Industrial Biotechnology and Fermentation Technology
This section covers industrial fermentation and product recovery. The exam tests bioreactor operation, batch, fed-batch and continuous modes, sterilization, and the difference between primary and secondary metabolites.
Core rules
Fermentation is the controlled conversion of a substrate into a product by microorganisms or cells. A bioreactor maintains temperature, pH, aeration, agitation, and sterility. Batch culture is closed except for air; nutrients fall and products accumulate. Fed-batch adds substrate during the run to avoid repression or overflow metabolism. Continuous culture adds fresh medium and removes culture at a steady rate; if the dilution rate exceeds growth rate, washout occurs. Primary metabolites such as ethanol, citric acid, and amino acids form during active growth. Secondary metabolites such as penicillin form mainly near stationary phase. Downstream processing includes filtration, centrifugation, cell disruption, extraction, precipitation, and chromatography.
Worked example
A batch fermentation produces 40 g/L of product in 20 hours. Volumetric productivity is 40/20 = 2 g/L per hour. A fed-batch run reaches 60 g/L in 30 hours, also 2 g/L per hour. The fed-batch has a higher final titre but not a higher average rate. If the question asks for yield, divide product mass by substrate consumed; if it asks for productivity, divide by time as well.
Traps that cost marks
Not all fermentation is anaerobic; penicillin production is aerobic. Do not confuse titre, yield, and productivity. Continuous culture is not simply a longer batch. Oversterilization can damage medium components. Do not assume secondary metabolites form fastest during log phase.