Chemical Agents for Controlling Microbial Growth: Usage in Food Preservation

Every piece of food you eat has been in a silent battle with microorganisms – bacteria, moulds, and yeasts – that want to break it down. Left unchecked, these microbes cause spoilage, off-flavours, and, in serious cases, deadly foodborne illness. Chemical agents are one of the most important tools the food industry uses to win that battle. They either kill harmful microorganisms outright (bactericidal action) or stop them from multiplying (bacteriostatic action), keeping food safe for longer periods. Let’s look at how these agents work, what types are commonly used, and where the science is heading.

What are chemical agents in food preservation? 🔗

Chemical agents used in food preservation are substances – synthetic or naturally derived – that are added to food products to control microbial growth and minimise spoilage. They work through a variety of mechanisms: lowering the pH inside microbial cells, disrupting cell membranes, inhibiting critical enzymes, or interfering with DNA and protein function. The goal is always the same – to create conditions in which harmful microorganisms cannot survive or reproduce.

An important distinction to understand is the difference between a bactericidal agent (one that kills bacteria) and a bacteriostatic agent (one that merely prevents bacteria from growing). Many chemical preservatives in food are bacteriostatic at normal usage concentrations. They don’t sterilise the product, but they keep microbial populations low enough to maintain safety and quality throughout the product’s shelf life.

Organic acid preservatives 🔗

Organic acids are among the most widely used chemical preservatives in the food industry. They are safe, non-toxic to humans at approved levels, and largely flavourless – meaning they don’t change the taste of the food they protect.

Sorbic acid and potassium sorbate 🔗

Sorbic acid is particularly effective at controlling mould growth. It works by interfering with several cellular enzymes, including those involved in the citric acid cycle, catalases, and peroxidases. Its salt form, potassium sorbate, is more soluble and easier to use in food formulations. Sorbic acid becomes more effective as pH drops, which is why it is heavily used in acidic foods such as dairy products, bread, fruit preparations, and vegetable products.

Benzoic acid and sodium benzoate 🔗

Benzoic acid occurs naturally in many fruits, berries, and fermented foods. As a preservative, it lowers the pH inside microbial cells, disrupting processes like oxidative phosphorylation and amino acid uptake. Sodium benzoate, its more soluble salt, is commonly added to fruit juices, jams, soft drinks, pickles, and ice creams. Like sorbic acid, benzoic acid works best in low-pH environments.

Propionic acid and calcium propionate 🔗

Propionic acid functions similarly – it inhibits enzymes and lowers intracellular pH – but it has a notable advantage: it remains effective at slightly higher pH levels than sorbic or benzoic acid. Some cheeses naturally produce propionic acid during ripening. Calcium propionate is frequently added to bread and baked goods to prevent mould and to control the bacterium Bacillus mesentericus, which causes a defect known as “ropy bread.”

Nitrites and nitrates in meat preservation 🔗

If you’ve ever eaten ham, bacon, or salami, you’ve consumed food preserved with nitrites or nitrates. These compounds have been part of meat curing since ancient times, when early civilisations used salt – often naturally contaminated with saltpetre (potassium nitrate) – to preserve meat and stabilise its red colour.

In modern meat processing, sodium nitrite (NaNO₂) is the primary curing agent. It serves multiple critical functions. First, it inhibits the growth of dangerous bacteria, most importantly Clostridium botulinum, the organism responsible for botulism. Nitrite also suppresses Listeria monocytogenes, Bacillus cereus, Clostridium perfringens, and Staphylococcus aureus in various meat products. Second, nitrite reacts with myoglobin in meat to form nitrosylmyoglobin, the pigment responsible for the characteristic pink colour of cured meats. Third, it acts as an antioxidant, preventing fat oxidation and rancidity, which extends shelf life and preserves flavour.

However, nitrites are not without concern. When nitrite-preserved meats are exposed to high heat during cooking, they can form nitrosamines, which are classified as carcinogenic compounds. This is why regulatory bodies worldwide have restricted the amount of nitrite allowed in processed meats and why active research is underway to find alternatives.

