Introduction to Fermentation Aspergillus niger and Lactobacillus

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

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)

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.

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

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.

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

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

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

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

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

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)

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

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

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.