solid substrate fermentation

Solid substrate fermentation


Definition- Solid substrate fermentation used for cultivation of micro-organisms on solid substrate containing no or limited amount of water.

Used in oriental fermentations, fungal enzyme production by surface culture, mushroom production

Substrate used-
 Wheat bran
 cereal grains
 legume seeds
 wood and straw.

Types of Microorganisms grow –

Microorganisms, which grow well in solid substrate fermentation, are usually those which can tolerate a low water activity (Aw).

Micro-organisms respond differently to water activity. By reducing water activity (aw) 0.95 bacterial growth is inhibited. Fungi and yeast can grow at a water activity of 0.70 Solid substrate fermentation take different forms depending upon micro-organisms used are indigenous or pure isolated culture.

Examples:

• Composting for mushroom production involves successive activities of range of indigenous micro-organisms from mesophilic bacteria, yeasts and moulds through to thermophilic fungi and actinomycetes.
• The traditional koji process for fermentation of grains and soya beans and similar processes for production of mould industrial enzymes both using culture of Aspergillus oryzae and related species involving pure culture

Conditions suitable for Solid substrate fermentation:

• Micro-organisms industrial Solid substrate fermentation are aerobic, fermentation conditions must be designed to promote efficient transfer of oxygen and CO2 removal from substrate medium.
• Because of high concentrations of substrate per unit volume heat generation during fermentation is usually much higher p per unit volume than in liquid fermentations and low moisture content makes heat removal difficult.
• Choice of substrate particle size is of critical importance in order to minimize inter particle void spaces to facilitate gas and heat transfer. Heat removal can be facilitated by increasing aeration rate of system.

Advantages:

• Superior productivity
• Simpler technique
• Low capital investment
• Reduced energy requirement
• Low waste water output
• Lack of foam problems

Limitations:

• Heat build up
• Bacterial contamination
• Problem of scale up
• Difficulty of controlling substrate moisture level

Examples of design:

Slow continuous agitation system such as-

• rotating drums,
• tray systems and
• air flow systems

where conditioned air is blown through substrate bed in a cultivation chamber.

Rotating drums are usually equipped with an inlet and outlet for circulation of humidified air and often contain baffles or sections to agitate the contents.

Tray fermenters holding 1-2 inch deep layers of substrate are stacked in chambers usually force aerated with humidified air.

In force air cultivation chamber, bed temperature is monitored and the appropriate temperature adjustment is made to the recycling air flow.