2009_Book_FoodChemistry

294 4 Carbohydrates
tose and the C-2 of the glucose residues, and the
second between the HO-group on the C-6 of the
fructose residue and the ring oxygen of the glucose
residue:
rotation in the D-series than the β-anomer, cleavage
of β-glycosides increases the specific rotation
while cleavage of α-glycosides decreases it:
(4.121)
4.3.2 Properties and Reactions
The oligosaccharides of importance to food, together
with data on their occurrence, are compiled
in Table 4.18. The physical and sensory
properties were covered with monosaccharides,
as were reaction properties, though the difference
between reducing and nonreducing oligosaccharides
should be mentioned. The latter do not have
a free lactol group and so lack reducing properties,
mutarotation and the ability to react with alcohols
and amines.
As glycosides, oligosaccharides are readily hydrolyzed
by acids, while they are relatively stable
against alkalies. Saccharose hydrolysis is denoted
as an inversion and the resultant equimolar mixture
of glucose and fructose is called invert sugar.
The term is based on a change of specific rotation
during hydrolysis. In saccharose the rotation
is positive, while it is negative in the hydrolysate,
since D-glucose rotation to the right (hence its
name dextrose) is surpassed by the value of the
left-rotating fructose (levulose):
(4.123)
Enzymatic cleavage of the glycosidic linkage is
specified by the configuration on anomeric C-1
and also by the whole glycosyl moiety, while the
aglycone residue may vary within limits.
The methods used to elucidate the linkage positions
in an oligosaccharide (methylation, oxidative
cleavage of glycols) were outlined under
monosaccharides.
The cyclodextrins listed in Table 4.18 are
prepared by the action of cyclomaltodextrin glucanotransferase
(E. C. 2.4.1.19), obtained from
Bacillus macerans, on maltodextrins. Maltodextrins
are, in turn, made by the degradation of
starch with α-amylase. This glucanotransferase
splits the α-1,4-bond, transferring glucosyl
groups to the nonreducing end of maltodextrins
and forming cyclic glucosides with 6-12
glucopyranose units. The main product, β-cyclodextrin,
consists of seven glucose units and is
a non-hygroscopic, slightly sweet compound:
(4.122)
Conclusions can be drawn from mutarotation,
which follows hydrolysis of reducing disaccharides,
about the configuration on the anomeric
C-atom. Since the α-anomer has a higher specific
(4.124)