The hurdle concept with nitrites 🔗

Nitrites rarely work alone. Their antimicrobial effectiveness depends on several interacting factors – pH, salt concentration, water activity, iron content, and storage temperature. This is an example of the hurdle concept, where multiple preservation methods are combined to create overlapping barriers that microorganisms cannot overcome. A processed salami, for instance, combines salt curing, nitrite addition, drying, fermentation-driven pH reduction, and sometimes smoking – each creating a “hurdle” against microbial growth.

Sulfites in food and beverages 🔗

Sulfur dioxide and its derivatives – collectively called sulfites – have been used in winemaking since ancient times and remain important preservatives today. Sulfites prevent enzymatic and non-enzymatic browning in foods. When sulfur dioxide dissolves in water, it forms sulfite and bisulfite ions that interfere with disulfide bond formation in microbial proteins, thereby inhibiting enzyme function. Sulfites may also reduce the intracellular pH of microorganisms.

Sulfites are commonly used in dried fruits, wine, fruit juices, and various processed foods. Despite their effectiveness, they can trigger allergic reactions in some individuals – particularly those with asthma – and they degrade thiamine (vitamin B₁), which is an essential nutrient. For these reasons, regulatory agencies require sulfite declaration on food labels when concentrations exceed certain thresholds.

Other synthetic chemical agents used in food safety 🔗

Beyond the preservatives added directly to food, several other chemical agents play important roles in maintaining food safety throughout the production chain.

Chlorine compounds 🔗

Chlorine-based compounds such as sodium hypochlorite (household bleach) and calcium hypochlorite are widely used to sanitise food processing equipment, surfaces, and fresh produce. Chlorine works by producing hypochlorous acid when dissolved in water, which is a strong oxidant that damages microbial cell components. A joint statement by the WHO and FAO has confirmed that the beneficial uses of chlorine products in food processing do not pose risks to consumers when used properly.

Hydrogen peroxide and ozone 🔗

Hydrogen peroxide and ozone are powerful oxidising agents classified as peroxygens. They generate free radicals that damage microbial macromolecules – DNA, proteins, and lipids. Ozone, in particular, is used for surface decontamination of fruits, vegetables, and cereals, as well as water treatment in food processing plants. Both agents are environmentally friendly because they break down into harmless by-products: water and oxygen (hydrogen peroxide) or just oxygen (ozone).

Organic acids for surface treatment 🔗

Organic acids like lactic acid, acetic acid, and citric acid are also commonly applied as surface sanitisers for meat carcasses and fresh produce. Sodium and calcium lactates, for example, have been shown to be effective at inhibiting the growth of Listeria monocytogenes in seafood and ready-to-eat meat products.

Natural antimicrobial agents 🔗

Consumer demand for “clean label” products – foods with fewer synthetic additives – has driven significant research into natural antimicrobial compounds as alternatives to traditional chemical preservatives. These natural agents fall into three main categories: plant-derived, animal-derived, and microbial-derived.

Essential oils 🔗

Essential oils from herbs and spices such as oregano, thyme, cinnamon, clove, and rosemary contain volatile compounds with proven antimicrobial properties. They are effective against a range of foodborne pathogens including Salmonella, Listeria monocytogenes, Escherichia coli, Bacillus cereus, and Staphylococcus aureus. Essential oils also show antifungal activity, inhibiting mould growth and even mycotoxin production.

The main challenge with essential oils is concentration. Higher amounts are typically needed in actual food systems compared to laboratory settings, and at those concentrations, the strong aroma can alter the food’s flavour profile. To address this, researchers are exploring nanoencapsulation – encapsulating essential oils in tiny biopolymer particles that allow controlled, gradual release throughout the product’s shelf life.

Bacteriocins: nisin and beyond 🔗

Bacteriocins are antimicrobial peptides produced by certain bacteria, primarily lactic acid bacteria (LAB). The most well-known is nisin, produced by Lactococcus lactis. Nisin works by forming pores in bacterial cell membranes and blocking cell wall synthesis. It is the only bacteriocin approved by the U.S. FDA as a food preservative and is used in over 50 countries. It is particularly effective against gram-positive bacteria, including Clostridium species in cheese and Listeria monocytogenes in meat products.

