Chemistry Reference
In-Depth Information
these thermostable enzymes at high temperatures for a prolonged period
under realistic bioprocessing conditions.
The properties of the
-fructofuranosidase extracted from Arthrobacter
sp. K1 have been described by Fujita et al. (1990a). The enzyme has an
isoelectric point of 4.3, an optimum pH of 6.5-6.8, but the enzyme remains
stable between pH 5.5 and 10.00. It has an optimum temperature of 558C, but
is stable between 45 and 608C. It is inhibited by several heavy metals. Fujita
et al. (1990b) also describe the acceptor specificity for a wide range of mono-
and oligo-saccharides and glycosides.
5.4.4.
Lactitol
Lactitol (Figure 5.5) is well established as a replacement sweetener for
low-calorie foods. In recent years, interest in it as a prebiotic carbohydrate
has developed. This sugar alcohol was discovered in 1912 and was first used in
foods in the 1980s. It is formed when lactose is hydrogenated in the presence
of Raney-nickel catalyst. The conversion of a sugar to a sugar alcohol always
involves the reduction of a carbonyl group. The preferred reducing agent is
hydrogen gas under high pressure (e.g., 40 bar) at 1008C in the presence of a
nickel catalyst. This synthesis has been used widely at both laboratory and
industrial scale for many years. Ipatiew (1912) first produced a lactitol syrup
by such a process, but lactitol was first crystallized by Senderens (1920).
Lactitol is produced either as a syrup, as dihydrate or monohydrate crystals
or in anhydrous form. Van Velthuijsen (1979) has described a typical modern
industrial process and specifications of the product obtained in such pro-
cesses. Less than 2.5% other polyols and 0.1% reducing sugars are present in
the
food-grade
lactitol
products
which
are
97.5%
lactitol.
Thus,
this
H
H
H
H
OH
OOH
H
H
H
H
H
H
OH
OOH
H
H
HOH
2
C
HOH
2
C
C
C
C
C
C
C
C
C
CH
2
OH
CH
2
OH
HOH
2
C
HOH
2
C
C
C
C
C
C
C
C
C
COOH
COOH
HO
HO
O
O
H
H
OH
OH
HO
HO
O
O
H
H
OH
OH
HOCH
2
HOCH
2
HOCH
2
HOCH
2
O
O
HO
HO
O
O
HO
HO
OH
OOH
OH
OOH
OH
OOH
OH
OOH
lactitol
lactobionic acid
Figure 5.5.
The chemical structures (Haworth) of lactitol and lactobionic acid.
