An Overview of Common Food Preservatives and Their Uses

Every food product you pick up from a store shelf has a limited window before it starts to spoil. Microorganisms like bacteria, yeasts, and moulds are constantly working to break food down – causing off-flavours, discolouration, and even foodborne illness. Preservatives are the substances that slow or stop this process. They inhibit microbial growth, prevent fermentation and acidification, and keep food safe and edible for much longer than it would last on its own. Understanding the different types of preservatives, how they work, and where they are used is essential for anyone studying food science or working in the food industry.

What exactly are food preservatives? 🔗

A food preservative is any substance that, when added to food, is capable of inhibiting, retarding, or arresting the process of fermentation, acidification, or other decomposition. This definition comes directly from India’s FSSAI regulations, which govern how preservatives are classified and used in the country. Preservatives can be natural or synthetic in origin. Some – like salt and sugar – have been used for thousands of years, long before anyone understood the science behind microbial spoilage. Others are modern chemical compounds developed to target specific types of microorganisms with precision.

The primary goals of adding preservatives to food are straightforward: extend shelf life, maintain food safety by preventing harmful microbial growth, and preserve the taste, texture, and appearance of the product during storage and transport.

Classification of preservatives: Class I and Class II 🔗

In India, preservatives are officially divided into two categories under food safety regulations – Class I (natural preservatives) and Class II (chemical preservatives). This classification is based on the origin and nature of the substance.

Class I preservatives (natural) 🔗

Class I preservatives are traditional, naturally occurring substances that humans have relied on for centuries. They include common salt, sugar, dextrose, glucose, spices, vinegar (acetic acid), honey, and edible vegetable oils. A key point about Class I preservatives is that there is no legal restriction on the quantity that can be added to any food product. They are considered inherently safe for consumption.

Salt, for instance, works by reducing the water activity in food, creating an environment where most bacteria cannot survive. Sugar functions similarly – in high concentrations (as in jams and jellies), it binds water molecules, making them unavailable for microbial growth. Vinegar lowers the pH of food, making it too acidic for many spoilage organisms. Spices like cloves, cinnamon, and mustard contain natural antimicrobial compounds such as eugenol that actively inhibit bacteria and moulds.

Class II preservatives (chemical) 🔗

Class II preservatives are synthetic or chemically derived compounds. They are more potent than natural preservatives, particularly in foods with low pH. Common Class II preservatives include benzoic acid and its salts, sulphurous acid and its salts (sulphites), nitrates and nitrites of sodium or potassium, sorbic acid and its salts, and calcium or sodium propionate.

Unlike Class I preservatives, the use of Class II preservatives is strictly regulated by food safety authorities. Specific limits are set for which preservatives can be used, in which foods, and at what maximum concentration. These regulations exist because excessive intake of chemical preservatives can pose health risks.

Sulphur dioxide (SO₂) and sulphites 🔗

Sulphur dioxide is one of the most widely used Class II preservatives in the food and beverage industry. It is a colourless gas with a sharp, suffocating odour that dissolves in water to form sulphurous acid. It is commonly applied as sulphur dioxide gas or through its salts – sodium bisulphite, sodium metabisulphite, and potassium metabisulphite.

How sulphur dioxide works 🔗

Sulphur dioxide functions both as an antimicrobial agent and an antioxidant. As an antimicrobial, it crosses the cell walls of microorganisms and disrupts their normal cellular functioning, effectively inhibiting the growth of yeasts, bacteria, and moulds. As an antioxidant, it prevents browning caused by oxidation – particularly important in dried fruits and vegetables. Without sulphur dioxide treatment, light-coloured fruits like dried apricots would darken rapidly upon exposure to air.

Common uses 🔗

Sulphur dioxide is primarily found in dried fruits and vegetables, fruit juices, grape wines, pickled vegetables, and soft drinks. It is also widely used in winemaking to prevent spoilage and oxidation, helping preserve the quality and freshness of wine. According to a study published in PubMed, foods commonly containing sulphur dioxide are predominantly dried fruits and vegetables, soft drinks, and alcoholic beverages.

