Production of dextran by fermentation

 The production of dextran by fermentation involves several steps, which include the selection of microorganisms, fermentation, recovery, and purification. Here’s a breakdown of the process:

1. Selection of Microorganisms

• Microorganism Used: Dextran is primarily produced by certain strains of Leuconostoc mesenteroides or Streptococcus mutans, which are lactic acid bacteria. These microorganisms synthesize dextran from sucrose.
• Substrate: Sucrose is the main substrate used for dextran production since the enzyme dextransucrase converts sucrose into dextran.

2. Inoculum Preparation

• Culture Development: The microorganism is first cultured in a suitable growth medium containing sucrose as the carbon source. The inoculum preparation is done in a sterile environment to ensure purity.
• Growth Medium: The medium typically contains sucrose, peptone, yeast extract, and other nutrients required for bacterial growth.

3. Fermentation Process

• Batch or Continuous Fermentation: The fermentation is carried out in either batch or continuous fermenters. For industrial production, large bioreactors are used.
• Fermentation Conditions: Conditions such as pH, temperature (usually around 25–30°C), and oxygen levels are controlled to optimize the activity of dextransucrase and maximize dextran yield.
• Enzyme Activity: Dextransucrase, produced by the bacteria, converts sucrose into dextran while releasing fructose as a by-product.

4. Dextran Recovery

• Broth Clarification: After fermentation, the culture broth containing dextran is filtered or centrifuged to remove bacterial cells and other solid impurities.
• Alcohol Precipitation: Dextran is precipitated by adding alcohol (typically ethanol or isopropanol) to the culture broth. Dextran forms a gel-like substance that can be separated from the liquid.
• Washing: The precipitated dextran is washed with alcohol to remove impurities like sugars, proteins, and salts.

5. Purification

• Dissolution: The crude dextran is dissolved in water and may undergo additional filtration to remove any remaining contaminants.
• Purification Techniques: Techniques such as ultrafiltration, dialysis, or chromatography may be employed to further purify the dextran, especially when producing medical-grade dextran.
• Drying: The purified dextran solution is concentrated and dried to obtain the final product in powder form.

6. Characterization and Quality Control

• Molecular Weight Determination: The molecular weight of dextran is controlled depending on its intended use, such as in pharmaceuticals or food. Gel filtration chromatography or other methods are used to determine molecular weight distribution.
• Sterilization: The final dextran product may be sterilized if it is intended for medical applications.

7. Storage

• The dextran powder is packaged and stored under appropriate conditions to maintain its stability and prevent degradation.

These steps are essential in producing dextran for various applications, including medical uses (like blood plasma expanders), the food industry (as thickeners), and cosmetics.