Chemistry Reference
In-Depth Information
Streptococcus thermophilus
S. thermophilus is used widely in fermented dairy foods and is a GRAS
organism. The use of non-GRAS status bacteria limits their commercial
use in many countries. For example, the use of Escherichia coli strains is
not permitted in the food industry in most countries. The
-galactosidase
of S. thermophilus is a useful enzyme for commercial hydrolysis of
lactose in milk and cheese whey (Greenberg and Mahoney, 1982).
These authors pointed out that the thermal stability of the enzyme is
greater in milk and whey than in buffer. The enzyme from this bacterium
is more heat stable than that of K. marxianus (Linko et al., 1992) and it
is produced intracellularly. The inhibitors and stimulants of the enzyme
have been studied (Greenberg and Mahoney, 1982). The (1
!
3) glycosyl
linkage is cleaved first by this enzyme, but later it also cleaves the (1
!
4)
and (1
!
6) linkages.
The ability of the
-galactosidase of S. thermophilus to undergo trans-
galactosylation reactions was recognized by Toba et al. (1981) and by Green-
berg and Mahoney (1983) and further studied by Smart and co-workers in
more detail (Smart, 1989, 1991, 1993; Garman et al., 1996). Playne et al.
(1993) have also described successful laboratory production of oligosacchar-
ide mixtures from lactose using a crude enzyme extract from a strain of S.
thermophilus. Oligosaccharide production was higher than that by commer-
cial enzymes from Aspergillus and Kluyveromyces. The company, Yakult
Honsha Co., Ltd., uses a
-galactosidase from S. thermophilus as well as an
enzyme from A. oryzae in a two-stage process to produce their oligosacchar-
ide product (Matsumoto et al., 1993).
Because of its long-standing importance in the manufacture of
yoghurt and in other fermented dairy products, a considerable body of
knowledge has been established for S. thermophilus. The complete genomic
sequences for two strains have been determined (Bolotin et al., 2004). This
genomic analysis allows a new understanding of its biochemistry and
physiology.
Lactobacillus Species
Most species of Lactobacillus possess high
-galactosidase activity. Thus,
there have been a number of investigations of enzymes from this source and
their possible application for the production of
-galacto-oligosaccharides
(Toba et al., 1981). Garman et al. (1996), in a study of a number of species of
Lactobacillus and S. thermophilus, found that a strain of Lb. delbrueckii
subsp. bulgaricus possessed a
-galactosidase with transgalactosylation activ-
ity similar to the enzyme from S. thermophilus. As an example of the use of
