presence of a thermostable α-amylase from Bacillus licheniformis (e.g. Termamyl
from Novozymes) or Bacillus amyloliquefaciens, although the B. licheniformis
enzyme is preferred due to its higher temperature stability. Furthermore, due to
the enzyme’s superior thermal stability, gelatinization and liquefaction can be
combined, whereby the enzyme is added to the starch slurry prior to gelatinization,
with a minimum adjustment of pH and calcium ion concentration in order to
accommodate the enzyme.
Liquefaction is stopped once the required dextrose equivalent (DE) value is
obtained, typically between 8 and 12. The DE value is defined as the amount of
reducing sugars in a product and often expressed as percentage on dry basis relative
to pure glucose (dextrose), with glucose having a DE of 100 and that of starch at near
zero. The maximum DE value that can be obtained by Bacillus amylases used in
this process is 40. The final stage is saccharification, which involves the production
of glucose and maltose via further enzymatic hydrolysis. This involves the use of
exo-acting enzymes such as β-amylase, pullulanase or glucoamylase. The liquefied
starch with a DE of 8–12 is pumped into a large stirred vessel and after adjusting the
pH to 4–5 and the temperature to about 60
C. The exoamylases are added to further
degrade the liquefied starch into maltodextrins and maltose or glucose syrups. For
the production of high-glucose syrup, the enzymes glucoamylase and pullulanase
are used during saccharification, while, for the production of maltose syrup, fungal
α-amylase is used at a pH of 5.5 at 55
C.
The conditions applied for liquefaction and saccharification largely depend on
the enzyme used for these processes. Several alkaliphiles have been reported to
produce thermostable, liquefying and saccharifying amylases suitable for starch
processing and have been proposed for potential application in these processes.
These include a novel liquefying α-amylase (LAMY) from the alkaliphilic
Bacillus isolate, KSM-1378 [31]; saccharifying amylase from Bacillus sp. A3-15
[27], Bacillus sp. PN-5 [28], Bacillus sp. BCC 01-50 [93], Bacillus species IMD
435 which produce glucose and maltose from both soluble starch and raw corn starch
[94] and Bacillus subtilis JS-2004 [95]; and several pullulanases that have been
reported [35–40, 96].
The baking industry is another large consumer of starch and starch-modifying
enzymes. It is one of the oldest industries to use α-amylases. These enzymes give
the baked products, such as bread, a higher volume, better colour and a softer crumb,
as they degrade the starch into smaller dextrins, thereby allowing the yeast to
continuously ferment the dough during production [10]. In addition, the small
oligosaccharides and sugars such as glucose and maltose produced by these enzymes
enhance the Maillard reactions responsible for the browning of the crust and the
development of an attractive baked flavour.
During storage of bread, the crumb becomes dry and firm, the crust loses
its crispness and the flavour of the bread deteriorates. These undesirable changes
are referred to as staling. Additives such as sugars, salts, milk powder, emulsifiers,
monoglycerides/diglycerides, sugar esters, lecithin, granulated fat and anti-oxidants
(ascorbic acid or potassium borate) have been conventionally used to prevent staling
[97]. Many starch-modifying enzymes are now used as anti-staling agents. These
234
S. O. Hashim
from Novozymes) or Bacillus amyloliquefaciens, although the B. licheniformis
enzyme is preferred due to its higher temperature stability. Furthermore, due to
the enzyme’s superior thermal stability, gelatinization and liquefaction can be
combined, whereby the enzyme is added to the starch slurry prior to gelatinization,
with a minimum adjustment of pH and calcium ion concentration in order to
accommodate the enzyme.
Liquefaction is stopped once the required dextrose equivalent (DE) value is
obtained, typically between 8 and 12. The DE value is defined as the amount of
reducing sugars in a product and often expressed as percentage on dry basis relative
to pure glucose (dextrose), with glucose having a DE of 100 and that of starch at near
zero. The maximum DE value that can be obtained by Bacillus amylases used in
this process is 40. The final stage is saccharification, which involves the production
of glucose and maltose via further enzymatic hydrolysis. This involves the use of
exo-acting enzymes such as β-amylase, pullulanase or glucoamylase. The liquefied
starch with a DE of 8–12 is pumped into a large stirred vessel and after adjusting the
pH to 4–5 and the temperature to about 60
C. The exoamylases are added to further
degrade the liquefied starch into maltodextrins and maltose or glucose syrups. For
the production of high-glucose syrup, the enzymes glucoamylase and pullulanase
are used during saccharification, while, for the production of maltose syrup, fungal
α-amylase is used at a pH of 5.5 at 55
C.
The conditions applied for liquefaction and saccharification largely depend on
the enzyme used for these processes. Several alkaliphiles have been reported to
produce thermostable, liquefying and saccharifying amylases suitable for starch
processing and have been proposed for potential application in these processes.
These include a novel liquefying α-amylase (LAMY) from the alkaliphilic
Bacillus isolate, KSM-1378 [31]; saccharifying amylase from Bacillus sp. A3-15
[27], Bacillus sp. PN-5 [28], Bacillus sp. BCC 01-50 [93], Bacillus species IMD
435 which produce glucose and maltose from both soluble starch and raw corn starch
[94] and Bacillus subtilis JS-2004 [95]; and several pullulanases that have been
reported [35–40, 96].
The baking industry is another large consumer of starch and starch-modifying
enzymes. It is one of the oldest industries to use α-amylases. These enzymes give
the baked products, such as bread, a higher volume, better colour and a softer crumb,
as they degrade the starch into smaller dextrins, thereby allowing the yeast to
continuously ferment the dough during production [10]. In addition, the small
oligosaccharides and sugars such as glucose and maltose produced by these enzymes
enhance the Maillard reactions responsible for the browning of the crust and the
development of an attractive baked flavour.
During storage of bread, the crumb becomes dry and firm, the crust loses
its crispness and the flavour of the bread deteriorates. These undesirable changes
are referred to as staling. Additives such as sugars, salts, milk powder, emulsifiers,
monoglycerides/diglycerides, sugar esters, lecithin, granulated fat and anti-oxidants
(ascorbic acid or potassium borate) have been conventionally used to prevent staling
[97]. Many starch-modifying enzymes are now used as anti-staling agents. These
234
S. O. Hashim