The core role of Nisin in the preservation of dairy products

Nisin, an antimicrobial peptide naturally produced by lactic acid bacteria, has become a widely used natural preservative in dairy product preservation due to its unique bacteriostatic properties, safety, and compatibility. Its core role is reflected in multiple dimensions: precisely inhibiting spoilage bacteria, extending product shelf life, reducing reliance on processing, and ensuring food safety. It is highly compatible with the physicochemical properties of dairy products and consumer demands.

I. Targeted Inhibition of Gram-Positive Spoilage Bacteria, Blocking the Deterioration Chain of Dairy Products

Dairy products are rich in protein, fat, and lactose, making them ideal substrates for microbial growth. Among them, Gram-positive bacteria (such as Bacillus, Listeria, and Staphylococcus) are the main culprits behind spoilage and safety risks. For example, spores of Bacillus can survive pasteurization, germinate under refrigerated conditions, and produce proteases and lipases, leading to milk stratification and off-flavors. Listeria monocytogenes, a pathogenic bacterium, can multiply at low temperatures (4°C) and cause foodborne diseases.

Nisin exhibits high specificity in inhibiting these bacteria: it binds to lipid II (a peptidoglycan synthesis precursor) on bacterial cell membranes, blocking cell wall synthesis and forming pores to cause leakage of intracellular substances, ultimately killing or inhibiting bacterial proliferation. This mechanism is particularly effective against Gram-positive bacteria but has minimal impact on lactic acid bacteria required for dairy fermentation (such as Lactobacillus bulgaricus and Streptococcus thermophilus)—because the lipid composition and structure of lactic acid bacteria membranes make them insensitive to Nisin. Therefore, Nisin can precisely eliminate spoilage bacteria and pathogens without damaging the fermented flavor of dairy products, blocking the deterioration chain from the source.

II. Enhancing Stress Resistance, Adapting to Dairy Processing and Storage Conditions

The processing and storage environments of dairy products impose strict requirements on the stability of preservatives, and Nisin’s structural characteristics allow it to perfectly adapt to these conditions. On one hand, the rigid internal ring structure formed by thioether bonds in Nisin molecules ensures its stability in acidic environments (e.g., yogurt with pH 4.0-4.5) and its ability to withstand short-term heating during pasteurization (72-85°C) or even ultra-high temperature (UHT) sterilization (above 135°C) without inactivation during processing. On the other hand, Nisin maintains bacteriostatic activity during refrigeration (0-4°C) or room temperature storage, compensating for the insufficient inhibition of some psychrophilic bacteria at low temperatures.

For example, adding 100-500 IU/g of Nisin to pasteurized milk can significantly inhibit the germination of residual spore-forming bacteria, extending the shelf life from 7 days to 14-21 days. In cheese production, Nisin can inhibit acid-producing bacteria or mold contamination during maturation, preventing excessive acidification, mold spots, or flavor deterioration. This stress resistance enables it to achieve preservative effects without relying on excessively high processing temperatures or excessive chemical additives.

III. Reducing Dependence on Thermal Processing, Preserving Dairy Nutrition and Flavor

Traditional dairy preservation often relies on high-temperature sterilization (e.g., UHT milk), but excessive heating destroys vitamins (such as B vitamins), whey proteins, and flavor substances (such as volatile fatty acids) in milk, reducing nutritional value and resulting in a bland taste. The application of Nisin can reduce dependence on high-temperature processing, achieving preservation through a combination of "moderate heating + Nisin synergy," ensuring safety while retaining the natural properties of dairy products.

For example, in the production of low-temperature milk (pasteurized milk), combining Nisin allows for appropriate reduction in sterilization temperature or time, reducing whey protein denaturation and lactose caramelization, making the milk closer to the flavor and nutrition of fresh milk. In fermented milk, Nisin can replace some chemical preservatives, avoiding interference with lactic acid bacteria fermentation and ensuring the acidity, texture, and probiotic activity of yogurt. This "mild preservation" model not only meets consumers’ demand for natural and nutritious products but also provides possibilities for quality upgrading in the dairy industry.

IV. Natural Origin and Safety, Aligning with Dairy Consumption Demands

As a daily high-frequency consumed nutritional food, the safety of dairy products is of great concern. Nisin’s natural origin (a product of lactic acid bacteria fermentation) and metabolic characteristics give it extremely high safety: there are no Nisin receptors in the human digestive tract, and it is degraded into amino acids by digestive enzymes such as trypsin without accumulation in the body. Therefore, it has been recognized as a "GRAS" (Generally Recognized as Safe) substance by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), allowing its use in various foods as needed without daily intake restrictions.

This safety makes it particularly suitable for preserving dairy products for sensitive populations such as infant formula and elderly dairy products. For example, in infant milk powder, Nisin can inhibit pathogenic bacteria such as Cronobacter sakazakii without interfering with the infant’s intestinal flora. In products such as cheese and cream, it has good compatibility with milk components, without affecting product color, taste, or nutritional value, meeting consumers’ pursuit of "clean labels" (fewer additives, no chemical preservatives).

The core role of Nisin in dairy preservation essentially lies in building an efficient and mild preservative system through multiple advantages: targeted bacteriostasis, environmental adaptability, quality protection, and safety compatibility. It not only solves the industry pain point of dairy products being susceptible to Gram-positive bacterial contamination but also balances preservative effects with product quality and safety, becoming a model for the application of natural preservative technology in the food industry. With the increasing consumer demand for natural and healthy dairy products, the application scenarios of Nisin will further expand, providing key support for the sustainable development of the dairy industry.