Back to: MICROBIOLOGY 400 LEVEL
Welcome to class!
Hello my brilliant scholar! It’s always a great moment when you show up for your learning journey. You are doing something that not only builds your mind but also empowers your future. Today, we’re going into a very practical and exciting topic in industrial microbiology—Primary Metabolites: Ethanol and Citric Acid. These are substances produced by microbes that industries rely on every single day. You’ve probably used or consumed them without even realising!
Primary Metabolites: Ethanol, Citric Acid
Let’s begin by understanding what primary metabolites are. Simply put, they are substances produced by microorganisms as part of their normal growth. These are essential for the survival of the microbe and are typically produced during the log phase of growth when the microbe is actively multiplying. These metabolites include things like amino acids, alcohols, organic acids, and vitamins.
Unlike secondary metabolites (which are usually produced later and aren’t necessary for growth), primary metabolites are directly linked to the organism’s normal metabolic activities. Two very important examples that are used widely in industries are ethanol and citric acid.
Ethanol
Ethanol is a type of alcohol that many of us know from alcoholic beverages, but it’s much more than that. Ethanol is also used as a biofuel, solvent, and in pharmaceutical preparations. It is produced by the fermentation of sugars by yeast, especially Saccharomyces cerevisiae.
In industries, ethanol is made in large fermenters where conditions like temperature, pH, and sugar concentration are carefully controlled. Sugar sources like molasses (from sugarcane), cassava, or corn are commonly used, especially in countries like Nigeria where these crops are abundant.
The yeast consumes the sugars and, in the absence of oxygen, converts them to ethanol and carbon dioxide. This process is known as anaerobic fermentation.
Citric Acid
Citric acid is another important primary metabolite. If you’ve ever tasted zobo, soft drinks, or vitamin C tablets, you’ve likely consumed citric acid. It is widely used in the food industry as a flavouring and preservative, and in the pharmaceutical and cosmetic industries.
Citric acid is produced mainly by the fungus Aspergillus niger. When this fungus is grown on a carbohydrate-rich medium (like molasses or maize starch), it produces citric acid as part of its normal metabolism under specific conditions—limited nitrogen, sufficient sugar, and proper aeration.
If you’ve ever seen palm wine ferment or watched your aunt bake with yeast, you’ve witnessed ethanol fermentation in action. And when you enjoy a fizzy soft drink with that tangy taste, you’re likely tasting citric acid. These aren’t just science terms—they’re part of your daily life.
Also, Nigerian industries use ethanol in the making of sanitisers and medicines, while citric acid is added to zobo and fruit juices to improve shelf life and taste.
Summary
- Primary metabolites are substances produced by microorganisms during their normal growth, essential for their survival.
- Ethanol is a primary metabolite produced by Saccharomyces cerevisiae through anaerobic fermentation of sugars.
- Ethanol is used in beverages, biofuels, pharmaceuticals, and as a solvent.
- Citric acid is a primary metabolite produced by Aspergillus niger when grown on sugar-rich media under specific conditions.
- Citric acid is widely used in food, medicine, and cosmetic industries as a preservative and flavouring agent.
Evaluation
- What are primary metabolites, and when are they produced by microorganisms?
- Name the organism used for industrial ethanol production and the process involved.
- List two industrial uses each for ethanol and citric acid.
lesson adds to your knowledge and confidence. Remember, the world of microbiology is full of opportunities, and you are growing into one of its future leaders. Keep your focus, stay curious, and let’s continue to thrive together with Afrilearn. See you in the next class!