The applicability of Nisin in infant and toddler food

As a natural antimicrobial peptide food additive approved by the European Union, U.S. FDA, and Chinese national standards, Nisin is widely used in food preservation due to its non-toxicity, biodegradability, and targeted inhibition of Gram-positive pathogenic bacteria. Infants aged 0–36 months have immature physiological development, with unique digestive, immune, and metabolic systems, imposing more stringent requirements on the safety and functionality of food additives. This article systematically evaluates the applicability of Nisin in infant food from four dimensions: safety foundation, necessity of bacteriostasis, limiting factors, and compliant application strategies. It provides a scientific basis for industry-compliant production and supervision, as well as technical reference for infant food safety protection.

I. Safety Foundation of Nisin Application in Infant Food

1. Toxicological Safety Verification

Nisin’s safety has been confirmed by multiple authoritative toxicological tests, with its toxicological characteristics highly compatible with infants’ physiological tolerance requirements:

Acute Toxicity: The median lethal dose (LD₅₀) is >2000 mg/kg body weight (BW) via oral administration in rats, classified as practically non-toxic. Long-term feeding trials (12 months) showed no growth retardation, organ damage, or metabolic abnormalities in rats when the acceptable daily intake (ADI) reached 1500 IU/kg BW.

Metabolic Characteristics: As a peptide composed of 34 amino acids, Nisin is completely degraded into amino acids by trypsin and pepsin in the infant gastrointestinal tract, with no risk of residue accumulation. The degradation products can participate in the body’s protein metabolism without burdening metabolic organs such as the liver and kidneys.

Extremely Low Allergy Risk: Nisin’s molecular structure has no homology with human proteins, and purification processes during fermentation remove miscellaneous proteins. Clinical data show that the incidence of Nisin allergy in infants is <0.01%, significantly lower than common allergens such as milk and eggs.

Recognition by Authoritative Institutions: The Joint FAO/WHO Expert Committee on Food Additives (JECFA) established an ADI of 0–3300 IU/kg BW (approximately 0–0.13 mg/kg BW) for Nisin. Chinese GB 2760-2014 and EU Regulation (EC) No 1333/2008 both approve its use in certain infant foods, establishing a legal basis for safe application.

2. Compatibility with Infants’ Physiological Characteristics

The uniqueness of infants’ physiological systems requires food additives to be "low-irritant and highly compatible," which Nisin’s properties satisfy:

Digestive System Compatibility: Infants have low gastric acid secretion (gastric pH 3.5–5.0), which falls within Nisin’s optimal pH range for bacteriostatic activity (2.0–6.0). This environment neither inactivates Nisin nor causes gastrointestinal mucosal irritation.

Immune System Compatibility: Nisin specifically inhibits Gram-positive pathogenic bacteria (e.g., Staphylococcus aureus, Listeria monocytogenes, Bacillus subtilis) without affecting beneficial intestinal flora (e.g., Bifidobacterium, Lactobacillus) in infants. It maintains intestinal microecological balance and has no antagonistic effect when used in combination with probiotic supplements.

Minimal Metabolic Burden: Nisin does not participate in key physiological processes such as hormone synthesis or neurotransmitter metabolism in infants. Its degradation products are essential amino acids, which do not interfere with normal growth and development.

II. Necessity of Nisin Application in Infant Food

1. Microbial Contamination Risks in Infant Food

Infant food (e.g., formula milk powder, complementary food puree, infant biscuits) faces significantly higher microbial contamination risks than ordinary food during production, storage, and consumption:

Raw Material Contamination: Raw materials such as milk powder, grains, fruits, and vegetables may carry pathogenic bacteria (e.g., Salmonella, Listeria monocytogenes, Bacillus cereus). Infants with weak immunity are prone to severe gastrointestinal diseases (e.g., diarrhea, sepsis) after infection.

Processing Contamination: Incomplete sterilization during wet-process production of formula milk powder may allow residual Bacillus spores to germinate during storage. Ready-to-eat foods such as complementary food puree are susceptible to mold and yeast contamination during packaging and transportation.

Consumption Scenario Risks: After opening, infant food is frequently exposed to air and tableware, facilitating bacterial growth. Infants consume small portions, resulting in short shelf lives (typically 1–3 days) after opening, increasing contamination probability.

2. Targeted Bacteriostatic Value of Nisin

Nisin addresses key microbial safety challenges in infant food, outperforming chemical preservatives:

Precise Pathogen Inhibition: It exhibits potent inhibition against common Gram-positive pathogenic bacteria in infant food (e.g., Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus) with a minimum inhibitory concentration (MIC) of only 0.01–5 μg/mL, effectively reducing infection risks.

Replacement of High-Risk Preservatives: Traditional chemical preservatives (e.g., sodium benzoate, potassium sorbate) are low-cost but may irritate infants’ gastrointestinal tracts and have potential metabolic toxicity. As a natural antimicrobial peptide, Nisin meets preservation needs while reducing reliance on chemical preservatives.