Safety considerations 🔗

While sulphur dioxide is considered safe at recommended concentrations for healthy individuals, it can trigger allergic reactions in sensitive people – especially asthmatics. Symptoms may include breathing difficulties, headaches, and nausea. Research suggests that roughly 3-10% of people with asthma are sensitive to sulphites. In many countries, foods containing more than 10 ppm of sulphites must declare this on the label. The FDA banned the use of sulphites on fresh fruits and vegetables in 1986 after reports of adverse reactions.

Benzoic acid and sodium benzoate 🔗

Benzoic acid and its sodium salt – sodium benzoate – are among the most commonly used chemical preservatives in the food industry. Sodium benzoate was, in fact, the first preservative the FDA permitted for use in foods.

Mechanism of action 🔗

Benzoic acid is most effective in acidic environments, typically at a pH below 4.5. In its undissociated form, it enters microbial cells and disrupts their internal metabolic processes. Specifically, it interferes with the enzyme phosphofructokinase, sharply reducing the cell’s ability to ferment glucose. This disruption of energy metabolism, combined with changes in membrane permeability and internal pH, ultimately prevents microbial growth and reproduction.

Benzoic acid itself has poor water solubility, which is why it is commonly converted to sodium benzoate – a highly water-soluble salt that dissolves easily in food products. Once dissolved in an acidic product, sodium benzoate converts back to benzoic acid, which is the active antimicrobial form.

Common uses 🔗

Sodium benzoate is widely used in carbonated drinks, fruit juices, pickles, salad dressings, soy sauce, jams, and other condiments. It is particularly effective against yeasts and bacteria, and moderately effective against moulds. The typical usage level in food products ranges from 0.05% to 0.1%, and regulatory bodies such as the FDA, FSSAI, and EFSA all approve its use within prescribed limits.

A note on benzene formation 🔗

One concern with sodium benzoate is that when combined with ascorbic acid (vitamin C) in beverages, it can potentially form benzene – a known carcinogen. This reaction is more likely in diet beverages and under conditions of heat and light exposure. Manufacturers must carefully control formulation and storage conditions to minimise this risk.

Nitrates and nitrites 🔗

Sodium nitrate (NaNO₃) and sodium nitrite (NaNO₂) are preservatives used primarily in cured and processed meat products such as ham, bacon, sausages, and pickled meats. Their use in meat curing dates back centuries, when these compounds were found as natural contaminants in the salt used for meat preservation.

How they work 🔗

Nitrites serve multiple functions in cured meats. Their most critical role is as a powerful antimicrobial agent, particularly against Clostridium botulinum – the bacterium responsible for botulism, a potentially fatal illness. According to the Food Safety Institute, since sodium nitrite was authorised for meat curing by the USDA in 1925, there have been no reported cases of botulism from commercially prepared cured meats.

Beyond antimicrobial action, nitrites also give cured meats their characteristic pink colour. When nitrite is added to meat, it converts to nitric oxide, which binds with myoglobin to produce the distinctive cured pink colour. Nitrites also help delay fat oxidation (rancidity) and contribute to the characteristic cured meat flavour.

Health concerns 🔗

The use of nitrates and nitrites remains a subject of ongoing debate. Nitrites can react with amino acids in meat to form N-nitroso compounds (nitrosamines), which have been classified as potentially carcinogenic. The IARC has classified processed meat as a Group 1 carcinogen, partly due to these compounds. However, it is worth noting that vegetables actually account for about 80% of our dietary nitrate intake – far more than meat products. Regulatory authorities set strict limits on permissible levels (typically around 200 ppm for sodium nitrite in preserved meats) to balance food safety with health risks.

Sorbic acid and sorbates 🔗

Sorbic acid and its salts – especially potassium sorbate – are widely used preservatives effective against moulds and yeasts. Sorbic acid works by inhibiting enzymes involved in carbohydrate metabolism, essentially starving the microorganism by disrupting its ability to generate energy. It also alters the membrane integrity of fungi, preventing their growth and reproduction.

