The preservative effect of Nisin in baked goods

As a natural antimicrobial peptide produced by the fermentation of Streptococcus lactis, Nisin has emerged as an ideal choice for bakery food preservation due to its high-efficiency inhibition of Gram-positive bacteria, food-grade safety, and thermal stability. Bakery foods are prone to contamination by molds (e.g., Penicillium, Aspergillus) and bacteria (e.g., Bacillus cereus, Staphylococcus aureus) during production and storage, leading to mold growth, rancidity, and shortened shelf life. By targeting microbial cell membrane synthesis and metabolism, Nisin effectively delays the spoilage process while avoiding safety hazards associated with chemical preservatives. This article systematically analyzes Nisin’s antimicrobial mechanisms, application characteristics in bakery foods, preservation effects, and optimization strategies, providing theoretical and practical references for quality control in the bakery industry.

I. Core Antimicrobial Mechanisms and Compatibility with Bakery Food Spoilage Microflora

1. Antimicrobial Mechanisms

Nisin’s antimicrobial activity is primarily directed against Gram-positive bacteria, with specific and targeted mechanisms:

Disrupting Cell Membrane Integrity: Special structures in the Nisin molecule, such as lanthionine and methyllanthionine, bind to Lipid II (a peptidoglycan precursor) on bacterial cell membranes, forming transmembrane pores. This increases membrane permeability, causing massive leakage of intracellular substances (e.g., potassium ions, amino acids) and ultimately leading to bacterial lysis.

Inhibiting Cell Wall Synthesis: By blocking the transport and polymerization of Lipid II, Nisin inhibits bacterial peptidoglycan synthesis, preventing cell wall formation. Bacteria are unable to maintain morphological stability and rupture under osmotic pressure.

Synergistic Antimicrobial Effects: Nisin enhances the permeability of cell membranes to other antimicrobial components (e.g., organic acids, EDTA). When used in combination with these substances, it expands the antimicrobial spectrum (inhibiting some Gram-negative bacteria) and improves preservation efficacy.

2. Compatibility with Bakery Food Spoilage Microflora

The spoilage microflora of bakery foods is dominated by Gram-positive bacteria, which highly aligns with Nisin’s antimicrobial spectrum:

Bacterial Contamination: Major contaminants include Bacillus cereus (producing toxins that cause food poisoning), Staphylococcus aureus (producing enterotoxins), and lactic acid bacteria (causing rancidity). Nisin’s minimum inhibitory concentration (MIC) against these bacteria ranges from 0.05 to 5 μg/mL, and effective inhibition can be achieved with the addition levels permitted in bakery foods.

Fungal Contamination: Although Nisin has no direct inhibitory effect on molds, it indirectly delays mold proliferation by inhibiting Gram-positive bacteria required for mold growth (e.g., mold symbionts). When combined with mold inhibitors (e.g., calcium propionate, sodium dehydroacetate), it produces synergistic preservation effects.

Spore Inhibition: Nisin significantly inhibits the germination and kills bacterial spores (e.g., Bacillus cereus spores). Particularly under heating conditions (e.g., baking), it enhances spore destruction, reducing the risk of bacterial reactivation during subsequent storage.

II. Application Characteristics and Influencing Factors in Bakery Foods

1. Key Application Characteristics

Thermal Stability: Nisin exhibits excellent thermal stability in dry form, retaining over 80% of its activity during baking (150~200℃ for 10~30 minutes). Its stability is even higher in acidic environments (pH 4.5~6.0 of bakery foods), making it suitable for high-temperature processed bakery products such as bread, cakes, and biscuits.

Safety: Nisin is a natural food preservative approved by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO). It is decomposed into amino acids by digestive enzymes in the human body, with no residues or toxicity. The acceptable daily intake (ADI) is unlimited, meeting consumers’ demand for "natural and healthy" foods.

Compatibility: Nisin is well-compatible with proteins, starches, fats, and other components in bakery foods, without affecting the taste, flavor, or color of the products. It can be used synergistically with other preservatives, emulsifiers, humectants, and other additives.

2. Core Factors Influencing Preservation Efficacy

Addition Dosage: According to GB 2760 standards, the maximum usage level of Nisin in bakery foods is 0.5 g/kg (based on pure product). The actual dosage needs to be adjusted according to food type and spoilage risk: 0.2~0.5 g/kg for high-moisture products (water activity Aw 0.85~0.90) such as bread and cakes; 0.1~0.3 g/kg for low-moisture products (Aw 0.60~0.75) such as biscuits.

Water Activity (Aw) and pH Value: Nisin exhibits optimal antimicrobial activity at Aw 0.80~0.90 and pH 4.0~6.0. Its activity decreases significantly when Aw < 0.70 or pH > 7.0, requiring appropriate dosage increases or combination with other preservatives.

Food Components: Fats and proteins in bakery foods may bind to Nisin, reducing its free concentration and affecting antimicrobial efficacy. For example, the Nisin dosage for high-fat cakes needs to be 10%~20% higher than that for bread.