Nutrition and Flavor Preservation: At bacteriostatic concentrations, Nisin does not affect nutrients (e.g., proteins, vitamins, minerals) in infant food, nor does it produce off-odors or alter texture. Compared with high-temperature sterilization, it better retains the original nutrition and flavor of food.

III. Limiting Factors of Nisin Application in Infant Food

1. Limited Antibacterial Spectrum and Application Scenario Restrictions

Insufficient Gram-Negative Bacteria Inhibition: Nisin has weak activity against Gram-negative pathogenic bacteria (e.g., Escherichia coli, Salmonella), requiring combination with chelating agents such as EDTA to penetrate the outer membrane barrier. However, EDTA addition in infant food is strictly limited (Chinese GB 2760-2014 specifies a maximum dosage of 0.075 g/kg).

No Fungal Inhibition: Nisin is ineffective against molds and yeasts, which commonly contaminate complementary food purees and fruit/vegetable products. This necessitates combination with other natural bacteriostatic agents (e.g., ε-polylysine, plant extracts), increasing formulation complexity.

Significant Matrix Interference: In high-protein infant food (e.g., formula milk powder, high-protein complementary food), macromolecules such as casein and whey protein form complexes with Nisin, reducing its bacteriostatic activity. Increasing the dosage is constrained by the ADI, making it difficult to achieve efficient bacteriostasis.

2. Usage Constraints Due to Infants’ Physiological Specificities

Strict Dosage Control: Infants’ daily intake must strictly comply with the ADI standard (0–3300 IU/kg BW). For example, an infant weighing 10 kg should not consume more than 33,000 IU (approximately 1.3 mg) of Nisin per day. The limited daily consumption of formula milk powder and complementary food results in extremely low allowable Nisin concentrations (typically ≤500 IU/g), which may not meet the preservation needs of high-risk foods.

Processing Stability Issues: Infant food processing technologies (e.g., spray drying of formula milk powder, high-temperature sterilization of complementary food) may cause Nisin activity attenuation. For instance, heating at 120℃ for 10 min results in 30%–50% activity loss. Late-stage addition or formulation protection technologies are required.

3. Compliance and Consumer Perception Limitations

Restricted Application Scope: Chinese GB 2760-2014 approves Nisin for infant formula food and complementary food but specifies limits (e.g., maximum 500 IU/g in formula milk powder). Some countries (e.g., Japan) remain cautious about Nisin use in infant food, restricting formula design for export products.

Consumer Perception Bias: Some consumers resist "food additives," believing infant food should be "additive-free." This places market pressure on enterprises using Nisin, requiring science popularization and transparent labeling to build trust.

IV. Compliant Application Strategies of Nisin in Infant Food

1. Strict Adherence to Compliance Requirements

Restricted Application Scope and Dosage: Apply Nisin only in GB 2760-2014 approved infant food categories (e.g., formula milk powder, infant rice flour, complementary food puree) with dosages strictly within limits (typically ≤500 IU/g). Dietary exposure assessments must confirm daily intake does not exceed the ADI.

Standardized Labeling: Clearly mark "Nisin (Lacticin)" under the "Food Additives" section of product labels, including dosage, to protect consumer right to know.

Compliant Raw Materials and Production: Use food-grade Nisin with purity ≥90% to ensure no fermentation residues or excessive heavy metals. Implement GMP standards during production to avoid cross-contamination.

2. Optimized Formulation Design and Bacteriostatic Systems

Synergistic Composite Bacteriostasis

Compound with Natural Bacteriostatic Agents: Nisin (300–400 IU/g) + ε-polylysine (0.01%–0.02%) + plant extracts (e.g., tea polyphenols 0.05%, clove extract 0.03%) expands the antibacterial spectrum to cover Gram-positive bacteria, Gram-negative bacteria, and fungi while reducing individual component dosages.

Rational Combination with Chelating Agents: Add EDTA (≤0.075 g/kg) within approved limits to disrupt Gram-negative bacterial outer membranes, enhancing Nisin activity. Suitable for high-risk infant foods (e.g., ready-to-eat complementary food puree).

Matrix Interference Mitigation: In high-protein/high-fat infant food, optimize formula ratios (e.g., moderately reduce milk protein content) or add small-molecule emulsifiers (e.g., glycerol monostearate) to reduce Nisin-macromolecule binding and increase free Nisin concentration.

3. Adaptation to Infant Food Processing Technologies

Optimized Addition Timing: Adopt a "late-stage addition" strategy, adding Nisin during the cooling phase (temperature <60℃) to minimize high-temperature damage. For example, adding Nisin during the mixing stage after spray drying in formula milk powder production achieves >90% activity retention.

