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Carbohydrates 373

TABLE III Oligosaccharides a
Reducing Nonreducing
Homooligosaccharides Heterooligosaccharides Homooligosaccharides Heterooligosaccharides

Simple oligosaccharides
Disaccharides
Maltose Lactose Trehalose Sucrose
4-α-D-Glcp-D-Glc 4-β-D-Galp-α-D-Glc α-D-Glcp-α-D-Glcp β-D-Fru f -α-D-Glcp
Cellobiose Lactulose Isotrehalose Isosucrose
4-β-D-Glcp-D-Glc 4-β-D-Galp-D-Fru β-D-Glcp-β-D-Glcp α-D-Fru f -β-D-Glcp
Isomaltose Melibiose
6-α-D-Glcp-D-Glc 6-α-D-Galp-D-Glc
Gentiobiose Turanose
6-β-D-Glcp-D-Glc 3-α-D-Glcp-D-Fru
Trisaccharides
Maltotriose Manninotriose Raffinose
4-α-D-Glcp-Maltose 6-α-D-Galp-Melibiose 6-α-D-Galp-Sucrose
Tetrasaccharides
Maltotetraose Stachyose
4-α-D-Glcp-Maltotriose 6-α-D-Galp-Raffinose
Pentasaccharides
Hexasaccharides
Heptasaccharides
Octasaccharides
Nonasaccharides
Decasaccharides
Conjugate oligosaccharides Glycolipids
Gangliosides
a
Glc, Glucose; Gal, galactose; Fru, fructose; f , furanose; p, pyranose.
possessing these groups are referred to as reducing,in of 11 and those of a higher (DP = 10) oligosaccharide can
contradistinction to those that resist such oxidation and hardly be detected. However, most polysaccharides have
are designated nonreducing (see Table III). Thus. whereas a much higher DP than oligosaccharides, which renders
all monosaccharides are reducing, there are reducing and quite significant the sum of the gradual changes that occur
nonreducing disaccharides, trisaccharides, and so on. Be- in their physical properties with increasing DP. For exam-
cause monosaccharides and simple oligosaccharides are ple, because, with a rise in DP, the solubility decreases and
soluble in water and sweet tasting, they are called sugars. the viscosity increases, some higher polysaccharides, for
Itshouldbenoted,however,thatthesweetnessofoligosac- example, cellulose, are completely insoluble in water (all
charides decreases with increasing DP and disappears at oligosaccharides are soluble), while the increase in vis-
DP 4–5. cosity may cause the solutions of other polysaccharides to
set and gel.
There are several ways to classify polysaccharides; a
3. Polysaccharides
common one is to group them according to their sources,
Polysaccharides and oligosaccharides are polymeric in that is, into plant and animal polysaccharides, and then
nature and are structurally similar (both are polyac- subdivide the former into skeletal polysaccharides (cel-
etals having oxygen bridges linking the monosaccharide lulose, etc.), reserve polysaccharides (starch, etc.), gums
monomers), but they may differ markedly in DP; the and mucilages, algal polysaccharides, bacterial polysac-
5
polysaccharides may reach a DP of 10 , whereas, by def- charides, and so on. The disadvantage of this classification
inition, the maximum DP for oligosaccharides is 10. Al- is that it tells us very little about the chemistry of these
though, by convention, compounds having a DP of 11 polymers.
or more are designated polysaccharides, a difference be- The classification used in chemistry texts usually dis-
tween the properties of a lower polysaccharide with a DP tinguishes between (1) simple (true) polysaccharides that