2009_Book_FoodChemistry

2.7 Enzyme Utilization in the Food Industry 149
2.7.2 Individual Enzymes
2.7.2.1 Oxidoreductases
Broader applications for the processing industry,
besides the familiar use of glucose oxidase, are
found primarily for catalase and lipoxygenase,
among the many enzymes of this group. A number
of oxidoreductases have been suggested or
are in the experimental stage of utilization, particularly
for aroma improvement (examples under
2.7.2.1.4 and 2.7.2.1.5).
2.7.2.1.1 Glucose Oxidase
The enzyme produced by fungi such as Aspergillus
niger and Penicillium notatum catalyzes
glucose oxidation by consuming oxygen from
the air. Hence, it is used for the removal of
either glucose or oxygen (Table 2.20). The H 2 O 2
formed in the reaction is occasionally used as an
oxidizing agent (cf. 10.1.2.7.2), but it is usually
degraded by catalase.
Removal of glucose during the production of egg
powder using glucose oxidase (cf. 11.4.3) prevents
the Maillard reaction responsible for discoloration
of the product and deterioration of its
whippability. Similar use of glucose oxidase for
some meat and protein products would enhance
the golden-yellow color rather than the brown
color of potato chips or French fries which is obtained
in the presence of excess glucose.
Removal of oxygen from a sealed package system
results in suppression of fat oxidation and oxidative
degradation of natural pigments. For example,
the color change of crabs and shrimp from
pink to yellow is hindered by dipping them into
a glucose oxidase/catalase solution. The shelf life
of citrus fruit juices, beer and wine can be prolonged
with such enzyme combinations since the
oxidative reactions which lead to aroma deterioration
are retarded.
2.7.2.1.2 Catalase
The enzyme isolated from microorganisms is important
as an auxiliary enzyme for the decomposition
of H 2 O 2 :
(2.108)
Hydrogen peroxide is a by-product in the treatment
of food with glucose oxidase. It is added to
food in some specific canning procedures. An example
is the pasteurization of milk with H 2 O 2 ,
which is important when the thermal process is
shut down by technical problems. Milk thus stabilized
is also suitable for cheesemaking since the
sensitive casein system is spared from heat damage.
The excess H 2 O 2 is then eliminated by catalase.
2.7.2.1.3 Lipoxygenase
The properties of this enzyme are described under
section 3.7.2.2 and its utilization in the bleaching
of flour and the improvement of the rheological
properties of dough is covered under section
15.4.1.4.3.
2.7.2.1.4 Aldehyde Dehydrogenase
During soya processing, volatile degradation
compounds (hexanal, etc.) with a “bean-like”
aroma defect are formed because of the enzymatic
oxidation of unsaturated fatty acids. These
defects can be eliminated by the enzymatic
oxidation of the resultant aldehydes to carboxylic
acids. Since the flavor threshold values of
these acids are high, the acids generated do not
interfere with the aroma improvement process.
(2.109)
Of the various aldehyde dehydrogenases, the
enzyme from beef liver mitochondria has
a particularly high affinity for n-hexanal (Table
2.21). Hence its utilization in the production
of soya milk is recommended.
2.7.2.1.5 Butanediol Dehydrogenase
Diacetyl formed during the fermentation of beer
can be a cause of a flavor defect. The enzyme
from Aerobacter aerogenes, for example, is able
to correct this defect by reducing the diketone to
the flavorless 2,3-butanediol:
(2.110)