Chemistry Reference
In-Depth Information
OH
HO
HO
HO
OH
O
O
HO
HO
OH
OH
Figure 3.15
Lactitol structure.
solution of the monohydrate at 20°C) is low. Anhydrous lactitol has a very low hygroscopicity. It has
the lowest hygroscopicity with the exception of mannitol. This effect can be used for application as
food ingredient if moisture pick-up should be avoided, that is, as dusting agent in chewing gum or
hard-boiled candies (Schiweck et al. 2011).
The sweetness of lactitol is 30%-40% that of sucrose. The taste is clean and sweet. Lactitol
exhibits the lowest sweetness among the polyols. This might be beneicial for applications where a
signiicant sweetness is not desired, for example, in products (Schiweck et al. 2011) like marzipan or
surimi. On the other hand, sweetness can be slightly increased by adding high-intensity sweeteners
(aspartame, acesulfame-K, and sucralose). With addition of 0.03% aspartame or acesulfame-K to
a 10% aqueous solution of lactitol, the sweetness of a 10% sucrose solution is achieved (Smith and
Hong-Shun 2003).
The preparation of lactitol by hydrogenation of lactose is realized with a nickel catalyst (van
Velthuijsen 1979; Wolfrom et al. 1938). Lactitol can be prepared by reduction of lactose with sodium
borohydride (Scholnick et al. 1975; van Velthuijsen 1979), but technically lactitol is prepared by
hydrogenation of a lactose solution at about 100°C with a Raney nickel catalyst, as lactitol is pro-
duced essentially in the same way from lactose as sorbitol is produced from glucose. The reaction
is carried out in an autoclave under a pressure of 40 atm or more. Due to the lower solubility of lac-
tose, compared to glucose, the lactose concentration at the beginning of the reaction is only 30-40
wt%. When the hydrogenation reaction is completed, the catalyst is sedimented and iltrated, and
the lactitol solution is puriied by ion-exchange resins and activated carbon. The puriied lactitol
solution is then concentrated by evaporating the water, the obtained syrup is crystallized, and the
crystals are separated with a centrifuge and inally dried. The lactitol mother liquor is concentrated
again, giving more crops of the lactitol monohydrate. The inal mother liquor can be used as a 64%
solution or in mixtures with sorbitol to prepare noncrystallizing lactitol syrup at a concentration of
70% (Figure 3.16; van Velthuijsen 1979).
On hydrolysis, the molecule is split into d-galactose and d-sorbitol, both occurring widely in
nature. Due to the absence of a carbonyl group, lactitol is chemically more stable than the related
CH
2
OH
OH
OH OH
OH
O
HO
O
OH
CH
2
OH
HO
O
OH
O
O
OH
OH
OH
OH
HO
OH
OH
Lactose (galactose + glucose)
Lactitol
Figure 3.16
Lactitol formation from lactose.
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