172 ◾ Fundamental Food Microbiology
Controlled Fermentation
The starting materials (may be heat treated) are inoculated with a high population (10 6 cells/mL
or more) of a pure culture of single or mixed strains or species of microorganisms (starter culture).
Incubation conditions are set for the optimum growth of the starter cultures. Large volumes of
products can be produced with consistent and predictable characteristics each day. Generally,
there is less chance of product failure and foodborne diseases. However, there may be no growth of
desirable secondary flora. As a result, a product may not have some delicate flavor characteristics.
As indicated before, worldwide there are more than 3500 types of fermented foods. Different
methods have been used to arrange them in several major groups. One such method divides fermented foods in nine groups and is presented in Table 15.1.
As it is beyond the scope of this textbook to describe even a few from each group, only the
microbiological criteria of several fermented dairy, meat, and vegetable products are briefly discussed here to understand the methods involved in controlled and natural fermentation. For more
detailed information, books on fermentation of different food groups can be consulted, some of
which have been used as references in this chapter.
Fermented Dairy Products
Fermented dairy products can be broadly divided into two groups: fermented milk products and
cheeses. In fermented milk products, all the constituents of the milk are retained in the final products with the exception of those partially metabolized by the bacteria. In cheeses, a large portion
of the milk constituents is removed in whey to obtain the final products.
Milk Composition and Quality
The growth of desirable microorganisms and the quality of a fermented dairy product are influenced by the composition and quality of the milk used in a fermentation process. Cow’s milk contains approximately 3.2% protein, 4.8% lactose, 3.9% lipids, 0.9% minerals, traces of vitamins,
and approximately 87.2% water. Among the proteins, casein in colloidal suspension as calcium
caseinate is present in higher amounts than the other two soluble proteins, albumin and globulin.
Lactose is the main carbohydrate and is present in solution, and lipids are dispersed as globules
of different sizes in emulsion (fat in water). Minerals are present in solution and as colloid with
casein. Water-soluble vitamins are present in the aqueous phase, whereas fat-soluble vitamins are
present with the lipids. The solid components (ca. 12.8%) are designated as total solids (TS), and
TS without lipids are designated as solid-not-fat (SNF; ca. 8.9%). The whey contains principally
the water-soluble components, some fat, and water.
The growth of desirable microorganisms can be adversely affected by several components that
are either naturally present or have entered in the milk as contaminants. The natural antimicrobials are agglutinins and the lactoperoxidase-isothiocynate system. The agglutinins can induce
clumping of starter-culture cells and slow their growth and metabolism. The lactoperoxidaseisothiocynate system can inhibit starter cultures. Antimicrobials can cause problems only when
raw milk is used because both are destroyed by heating milk. Milk can also contain antibiotics,
either used in the feed or used to treat animals for some infections, such as mastitis. Their presence
can also affect the growth of starter cultures. Some milk can contain heat-stable proteases and
lipases produced by some psychrotropic bacteria, such as Pseudomonas species, during refrigerated
Controlled Fermentation
The starting materials (may be heat treated) are inoculated with a high population (10 6 cells/mL
or more) of a pure culture of single or mixed strains or species of microorganisms (starter culture).
Incubation conditions are set for the optimum growth of the starter cultures. Large volumes of
products can be produced with consistent and predictable characteristics each day. Generally,
there is less chance of product failure and foodborne diseases. However, there may be no growth of
desirable secondary flora. As a result, a product may not have some delicate flavor characteristics.
As indicated before, worldwide there are more than 3500 types of fermented foods. Different
methods have been used to arrange them in several major groups. One such method divides fermented foods in nine groups and is presented in Table 15.1.
As it is beyond the scope of this textbook to describe even a few from each group, only the
microbiological criteria of several fermented dairy, meat, and vegetable products are briefly discussed here to understand the methods involved in controlled and natural fermentation. For more
detailed information, books on fermentation of different food groups can be consulted, some of
which have been used as references in this chapter.
Fermented Dairy Products
Fermented dairy products can be broadly divided into two groups: fermented milk products and
cheeses. In fermented milk products, all the constituents of the milk are retained in the final products with the exception of those partially metabolized by the bacteria. In cheeses, a large portion
of the milk constituents is removed in whey to obtain the final products.
Milk Composition and Quality
The growth of desirable microorganisms and the quality of a fermented dairy product are influenced by the composition and quality of the milk used in a fermentation process. Cow’s milk contains approximately 3.2% protein, 4.8% lactose, 3.9% lipids, 0.9% minerals, traces of vitamins,
and approximately 87.2% water. Among the proteins, casein in colloidal suspension as calcium
caseinate is present in higher amounts than the other two soluble proteins, albumin and globulin.
Lactose is the main carbohydrate and is present in solution, and lipids are dispersed as globules
of different sizes in emulsion (fat in water). Minerals are present in solution and as colloid with
casein. Water-soluble vitamins are present in the aqueous phase, whereas fat-soluble vitamins are
present with the lipids. The solid components (ca. 12.8%) are designated as total solids (TS), and
TS without lipids are designated as solid-not-fat (SNF; ca. 8.9%). The whey contains principally
the water-soluble components, some fat, and water.
The growth of desirable microorganisms can be adversely affected by several components that
are either naturally present or have entered in the milk as contaminants. The natural antimicrobials are agglutinins and the lactoperoxidase-isothiocynate system. The agglutinins can induce
clumping of starter-culture cells and slow their growth and metabolism. The lactoperoxidaseisothiocynate system can inhibit starter cultures. Antimicrobials can cause problems only when
raw milk is used because both are destroyed by heating milk. Milk can also contain antibiotics,
either used in the feed or used to treat animals for some infections, such as mastitis. Their presence
can also affect the growth of starter cultures. Some milk can contain heat-stable proteases and
lipases produced by some psychrotropic bacteria, such as Pseudomonas species, during refrigerated