Processing and Storage Conditions: Baking temperatures exceeding 220℃ or durations longer than 40 minutes result in over 30% loss of Nisin activity. High storage temperatures (>25℃) and humidity (relative humidity >70%) accelerate microbial growth, requiring combination with low-temperature storage to further extend shelf life.

III. Preservation Effects in Different Types of Bakery Foods

1. Bread (Toast, European-Style Bread, Whole-Wheat Bread)

Bread has high moisture content and rich nutrition, making it prone to contamination by Bacillus cereus and molds, with a typical shelf life of 2~3 days. Nisin can significantly extend its freshness:

Studies have shown that adding 0.3 g/kg Nisin combined with 0.2% calcium propionate to toast delays mold growth from day 3 to day 8~10 under room temperature storage (25℃). The total bacterial count is reduced by 2~3 log cycles compared to the control group, extending the shelf life by 2~3 times.

Whole-wheat bread, with high dietary fiber content, has a higher risk of microbial adhesion. Adding 0.4~0.5 g/kg Nisin prevents mold growth for 7 days under room temperature storage, with minimal changes in texture indicators (e.g., hardness, elasticity) and maintained good taste.

For bread made from frozen dough, Nisin inhibits miscellaneous bacterial contamination during dough fermentation, improves dough stability, and extends the shelf life of finished bread. After 30 days of frozen storage (-18℃), thawed and baked bread shows no obvious spoilage signs.

2. Cakes (Sponge Cakes, Chiffon Cakes, Cream Cakes)

Cakes are rich in fats and proteins, making them prone to rancidity and mold growth. Cream and other ingredients are susceptible to Staphylococcus aureus contamination, and Nisin exhibits significant preservation effects:

Adding 0.25 g/kg Nisin to sponge cakes reduces the rancidity rate from 60% (control group) to 15% under room temperature storage (20℃), delays mold growth to day 7~9, and extends the softness and flavor retention period by 5~7 days.

Due to the high bacterial growth risk on the surface cream of cream cakes, adding 0.3 g/kg Nisin to the cream effectively inhibits the growth of pathogenic bacteria such as Staphylococcus aureus and Escherichia coli. After 48 hours of room temperature storage, the total bacterial count still meets food safety standards (≤10⁵ CFU/g), avoiding food poisoning risks.

Low-sugar and additive-free cakes, lacking traditional preservatives, have their shelf life extended from 2~3 days to 5~7 days by adding 0.3~0.4 g/kg Nisin, meeting the market demand for natural foods.

3. Biscuits (Shortbread Biscuits, Tough Biscuits, Sandwich Biscuits)

Biscuits have low water activity (Aw 0.60~0.75), with spoilage risks mainly from molds and bacilli. Nisin provides targeted inhibition:

Adding 0.15~0.2 g/kg Nisin to shortbread biscuits reduces mold count by over 90% after 6 months of room temperature storage, with no obvious rancidity or mold growth, maintaining stable product quality.

The filling of sandwich biscuits (e.g., cream, jam) has high moisture content, making it a hotbed for microbial growth. Adding 0.2~0.3 g/kg Nisin to the filling inhibits the growth of bacilli and molds, extending the shelf life of sandwich biscuits to over 12 months.

Sugar-free biscuits, using sugar substitutes, may have enhanced microbial tolerance. Combined addition of 0.2 g/kg Nisin and 0.1% sodium dehydroacetate achieves significantly better preservation effects than single additives, extending the shelf life by over 30%.

4. Other Bakery Foods (Pastries, Rusks, Mooncakes)

Chinese pastries (e.g., peach cakes, wife cakes) with 0.2~0.3 g/kg Nisin show no mold growth after 30 days of room temperature storage, reduced fat rancidity, and a 40%~50% decrease in peroxide value (POV) compared to the control group.

Leisure bakery foods such as rusks, with 0.1~0.15 g/kg Nisin, inhibit bacterial proliferation during storage, avoiding off-odors and softening, and extending the shelf life to 12 months.

Mooncakes, with high sugar content and moderate moisture, are prone to mold contamination. Adding 0.2 g/kg Nisin to both mooncake crust and filling, combined with low-temperature storage (10~15℃), extends the shelf life from 30 days to 60~90 days without affecting flavor and taste.

IV. Application Optimization Strategies in Bakery Foods

1. Combined Preservation Schemes

Nisin has limited direct inhibitory effects on molds. Combined use with other preservatives or preservation technologies achieves "synergistic enhancement and expanded antimicrobial spectrum":

Combination with Chemical Preservatives: Nisin + calcium propionate (ratio 1:2~1:3) or Nisin + sodium dehydroacetate (ratio 1:1) inhibits both bacteria and molds, suitable for various bakery foods. The dosage can be reduced by 30%~50% compared to single use, minimizing chemical preservative residues.

Combination with Natural Preservatives: Nisin + plant extracts (e.g., clove essential oil, cinnamon essential oil, dosage 0.05%~0.1%) or Nisin + probiotic metabolites leverages the antimicrobial effects of natural ingredients, enhancing the "natural and healthy" attribute of products while improving preservation efficacy.

