial digestion.
2. In the small intestine, pancreatic amylase continues and completes this breakdown, converting essentially all remaining starch into maltose.

Disaccharides — maltose (from starch digestion), and dietary sucrose and lactose — are then digested by specific disaccharidase enzymes present at the brush border (microvilli) of the intestinal mucosal cells, as part of the succus entericus (intestinal juice):

• Maltase hydrolyses maltose into two molecules of glucose.
• Sucrase hydrolyses sucrose into glucose + fructose.
• Lactase hydrolyses lactose into glucose + galactose. …

Separate the two stages: starch (polysaccharide) → maltose via salivary and pancreatic amylase; then maltose/sucrose/lactose (disaccharides) → their monosaccharides …

• Saying amylase directly produces glucose — amylase only produces maltose; further breakdown to glucose needs maltase. …