Formulation Technology Application: Use microencapsulation technology with wall materials such as maltodextrin, β-cyclodextrin, or chitosan to prepare Nisin microcapsules (particle size 1–10 μm). This protects Nisin from temperature and humidity during processing, enabling sustained release and prolonged bacteriostatic effect.

Process Parameter Adaptation: Adjust processing parameters (e.g., lower sterilization temperature, shorter time) combined with Nisin’s bacteriostatic effect to ensure food safety while reducing nutrient loss.

4. Targeted Application Scenario Design

Formula Milk Powder: Add 300–500 IU/g to inhibit germinating Bacillus spores during storage, extending the shelf life after opening from 1–2 days to 3–5 days without affecting probiotic activity.

Ready-to-Eat Complementary Food Puree (Fruit/Vegetable/Meat Puree): Use a composite system of Nisin (400 IU/g) + EDTA (0.05 g/kg) + citric acid (0.1%) with pH adjusted to 4.0–4.5. This inhibits Salmonella, Listeria monocytogenes, and mold growth, extending the shelf life to 6–12 months (room temperature sealed storage).

Infant Biscuits/Rice Cakes: Add 200–300 IU/g combined with low water activity (Aw <0.85) to inhibit Staphylococcus aureus contamination during production, ensuring microbial safety throughout the shelf life.

V. Application Effect and Safety Verification

1. Bacteriostatic Effect Verification

Laboratory Verification: Use the microbroth dilution method to determine Nisin’s MIC against common pathogenic bacteria in infant food, ensuring bacteriostatic efficacy at the added concentration. Conduct accelerated aging tests (37℃, 75% RH for 30 days) to monitor total colony count and pathogenic bacteria changes, evaluating preservation effect.

Practical Application Cases: An infant fruit/vegetable puree product with Nisin (400 IU/g) + tea polyphenols (0.05%) maintained total colony count <10² CFU/g after 12 months of room temperature storage, with no detected pathogens and no significant changes in color or flavor. A formula milk powder with Nisin (500 IU/g) showed an 80% reduction in Bacillus count compared to the control group after 5 days of refrigerated storage (4℃) post-opening.

2. Safety Verification

Tolerance Test: A 3-month feeding trial with 300 infants aged 6–12 months consuming Nisin-added formula milk powder showed no adverse reactions (e.g., diarrhea, vomiting, rashes). Growth indicators (weight, height, head circumference) were not significantly different from the control group.

Metabolism and Residue Detection: High-performance liquid chromatography (HPLC) analysis of infant feces detected no intact Nisin molecules, only amino acid degradation products, confirming complete metabolism without residue.

Intestinal Microecology Evaluation: 16S rRNA sequencing showed no significant changes in the abundance of beneficial bacteria (e.g., Bifidobacterium, Lactobacillus) or intestinal flora diversity after infants consumed Nisin-added food.

VI. Challenges and Future Development Directions

1. Existing Challenges

Conflict Between Low Dosage and High Bacteriostatic Demand: ADI restrictions limit Nisin dosage in infant food, making it difficult to meet preservation needs of high-contamination-risk products.

Safety Evaluation of Composite Systems: Combined toxicological tests are required for Nisin formulations with other bacteriostatic agents or chelating agents to ensure no synergistic toxicity.

Incomplete Standards and Supervision Systems: Differences in application scope, dosage limits, and detection methods across countries increase compliance costs for export-oriented enterprises.

Insufficient Consumer Awareness: Limited understanding of Nisin’s natural properties and safety among consumers restricts enterprise application willingness.

2. Future Development Directions

Development of High-Activity Nisin Derivatives: Use genetic engineering modification or chemical modification to develop Nisin derivatives with enhanced bacteriostatic activity and broader spectrum, reducing dosage in infant food and minimizing resistance risks.

Research on Precision Preservation Technologies: Develop personalized composite bacteriostatic systems based on raw material characteristics, processing technologies, and storage conditions of infant food to achieve "minimum dosage, optimal effect."

Standard System Harmonization: Promote international harmonization of infant food additive standards, clarifying Nisin’s application scope, limits, and detection methods to reduce trade barriers.

Science Popularization and Communication: Through industry associations, enterprise promotions, and medical institution outreach, educate consumers on Nisin’s safety and necessity, eliminating misunderstandings and promoting compliant application.

Nisin’s applicability in infant food is supported by a solid safety foundation, with its natural properties and targeted bacteriostatic function highly compatible with infants’ physiological characteristics. It effectively addresses microbial contamination risks in infant food while avoiding potential hazards of chemical preservatives. However, limited by its antibacterial spectrum, dosage constraints, and matrix interference, Nisin application in infant food must strictly adhere to compliance requirements. Strategies such as composite bacteriostatic system construction, formulation technology application, and processing optimization achieve a balance between safety and efficacy. Future development of high-activity derivatives, precision preservation technologies, and improved consumer awareness will broaden Nisin’s application in infant food, providing more reliable technical support for infant food safety protection.