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Cheese, koji and tempeh are all traditional solid-state fermented food products
(Rosales et al. 2018). However, in recent years solid-state fermentation by fungi
has received growing interest among researchers especially in the food industry
for enrichment of solid food with desired nutrients. Japan is one of the leading
countries that has exploited SSF in the world with large-scale production plants
(Gowthaman et al. 2001). Filamentous fungi are primarily exploited in SSF due to
their ability to tolerate low water condition. In food industries, the ability of filamentous fungi to inhibit anti-nutrients and hydrolyze a number of substrates
expands its potential to produce valuable food products from previously underutilized substrates. A number of agro-industrial wastes such as whey, wheat bran,
grape pomace and apple byproducts have shown promising results for production
of PUFA in SSF (Dulf et al. 2020). The PUFA-rich oil produced in this manner
can find application as emulsifiers, as blends with other oils or as direct food
supplements. Besides, the already edible solid food can also be enriched with
PUFA using GRAS fungi and consumed directly (Diwan and Gupta 2019).
FAOSTAT 2019 data indicate that worldwide cereals provide 50% of dietary
energy in humans (Klempová et al. 2020). However, cereals have low lipid content but a good C/N ratio ranging from 20 to 60 (Čertík et al. 2013). Therefore,
their nutritional value can be improved by fortifying them with functional lipids.
To improve PUFA production of solid substrates in SSF, mainly three different
strategies are employed:
• Gradual increase in C/N ratio by addition of a carbon source such as glucose/whey
• Optimization of physical conditions such as temperature, oxygen availability and
water activity
• Addition of exogenous oil (Sláviková and Čertik 2005)
Nitrogen is essential for fungi growth especially during stationary phase.
Organic nitrogen is a more preferred source for fungi in contrast to inorganic
nitrogen (Asadi et al. 2015). However, after a certain period, high C/N ratio
favours increased PUFA formation. GLA formation is highly elevated at a C/N
ratio of around 160 (Dulf et al. 2020). Therefore, gradual addition of different
carbon sources is preferred at different growth stages of fungi. It was reported that
glucose supplementation of 30 and 40% in SSF of cereals by M. circinelloides
CCF-2617 increased GLA yields as high as 3.5 times in comparison to control
without glucose addition (Čertík et al. 2013). In a column reactor, high temperature and low oxygen availability at the bottom of the chamber are often the most
encountered problems. A temperature in the range of 23–30 °C often promotes
fungal growth. However, lower temperatures can substantially increase PUFA
production (Asadi et al. 2015). Therefore, proper aeration and temperature maintenance are important parameters that need to be regulated for high product yield.
Spent malt grain (SMG) is often used in SSF in a substrate: SMG ratio of 3:1. It
has been found to act as an inert material highly improving the oxygen availability
in the medium. Addition of SMG has also been shown to positively correlate with
7 Production of Polyunsaturated Fatty Acids by Fungal Biofactories…
Cheese, koji and tempeh are all traditional solid-state fermented food products
(Rosales et al. 2018). However, in recent years solid-state fermentation by fungi
has received growing interest among researchers especially in the food industry
for enrichment of solid food with desired nutrients. Japan is one of the leading
countries that has exploited SSF in the world with large-scale production plants
(Gowthaman et al. 2001). Filamentous fungi are primarily exploited in SSF due to
their ability to tolerate low water condition. In food industries, the ability of filamentous fungi to inhibit anti-nutrients and hydrolyze a number of substrates
expands its potential to produce valuable food products from previously underutilized substrates. A number of agro-industrial wastes such as whey, wheat bran,
grape pomace and apple byproducts have shown promising results for production
of PUFA in SSF (Dulf et al. 2020). The PUFA-rich oil produced in this manner
can find application as emulsifiers, as blends with other oils or as direct food
supplements. Besides, the already edible solid food can also be enriched with
PUFA using GRAS fungi and consumed directly (Diwan and Gupta 2019).
FAOSTAT 2019 data indicate that worldwide cereals provide 50% of dietary
energy in humans (Klempová et al. 2020). However, cereals have low lipid content but a good C/N ratio ranging from 20 to 60 (Čertík et al. 2013). Therefore,
their nutritional value can be improved by fortifying them with functional lipids.
To improve PUFA production of solid substrates in SSF, mainly three different
strategies are employed:
• Gradual increase in C/N ratio by addition of a carbon source such as glucose/whey
• Optimization of physical conditions such as temperature, oxygen availability and
water activity
• Addition of exogenous oil (Sláviková and Čertik 2005)
Nitrogen is essential for fungi growth especially during stationary phase.
Organic nitrogen is a more preferred source for fungi in contrast to inorganic
nitrogen (Asadi et al. 2015). However, after a certain period, high C/N ratio
favours increased PUFA formation. GLA formation is highly elevated at a C/N
ratio of around 160 (Dulf et al. 2020). Therefore, gradual addition of different
carbon sources is preferred at different growth stages of fungi. It was reported that
glucose supplementation of 30 and 40% in SSF of cereals by M. circinelloides
CCF-2617 increased GLA yields as high as 3.5 times in comparison to control
without glucose addition (Čertík et al. 2013). In a column reactor, high temperature and low oxygen availability at the bottom of the chamber are often the most
encountered problems. A temperature in the range of 23–30 °C often promotes
fungal growth. However, lower temperatures can substantially increase PUFA
production (Asadi et al. 2015). Therefore, proper aeration and temperature maintenance are important parameters that need to be regulated for high product yield.
Spent malt grain (SMG) is often used in SSF in a substrate: SMG ratio of 3:1. It
has been found to act as an inert material highly improving the oxygen availability
in the medium. Addition of SMG has also been shown to positively correlate with
7 Production of Polyunsaturated Fatty Acids by Fungal Biofactories…