Fundamental Food Microbiology, Third Edition - Fuad Fathir

244 FUNDAMENTAL FOOD MICROBIOLOGY
IV. Conclusion ................................................................................................253
References..............................................................................................................253
Questions ..............................................................................................................254
I. INTRODUCTION
Many microbial metabolites can be used as food additives to improve nutritional
value, flavor, color, and texture. Some of these include proteins, essential amino
acids, vitamins, aroma compounds, flavor enhancers, salty peptides, peptide sweeteners,
colors, stabilizers, and organic acids. Because they are used as ingredients,
they need not come only from microorganisms used to produce fermented foods but
can be produced by many other types of microorganisms (also algae) with regulatory
approval for safety before use in foods. Many enzymes from bacteria, yeasts, molds,
as well as from plant and mammalian sources, are currently used for the processing
of foods and food ingredients. Some examples are production of high-fructose corn
syrups, extraction of juice from fruits and vegetables, and enhancement of flavor in
cheese.
Recombinant DNA technology (or biotechnology) has opened up the possibilities
of identifying and isolating genes or synthesizing genes encoding a desirable trait
from plant and animal sources, or from microorganisms that are difficult to grow
normally, clone it in a suitable vector (DNA carrier), and incorporate the recombinant
DNA in a suitable microbial host that will express the trait and produce the specific
additive or enzyme economically. In addition, metabolic engineering, by which a
desirable metabolite can be produced in large amounts by a bacterial strain, is being
used to produce food additives from new sources. The metabolites can then be
purified and used as food additives and in food processing, provided they are safe
to use generally regarded as safe (GRAS)-listed compound. Some of these aspects
involving genetic manipulations are discussed in Chapter 12. The microbiology of
the production and uses of some additives and enzymes are discussed here.
II. MICROBIAL PROTEINS AND FOOD ADDITIVES
This section discusses the different types of food additives that are and can be
produced through microorganisms. Genetic and metabolic engineering are currently
being studied to modify microorganisms that can economically produce many of
the food additives. In the future, uses of food additives from these sources will
increase. However, before they can be used in food systems, they have to be approved
by regulatory agencies.
A. Single-Cell Proteins (SCPs)
Molds, yeasts, bacteria, and algae are rich in proteins, and the digestibility of these
proteins ranges from 65 to 96%. 1,2 Proteins from yeasts, in general, have high digest-