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.

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.


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