Fundamental Food Microbiology, Third Edition - Fuad Fathir

248 FUNDAMENTAL FOOD MICROBIOLOGY
III. MICROBIAL ENZYMES IN FOOD PROCESSING
Many enzymes are used in the processing of food and food additives. 7,8 About 80%
of the total enzymes produced, on a dollar basis, is used by the food industries. Use
of specific enzymes instead of microorganisms has several advantages. A specific
substrate can be converted into a specific product by an enzyme through a singlestep
reaction. Thus, production of different metabolites by live cells from the same
substrate can be avoided. In addition, a reaction step can be controlled and enhanced
more easily by using purified enzymes. Finally, by using recombinant DNA technology,
the efficiency of enzymes can be improved and, by immobilizing, they can
be recycled. The main disadvantage of using enzymes is that if a substrate is
converted to a product through many steps (such as glucose to lactic acid), microbial
cells must be used for their efficient and economical production.
A. Enzymes Used
Among the five classes of enzymes, three are predominantly used in food processing:
hydrolases (hydrolyze C–C, C–O, C–N, etc., bonds), isomerases (isomerization and
racemization), and oxidoreductases (oxygenation or hydrogenation). Some of these
are listed in Table 17.1 and their uses are discussed here. 7
1. aaaa-Amylase, Glucoamylase, and Glucose Isomerase
Together, these three enzymes are used to produce high-fructose corn syrup from
starch. a-Amylase hydrolyzes starch at a-1 position randomly and produces oligosaccharides
(containing three hexose units or more, e.g., dextrins). Glucoamylase
hydrolyzes dextrins to glucose units, which are then converted to fructose by glucose
isomerase.
a-Amylase is also used in bread-making to slow down staling (starch crystallization
due to loss of water). Partial hydrolysis of starch by a-amylase can help
reduce the water loss and extend the shelf life of bread.
2. Catalase
Raw milk and liquid eggs can be preserved with H 2O 2 before pasteurization. However,
the H 2O 2 needs to be hydrolyzed by adding catalase before heat processing of
the products.
3. Cellulase, Hemicellulase, and Pectinase
Because of their ability to hydrolyze respective substrates, the use of these enzymes
in citrus juice extraction has increased juice yield. Normally, these insoluble polysaccharides
trap juice during pressing. Also, they get into the juice and increase viscosity,
causing problems during juice concentration. They also cloud the juice. By
using these hydrolyzing enzymes, such problems can be reduced.