1. Introduction to Fermentation
Aspergillus niger and Lactobacillus

2. Introduction to Fermentation
Aspergillus niger and Lactobacillus Delbruckii are the microbes used to commercially produce citric acid and lactic acid, respectively. The production takes place in a batch fermenter. This tutorial will introduce you to the following areas regarding batch fermentation
Microbial Growth Kinetics
Media for Industrial Fermentations
Sterilization
The Development of Inocula for Industrial Fermentations
Design of a Fermenter
Instrumentation and Control
Aeration and Agitation

3. Microbial Growth Kinetics
Microbial Growth Kinetics describe how the microbe grows in the fermenter. This information is important to determine optimal batch times. The growth of microbes in a fermenter can be broken down into four stages:
Lag Phase
Exponential Phase
Stationary Phase
Death Phase
(Growth curve is from Shuler p. 161)

4. Microbial Growth Kinetics
Lag Phase
This is the first phase in the fermentation process
The cells have just been injected into a new environment and they need time to adjust accordingly
Cell growth is minimal in this phase.

5. Microbial Growth Kinetics
Exponential Phase
The second phase in the fermentation process
The cells have adjusted to their environment and rapid growth takes place
Cell growth rate is highest in this phase

6. Microbial Growth Kinetics
Exponential Phase (Continued)
At some point the cell growth rate will level off and become constant
The most likely cause of this leveling off is substrate limited inhibition
Substrate limited inhibition means that the microbes do not have enough nutrients in the medium to continue multiplying.

7. Microbial Growth Kinetics
Stationary phase
This is the third phase in the fermentation process
The cell growth rate has leveled off and become constant
The number of cells multiplying equals the number of cells dying

8. Microbial Growth Kinetics
Death phase
The fourth phase in the fermentation process
The number of cells dying is greater than the number of cells multiplying
The cause of the death phase is usually that the cells have consumed most of the nutrients in the medium and there is not enough left for sustainability

9. Media for Industrial Fermentations
The media is the feed solution
It must contain the essential nutrients needed for the microbe to grow
Factors of consideration when choosing media
-Quality consistence and availability
-Ensure there are no problems with Media Prep or other aspects of production process
Ex. Cane molasses, beet molasses, cereal grains

10. Sterilization
Sterilizing the feed solution is essential because the media cannot contain foreign microbes because this could severely hinder the growth of the production microbe
Most popular method is heat sterilization of the feed solution

11. The Development of Inocula for Industrial Fermentations
The inoculum is the starter culture that is injected into the fermenter
It must be of sufficient size for optimal growth kinetics
Since the production fermenter in industrial fermentations is so large, the inoculum volume has to be quite large
- A seed fermenter is usually required to produce the inoculum volume
-The seed fermenter’s purpose is not to produce product but to prepare inoculum

12. Design of a Fermenter Factors to consider when designing a fermenter
Aseptic and regulatory capability, long-term reliability
Adequate aeration and agitation
Low power consumption
Temperature and pH controls
Sampling facilities
(14 L fermenter shown is a copyright of New Brunswick Scientific)

13. Instrumentation and Control
The success of a fermentation process is highly dependent on environmental factors
The fermenter needs to be able to control such factors as temperature, pH, and dissolved oxygen levels

14. Aeration and Agitation
Most industrial fermentations are aerobic processes meaning that the production microbe requires oxygen to grow
The oxygen demand is met by sparging air through the fermentation vessel and using an agitator increase the amount of dissolved oxygen

15. References
Stanbury, P.F., A. Whitaker, and S. J. Hall, Principles of Fermentation Technology, 2nd ed., Butterworth Heinemann, Oxford, 2000.
Shuler, M. L. and F. Kargi. Bioprocess Engineering Basic Concepts, 2nd ed., Prentice Hall, Upper Saddle River, NJ, 2002.