This document discusses solid state fermentation and provides details about the process. It describes that solid state fermentation involves fermentation using solids in the absence of free water, though some moisture is needed. Microorganisms like fungi grow on the surface of solid substrates to produce things like enzymes, organic acids, and flavors. Agriculture wastes are commonly used as substrates. Fungi like Trichoderma and Aspergillus species are widely used to produce hydrolytic enzymes. Tray fermenters and rotating drum reactors are two common types of bioreactors used in solid state fermentation.

1. Solid state fermentation

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3.  Solid-state fermentation (SSF) is defined as fermentation using
solids in the absence (or near absence) of free water.
 But the presence of moisture (About 15%) is necessary for solid
substrate fermentation.
 Microorganisms, most commonly filamentous fungi, grow on the
surface of solid substrates.

4.  SSF has been used to produce edible mushrooms, cheese,
enzymes and organic acids and flavours.
 SSF also used to produce bio-fuels, industrial chemicals,
Antibiotics and many other biological products.
 SSF is normally carried out as a non aseptic process. This saves
sterilization costs.

5. Substrates used for the production of enzymes in SSF systems:
 Agriculture wastages are generally considered the best substrates for the SSF
processes.
 A number of such substrates have been employed for the cultivation of
microorganisms to the production of enzymes.

6.  Wheat bran, rice bran, wheat straw, rice straw, rice husk, wheat
flour, starch and Food wastage also used as substrates for SSF.
 Most of these compounds are polymeric molecules – insoluble in
water – but most are cheap and easily obtainable and source of
nutrients for microbial growth.

7. Microorganisms used for the production of enzymes on solid state
fermentation systems:
 Generally, hydrolytic enzymes, e.g., proteases, cellulases
pectinases, etc. are produced by fungal cultures.
 Trichoderma spp. and Aspergillus spp. have most widely been used
for these enzymes.
 Amylase enzymes too are commonly produced by filamentous
fungi (Aspergillus and Rhizopus)

8. Bioreactors used in SSF:
 Most SSF processes are batch fermentations.
 Some processes do not require reactors and require spreading of
substrate on a suitable floor surface.
 Bioreactor designs for SSF are simpler than for liquid cultivations.
 Bioreactor classified into two types in SSF, Bioreactor without
agitation (tray systems) and with continuous agitation (slow
rotating drums).

9. Tray fermenters:
 Tray fermenters: used extensively for the production of fermented
foods and enzymes in SSF.
 Trays hold layers of substrate 3.5-5 cm deep and are stacked in
chambers usually force aerated with humidified air.

10. Rotating drum reactors:
 Usually Rotating drum reactors consists of cylindrical drum
mounted to rollers that support and rotate the drum.
 They are equipped with an inlet and outlet for circulation of
humidified air and often contain baffles to agitate the contents.
 They are used in enzyme and microbial biomass production.
 Their main disadvantage is that the drum is not filled to capacity
(only 30% capacity) other wise mixing is inefficient.

11. Advantages of SSF:
 Low moisture content of the substrates allow for minimal
contamination.
 Less operational cost of the reactors.
 Product separation is easy
 Low cost media.
 No problems with foaming.
 Low waste water output.

12. Disadvantages of SSF:
 Substrate moisture level is difficult to control.
 Precise monitoring of pH, temperature and dissolved oxygen not
possible.
 Continuous mixing or agitation of the medium is required to
overcome control parameters.
 Continuous agitation of the medium often damages the mycelia,
retarding their growth and resulting in poor growth of the
organisms.

13. Submerged fermentation

14.  Submerged fermentation is the cultivation of microorganisms in
liquid nutrient broth.
 This involves growing carefully selected microorganisms
(bacteria and fungi) in closed bioreactors containing a rich broth of
nutrients (the fermentation medium).
 Submerged fermentation is a method for synthesis of alcohols,
organic solvents biofuels, recombinant vaccines and probiotics.

16.  Submerged fermentation is a process involving the development of
microorganisms in a liquid broth.
 This liquid broth contains nutrients and it results in the
production of industrial enzymes, antibiotics and other products.

17. There are three common methods by which submerged
fermentation takes place;
They are
1) Batch fermentation,
2) Fed batch fermentation
3) Continuous fermentation.

18.  In Fed bacth fermentation sterilised growth nutrients are added
to a culture. It is most common in bio-industries.
 In continuous fermentation the sterilised liquid nutrients are
slowly and continuously added to the bioreactor at the same
rate the products recovered from the system.

19.  An open system is constructed for continuous fermentation.
 This results in a steady-rate production of the fermentation broth.
Continuous fermentation

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