1.What
is Gluten?
Gluten is often
equated with the proteins of the wheat that are insoluble in water. It is a
fact that glutenin and gliadin are the main constituents of gluten in terms of
quantity and determine its basic character. But smaller components such as
lipids or pentosans are firmly and in some cases even covalently bonded to the
gluten and have a corresponding influence on its properties. Commercial gluten
(dried vital wheat gluten) also contains starch and minerals that cannot be
completely removed by aqueous extraction. That is why dried gluten only
contains about 80% protein.
2. Is
there a connection between the quality of the protein and its chemical
structure?
The baking
properties of wheat flour depend to a large extent on the amount of protein,
the ratio of gliadin to glutenin and the properties of the latter, especially
the disulphide bridges.
3.
How are proteins and gluten determined analytically?
Protein in wheat
flour can be determined chemically by the Kjeldahl method, but the procedure is
very complex. A simpler method is to use a modern analytical system that works
according to the Dumas method. The indirect test by near-infrared spectroscopy
(NIR) is very widely used in the milling industry. If calibration is carried
out carefully, near-infrared transmission (NIT) also yields very precise
results.
4.
What effect do the proteins of the gluten and added vital wheat gluten have on
water absorption?
The water
absorption capacity of native gluten is about 2.5-3 times its dry weight, i.e.
a flour with 10% protein will result in approx. 25% wet gluten although not all
of the protein ends up in the wet gluten.
5.
What effect does the addition of vital wheat gluten have on the rheological
properties of dough?
Dry vital wheat
gluten has a rather short gluten structure, so it reduces the extensibility of
the dough and increases its resistance to extension. The energy input (area
under the curve of the Alveogram and the Extensogram) does not necessarily
increase. In the Farinograph the curve will be broader, with better stability
and less softening.
6.
How do the proteins of the gluten affect the shelf-life of the bread?
Gluten increases
the water absorption of the dough and the bread, and it improves the volume
yield and crumb structure. So gluten also enhances the softness of the crumb
and its ability to stay soft. Baked goods that are meant to stay crisp after
baking (German breakfast rolls, French baguettes) should not contain too much
protein because it will soften the crust too soon.
7.
What importance do the wheat proteins have for the production of cake doughs
and wafer batters?
In most cases
cake is a foam in which protein is a structural component. Too much protein
makes the structure rubbery. Many recipes therefore contain starch, which
results in a shorter bite. For wafer batter, a low protein content is useful
because it reduces the tendency to form gluten lumps. Furthermore, lower
protein results in soft-melting wafers. On the other hand, higher protein
levels can be used to produce very stable and crisp wafers (e.g. for ice cream
cones) with reduced permeability for water. In this case, proteolytic enzymes
should be used to avoid lump formation in the batter.
8.
How does wheat gluten react with flour improvers and baking agents?
When vital wheat
gluten is added, oxidation should be reduced because the dry gluten already has
a short structure. Sometimes it is even useful to add softening agents
(cysteine, protease). Emulsifiers have at least and additive if not synergistic
effect on the improving function of wheat gluten.
9. Is
it possible to increase or reduce the gluten content without adding dried
gluten?
There seem to be
some additives with the potential to improve the swelling of protein. Of these,
fungal proteases are mentioned most often.
10.
Can I use flour with 12% protein as biscuit, cracker or wafer flour?
Although flour
with less than 10% protein is preferable for many biscuits, crackers and
wafers, it is nevertheless possible in many cases to obtain good products with
a higher protein level. If gluten formation occurs in the course of the
processing, sufficient softening will be required, e.g. by reducing agents or
enzymes. In the case of wafers the protein has to be destroyed in order to
avoid lumping. An increased protein level then results in products with a
firmer texture which are less prone to breakage and water migration. The use of
starch to dilute the protein is only necessary if a very soft-melting texture
is desired.
11.
Does an increase in the gluten content of a bread mix always result in improved
volume yield?
The addition of
dry vital wheat gluten results in a strengthening of the dough and increased
water absorption (about 1.5 times the amount of added gluten). Gluten generally
improves the tolerance of the dough and its gas holding capacity, and therefore
increases the volume yield. But if the dough is too stiff for the chosen processing
method, the volume yield will in fact decrease.
12.
Should a flour mill be able to offer gluten free mixes too?
Any mill processing
wheat, rye or barley would have substansial difficulty in making gluten free
products, because the whole mill is contaminated with gluten traces. The actual
limit for “gluten-free” is 20 ppm in many countries. “Gluten-reduced” is the
term for gluten levels below 200 ppm. 20 ppm gluten is equivalent to 0.02 g of
wheat flour in 1 kg of mix, a quantity that can easily result from
cross-contamination or residues in the plant. The production of gluten-free
goods should therefore be reserved for specialists, e.g. rice mills or mixing
companies with a near-pharmaceutical hygiene level.
13.
Why are there different factors for protein for food and feed wheat?
Methods such as
protein determination after kjedahl ascertain the nitrogen content of a sample.
If the normal nitrogen content of the protein to be determined is known ( e.g.
from the literature), the nitrogen content found by analysis is multiplied by
the reciprocal of the known quantity in order to calculate the actual protein
content. For wheat this factor is 5.7, corresponding to 17.5% nitrogen in the
protein. For composite foods, proteins
of unknown origin and also for nutritional purposes (human and animal) the
crude protein is calculated. In this case a factor of 6.25 (corresponding to
16% nitrogen) is used. The latter is being used more and more often to avoid
confusing people who are not experts.
Since wheat
gluten, for example, is used in both food and feed, the information on the
protein content of samples from different sources may differ because different
factors has been used. A protein content of 78% (factor 5.7) would then be
equivalent to a value of 85.5% (at factor 6.25)
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