Chemistry Reference
In-Depth Information
Table 9.2
Activity dependence of
α
-amylases on temperature and pH.
α
-Amylase source
Cereal (malt)
Bacteria
Moulds
pH range
4.5-8.5
4.8-7.5
4.3-6.0
pH-optimum
5.0-5.6
5.3-6.5
4.5-5.5
70-80
◦
C
65-95
◦
C
45-60
◦
C
Temperature range
Approx. 75
◦
C
Approx. 70
◦
C
Approx. 55
◦
C
Optimum temperature
the generated maltose blocks the effect of
α
-amylase. Only when the maltose fermentation
starts, the
-amylase will continue to saccharify virtually all the remaining dextrins.
Kreipe
5
referred to the importance of
α
α
-amylases for the saccharification within distillery
companies.
It is remarkable that various
-amylases differ substantially in their activity relative to
temperature and pH-value. The average values of the most important technical
α
α
-amylases
are shown in Table 9.2.
Although the pH activity dependences of the various amylases are relatively unimportant,
major differences are found in temperature dependences. The temperature optimum of fungal
α
-amylase is approximately 20
◦
C below that of bacterial
-amylases. This has to be regarded
in practical applications. Observations by Underkofler and Hickey
25
α
showed that bacterial
α
-amylases produce dextrins faster than fungal amylases.
As demonstrated by Aschengreen,
7
the presence of calcium-ions (Ca
++
) is required for
the adequate effectiveness and stability of microbial
-amylases. This finding led to the
addition of defined doses of calcium salts especially in potato processing.
Furthermore, the pH-optimum of the first technical
α
-amylases was quite high (around 6).
Therefore the pH of the mashes had to be raised in most cases. To meet both demands of pH
and Ca
++
requirement, lime hydrate Ca(OH)
2
was applied successfully.
Technical bacterial
α
-amylases that show high activity without the need for adding calcium
are nowadays available for distilleries. Furthermore, these enzymes are optimally suited
because of their complete effectiveness at pH-values up to 5.0 and at temperatures up to
90
◦
C. They also secure a flawless liquefaction of potato mashes. This can be achieved
without the addition of calcium, assuming that the amount of existing calcium present in
potatoes is sufficient to ensure the full effect of these
α
-amylases.
Extensive formation of maltose is a characteristic of fungal
α
-amylases from
A. oryzae
-
and this is obviously beneficial for the fermentation processes in a distillery. With the help
of these amylases the fermentation period can be reduced to 34 h, even in potato mashes.
Furthermore it appears that upon fermenting wheat mashes, there is a lower tendency to form
a solid top layer when fungal
α
-amylases are used for starch reduction. However, a faultless
degradation of starch during the steaming process is an absolute requirement.
α
9.1.1.2
β
-Amylase
β-Amylase (
-1,4-glucane-maltohydrolase) is characterized by an extremely slow viscosity
reduction and a high capability of sugar formation; that is this enzyme shows a weak
liquefying but a strong 'sugaring' effect. Hence it is declared as saccharogen-amylase. Out
of the two components of natural starch (amylose and amylopectin), β-amylases degrade
the 1,4-glucosidic linear chain of amylose - as exo-enzyme - from the non-reducing end
completely. On the other hand, amylopectin is only incompletely degraded into maltose. The
α
