Chemistry Reference
In-Depth Information
1.3.
Derivatives of Lactose
Like other sugars, lactose has reactive functional groups and can be con-
verted to several more valuable food-grade derivatives (see Yang and Silva,
1995), of which the following are the most significant:
Glucose-galactose syrups, which are
3
as sweet as lactose, can be
produced by hydrolysis by a strong acid but are usually prepared
by
-galactosidase. The technology for the production of glucose-
galactose syrups, by acid or
-galactosidase, is well developed (see
Mahony, 1997; Chapter 5) but the products are not cost-competitive
with other sweeteners (sucrose, glucose, high-fructose syrups or syn-
thetic sweeteners).
Owing to the several alcohol groups, sugars, including lactose, are
reactive molecules, from which a great variety of derivatives can be
produced (see Thelwall, 1997). However, the chemical derivatives of
lactose are not being produced commercially, probably because
similar products can be produced from other, cheaper, sugars, e.g.
a trichlorinated derivative of sucrose, sucralose, commercialized
under the trade name ''Splenda'' [E955], is a very successful artificial
sweetener (up to 1000 times as sweet as sucrose or twice as sweet as
saccharine and four times as sweet as aspartame). I am not aware of
studies on the sweetness of chlorinated lactose.
Probably the most commercially successful derivative of lactose is lactu-
lose (galactose-fructose) produced by the epimerization of the glucose
moiety of lactose to fructose under mildly alkaline conditions. Lactulose
has many applications including use as a prebiotic and a mild laxative
(see Timmermans, 1998; Aider and de Halleux, 2007; Chapter 5).
The carbonyl group of lactose can be reduced to lactitol (the alcohol
of lactose) or oxidized to lactobionic acid. The production and
properties of lactitol were described by Timmermans (1998). Lactitol
can be esterified with various fatty acids and used as emulsifiers
analogous to sorbitans (esters of sorbitol).
Lactobionic acid is a sweet-tasting acid, which is a very rare property
and can be exploited in processed foods. It can be produced by
electrochemical oxidation (Gerling, 1998), enzymatically, using glu-
cose-fructose oxidoreductase (Satory et al., 1997) or by living micro-
organisms (Murakami et al., 2002a,b). A method for the production
of lactose-free galactosaccharides was described by Splechtna et al.
(2001); lactose was first treated with
-galactosidase to yield a
mixture of galactooligosaccharides, lactose and monosaccharides.
The residual lactose was oxidized by cellobiose dehydrogenase to
