Industrial Fermentation: Basic Considerations

Introduction

• Definition: Fermentation processes utilize microorganisms to convert substrates into various products.
• Common Products: Bread, cheese, sausage, pickled vegetables, cocoa, beer, wine, citric acid, glutamic acid, and soy sauce.

Types of Fermentation

• Solid-State Fermentation
  • Microorganisms grow on moist solid with little/no free water.
  • Examples: Mushroom cultivation, processing of cocoa, traditional foods like miso, sake.
• Submerged Fermentation
  • Uses dissolved or suspended solid substrates in water.
  • Examples: Pickling vegetables, yogurt, beer, wine production.
• Aerobic vs. Anaerobic
  • Aerobic: Requires oxygen (e.g., citric acid production by Aspergillus niger).
  • Anaerobic: Absence of oxygen (e.g., yogurt production).

Factors Influencing Fermentations

• Variables: Temperature, pH, medium composition, oxygen/carbon dioxide levels.
• Impact on: Fermentation rate, yield, product quality (taste, smell, texture).
• Medium Formulation: Carbon, nitrogen, trace elements need control; cost and availability are considerations.

Submerged Fermentations

• Fermentation Schemes
  • Batch: Single inoculation, fixed duration.
  • Fed-batch: Medium added periodically.
  • Continuous: Steady inflow and outflow; susceptible to contamination.
• Microbial Growth Phases
  • Lag Phase: Adaptation, no growth.
  • Exponential Growth: Rapid cell division.
  • Stationary Phase: Nutrient depletion.
  • Death Phase: Cell death exceeds growth.
• Growth Dynamics
  • Described by Monod kinetics; specific growth rate depends on substrate concentration.

Aeration and Oxygen Demand

• Importance: Ensures adequate oxygen supply; interruption can damage cultures.
• Aeration Methods: Bubbling with sterile air, filtering to remove contaminants.
• Challenges: High demand in viscous or dense broths.

Heat Generation and Removal

• Sources of Heat: Microbial activity, mechanical agitation.
• Cooling: Essential to prevent temperature rise; challenges in large fermenters.

Photosynthetic Microorganisms

• Requirements: Light and CO2; used in aquaculture.
• Systems: Open ponds, photobioreactors.

Submerged Culture Fermenters

• Types
  • Stirred-tank: Common, versatile.
  • Bubble column: Gas agitation.
  • Airlift fermenter: Internal/external loop designs.
  • Fluidized-bed: Continuous liquid flow.
  • Trickle-bed: Packed supports for growth.
• Design Considerations: Sterility, pressure capabilities, material choice.

Solid-State Fermentations

• Characteristics
  • Low water activity; favors yeasts and fungi.
  • Particle Size: Impacts growth and extraction.
  • Aeration: Removes CO2, controls temperature.
• Koji Fermentations
  • Example: Soy sauce production.
  • Processes: Mold on soybeans/wheat; highly automated in Japan.

Safe Fermentation Practice

• Risks: Potentially harmful microorganisms; occupational diseases.
• Safety Measures: Good manufacturing practices to ensure consumer safety and product quality.

Further Reading

• Recommended literature for advanced understanding and specific case studies on fermentation technology and safety.