Food Chemistry

4.2 Monosaccharides 291

of these compounds is that they simplify a chro-
matogram since there are no anomeric peaks:

(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 hydroly-
sis of the diketal:

(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 intermedi-
ary 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):

(4.110)

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 us-

ing dimethylsulfate or methyliodide as the methy-

lating 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:

(4.111)

Trimethylsilyl ethers (TMS-ethers) are unstable

against hydrolysis and alcoholysis, but have re-

markable thermal stability and so are suitable

for gas chromatographic sugar analysis. Treat-

ment of a sugar with hexamethyldisilazane and