262 4 Carbohydrates
copyranosyl mannitol) is a sugar alcohol. It is
produced using biotechnological methods by the
rearrangement of sucrose (1→2to1→6), fol-
lowed by reduction. Maltitol, the reduction prod-
uct of the disaccharide maltose, is being consid-
ered for wider use in food formulations.
4.2.4.2 Oxidation to Aldonic, Dicarboxylic and Uronic Acids
Under mild conditions, e. g., with bromine water
in buffered neutral or alkaline media, aldoses are
oxidized to aldonic acids. Oxidation involves the
lactol group exclusively.β-Pyranose is oxidized
more rapidly than theα-form. Since theβ-form is
more acidic (cf. 4.2.1.3), it can be considered that
the pyranose anion is the reactive form. The oxi-
dation product is theδ-lactone which is in equi-
librium with theγ-lactone and the free form of
aldonic acid. The latter form prevails at pH>3.
(4.27)The transition of lactones fromδ-toγ-form and
vice versa probably proceeds through an interme-
diary bicyclic form.
The acid name is obtained by adding the suffix–
onic acid (e. g. aldose→aldonic acid).
Glucono-δ-lactone is utilized in food when a slow
acid release is required, as in baking powders, raw
fermented sausages or dairy products.
Treatment of aldose with more vigorous oxi-
dizing agents, such as nitric acid, brings about
oxidation of the C-1 aldehyde group and the
CH 2 OH-group, resulting in formation of a dicar-
boxylic acid (nomenclature: stem name of the
parent sugar+the suffix -aric acid, e. g. aldose
→aldaric acid). Thus, galactaric acid (common
or trivial name: mucic acid) is obtained from
galactose:(4.28)The dicarboxylic acid can, depending on its con-
figuration, form mono- or dilactones.
Oxidation of the CH 2 OH-group by retaining the
carbonyl function at C-1, with the aim of ob-
taining uronic acids (aldehydocarboxylic acids),
is possible only by protecting the carbonyl group
during oxidation. A suitable way is to temporarily
block the vicinal HO-groups by ketal formation
which, after the oxidation at C-6 is completed, are
deblocked under mild acidic conditions:(4.29)An additional possibility for uronic acid synthe-
sis is the reduction of monolactones of the corres-
ponding aldaric acids:(4.30)