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 glu-
cose residue:
(4.121)4.3.2 PropertiesandReactions
The oligosaccharides of importance to food, to-
gether with data on their occurrence, are com-
piled in Table 4.18. The physical and sensory
properties were covered with monosaccharides,
as were reaction properties, though the difference
between reducing and nonreducing oligosaccha-
rides should be mentioned. The latter do not have
a free lactol group and so lack reducing proper-
ties, mutarotation and the ability to react with al-
cohols and amines.
As glycosides, oligosaccharides are readily hy-
drolyzed by acids, while they are relatively stable
against alkalies. Saccharose hydrolysis is denoted
as an inversion and the resultant equimolar mix-
ture of glucose and fructose is called invert sugar.
The term is based on a change of specific rota-
tion during hydrolysis. In saccharose the rotation
is positive, while it is negative in the hydrolysate,
sinceD-glucose rotation to the right (hence its
name dextrose) is surpassed by the value of the
left-rotating fructose (levulose):
(4.122)Conclusions can be drawn from mutarotation,
which follows hydrolysis of reducing disaccha-
rides, about the configuration on the anomeric
C-atom. Since theα-anomer has a higher specific
rotation in theD-series than theβ-anomer, cleav-
age ofβ-glycosides increases the specific rotation
while cleavage ofα-glycosides decreases it:(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 pos-
itions in an oligosaccharide (methylation, oxi-
dative cleavage of glycols) were outlined under
monosaccharides.
The cyclodextrins listed in Table 4.18 are
prepared by the action of cyclomaltodextrin glu-
canotransferase (E. C. 2.4.1.19), obtained from
Bacillus macerans, on maltodextrins. Malto-
dextrins are, in turn, made by the degradation of
starch withα-amylase. This glucanotransferase
splits the α-1,4-bond, transferring glucosyl
groups to the nonreducing end of maltodex-
trins and forming cyclic glucosides with 6-12
glucopyranose units. The main product,β-cyclo-
dextrin, consists of seven glucose units and is
a non-hygroscopic, slightly sweet compound:(4.124)