Batch Fermentation Systems (Module 3.1) PDF

# Batch fermentation ## 1.2.1 Stirred Tank Reactor: Batch culture - X, S, P: biomass, substrate, and product concentrations The image shows a diagram of a stirred tank reactor with the following labels: - **fermentation**: the process of converting substrate to product - **So**: initial substr...

# Batch fermentation ## 1.2.1 Stirred Tank Reactor: Batch culture - X, S, P: biomass, substrate, and product concentrations The image shows a diagram of a stirred tank reactor with the following labels: - **fermentation**: the process of converting substrate to product - **So**: initial substrate concentration - **S**: substrate concentration - **C**: cell concentration - **P**: product concentration - **Xo**: initial biomass concentration - **X**: biomass concentration - **Po**: initial product concentration - **time**: the independent variable - **emptying, cleaning, filling**: processes involved in the batch reactor cycle - **inoculation**: the initial addition of cells to the reactor - **MOST used culture mode for food**: batch culture is the most common method for producing food products ## **Continuous fermenter** ## Operation conditions of a CSTR reactor - Constant volume: feed rate = harvest rate - D < µmax maximum specific growth rate of the culture - At steady state: D = µ (h-1) ### Diagram of a CSTR reactor The image shows a diagram of a CSTR reactor with the following labels: - **P**: product concentration - **C**: cell concentration - **X**: biomass concentration - **So**: initial substrate concentration - **S**: substrate concentration - **Po**: initial product concentration - **Xo**: initial biomass concentration - **V = cte**: Constant volume of the reactor The image also shows the following: - **inoculation**: initial introduction of cells - **time**: independent variable Growth-limiting factor concentration (C, N or other) in the effluent should be close to 0 For optimal utilization of the medium: medium formulation or fermentors in series. ## Characteristics of CSTR reactor - Cells ### Advantages - Constant output, increased productivity - Decreased vessel size - Decreased downstream processing - Controlled culture physiology (flow rate) - High cell activity and reduced lag time ### Limits - High risk of contamination (competing microbes and bacteriophages)!! - In general, requires sterility of medium supply - Genetic instability: loss of plasmids for recombinant and natural strain - Fouling by medium or products - Generally not suitable for secondary products (stationary phase, no growth) ## Applications of CSTR reactors in the food industry ### Continuous cultures in the food industry: - **VERY FEW APPLICATIONS!** - Requires contamination protection: absolute sterility, non-permissive culture conditions (e.g., low pH, ethanol) or highly competitive microorganism - Requires high stability of the culture: e.g., bacteriophage resistance, genetic stability (e.g., no plasmid loss) - Necessitates reorganization of production-worker shifts (24 h/7 d) - Used for vinegar production (with immobilized cells of Acetobacter), beer fermentation, lactic acid bacteria starters (although very limited) - Possible solutions: semi-continuous or immobilized cell cultures ## Feb-batch fermentation ## B. Semi-continuous fed batch culture - V increase: increase in volume of the reactor - So: initial substrate concentration - Xo: initial biomass concentration - μ: specific growth rate - V: volume flow rate - S: substrate concentration - X: biomass concentration - time: independent variable - inoculation: initial introduction of cells - Step (or continuous) addition of substrate: the process of feeding fresh substrate to the reactor ### **Fed-batch process with periodical substrate addition** - e.g., aerobic yeast growth to avoid catabolite repression by glucose (upper limit to avoid Crabtree effect) and to avoid substrate limitation (lower limit) for high cell yield - **acetic acid production (Acetobacter sp.), to achieve higher product yield and productivity from ethanol (to prevent ethanol inhibition).**