The preservative and antiseptic role of Nisin in vegetarian products

Nisin (lacticin), a natural antimicrobial peptide derived from lactic acid bacteria fermentation, possesses characteristics such as a targeted antibacterial spectrum, high safety, and no chemical residues, aligning with the core demands of vegetarian products for "naturalness, health, and clean labels." In vegetarian products, it delays deterioration caused by microbial proliferation by specifically inhibiting Gram-positive pathogenic and spoilage bacteria, while not affecting product flavor, nutrients, or sensory quality, making it an ideal choice for vegetarian preservation. Detailed explanations are provided below regarding its mechanism of action, application scenarios, adaptation advantages, and key usage points:

I. Core Preservation Mechanisms

Nisin exerts its antibacterial effects primarily by targeting bacterial cell membranes, disrupting structural integrity and metabolic balance to achieve bactericidal/bacteriostatic outcomes:

Targeted Binding and Membrane Pore Formation: Nisin specifically recognizes lipid II (a precursor for bacterial cell wall synthesis) on the cell membrane of Gram-positive bacteria. Upon binding, it forms transmembrane pores, increasing membrane permeability and causing massive leakage of intracellular nutrients such as potassium ions and amino acids, ultimately leading to bacterial death.

Inhibition of Cell Wall Synthesis: By blocking the transport and cross-linking of lipid II, Nisin inhibits the synthesis of bacterial cell wall peptidoglycan, preventing bacteria from maintaining their morphology and causing them to rupture under osmotic pressure.

Synergistic Enhancement: Although it has weak direct inhibitory effects on Gram-negative bacteria, Nisin can act synergistically with chelating agents such as EDTA (ethylenediaminetetraacetic acid) and citric acid to disrupt the lipopolysaccharide structure of the outer membrane of Gram-negative bacteria, enhance membrane permeability, and expand the antibacterial spectrum.

Nisin exhibits significant inhibitory effects on common spoilage bacteria (e.g., Bacillus subtilis, Bacillus cereus, overproliferating lactic acid bacteria strains) and pathogenic bacteria (e.g., Staphylococcus aureus, Listeria monocytogenes) in vegetarian products. However, it has no direct inhibitory effect on yeasts and molds and thus needs to be used in combination with other natural preservatives (e.g., ε-polylysine, plant extracts).

II. Main Application Scenarios and Effects

1. Plant Protein-Based Vegetarian Products (Tofu, Dried Tofu, Vegetarian Meat, Plant-Based Milk)

Spoilage Pain Points: Rich in plant protein and moisture, they are prone to contamination by spore-forming bacteria and lactic acid bacteria, leading to sourness, stickiness, and softening of texture (e.g., tofu spoils within 24 hours).

Application Effects: Adding 0.05~0.1 g/kg of Nisin (based on pure product) can extend the refrigerated (4℃) shelf life of tofu and dried tofu from 2~3 days to 7~10 days, and the room-temperature shelf life of plant-based milk (e.g., soybean milk, oat milk) from 3~5 days (unsterilized) to 15~20 days. It does not affect the bean flavor, smooth texture, or protein nutritional value of the products.

Process Adaptation: Added after soybean milk boiling in tofu production, and after homogenization and before sterilization in plant-based milk production. This can enhance thermal sterilization efficiency, reduce sterilization temperature (e.g., from 121℃ to 110℃), and minimize nutrient destruction.

2. Vegetarian Sauces and Condiments (Vegetarian Salad Dressing, Vegetarian Broad Bean Paste, Plant-Based Seasoning Sauces)

Spoilage Pain Points: Containing fats, carbohydrates, and moisture, they are prone to lipid rancidity and mold contamination (e.g., salad dressing stratification, mold growth on broad bean paste).

Application Effects: Combined with ε-polylysine at a ratio of 3:1, with a total addition amount of 0.1~0.15 g/kg, the refrigerated shelf life of vegetarian sauces can be extended from 1~2 months to 3~4 months, and the room-temperature sealed shelf life from 3~6 months to 6~12 months. It effectively inhibits the rancid odor caused by lipid oxidation and maintains stable sauce flavor.

Adaptation Advantages: Strong acid resistance (stable within pH 2.5~6.5), suitable for acidic vegetarian condiments such as salad dressings and vinegar-based sauces, without affecting product sourness or flavor balance.