Potassium sorbate is commonly used in cheese, baked goods, wine, dried fruits, and prepared salads. It is also used in tinned foods and pickles. Sorbic acid was initially valued for its effectiveness against Clostridium botulinum, and it has strong antifungal properties that have made it one of the most extensively used preservatives in modern food manufacturing.

Propionic acid and propionates 🔗

Propionic acid and its salts – calcium propionate and sodium propionate – are primarily used as preservatives in baked goods. If you have ever noticed that commercial bread stays mould-free far longer than homemade bread, propionates are usually the reason. They create an environment that is unfavourable for mould growth while having minimal impact on taste.

Calcium propionate is particularly popular because, in addition to its antimicrobial properties, calcium is a nutrient, making it a dual-purpose additive. Propionates are classified as Class II preservatives and are regulated under food safety standards with defined maximum permissible limits.

Nisin: a microbial preservative 🔗

Not all preservatives fit neatly into the natural-versus-chemical classification. Nisin is a bacteriocin – an antimicrobial peptide produced by Lactococcus lactis, a strain of lactic acid bacteria. It is effective against many Gram-positive bacteria, including Clostridium and Listeria species, making it valuable for dairy products, canned foods, and processed cheese.

Nisin is listed as a permitted Class II preservative under Indian food regulations and is recognised internationally as a safe food additive. It represents the growing interest in bio-preservation approaches – using natural microbial metabolites instead of synthetic chemicals to keep food safe.

How preservatives are regulated 🔗

The use of food preservatives is tightly controlled worldwide. In India, the Food Safety and Standards Authority of India (FSSAI) specifies which preservatives are permitted, in which foods, and at what maximum concentrations. Globally, organisations like the FDA (United States), EFSA (European Union), and the Joint FAO/WHO Expert Committee on Food Additives (JECFA) conduct rigorous safety evaluations and establish Acceptable Daily Intake (ADI) limits.

These regulations ensure that preservatives are used only in quantities that are safe for human consumption. Food manufacturers must also clearly declare the presence of preservatives on product labels, including their functional class and specific name or E-number/INS identification code. For example, sulphur dioxide is identified under INS numbers 220-228, and sodium benzoate is listed as E211 or INS 211.

The balance between preservation and health 🔗

Preservatives serve an essential function in the modern food supply chain. Without them, food waste would increase dramatically, foodborne illnesses would be far more common, and access to diverse, safe food products would be severely limited. At the same time, consumer awareness about chemical additives is growing, and there is increasing demand for “clean label” products that use fewer synthetic preservatives.

This has driven research into natural alternatives – plant-derived essential oils, microbial bacteriocins, and non-thermal processing technologies like high-pressure processing (HPP) that can extend shelf life without chemical additives. The food industry is actively exploring ways to reduce reliance on synthetic preservatives while still ensuring food safety and quality.

What do you think? Given the trade-off between food safety and chemical exposure, do you believe the current regulatory limits on food preservatives strike the right balance? And as natural preservation methods continue to advance, could we eventually move towards a food system that relies far less on synthetic preservatives?

References

1. https://fssai.gov.in/upload/uploadfiles/files/FOOD_ADDITVES.pdf
2. https://egyankosh.ac.in/bitstream/123456789/12002/1/Unit-6.pdf
3. https://fssai.gov.in/upload/uploadfiles/files/appendix_a_and_b_revised(30-12-2011).pdf
4. https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_175_01.html
5. https://pubmed.ncbi.nlm.nih.gov/7426352/
6. https://www.healthline.com/nutrition/sodium-benzoate
7. https://foodsafety.institute/food-fundamentals-chemistry/role-of-preservatives-in-food-safety/
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC9986499/
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC8535775/
10. https://www.sciencedirect.com/science/article/pii/S2665927123000382