Natamycin, produced by Streptomyces natalensis, is another naturally derived preservative approved for use in many countries. It is an antifungal compound used primarily in dairy products – cottage cheese, sliced cheese, and shredded cheese – to prevent mould growth.

Enzymes: lysozyme and lactoferrin 🔗

Animal-derived enzymes also contribute to the natural antimicrobial toolkit. Lysozyme, found in egg whites, tears, and saliva, breaks down the peptidoglycan layer of bacterial cell walls and is used commercially in certain cheese varieties. Lactoferrin, an iron-binding protein found in milk, deprives bacteria of the iron they need for growth. Both are considered safe for human consumption and are increasingly used in combination with other natural preservatives for enhanced effect.

Factors influencing the effectiveness of chemical agents 🔗

The effectiveness of any chemical agent depends on several key factors. Understanding these helps food scientists choose the right agent – or combination of agents – for a specific product.

Concentration is the most obvious factor – higher concentrations generally mean stronger antimicrobial activity, but regulatory limits and sensory acceptability set upper bounds. pH is critical for organic acid preservatives, whose undissociated (uncharged) form is the active antimicrobial; lower pH means more undissociated acid and greater effectiveness. Temperature influences both microbial growth rates and the chemical activity of preservatives. Water activity (a_w) determines how much free water is available for microbial growth – preservatives work more effectively in environments where water activity is already somewhat reduced. The type and load of microorganisms present also matters; a product with a very high initial microbial count will be harder to preserve than one with a low count.

The nature of the food matrix itself can interfere with preservative action. Fat, protein, and other food components can bind or inactivate chemical agents, reducing their availability. This is one reason why essential oils typically require higher concentrations in real foods than in laboratory tests.

Regulatory framework and safety considerations 🔗

The use of chemical preservatives in food is tightly regulated by national and international bodies. In the United States, the FDA evaluates and approves food additives, and many common preservatives carry GRAS (Generally Recognised as Safe) status. The European Food Safety Authority (EFSA) performs similar evaluations in the EU, setting acceptable daily intake levels and maximum permitted concentrations. Internationally, the Codex Alimentarius Commission, a joint body of the FAO and WHO, provides guidelines that many countries follow.

Safety evaluations consider both short-term toxicity and long-term health effects. This is why nitrites, despite their proven effectiveness in meat preservation, are used at strictly controlled levels – to balance the antimicrobial benefit against the potential risk of nitrosamine formation. It is also why the food industry is increasingly investing in natural alternatives that can deliver comparable preservation without the health concerns linked to some synthetic additives.

Emerging trends and the future of chemical preservation 🔗

The food preservation landscape is evolving rapidly. Several trends are shaping how chemical agents will be used going forward.

Combination approaches are gaining ground. By using multiple antimicrobial agents at lower individual concentrations – for example, combining essential oils with bacteriocins – food scientists can achieve effective preservation while minimising flavour impact and reducing the likelihood of microbial resistance developing.

Active packaging represents another frontier. Instead of adding preservatives directly to food, antimicrobial compounds can be incorporated into the packaging material. This allows controlled, sustained release of agents like essential oils or nisin onto the food surface over time, maintaining freshness throughout shelf life. Researchers have demonstrated, for instance, that biodegradable films containing antimicrobial fibres can significantly extend the shelf life of perishable fruits.

Plant-based nitrite alternatives are also being actively explored. Celery powder and other vegetable extracts that naturally contain nitrates are already used in “uncured” or “naturally cured” meat products. While these products still rely on the nitrate-to-nitrite conversion for their preservative effect, they meet growing consumer preference for ingredients perceived as more natural.

Finally, there is increasing interest in bioprotective cultures – live lactic acid bacteria added to food products where they produce bacteriocins and organic acids in situ, creating a self-preserving system. This approach is especially promising for fermented meats and dairy products.

What do you think? As consumers increasingly demand clean-label products, can natural antimicrobial agents fully replace traditional synthetic preservatives without compromising food safety? And how should regulators balance innovation in food preservation with the need for rigorous safety testing?

References

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