Antimicrobial agents for food processing: definition, types and uses

Foodborne illnesses and product spoilage are driven by microbial contamination. The effects are well-established and the cost due to health and environmental implications is amount to trillions of euros. Antimicrobial agents for food processing are among the most targeted tools available to manufacturers seeking to control pathogenic and spoilage microorganisms at critical points in the production chain.

What are antimicrobial agents?

In the context of food processing, an antimicrobial agent is any substance capable of slowing, inhibiting the growth of, or killing, microorganisms that pose a risk to food safety or product quality. This includes bacteria, yeasts, and molds. The functioning mechanism varies by agent. For example, organic acids act primarily through intracellular acidification and disruption of the proton motive force, bacteriocins such as nisin form pores in the cell membrane, chorline compounds oxidize cellular parts. Importantly, some agents are bactericidal, i.e. they kill cells, while others are bacteriostatic, inhibiting growth without achieving cell death. This distinction has practical consequences for application design and for the interpretation of the minimum inhibitory concentration.
The term “antimicrobial agent” is sometimes used interchangeably with “preservative”, but the two are not equivalent. Preservatives are a subset of food additives formally defined under food law, governed by approved use lists and maximum permitted levels. Antimicrobial agents is the broader technical category: it includes preservatives but also agents applied during processing such as surface decontamination treatments, wash and rinse solutions, carcass treatments, that may not be present in the final product label. Within a food safety management system, antimicrobial agents operate as one layer of the hurdle approach used to impose barriers to microbes, and should not be seen as a substitute for good manufacturing practice, temperature control, or general hygiene.

Why antimicrobial agents are used in food processing?

Foodborne pathogens such as Listeria monocytogenes, Salmonella spp., Escherichia coli O157:H7, Clostridium botulinum, and Campylobacter spp. represent both a public health risk and a significant liability for food brands and businesses. Antimicrobial agents are used at critical control points to reduce pathogen loads on raw materials, processing surfaces, and finished products. In ready-to-eat categories, where there is no terminal kill step after processing, this intervention becomes essential rather than precautionary and for certain microorganisms and food categories a rigorous legal framework exists.
Beyond pathogens, manufacturers apply antimicrobial agents to manage spoilage microorganisms, organisms that do not cause illness but degrade quality, reduce shelf life, and generate economic loss. Depending on the food matrix, packaging, and contamination, lactic acid bacteria and pseudomonads, are among the primary spoilage organisms leading to acidification, color change, slime, and the development of unpleasant aromas. In certain food categories such as bakery, visual mold growth is the dominant concern.

Types of antimicrobial agents used in food processing

Chemical antimicrobial agents

Organic acids and their salts are among the most widely applied chemical antimicrobials in food processing. Lactic acid, acetic acid, citric acid, and propionic acid in their sodium, potassium, and calcium salt forms act through a mechanism that begins at the cell membrane and continues intracellularly. The undissociated acid form, favored at low pH, crosses the membrane and dissociates inside the cell. The resulting proton release forces the organism to expend ATP restoring intracellular pH homeostasis, ultimately depleting energy reserves and inhibiting growth. Buffered salt systems deliver this activity with reduced sensory impact. Whereas these acids are often of petrochemical origin, it is not uncommon to find pure salts derived from sugar fermentation.

Sorbic acid and potassium sorbate are widely used in bakery, dairy, and beverage applications for their efficacy against yeasts and molds. Sorbate activity follows the same pH dependency, at lower pH the undissociated form is in larger concentration. It offers limited activity against most bacteria, making it a spoilage control tool in mildly acidic matrices rather than a broad-spectrum antimicrobial but is highly efficient against yeasts. Benzoic acid and sodium benzoate share this mechanism and spectrum profile. Their use is concentrated in acidic products, that’s why it is used in soft drinks, condiments, pickled vegetables where the low pH provides a favorable environment for yeasts and molds but also benzoate’s undissociated form is the highest. Above pH 5, benzoate activity diminishes substantially.

Sulfites is a broad distinct class combining antimicrobial and antioxidant functions and contains mostly sulfur dioxide, sodium sulfite, sodium bisulfite, and potassium metabisulfite. They also complement the overall flavor profile of the food product. Activity is attributed primarily to the free SO₂ molecule and the bisulfite ion, which react with cellular enzymes and nucleic acids. Sulfites are effective against yeasts and, to a lesser degree, bacteria and molds, and are used in wine production, dried fruits, and certain vegetable and seafood applications. Metabisulfites are commonly used in specific countries for certain meat applications such as fresh sausages. Their use requires careful management: sulfites are a declared allergen above threshold levels in the EU and most other regulated markets, with mandatory labelling obligations.
Chlorine-based compounds are used extensively in wash water treatments for fresh produce and poultry in many countries, and in equipment sanitation. Their efficacy against a broad bacterial spectrum is well established, though it is pH- and organic-load-dependent.

