Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
The main bottleneck in FOs synthesis is that glucose, a by-product in reactions
catalyzed by inulosucrase and levansucrase, negatively influences the degree of
sucrose conversion, and, therefore, either its oxidation with glucose oxidase or
polymerization with dextransucrase have been used to avoid the inhibiting effect. 21
Application of endodextranase coupled with dextransucrase facilitates concomitant
production of isomaltooligosaccharides, apart from the fructose oligomers.
10.3.2 ISOMALTOOLIGOSACCHARIDES
Pure isomaltooligosaccharides (IMOs), made up by exclusively α-1,6-linked glucose
residues, can be obtained from commercial dextrans synthesized from sucrose
by dextransucrases (see Table 10.2), and digested with endodextranase. 22 Dextran
can be also derived from linear 1,4-α-D-glucan by using dextrin dextranase, which
transfers α-1,4-linked glucosyl units to the nonreducing end of 1,6-α-D-glucan.
Dextransucrases usually form variable amounts of α-1,2-, α-1,3-, and α-1,4 glycosidic
bonds, apart from the α-1,6 ones. Even dextrans produced by the best
industrial Leuconostoc mesenteroides strains contain approximately 5% of branchings.
Some L. mesenteroides dextransucrases form up to 65% of α-1,2 bonds, and
the product has cosmetic and food applications. In the presence of efficient acceptor
carbohydrates such as maltose and isomaltose, dextransucrases transfer glucopyranosyl
units to the acceptor instead of to dextran, giving panose and related isomaltooligosaccharides,
respectively. When weak acceptors such as fucose are used,
only one type of acceptor products are formed, such as leucrose. The yield of the
latter reaction reaches 90% when high concentrations of fructose (3.3 M) are used
and the process is carried out below 0°C. Apart from sugars, some sugar derivatives
such as alcohols can also act as glucose acceptors in reactions catalyzed by dextransucrases.
Commercial preparations of IMOs are also derived from starch treated
with α-amylase, neopullulanase, and α-glucosidase (see Section 10.4.1). They
usually contain α-1,6- and α-1,4-linked glucose oligomers, because all three
enzymes hydrolyze α-1,4 glycosidic bonds in starch, and α-glucosidase additionally
synthesizes α-1,6 linkages.
10.3.3 GALACTOOLIGOSACHHARIDES
β-Galactooligosaccharides (β-GOS), also called transgalactooligosaccharides, display
nutraceutical properties because they promote the growth of bifidobacteria.
These beneficial dietary additives can be obtained by using either GTs or glycosidases.
However, application of the latter enzymes is more economically feasible. β-
GOS are produced from lactose through transgalactosylation catalyzed by β-galactosidases,
which can be coupled with manufacturing of low-lactose milk for people
with lactose intolerance, detected in nearly 70% of the human population. 23 An
application of exo-β-1,4-galactanases for this purpose also seems possible. 24 Some
β-galactosidases, which are retaining GHs, preferentially catalyze glycosidic bond
formation, thus enabling large-scale synthesis of galactooligosaccharides and other