2009_Book_FoodChemistry

262 4 Carbohydrates
copyranosyl mannitol) is a sugar alcohol. It is
produced using biotechnological methods by the
rearrangement of sucrose (1 → 2to1→ 6), followed
by reduction. Maltitol, the reduction product
of the disaccharide maltose, is being considered
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 the α-form. Since the β-form is
more acidic (cf. 4.2.1.3), it can be considered that
the pyranose anion is the reactive form. The oxidation
product is the δ-lactone which is in equilibrium
with the γ-lactone and the free form of
aldonic acid. The latter form prevails at pH > 3.
Treatment of aldose with more vigorous oxidizing
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 dicarboxylic
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 configuration,
form mono- or dilactones.
Oxidation of the CH 2 OH-group by retaining the
carbonyl function at C-1, with the aim of obtaining
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:
(4.27)
The transition of lactones from δ- toγ-form and
vice versa probably proceeds through an intermediary
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.
(4.29)
An additional possibility for uronic acid synthesis
is the reduction of monolactones of the corresponding
aldaric acids:
(4.30)