The application of Nisin in dairy products

As a natural antibacterial peptide produced by the fermentation of Lactococcus lactis, Nisin is widely used in the field of dairy product preservation and safety control due to its efficient inhibitory effect on Gram-positive bacteria, human safety, and biodegradability. In two typical dairy products—yogurt and cheese—its application logic centers on "targeted inhibition of spoilage bacteria and pathogenic bacteria," while aligning with the products’ processing characteristics and storage requirements to achieve dual improvements in preservation efficacy and safety without damaging the inherent quality of the products.

I. Application of nisin in Yogurt: Addressing Post-Fermentation and Pathogen Risks

In yogurt, the core role of nisin is to resolve two major issues affecting shelf life and safety: "excessive post-fermentation" and "specific pathogenic bacterial contamination."

Yogurt fermentation relies on the synergistic action of Lactobacillus bulgaricus and Streptococcus thermophilus. After fermentation, if these viable bacteria continue to multiply during low-temperature storage, they cause excessive increases in yogurt acidity, thinning of texture, and a sour taste—known as the "post-fermentation" problem—which directly shortens the product’s shelf life. Nisin has a weak inhibitory effect on these two fermentative strains (they belong to nisin-producing related strains and have a certain tolerance to it) but can efficiently inhibit other Gram-positive spoilage bacteria that may contaminate the product from the environment (such as heterozygous strains of some lactobacilli and streptococci). These spoilage bacteria often exacerbate post-fermentation or produce off-flavor substances. By adding an appropriate amount of Nisin at a specific stage of yogurt processing (e.g., after fermentation and before filling), the growth of spoilage bacteria can be inhibited, the rate of acidity increase slowed, and the stable taste and flavor of yogurt maintained, thereby extending the refrigerated shelf life (usually by 2–5 days under low-temperature storage, depending on the initial contamination level and storage conditions).

Meanwhile, yogurt production faces the risk of contamination by Gram-positive pathogenic bacteria such as Listeria monocytogenes and Staphylococcus aureus (mostly from raw milk, processing equipment, or the environment). These pathogens may multiply slowly under refrigeration, endangering food safety. Nisin exhibits a strong inhibitory effect on pathogens like Listeria monocytogenes; its mechanism of action involves disrupting the integrity of bacterial cell membranes, leading to leakage of cellular contents and bacterial death, and this mode of action rarely induces bacterial resistance. Adding Nisin to yogurt in compliance with national standards (China stipulates a maximum nisin usage of 0.2 g/kg in dairy products) can effectively reduce the contamination risk of such pathogens. This is particularly critical for low-temperature yogurt with a long shelf life or products requiring short-term room-temperature transportation, as nisin forms a "safety barrier" to prevent pathogen overgrowth caused by fluctuations in storage conditions. Additionally, the natural origin of nisin aligns with the "natural and healthy" positioning of yogurt, eliminating consumer concerns about chemical preservatives and without affecting the nutritional value of yogurt (e.g., protein and calcium content) or the activity of probiotics (provided that the timing and dosage of addition are controlled to avoid prolonged direct contact with probiotics).

II. Application of Nisin in Cheese: Covering Processing, Ripening, and Storage Stages

In cheese production and storage, nisin has more diverse application scenarios, targeting both "early-stage spoilage" during processing and "quality deterioration" and "safety hazards" during ripening and storage.

Cheese processing involves multiple stages, including curdling, cutting, and ripening. Spoilage bacteria in raw milk (such as certain slime-producing streptococci and bacilli) may multiply rapidly during curdling, resulting in loose curd texture, off-flavors, and compromised basic cheese quality. During ripening, mold (some molds are used to develop specific cheese flavors, but heterozygous mold causes spoilage), acid-producing bacteria, and other microorganisms tend to grow on the cheese surface, leading to black spots, sour flavors, and even the production of harmful substances. Nisin has a significant inhibitory effect on these Gram-positive bacteria (including the mycelium of some molds) that cause early-stage cheese spoilage and surface deterioration, and its application methods are flexible:

It can be directly added to raw milk to inhibit the growth of spoilage bacteria from the early processing stage, ensuring curd quality.

It can be formulated into a Nisin solution, which is sprayed or brushed onto the cheese surface before ripening to form an "antibacterial film," preventing subsequent growth of heterozygous bacteria and extending the ripening period and shelf life.

For enhancing cheese safety, the core value of Nisin lies in controlling Listeria monocytogenes contamination. Listeria monocytogenes is tolerant to low temperatures and high salt; however, the high-salt, low-moisture environment of cheese (especially hard cheese) during ripening and refrigerated storage may instead become a "favorable survival zone" for this pathogen. Once contaminated, it easily causes food poisoning. Nisin’s inhibitory effect on Listeria monocytogenes is not affected by the high-salt environment in cheese, and it can penetrate to a certain depth inside the cheese (depending on the cheese’s texture and porosity), inhibiting not only pathogens contaminating the surface but also reducing potential internal contamination risks. Additionally, in cheese production, Nisin can reduce "raw material loss" caused by spoilage bacterial growth: if raw milk has a high content of spoilage bacteria, traditional processes require prolonged sterilization time or increased sterilization temperature to control them, which may lead to excessive denaturation of milk proteins and affect curdling efficiency. Adding Nisin reduces the intensity of sterilization, ensuring sterilization efficacy while minimizing the loss of nutrients in milk and improving cheese yield and quality stability.

III. Key Considerations for nisin Application in Dairy Products

The application of Nisin in dairy products must strictly adhere to the principles of "dosage adaptation" and "process matching":

On one hand, excessive addition may cause a slight bitter or metallic taste in dairy products (though nisin itself is tasteless, it may interact with milk proteins at high concentrations), affecting flavor.

On the other hand, nisin has a weak inhibitory effect on Gram-negative bacteria (such as Escherichia coli) and cannot replace complete sterilization processes (e.g., pasteurization, ultra-high temperature instantaneous sterilization). It must be combined with good manufacturing practices (GMP) and raw material control to achieve comprehensive preservation and safety assurance.

Furthermore, different types of dairy products have varying tolerance and requirements for Nisin:

For high-fat cheese, fat may adsorb part of Nisin, reducing its free concentration, so the addition amount needs to be adjusted appropriately.

For fermented yogurt, nisin should be added avoiding the stage of vigorous probiotic proliferation to prevent weak inhibition of probiotic activity.

The application of nisin in yogurt and cheese essentially leverages its characteristics of "targeted antibacterial activity" and "natural safety" to make up for the preservation shortcomings and safety gaps in traditional processing and storage. In yogurt, it focuses on delaying post-fermentation, preventing and controlling pathogens, and extending the refrigerated shelf life; in cheese, it covers the early processing stage, ripening stage, and storage period, ensuring curd quality, inhibiting mold growth and pathogen contamination, while aligning with consumers’ demand for "natural and healthy" dairy products. Thus, Nisin has become a bio-preservative with both practicality and safety in the dairy industry.