As a rule, the traditional foods prepared by SSF do not produce an overall
enrichment of protein levels in the substrate. In fact, in substrates of higher
protein content, such as soya beans, there may be an overall loss of nutrients,
although these fermentation processes may enrich specific nutrients, improve
digestibility, destroy toxins or reduce toxicity, change the organic nitrogen
content, and cause favorable changes in taste [1]. However, with substrates comprised predominantly of starch, an overall enrichment of protein content is
possible. Cassava, a low protein staple root crop, can be fermented in SSF to produce a food of higher protein content. This result can be of great value to
nations whose people suffer from protein deficiency [6].
The traditional koji process may be considered the archetype of SSF. Koji is a
generic Japanese name for starters used in a variety of fermentations; its
functional importance lies in its high content of various amylolytic and proteolytic enzymes which can catalyze the degradation of starches and proteins to
soluble products capable of subsequent fermentation by yeasts or bacteria. A
variety of raw materials are used in the production of kojis but, typically,
steamed rice is inoculated with spores of an Aspergillus oryzae strain and incubated under carefully controlled conditions of temperature and humidity [7].
The introduction of the koji process to the West is chiefly due to the work of
Takamine, which started in 1891 in the USA using wheat bran to make the
preparation named Taka-Koji. Takamine introduced the technique of acclimatizing the mold to various antiseptics in order to minimize growth of contaminants during the process. The process was carried out on an industrial
scale in rotating drum bioreactors. Large scale trials of the use of Taka-Koji
instead of malt in distilleries were carried out in the plant of Hiram Walker &
Sons in Ontario Canada in 1913. This was marketed as a digestive aid under the
name of Takadiastase [8].
Solid-state fermentation has also been traditionally carried out in the West,
such as in the production of blue-veined cheese with Penicillium roqueforti, in
which the mycelium develops throughout the cheese, and of Camembert and
Brie in which molds such as Penicillium camemberti and Penicillium caseicolum
grow on the surface of the cheese [9]. There are also the classical processes of
ensiling, an anaerobic SSF process involving the lactic acid fermentation of
agricultural products at 25–40% dry matter and ambient temperatures of
25–30 °C, and composting, a thermophilic SSF which involves growth of a
succession of microorganisms on agricultural byproducts, starting with mesophiles and followed by thermophilic bacteria, actinomycetes, and fungi [10].
In the last two to three decades there has been a rapid growth of interest in
using SSF for the production of various bioproducts such as enzymes, organic
acids, ethanol, biogas, antibiotics, surfactants, toxins, bioremediation agents,
mushrooms, composts, microbial polysaccharides, biopesticides, proteinenriched fermented foods, pre-digested feeds for ruminants, reduced-toxicity
feedstuffs, and variants of traditional fermented foods. Applications of SSF have
been reviewed elsewhere [11] and therefore are not discussed here; however, a
selection of current research into products and processes involving SSF is given
in Table 2 [12–63]. Within these products there are many instances where the
product produced in SSF is superior to that produced in SLF. For example,
68
D.A. Mitchell et al.
enrichment of protein levels in the substrate. In fact, in substrates of higher
protein content, such as soya beans, there may be an overall loss of nutrients,
although these fermentation processes may enrich specific nutrients, improve
digestibility, destroy toxins or reduce toxicity, change the organic nitrogen
content, and cause favorable changes in taste [1]. However, with substrates comprised predominantly of starch, an overall enrichment of protein content is
possible. Cassava, a low protein staple root crop, can be fermented in SSF to produce a food of higher protein content. This result can be of great value to
nations whose people suffer from protein deficiency [6].
The traditional koji process may be considered the archetype of SSF. Koji is a
generic Japanese name for starters used in a variety of fermentations; its
functional importance lies in its high content of various amylolytic and proteolytic enzymes which can catalyze the degradation of starches and proteins to
soluble products capable of subsequent fermentation by yeasts or bacteria. A
variety of raw materials are used in the production of kojis but, typically,
steamed rice is inoculated with spores of an Aspergillus oryzae strain and incubated under carefully controlled conditions of temperature and humidity [7].
The introduction of the koji process to the West is chiefly due to the work of
Takamine, which started in 1891 in the USA using wheat bran to make the
preparation named Taka-Koji. Takamine introduced the technique of acclimatizing the mold to various antiseptics in order to minimize growth of contaminants during the process. The process was carried out on an industrial
scale in rotating drum bioreactors. Large scale trials of the use of Taka-Koji
instead of malt in distilleries were carried out in the plant of Hiram Walker &
Sons in Ontario Canada in 1913. This was marketed as a digestive aid under the
name of Takadiastase [8].
Solid-state fermentation has also been traditionally carried out in the West,
such as in the production of blue-veined cheese with Penicillium roqueforti, in
which the mycelium develops throughout the cheese, and of Camembert and
Brie in which molds such as Penicillium camemberti and Penicillium caseicolum
grow on the surface of the cheese [9]. There are also the classical processes of
ensiling, an anaerobic SSF process involving the lactic acid fermentation of
agricultural products at 25–40% dry matter and ambient temperatures of
25–30 °C, and composting, a thermophilic SSF which involves growth of a
succession of microorganisms on agricultural byproducts, starting with mesophiles and followed by thermophilic bacteria, actinomycetes, and fungi [10].
In the last two to three decades there has been a rapid growth of interest in
using SSF for the production of various bioproducts such as enzymes, organic
acids, ethanol, biogas, antibiotics, surfactants, toxins, bioremediation agents,
mushrooms, composts, microbial polysaccharides, biopesticides, proteinenriched fermented foods, pre-digested feeds for ruminants, reduced-toxicity
feedstuffs, and variants of traditional fermented foods. Applications of SSF have
been reviewed elsewhere [11] and therefore are not discussed here; however, a
selection of current research into products and processes involving SSF is given
in Table 2 [12–63]. Within these products there are many instances where the
product produced in SSF is superior to that produced in SLF. For example,
68
D.A. Mitchell et al.