Chemistry Reference
In-Depth Information
synthesis is from l-inositol (obtained from its monomethyl ether, quebrachitol) through the diaceto-
nate, periodate oxidation to the blocked dialdehyde, reduction, and removal of the acetone blocking
groups (Kuhn and Klesse 1958).
3.3.5
d
-tagatose
Tagatose, (
3S,4S,5R
)-1,3,4,5,6-pentahydroxy-hexan-2-one, is a ketohexose c-4 fructose epimer
potentially obtainable by the oxidation of the corresponding hexitol d-galactitol (Figure 3.10). It is
obtained from d-galactose by isomerization under alkaline conditions in the presence of calcium
(Manzoni et al. 2001). It has an excellent sucrose-like taste, has no cooling effect, has no aftertaste
or potentiation of off-lavor, and can thus be considered a possible alternative bulking sweetener.
Although tagatose is present in some foods and is obtainable from natural sources, its availability
appears limited and its recovery expensive, a major impediment to its use in the food industry
(Levin et al. 1995). However, the initial FDA proposal states the use of fungal enzymes in the prepa-
ration of this product, in its manufacture from lactose.
Compared to other polyols, tagatose is not common in nature. It is a sugar naturally found in
small amounts in milk. It can be produced commercially from lactose, which is irst hydrolyzed
to glucose and galactose. The galactose is isomerized under alkaline conditions to d-tagatose by
calcium hydroxide. The resulting mixture can then be puriied and solid tagatose produced by crys-
tallization (Figure 3.11).
It was reported that tagatose does not support fat deposition and appears to deliver less usable
energy than sucrose (Livesey and Brown 1996). Similar metabolic studies using [14C] tagatose
have demonstrated that it is metabolized in both the oral and intravenous routes of administration,
with an effective energy value of zero (Levin et al. 1995; Livesey and Brown 1995). Recent studies
CH
2
OH
C
H
HO
C
H
HO
C
H
H
C
OH
CH
2
OH
Figure 3.10
Structure of tagatose.
CH
2
OH
CH
2
OH
H
C
OH
C
O
HO
C
H
HO
C
H
HO
C
H
HO
C
H
H
C
OH
H
C
OH
CH
2
OH
CH
2
OH
D
-Galactitol
Tagatose
Figure 3.11
Formation of tagatose from
d
-galactitol.
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