Carbohydrate digestion

Carbohydrate digestion is necessary because the gastrointestinal tract can only absorb monosaccharides.

It is dependent on several types of enzyme:

• alpha-amylases:
  • hydrolyze alpha-1,4 bonds to convert polysaccharides with alpha-1,4 bonds e.g. glycogen and starch, into oligo- and disaccharides such as maltose and alpha-limit dextrins
  • the first amylase that food encounters is oral ptyalin which works until inactivated by stomach acidity
  • pancreatic amylase carries out the same reaction from the duodenum distally
    
    
• disaccharidases:
  • found in association with the small intestinal brush border
  • sucrase: hydrolyzes sucrose to glucose and fructose
  • maltase: hydrolyzes maltose to 2 glucose residues or maltose triose to 3 glucose residues
  • lactase: converts lactose into glucose and galactose
  • alpha-limit dextrinase: hydrolyzes dextrins into short chains of glucose residues
    
    
• 1,6-glucosidase:
  • secreted by the small intestine
  • hydrolyzes branched dextrins

Therefore ultimately, dietary carbohydrate is digested into glucose, fructose and galactose.