Citric acid is a naturally-occurring substance found in citrus fruits like lemons and limes, although it can also be manufactured on an industrial scale. When manufactured, it’s commonly used in food processing as a flavouring, preservative, or colourant. Citric acid is also an ingredient in some cosmetic and personal care products, as well as non-toxic cleaning agents.
In fact, this weak organic acid has many different uses in manufacturing and everyday life. Read on to find out more about citric acid and its various applications.
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What is citric acid?
Citric acid is an organic substance that’s naturally present in fruit and vegetables. It’s particularly abundant and concentrated in juicy citrus fruits such as limes, oranges, lemons, and grapefruits. A white crystalline powder at room temperature, citric acid is classified as a weak organic acid because it partially dissociates when dissolved in a solvent.
Although citric acid is molecularly and chemically similar to ascorbic acid (vitamin C), the two substances have distinct functions and properties. The chemical formula for citric acid is C₆H₈O₇, while the formula for ascorbic acid is C6H8O6.
As you can see, both have eight hydrogen atoms. However, they have different numbers of carbon and oxygen atoms per molecule.
What is citric acid used for?
As we explain below, citric acid is a versatile substance that has various applications in industry and everyday life.
1. As a food additive
Citric acid is a very effective food preservative that can be added to canned fruits to prevent botulism, a life-threatening condition that affects the nervous system. Although rare, the illness is primarily caused by toxins that are produced by Clostridium botulinum bacteria. These highly-poisonous toxins can develop in food that’s not been cooked, preserved, or canned correctly. The acidity of citric acid inhibits bacterial growth and neutralises the toxin that causes botulism.
As well as being a good preservative, citric acid is added as a flavouring to a variety of food and beverages including sweet treats, sorbets, soft drinks, and wine. It’s also used as an emulsifier in ice cream because it enables oil and water-based ingredients to combine.
2. Used in skincare products
Citric acid is added to cosmetic and personal care products as an antioxidant. Often hailed for its ability to brighten the skin and correct dark spots, it’s a common ingredient in many anti-ageing creams and lotions. There’s also evidence to suggest it may boost collagen production, which can help to minimise fine lines and wrinkles.
As a cosmetic additive, citric acid is generally considered to be non-toxic and a non-irritant. This means it’s safe to add to products like mascara and lipstick, which are used in delicate areas. The acid itself can help to preserve the stability of the enzymes in cosmetic goods and increase the product’s life span.
Many hairsprays, deodorants, and body sprays also use citric acid as a preservative and pH adjuster and corrector. In bath bombs, citric acid reacts with baking soda and releases carbon dioxide to create the characteristic ‘fizz’.
3. Production of cleaning supplies
Many kitchen and bathroom cleaning products contain citric acid because it can effectively remove hard water deposits from surfaces like ceramic dishes and glassware. Citric powder can also be dissolved in water and used as a cleaning agent.
It’s particularly good at removing tea and coffee stains. Alternatively, you can use lemon juice as a natural, environmentally-friendly cleaner around the home.
Is citric acid a weak or strong acid?
Citric acid is classed as a weak acid, which means it does not completely dissociate into ions when dissolved in water.
It has a pKa value of approximately 3.1, which means that in aqueous solutions, only a few citric acid molecules dissociate to release hydrogen and citrate ions. This is in contrast to strong acids, such as hydrochloric acid, which dissociate almost completely in water.
Is citric acid harmful?
Citric acid is safe to ingest and isn’t normally regarded as harmful. In fact, it’s naturally present in many fruits and is also added to a wide range of packaged foods. There’s even evidence to suggest that it may have some health benefits.
That being said, inhaling or ingesting excessive amounts of citric acid over a prolonged period may produce some adverse side effects, such as diarrhoea, stomach cramps, and vomiting. You should also be careful when using citric acid in its powder form in the kitchen as there is a slight fire risk.
How is citric acid made industrially?
Despite its namesake, commercial citric acid does not come from citrus fruits but rather from a filamentous fungus known as Aspergillus niger.
About two million metric tons of citric acid are produced annually through the fermentation of carbohydrates and agro-industrial residues using this fungus.
What foods contain citric acid?
Citric acid is naturally present in fruits and vegetables but it’s most concentrated in citrus fruits, particularly lemons and limes. Citric acid is also artificially added to some processed food and beverages.
Along with ascorbic acid, citric acid is commonly found in fruits as a byproduct of metabolic processes. Below are some common fruits and their citric acid concentrations:
- Lemons and limes: 5-6% citric acid
- Grapefruit and tangerines: 1.5-2.5% citric acid
- Oranges: 0.08-1% citric acid
- Pineapples: 0.6-1.2% citric acid
- Strawberries: 0.21% citric acid
Vegetables or edible root crops and leaves are also good sources of citric acid. Although the culinary definition of vegetables may vary, they’re generally defined as edible crops that must be cooked to be fully digestible. This includes whole plants or parts of plants like the roots, stem, and leaves. Some common vegetables which contain citric acid include tomatoes, potatoes, broccoli, carrots, and jalapeños.
Citric acid is a naturally-occurring organic substance mainly found in fruits and vegetables. Industrially-produced citric acid, however, is derived via the fermentation process of the Aspergillus niger fungus. Citric acid has several industrial and household applications. It’s often used as a food additive and preservative as it can kill bacteria. It also acts as an antioxidant in some cosmetic and skin care products and is a common ingredient in many household cleaning agents too, because it can remove hard water deposits and stains.
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