Combination with Physical Technologies: Nisin + low-temperature storage (0~10℃) or Nisin + vacuum packaging/modified atmosphere packaging (MAP, filled with CO₂/N₂ mixed gas) further delays microbial growth and extends shelf life, especially suitable for high-moisture bakery foods.

2. Optimization of Addition Methods and Processes

Addition Methods: ① Direct addition: Mix Nisin powder with flour, sugar, and other raw materials, suitable for products with high solid content such as biscuits and bread; ② Solution addition: Dissolve Nisin in a small amount of water and mix with liquid raw materials (e.g., egg liquid, milk) to ensure uniform dispersion, suitable for cakes, cream, and other products; ③ Surface spraying: Spray Nisin solution (concentration 0.1%~0.2%) on the surface of finished bakery foods (e.g., bread, mooncakes) to form an antimicrobial protective film, targeting surface microbial growth.

Process Optimization: Nisin should be added after dough fermentation and before baking to avoid decomposition by microorganisms such as yeast during fermentation. Baking temperature should be controlled at 150~190℃ for no more than 30 minutes to reduce Nisin activity loss. For high-moisture products, secondary sterilization (e.g., ultraviolet irradiation) after cooling can be combined with Nisin to further improve preservation efficacy.

3. Customized Schemes for Different Product Characteristics

High-Moisture Products (Bread, Cakes): Adopt "Nisin + calcium propionate + vacuum packaging" scheme, with Nisin dosage 0.3~0.5 g/kg and calcium propionate 0.3%~0.5%. Vacuum packaging reduces oxygen content to inhibit mold growth.

Low-Moisture Products (Biscuits, Rusks): Adopt "Nisin + sodium dehydroacetate" scheme, with Nisin dosage 0.1~0.2 g/kg and sodium dehydroacetate 0.05%~0.1%, achieving long-term preservation combined with low water activity.

Cream/Filling-Containing Products (Cream Cakes, Sandwich Biscuits): Add Nisin (0.2~0.3 g/kg) separately to the filling, combined with raw material sterilization (e.g., cream pasteurization), to avoid the filling becoming a spoilage source.

4. Quality Control and Safety Assurance

Dosage Control: Strictly adhere to GB 2760 standards to avoid excessive use, ensuring Nisin residue in products meets requirements (≤0.3 g/kg).

Purity Selection: Use food-grade Nisin products with purity ≥90% to avoid impurities affecting product quality and safety.

Storage Conditions: Store Nisin in a sealed, cool, and dry environment (temperature <25℃, relative humidity <60%), avoiding direct sunlight, high temperature, and humidity to prevent activity reduction.

V. Challenges and Future Development Directions

1. Existing Challenges

Limited Antimicrobial Spectrum: Nisin has weak direct inhibitory effects on Gram-negative bacteria and molds, relying on combined schemes, which increases application complexity.

Uniformity of Addition: The complex composition of bakery food raw materials causes Nisin to easily bind to proteins and fats, leading to uneven local concentrations and affecting preservation efficacy.

High Cost: The fermentation and purification costs of Nisin are higher than those of traditional chemical preservatives, limiting its large-scale application in mid-to-low-end bakery foods.

2. Development Directions

Modification and Efficiency Enhancement: Improve Nisin’s inhibitory activity against molds and Gram-negative bacteria through molecular modification (e.g., acetylation, PEGylation) to expand its antimicrobial spectrum. Develop Nisin microcapsule formulations to enhance dispersion and stability in foods, reduce binding with other components, and improve bioavailability.

Low-Cost Production: Optimize fermentation strains and processes, use low-cost culture media (e.g., agricultural waste) to reduce Nisin production costs. Develop composite Nisin formulations to reduce dosage and application costs.

Natural Synergistic Systems: Conduct in-depth research on the synergistic antimicrobial mechanisms of Nisin with natural plant extracts, probiotics, dietary fiber, etc., to develop all-natural preservation schemes, aligning with consumers’ demand for healthy foods.

Integration with Intelligent Packaging: Load Nisin into intelligent packaging materials (e.g., biodegradable films, nanofiber membranes) to achieve controlled release, extend preservation duration, and enhance the functionality of product packaging.

As a natural antimicrobial peptide, Nisin exhibits excellent preservation effects in bakery foods, effectively inhibiting bacterial and spore proliferation, delaying mold growth and rancidity, and extending shelf life. It also has the advantages of high safety, good thermal stability, and strong compatibility, conforming to the bakery industry’s development trend of "natural, healthy, and safe." Its application efficacy is influenced by factors such as addition dosage, water activity, and food components. Through combined preservation, optimized addition methods and processes, preservation efficiency can be further improved to meet the needs of different types of bakery foods.

Despite current challenges such as limited antimicrobial spectrum and high cost, with the innovation of modification technologies, fermentation processes, and the development of natural synergistic systems, Nisin has broad application prospects in bakery foods. In the future, it will gradually replace some chemical preservatives, becoming a core component of bakery food quality control, providing safer and more efficient preservation solutions for the industry, and promoting the high-quality development of the bakery food industry.