Continuous Cultivation - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 649

TABLE 12.5 Some Traditional Food Fermentations

Thermal processing Incubation

Initial
moisture,
%

Primary
genus

Common
substrate

Temperature,
C

Time,
min

Time,
h

Temperature,
C

Further
processing Product

Soy sauce Aspergillus Soybean,

wheat

110 30 45 72 30 Yes

Miso Aspergillus Rice,

soybean

100 40 35 44 30 Yes

Tempeh Rhizopus Soybean 100 30 40 22 32 No

Hamanatto Aspergillus Soybean,

wheat

36 Yes

Actinomucor

Sufu Tofu 100 10 74 15 Yes

the primary stage is an aerobic, fungal, solid-state fermentation of grains called the koji . The
second stage is an anaerobic SmF with a mixed bacterial culture called the moromi . The
moromi process may be realized by using the natural flora, or, usually, with externally added
bacteria and yeasts.
Some strains of Saccharomyces , Torulopsis , and Pediococcus are used as flavor producers in
soy sauce manufacture. The moromi is usually fermented for 8 e 12 months. However, the
processing time can be reduced to 6 months by temperature profiling. The final product is
pressed to recover the liquid soy sauce and is pasteurized, filtered, and bottled.
The major industrial use of the koji process is for the production of enzymes by fungal
species. Fungal amylases are produced by SSF of wheat bran by Aspergillus oryzae in a rotating
drum fermentor. Wheat bran is pretreated with formaldehyde, and the initial pH of the bran
is adjusted to pH

3.5 e 4.0 to reduce the chance of contamination. Usually, perforated pans,
rotating drums, or packed beds with air ventilation are used. Enzymes other than amylases,
such as cellulase, pectinase, protease, and lipases, can be produced by rotary drum fermen-
tations. Trichoderma viride species have been used for the production of cellulases from wheat
bran in a rotary tray fermentor.
Some secondary metabolites, such as antibacterial agents, are produced by Rhizopus and
Actinomucor species in some koji processes. Certain mycotoxins, such as aflatoxins, were
produced by SSF of rice (40% moisture) by Aspergillus parasiticus . Ochratoxins were also
produced by Aspergillus species on wheat in a rotary drum fermentor. Microbial degradation
of lignocellulosics can also be accomplished by solid-state fermentations for waste treatment
purposes or in biopulping of wood chips for use in paper manufacture. Spores from some
molds have found use as insecticides. Proper spore formation is difficult to obtain in
submerged culture, and SSF must be used.
Major process variables in SSF systems are moisture content (water activity), inoculum
density, temperature, pH, particle size, and aeration/agitation. Optimization of these param-
eters to maximize product yield and rate of product formation is the key in SSF systems and

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