Flour Treatment : Enzymes
1. Amylases
1.1. Enzyme-Active Malt Flour
Like all other living material, grain needs enzymes for its vital
functions. As it does not come back to life, so to speak, until germination,
this is the phase when enzymes are produced in large quantities. Bakers have
long put this characteristic to use by germinating cereals before processing
them further.
Malt flour is the dried product made from germinated barley, wheat or
rye. The functions of the three of them are largely identical. Malt flour contains
primarily α- and β-amylase, but it also contains protease, glucanase and many
other enzymes. Some of these may have a positive effect on the baking process
(amylases and glucanases), but some can also cause damage (proteases). Like the
flour's own amylases, the amylase of the malt flour has a pronounced effect on
the Falling Number. If this is very high (i.e., the flour's own enzymatic
activity is very low), anything up to 150 g or more of malt flour to 100 kg of
flour may be needed to bring the Falling Number into the range of 250 - 300 s.
With Falling Numbers around 300 s, no more than 50 g should be added, or the
doughs will become too sticky. The activity of malt flours is often expressed
in DP for diastatic power (or DU for diastatic units) and is usually about 400
DP. Occasionally it is stated in SKB/g (see below) and is in the range of 80 -
120.
1.2. Fungal Amylase
Moulds of the genus Aspergillus are often used in the production of
enzyme preparations for applications in food as this genus includes numerous
well-described strains that do not produce any toxins as by-products which
might find their way into the finished product. In large fermentation equipment
the moulds are made to produce amylase and give it off into their environment
(the culture medium) as far as possible. A multi-stage purification and
separation process (including centrifugation, precipitation, filtration and
ultrafiltration; Fig. 118) then results in a crude enzyme concentrate that is
usually spray-dried to form a powder with a good shelf-life. Various carriers –
mainly maltodextrin, starch or flour – are added to make the substance more
convenient to use at the mill with regard to dosing and flow properties.
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| Fig. 118: Flow diagram of microbial enzyme production |
Fungal amylase is usually α-amylase. Most side activities can be eliminated
by strain selection and in the production process. In contrast to the cereal
amylase in malt flour, it has only a very slight effect on the Falling Number
since it reacts more sensitively than cereal amylase to the high temperatures
at which the Falling Number is determined and is inactivated before it can
break down the starch gel. Fungal amylase can be detected with a modified
Falling Number method at a lower maximum temperature.
The dosage of α-amylase depends on its concentration, or more precisely
its activity. The usual international unit is SKB per gram, named after
Sandstedt, Kneen and Blish who developed the determination method (Sandstedt et
al., 1939). Many manufacturers do in fact use the units from their own assays,
but they can usually express them in terms of SKB/g if wished. A typical dose
for a wheat flour that is neither sprout-damaged nor treated with malt flour is
500 SKB per kg flour (i.e. 10 g of an amylase with 5,000 SKB/g to 100 kg of
flour). But even in the case of flours with a very low Falling Number it is
sometimes useful to add small amounts of fungal amylase (1 - 2 g at 5,000
SKB/g) as this slightly improves the properties of the dough and results of the
baking process without affecting the Falling Numbers. Values above 400 s
indicate a low endogenous enzyme content of the flour requiring a higher dosage
of fungal amylase, e.g. 30 g of a 5,000 SKB preparation or even more.
1.3. Amyloglucosidase
Amyloglucosidase (AMG; also called glucoamylase, sometimes referred to
as γ-amylase in the past) is a natural side activity of many amylase
preparations, but it can also be obtained in a purer form from specialised
Aspergillus strains. AMG breaks down starch into its smallest sub-units, namely
glucose, and in contrast to α-amylase it does not stop at the branching points
of amylopectin. However, it would take a very long time to reduce viscosity
through the effect of AMG alone, as the enzyme only acts on the starch from one
end (chemically called the reducing end) and only splits off a single glucose
molecule at a time. This means that the main significance of AMG lies in
browning and in maintaining the fermentation process over an extended period
(controlled fermentation). As it always occurs in conjunction with α-amylase,
AMG is usually dosed in very small amounts (less than 0.1 g to 100 kg), unless
the purpose of its use is to replace sugar.
