2009_Book_FoodChemistry

2.7 Enzyme Utilization in the Food Industry 145
additives provide a number of advantages in food
processing: exceptionally pronounced substrate
specificity (cf. 2.2.2), high reaction rate under
mild reaction conditions (temperature, pH), and
a fast and continuous, readily controlled reaction
process with generally modest operational costs
and investment. Examples for the application of
microbial enzymes in food processing are given
in Table 2.20.
Fig. 2.46. Forms of immobilized enzymes
2.7.1 Technical Enzyme Preparations
2.7.1.1 Production
The methods used for industrial-scale enzyme
isolation are outlined in principle under section
2.2.4. In contrast to the production of
highly purified enzymes for analytical use, the
production of enzymes for technical purposes
is directed to removing the interfering activities
which would be detrimental to processing and
to staying within economically acceptable costs.
Selective enzyme precipitation by changing the
ionic strength and/or pH, adsorption on inorganic
gels such as calcium phosphate gel or hydroxyl
apatite, chromatography on porous gel columns
and ultrafiltration through membranes are among
the fractionation methods commonly used. Ionexchange
chromatography, affinity chromatography
(cf. 2.2.4) and preparative electrophoresis are
relatively expensive and are seldom used. A few
temperature-stable enzymes are heat treated to
remove the other contaminating and undesired
enzyme activities.
Commercial enzyme preparations are available
with defined catalytic activity. The activity is usually
adusted by the addition of suitable inert fillers
such as salts or carbohydrates. The amount of
active enzyme is relatively low, e. g., proteinase
preparations contain 5–10% proteinase, whereas
amylase preparations used for treamtent of flour
contain only 0.1% pure fungal α-amylase.
2.7.1.2 Immobilized Enzymes
Enzymes in solution are usually used only once.
The repeated use of enzymes fixed to a carrier
is more economical. The use of enzymes in
a continous process, for example, immobilized
enzymes used in the form of a stationary phase
which fills a reaction column where the reaction
can be controlled simply by adjustment of
the flow rate, is the most advanced technique.
Immobilized enzymes are produced by various
methods (Fig. 2.46).
2.7.1.2.1 Bound Enzymes
An enzyme can be bound to a carrier by covalent
chemical linkages, or in many cases, by
physical forces such as adsorption, by charge attraction,
H-bond formation and/or hydrophobic
interactions. The covalent attachment to a carrier,
in this case an activated matrix, is usually
achieved by methods employed in peptide and
protein chemistry. First, the matrix is activated.
In the next step, the enzyme is coupled under
mild conditions to the reactive site on the matrix,
usually by reaction with a free amino group.
This is illustrated by using cellulose as a matrix
(Fig. 2.47). Another possibility is a process of
copolymerization with suitable monomers. Generally,
covalent attachment of the enzyme prevents
leaching or “bleeding”.
2.7.1.2.2 Enzyme Entrapment
An enzyme can be entrapped or enclosed in the
cavities of a polymer network by polymerization
of a monomer such as acrylamide or N,N ′ -
methylene-bis-acrylamide in the presence of
enzyme, and still remain accessible to substrate
through the network of pores. Furthermore,