Food Production
Use of Biological Resources
When a useful product (such as the protein insulin from genetically engineered bacteria in topic 18, mycoprotein, or an antibiotic) is made by culturing microorganisms on a large scale, the microorganisms are grown in a large stainless-steel vessel called an . The fermenter must provide and maintain the conditions the microorganisms need to grow quickly and make the product, while keeping unwanted microorganisms out.
| Condition the fermenter provides | Why it is needed | How the fermenter does it |
|---|---|---|
| Aseptic (sterile) conditions | Stop other microorganisms contaminating the culture, competing for nutrients or spoiling the product | The vessel and the nutrient medium are sterilised (e.g. with steam) before use, and only filtered air is let in |
| Nutrient medium | Supply the carbon, nitrogen and mineral ions the microorganisms need to respire and build new cells | A measured supply of nutrients (such as sugars and a nitrogen source) is added |
| Optimum temperature | Enzymes work fastest at the optimum; too hot and they denature, too cold and growth is slow | A water jacket around the vessel removes the heat released by respiration and a temperature probe keeps it steady |
| Optimum pH | Enzymes work best at a particular pH; the wrong pH slows growth | A pH probe monitors the culture and acid or alkali is added automatically to correct it |
| Oxygenation | Aerobic microorganisms need oxygen for respiration to release energy and grow | Sterile air is bubbled in through a sparger at the base |
| Agitation (stirring) | Keeps the microorganisms, nutrients, oxygen and heat evenly distributed so every cell has the conditions it needs | A motor-driven paddle or stirrer mixes the contents continuously |
When all of these are kept at their best values, the microorganisms multiply rapidly and make large amounts of the product, which is then extracted and purified.
Common exam question
Explaining how a fermenter controls its conditions
Question: Explain how named conditions in a fermenter are controlled, or the role of one labelled part: the water jacket, stirrer, air supply or air filter (2–4 marks per part).
Asked in 3 of the 23 papers. The four-mark version pairs a condition (oxygen, optimum temperature, optimum pH, aseptic conditions or even mixing) with its control, and the control scores only if the condition is named; "high temperature" is ignored.
Explaining one part needs its full purpose. The jacket removes the heat respiration releases, holding the optimum so enzymes do not denature; "warms it up" is ignored, as was "cools it down" alone for a part labelled cooling jacket. The stirrer keeps the temperature even, with no hot spots, and the bacteria in contact with nutrients; "stirs" and "keeps the optimum temperature" are ignored. Air supplies oxygen for respiration ("for anaerobic respiration" is rejected); the filter keeps out microorganisms that would contaminate the product ("keeps it clean" is ignored).