Biological and naturally derived antimicrobial agents

Fermentates have become commercially significant within this category. Produced through controlled fermentation of food-grade by selected bacterial strains, fermentates deliver a complex mixture of organic acids, bacteriocins, and other metabolites in a form that qualifies for clean label declarations under several regulatory frameworks. Their antimicrobial activity is not attributable to a single compound but to the combined metabolite profile, which can vary between batches and suppliers. Standardisation of activity across lots is an important quality parameter.

Bacteriocins are another class of biologically derived antimicrobials primarily produced by lactic acid bacteria to provide them with a competitive advantage in a food ecosystem. They act through pore formation in the target cell membrane causing cell death. Nisin, produced by Lactococcus lactis, is the most commercially established bacteriocin, with approved use across numerous markets in processed cheese, canned foods, and certain meat products. Its target spectrum covers gram-positive organisms including Listeria monocytogenes, Bacillus, and Clostridium. Nisin has very limited activity against gram-negative bacteria and no meaningful activity against yeasts or molds.

Plant-derived antimicrobials form a broad and heterogeneous subgroup. Polyphenolic compounds, essential oil components such as thymol and carvacrol, and botanical extracts all show antimicrobial activity in laboratory conditions, primarily through disruption of the cell membrane and interference with enzymatic activity. Extrapolating this effect to food matrices introduces considerable complexity. Volatility, interaction with lipid and protein fractions, pH sensitivity, and sensory impact all affect efficacy. A product containing carvacrol, one of the two main oils found in oregano, at a concentration active against Listeria in a broth system may deliver a fraction of that activity in a high-fat matrix, and may render the product organoleptically unacceptable. This gap between laboratory performance and in-product reality is the defining challenge of plant-derived antimicrobial formulation and is the main obstacle besides cost and extraction complexity on why this subgroup, despite strong scientific interest, remains less commercially established.

Effectiveness of antimicrobial agents against foodborne pathogens

A universal antimicrobial agent does not exist. Effectiveness is always relative to the target organism, the food matrix, processing conditions, and intended use. The outer membrane of gram-negative bacteria restricts the entry of some larger hydrophilic compounds, but small lipophilic molecules including undissociated organic acids traverse it with ease. Spores of spore-forming organisms resist most chemical antimicrobials at legally allowed concentrations.
pH is the most critical variable in many food systems. Organic acids depend on the undissociated form, as pH rises above the respective pKa value, activity diminishes significantly. The same concentration of sodium lactate at pH 4.5 delivers substantially more protection than at pH 6.0. Food matrix interactions compound this further: proteins can sequester antimicrobial agents, fat content affects distribution of lipophilic compounds such as nisin, and competing microorganisms modulate effective concentration reaching the target organism. In practice, effectiveness is most reliably achieved through combination strategies known as the hurdle concept which remains the most scientifically grounded framework for antimicrobial system design.

Safety and regulatory considerations

In the European Union, food additives are governed by Regulation (EC) No 1333/2008, which establishes an approved list, permitted food categories, and maximum use levels. Processing aids fall under a separate and less harmonized framework. In the United States, the FDA administers GRAS designations alongside formal food additive approvals under 21 CFR; meat and poultry antimicrobial interventions are additionally subject to USDA FSIS oversight. Codex Alimentarius provides the international harmonisation reference, though national implementation varies considerably.

Compliance is not only a legal obligation. Using an agent above its permitted maximum, in an unauthorized food category, or without adequate documentation creates regulatory exposure with real safety and commercial consequences. Agent selection must therefore begin with a regulatory check against the intended application and target markets, before efficacy or cost are evaluated. Health authorities also monitor the relationship between food antimicrobial use and resistance development. Overall, responsible use at effective rather than sub-inhibitory concentrations is both a regulatory expectation and a sound scientific practice.
Food processing and distribution has always been a negotiation between what microorganisms want to do in a specific food and what humans need from this food. Antimicrobial agents are one of the primary tools through which that negotiation is managed. The practical challenge is not finding an antimicrobial agent but rather designing a system where the right agent, at the right concentration, in the right matrix, is effective and provides value.

There is no single agent that solve all the problems. Organic acids, sorbates, benzoates, and sulfites, fermentates, and bacteriocins each cover part of the microbial spectrum, each carrying matrix sensitivities and regulatory constraints. The science of effectiveness is ultimately the science of context.