Food Chemistry

15.4 Baked Products 719

15.4.1.4.2 Bromate, Azodicarbonamide

Addition of alkali bromates to flour also prevents
excessive softening of gluten during dough
making. The reaction involves oxidation of
endogenous glutathione to its disulfide. Bromate
reacts slower than ascorbic acid (Table 15.44).
After a kneading time of 3 minutes, GSH de-
creases from 124 nmol/g to a concentration
of 40 nmol/g and cysteine increases from
22 nmol/gto52nmol/g. These values are
relatively close to the corresponding values in

dough without additives. On the other hand,
only 11 nmol/g of GSH remain and cysteine
increases only slightly after the addition of Asc.
The reactions of bromate in dough have not yet
been elucidated. Model experiments indicate that
it can link gluten proteins by the formation of in-
termolecular disulfide bonds. Then the oxidation
of GSH would not be the decisive step in flour
improvement. In comparison with Asc, bromate
can be overdosed, which also shows that another
mechanism must be involved here. During
baking, bromates are completely reduced to bro-
mides with no bromination of flour constituents.
Azodicarbonamide is of interest as a flour im-
prover

H 2 N CO N N CO NH 2 (15.7)

since it improves not only the dough properties
of weak gluten flour, but also lowers the energy
input in dough mixing (cf. Fig. 15.40). Details of
the reactions involved are unknown.

15.4.1.4.3 Lipoxygenase

The addition of a small amount of enzymeactive
soy flour to a wheat dough increases the mix-
ing tolerance, improves the rheological properties

and may increase the bread volume. The effect on
dough rheology is shown only with high-power
mixing in the presence of air. The carotenoid pig-
ments of wheat flour are bleached by the addit-
ion of enzyme-active soy flour. This is desirable
in the production of white bread. The amount of
enzyme-active soy flour is restricted to approxi-
mately 1% since higher levels may generate off-
flavors.
It was demonstrated that nonspecific lipoxy-
genase (cf. 3.7.2.2) is responsible for the

Fig. 15.35.Wheat flour quality improvement by the

nonspecific lipoxygenase enzyme of soybeana(accord-

ing toKiefferandGrosch, 1979). Additions: 1 control

(no addition, bread volume 31 ml), 2 extract of defatted

soya meal in which lipoxygenase was thermally inac-

tivated (31 ml), 3 extract of a defatted soya meal with

290 units of lipoxygenaseb(35 ml), 4 purified type-II

enzyme with 285 activity units (37 ml).

aResults in small-scale baking, 10 g flour cv. Clement.

bOne enzyme unit=1μmole·min−^1 oxygen uptake

with linoleic acid as substrate

improver action (Fig. 15.35) and the bleaching

effect caused by the enzyme-active soy flour.

This enzyme, in contrast to endogenous wheat

flour lipoxygenase, releases peroxy radicals

which cooxidize carotenoids and other flour

constituents.

15.4.1.4.4 Cysteine

Cysteine, in its hydrochloride form, softens

gluten due to a SH/SS interchange with the

glutenin fraction. The resistance to extension