2009_Book_FoodChemistry

4.2 Monosaccharides 291
of these compounds is that they simplify a chromatogram
since there are no anomeric peaks:
(4.110)
(4.107)
Selective esterification of a given HO-group
is also possible. For example, glucose can be
selectively acetylated in position 3 by reacting
1,2,5,6-di-O-isopropylidene-α-D-glucofuranose
with acetic acid anhydride, followed by hydrolysis
of the diketal:
Sugar esters or sugar alcohol esters with long
chain fatty acids (lauric, palmitic, stearic and
oleic) are produced industrially and are very
important as surface-active agents. These include
sorbitan fatty acid esters (cf. 8.15.3.3) and
those of saccharose (cf. 8.15.3.2), which have
diversified uses in food processing.
4.2.4.7 Ethers
Methylation of sugar HO-groups is possible using
dimethylsulfate or methyliodide as the methylating
agent. Methyl ethers are of importance in
analysis of sugar structure since they provide data
about ring size and linkage positions.
Permethylated saccharose, for example, after
acid hydrolysis provides 2,3,4,6-tetra-O-methyl-
D-glucose and 1,3,4,6-tetra-O-methyl-D-fructose.
This suggests the presence of a 1,2 ′ -linkage
between the two sugars and the pyranose and
furanose structures for glucose and fructose,
respectively:
(4.108)
Hydrolysis of acyl groups can be achieved by
interesterification or by an ammonolysis reaction:
(4.109)
Sugar esters are also found widely in nature.
Phosphoric acid esters are important intermediary
products of metabolism, while sulfuric acid
esters are constituents of some polysaccharides.
Examples of organic acid esters are vacciniin
in blueberry (6-benzoyl-D-glucose) and the
tannintype compound, corilagin (1,3,6-trigalloyl-
D-glucose):
(4.111)
Trimethylsilyl ethers (TMS-ethers) are unstable
against hydrolysis and alcoholysis, but have remarkable
thermal stability and so are suitable
for gas chromatographic sugar analysis. Treatment
of a sugar with hexamethyldisilazane and