Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
compounds such as para-nitrophenyl galactosyl chromogens, various chiral sugar
derivatives, and disaccharides such as galactosyl- xylose. 25
Generally, the molecules of β-GOS can be presented as:
Gal X (Gal) n Y Glc
where n is the number of β-1,4-linked galactose residues; x = β-1,6 > β-1,4, β-1,3;
and y = β-1,2, β-1,6 > β-1,4. This formula indicates that apart from the dominating
β-1,4 glycosidic bond, β-galactosidases synthesize some β-1,3 and β-1,6 linkages
too.
Apart from galactooligosaccharides, lactulose, tagatose, and lactobionic acid can
also be obtained from lactose, using relevant oxidoreductases (see Section 10.2.6).
Because lactose is an attractive starting material, the list of its derivatives continues
to grow. For example, hexyl glycosides have been prepared by lactose hydrolysis
with β-galactosidase, followed by a treatment with thermostable β-glycosidases from
hyperthermophiles. 26 It should be emphasized that their hydrolysis with α-galactosidase
preparations enhances digestibility of certain plant foods. 27 α-Galactosidases
are also applicable for synthesis of the so-called globo-oligosaccharides, having
terminal α-D-galactose-1,4-α-D-galactose sequences and involved in interactions
with pathogens and viruses.
10.4 POLYSACCHARIDES
10.4.1 STARCH
The application of enzymes in industrial starch processing dates back to the 1970s.
Currently, amylolytic enzymes constitute approximately 30% of total market of
biocatalysts. Starch-converting enzymes, listed in Table 10.4, comprise endo- and
exoamylases, debranching enzymes, and transferases. 11 Their majority (except glucoamylase
and β-amylase) belong to the α-amylase family, comprising numerous
hydrolases and transferases, though some are active against substrates other than
starch or dextrins. Enzymes of Family 13 of GHs, with a retaining mechanism of
attack, dominate the α-amylase family, but some catalytic proteins assigned to the
Family 70 (dextransucrase and alternansucrase) and Family 77 (4-α-glucanotransferase)
GHs also share the structure of the catalytic domain [in the form of (β/α) 8
barrel] and mechanism of the action with α-amylase.
Apart from amylolytic enzymes, some other enzymatic activities are also found
to be necessary for a satisfactory degree of large-scale starch conversion. For
instance, enzymatic starch processing has to face some problems related to the
presence of amylose–lipid complexes formed either in situ in wheat starch granules
or generated on gelatinization of containing lipids starch slurries. Lipases, mainly
lysophospholipases, are applied together with amylolytic enzymes to improve the
yield of processing.