Harper's Illustrated Biochemistry, Volume 1 - Murray R. 1993

Bioenergetics and Metabolism of Carbohydrates and Lipids
Physiologically Important Carbohydrates
Classification of Carbohydrates

Chemically, CARBOHYDRATES can be defined as aldehyde or ketone derivatives of polyhydric alcohols (containing more than one OH group) or as compounds that yield these derivatives upon Hydrolysis.

1) Monosaccharides are carbohydrates that cannot be hydrolyzed into simpler forms. They can be classified into trioses, tetroses, pentoses, hexoses, heptoses, and octoses depending on the number of carbon atoms in their molecules; they can also be divided into aldoses and ketoses based on the presence of an aldehyde or ketone group. Examples include

2) Disaccharides yield two molecules of monosaccharides (identical or different) upon hydrolysis. Examples include sucrose, lactose, and maltose.

3) Oligosaccharides yield 3–6 monosaccharides upon hydrolysis. An example is maltotriose¹.

4) Polysaccharides yield more than 6 monosaccharide molecules upon hydrolysis. They can be linear or branched. Examples include starch and dextrins. They are sometimes referred to as hexosans or pentosans, as well as Homopolysaccharides or Heteropolysaccharides, depending on whether identical or non-identical monosaccharides are formed upon their hydrolysis.

¹ This is not a triose, but a trisaccharide containing three a-glucose residues.