Chemistry Reference
In-Depth Information
6.7
OTHER ENZYMES
Besides amylases, xylanases, lipases, oxidases and proteases, several other (classes of)
enzymes have been investigated for their effects in bread making and several other types
mentioned above have been reported to have beneficial effects on one or more characteristics
of dough or bread. And indeed some of them have been commercialized.
6.7.1 Transglutaminase
In the preparation of yeast-leavened goods from weak wheat flour, the dough often has an
unsatisfactory stability. Such a dough has not been able to retain the carbon dioxide gas
that is formed during fermentation. For this reason, it is generally common to add oxidizing
compounds to the flour to improve the resistance to stretching.
191
Because of the effort to
reduce the addition of chemicals to foodstuffs and instead to use natural auxiliaries, like
enzymes, the problem arose of improving the resistance of dough without the addition of
inorganic chemicals. It has been found that transglutaminase improves the resistance of
dough, particularly yeast dough from wheat flour, in a manner comparable to potassium bro-
mate.
192, 193
Transglutaminase (TGase; synonym: Protein-Glutamine-
γ
-Glutamyltransferase
and Protein-glutamine:amine
-glutamyl-transferase;
EC 2.3.2.13
) is an enzyme accessible
from various sources that is widespread in the animal and plant kingdoms. It is known that
transglutaminase has a cross-linking effect on proteins independent of the redox system of
the dough, not involving the thiol groups and disulphide bonds in the dough. The basic
reaction is shown in Fig. 6.12.
However, the effect on the rheological properties of dough is similar to oxidation and
the effects are the result from an increased number of disulphide bonds. The need for
TGase for improvement of the stretching properties depends in individual cases on the
nature of the flour. TGase can be added in different ways in the preparation of baked goods.
The enzyme preparation can be used together with the remaining components of a bread
improver system, but it can also be mixed with the flour at the mill. This has the advantage
that the dosage can be based on the properties of the flour, that is on its natural gluten
properties. In this way, a flour of consistent baking properties can always be supplied to the
baker. Thus, TGase is preferably added to weak wheat flours in order to strengthen gluten
properties.
The
γ
effect
of
TGase
on
the
dough
can
be
visualized
in
an
extensogram
(see
Table 6.5).
Addition of TGase leads to strongly increased dough resistance and a reduced extensibility.
Combining TGase with a protease can overcome too strong effects of the coupling enzyme.
The results of TGase addition on bread quality can be seen in Table 6.6.
In addition to the desired increase in the dough resistance, a reduction in extensibility
is sometimes observed, which leads to an earlier breakage of the dough when testing ex-
tensibility. It has been found that this undesired side effect can be excluded by combining
Transglutaminase
Glu - C - NH
2
+ H
2
N - Lys
Glu - C - NH - Lys
O
O
Fig. 6.12
Schematic representation of the transglutaminase reaction.