3. Ready-to-Eat Vegetarian Dishes (Stir-Fried Vegetables, Vegetarian Braised Products, Plant-Based Fast Food)

Spoilage Pain Points: Residual moisture and nutrients after processing, making them susceptible to bacterial growth during cooling, leading to spoilage within 2~3 days of refrigeration.

Application Effects: Sprayed or soaked at a concentration of 0.08~0.12 g/kg when the cooked dishes are cooled to below 60℃. This can extend the refrigerated (0~4℃) shelf life of ready-to-eat vegetarian dishes from 3~5 days to 7~10 days. They retain their original texture and flavor after microwave reheating without off-odors.

Safety Advantages: Nisin can be degraded into amino acids by proteases in the human digestive tract, with no residues or toxicity. Its ADI (Acceptable Daily Intake) value is unrestricted, meeting the consumer demand for "natural safety" in vegetarian products.

4. Vegetarian Baked Goods and Pastries (Vegetarian Bread, Vegetarian Cake, Plant-Based Cookies)

Spoilage Pain Points: Containing starch and sugars, they are prone to mold contamination (e.g., Penicillium, Aspergillus), leading to surface mold growth and poor texture.

Application Effects: Combined with natamycin at a ratio of 5:1, with a total addition amount of 0.06~0.1 g/kg, the room-temperature shelf life of vegetarian baked goods can be extended from 7~10 days to 15~20 days. It effectively inhibits mold growth without affecting product fluffiness, texture, or flavor.

Process Adaptation: Can be added during dough mixing. It has good heat resistance (retains more than 80% activity after sterilization at 121℃ for 30 minutes), adapting to high-temperature baking processes.

III. Adaptation Advantages in Vegetarian Products

Alignment with Clean Label Trends: Nisin is derived from microbial fermentation and classified as a natural food additive, meeting the demand for "no synthetic preservatives" in vegetarian products. It can be labeled as "nisin (lacticin)" on the ingredient list, enhancing consumer trust.

No Impact on Vegetarian Flavor and Nutrition: Nisin itself has no off-odor and does not damage nutrients such as plant proteins, dietary fiber, and vitamins. It does not alter the natural flavor of vegetarian products (e.g., bean aroma, vegetable freshness), outperforming chemical preservatives (e.g., sodium benzoate, potassium sorbate) that may cause off-odors.

High Safety for Special Vegetarian Populations: Non-allergenic, suitable for vegetarians, vegans, and lactose-intolerant individuals. It contains no animal-derived ingredients, fully complying with the ethical requirements of vegetarian products.

Low Usage Cost and Strong Process Compatibility: Added in extremely low amounts (mg/kg), without significantly increasing production costs. It can synergize with preservation technologies such as heating, refrigeration, and vacuum packaging, adapting to various processing technologies of vegetarian products (e.g., boiling, baking, fermentation).

IV. Key Usage Points and Precautions

Addition Amount Control: Strictly follow GB 2760 National Food Safety Standard for the Use of Food Additives. The maximum usage amount of Nisin in different vegetarian products is 0.3 g/kg (based on pure product). Excessive addition will not improve preservation effects but may increase costs.

Combined Use to Expand Antibacterial Spectrum: Due to Nisin's weak inhibitory effects on yeasts and molds, it is recommended to combine it with natural preservatives (e.g., natamycin, plant extracts, ε-polylysine) to achieve comprehensive preservation against "bacteria + molds + yeasts."

Process Adaptation Requirements: Avoid prolonged contact with strong acids and alkalis (stability decreases when pH < 2 or pH > 8). For high-temperature processing, it is advisable to add Nisin in the later stage or combine it with heat-resistant preservatives to ensure antibacterial activity.

Storage Conditions: Nisin products should be stored in sealed, light-shielded, and refrigerated (below 4℃) environments to avoid reduced activity caused by high temperature and humidity, which affects preservation effects.

With its core advantages of "natural origin, targeted antibacterial activity, and safety without residues," Nisin plays an important role in the preservation of vegetarian products. It can effectively extend the shelf life of various vegetarian products, inhibit the proliferation of spoilage bacteria, and maintain their natural flavor and nutrients, aligning with the health demands and clean label trends of vegetarian consumption. By reasonably controlling the addition amount, combining with other natural preservatives, and optimizing process adaptability, Nisin can further improve the storage stability and market competitiveness of vegetarian products, providing technical support for the large-scale development of the vegetarian industry.