From canning and freezing to drying and salting, there are various ways to preserve food. There’s even evidence to suggest food preservation methods were being used 14,000 years ago in the Middle East and the Orient. People back then were actively preserving their food by drying it under the sun.
Fast forward to the present day and chemicals now play a key role in extending the shelf life of food products. Modern industrial-scale food preservation methods typically use three main types of chemical preservatives – benzoates, nitrites, and sulphites.
Continue reading to learn more about the chemical methods of food preservation, along with the potential impact on human health and the environment.
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Understanding methods of food preservation
Since the discovery of fire and cooking, humans have invented methods of preserving food. Although the specific techniques may vary, the main principle is the same – to prevent the growth of fungi and bacteria that cause food to spoil. Whichever method you use, food preservation involves physical and chemical changes in food.
Here are some common methods of food preservation. These techniques can be used both at home and on a large scale in the food processing industry.
Arguably the newest form of food preservation, this method was pioneered by French confectioner, Nicolas Appert, in the 1790s. Canning involves sealing and heating food in jars or cans. The heat kills bacteria and destroys enzymes while the sealing prevents the food from being contaminated.
Although people didn’t initially understand the exact reasons why food spoils, canning was an effective method. It was only in 1864 that Louis Pasteur clearly demonstrated the relationship between microorganisms and food spoilage.
Freezing works by lowering the temperature of food to inhibit the growth of microorganisms and bacteria. Before mechanical refrigeration was invented in the 1800s, freezing was only possible in very cold regions. Cold cellars, caves, and streams were used to preserve food during the winter months.
Today, the food industry uses blast freezing (a process in which cold air is blasted and circulated around the product) and contact freezing (food is put into trays or containers and stored on a refrigerated surface).
Evidence suggests that as early as 14,000 years ago people dried fish, meat, and fruits under the heat of the sun to preserve them. Dehydrating works by removing water from the food, which inhibits the growth of bacteria, mould and yeast (these microorganisms need water to multiply).
Dried meats such as beef jerky and parma ham are preserved in this way, as are dried fruits like raisins, dates, and prunes.
Salting is a method of dehydrating/drying food through osmosis. The water in food cells migrates outside and is absorbed by the salt. Like many of the other methods we’ve talked about, salting is also an ancient method of food preservation.
Using sea salt, which is mainly sodium chloride, is an effective way of dehydrating food. Plus, it has the added benefit of improving the flavour. Salting may also refer to the addition of preservatives like benzoates and nitrates.
What chemicals are used in food preservation?
Industrial food preservation typically involves three main types of preservatives – benzoates, nitrates and nitrites, and sulphites. However, before any of these chemical preservatives are added, food products normally undergo various other steps in the preservation process. This might include pasteurisation, cooking and irradiation.
Although the use of some types of chemical food preservatives can be detrimental to our health (more on this later), others are completely safe. For example, vinegar is a common preservative used in pickling food such as cucumbers. The acidity of vinegar prevents microorganisms from multiplying but it’s non-toxic to humans.
Benzoates as food preservatives
Benzoates are the salt of the conjugate base. The most common type of benzoate salt used as a preservative is sodium benzoate, which has a benzene ring and the chemical formula C6H5COONa. As a salt, it dissociates into ions in an aqueous solution. The benzoate ion acts as a base, forming the conjugate acid and a hydroxide ion.
Sodium benzoate is industrially produced through the neutralisation reaction between benzoic acid and sodium hydroxide. It’s also naturally present in berries, cranberries, seafood, and dairy products.
Sodium benzoate is a white crystalline substance at room temperature. When dissolved in water, it becomes acidic. This acidity inhibits microbial growth and prolongs the shelf life of food.
Nitrates and nitrites in food preservation
Meat products such as bacon, sausages, and corned beef all contain nitrates or nitrites. Much like benzoates, these chemicals are effective in inhibiting bacterial and fungal growth. Nitrates and nitrites are particularly useful in preventing the reproduction of the bacterium species, Clostridium botulinum, which causes botulism or food poisoning. They can also improve the flavour and help to preserve the appealing reddish appearance of processed meat.
In addition to meat, nitrates are used in other food processing methods, such as cheese manufacturing. They can stop certain types of cheeses from bloating while they’re being fermented. Nitrates are also present in leafy green vegetables such as lettuce and spinach due to the presence of nitrogen-fixing bacteria in the soil. In some agricultural lands, nitrates are even artificially added to help plants grow.
Sulphites in food preservation
Sulphites are antioxidants that are commonly used to extend the shelf life of foods such as radishes, dried fruits and potatoes. Primarily used for aesthetic purposes, they stop the oxidation process that causes dried fruit and vegetables to turn brown. Sulphites also help to preserve nutrients by slowing the breakdown of vitamins C and A.
The impact on health and the environment
Chemical methods of food preservation have both positive and negative impacts on health and the environment. On one hand, they make food safer by preventing the growth of harmful microorganisms that cause food poisoning. They can also help to reduce the use of electricity by minimising the need for certain food items to be refrigerated.
On the other hand, many artificial food preservatives such as nitrates and nitrites have been shown to have a detrimental effect on our health. Long-term consumption of processed meat, for instance, has been linked to an increased risk of developing certain types of cancer. You can read more about the effects of food additives and preservatives here.
The industrial production of processed food also contributes to pollution and the depletion of natural resources. For example, the metals used by the canning industry usually come from non-renewable resources.
Government regulations and international treaties, as well as industry standards, are designed to minimise the detrimental effects of food processing on health and the environment. For example, the European Food Safety Authority (EFSA) set the standards and safety limits for the use of artificial food preservatives.
In the UK, the Food Standards Agency is responsible for approving and monitoring the use of preservatives and additives in the food and beverage industry.
Food preservation is almost as old as humanity itself. The main methods of food preservation include canning, freezing, drying and salting. Today, the food manufacturing industry relies heavily on the use of chemical preservatives like benzoates, nitrates or nitrites, and sulphites. These kinds of chemical preservatives can make food products safer to eat because they prohibit the growth of potentially harmful bacteria. However, there’s also evidence to suggest that consuming too much of certain types of preservatives can be detrimental to our health.