Nisin's microencapsulation technology

The microencapsulation technology of Nisin forms tiny capsules by wrapping it in polymer materials, which not only protects its biological activity but also enables controlled release, significantly improving the anti-corrosion effect and applicability in food applications. The following analysis covers technical principles, preparation methods, and food application scenarios:

I. Core Principles and Advantages of Microencapsulation Technology

1. Protecting Activity from Environmental Damage

Nisin is prone to inactivation by high temperature, acid-base, proteases, etc. (e.g., over 50% activity loss during high-temperature sterilization under neutral conditions). Microencapsulation creates a physical barrier through wall materials (e.g., gelatin, chitosan, sodium alginate) to isolate Nisin from direct environmental effects. For example, microcapsules prepared by sodium alginate-calcium chloride gel method increase Nisin activity retention rate from 32% (free state) to 78% after heating at 70℃ for 30 minutes in pH 6.0 buffer.

2. Achieving Controlled Release for Prolonged Action

The pore size or degradation properties of microcapsule walls regulate Nisin release rate. In liquid foods, the wall material swells in water to slowly release Nisin, avoiding concentration decay from rapid diffusion; in solid foods (e.g., meat products), the wall material gradually releases active components via enzymatic hydrolysis or mechanical damage for long-term anti-corrosion.

II. Main Preparation Methods and Technical Characteristics

1. Emulsification-Curing Method (Physical Embedding)

Principle: Mix Nisin aqueous solution with oil phase (e.g., vegetable oil) for emulsification, add wall materials (e.g., gelatin, gum arabic) to form a water-oil-water (W/O/W) multiple emulsion system, and form microcapsules via crosslinkers (e.g., glutaraldehyde) or cooling curing.

Advantages: Simple process, suitable for batch production, flexible wall material selection. For instance, microcapsules prepared by gelatin-gum arabic complex coacervation have an encapsulation efficiency >85%, delaying Nisin release in meat products to extend anti-corrosion effect by 2-3 times.

2. Spray Drying Method (Thermal Curing Embedding)

Principle: Spray a mixed solution of Nisin and wall materials (e.g., maltodextrin, whey protein) into hot air flow, forming dry microcapsules as the solvent evaporates.

Characteristics: High efficiency, suitable for industrial production, but inlet temperature must be controlled (usually ≤180℃) to avoid Nisin thermal inactivation. Optimized processes achieve an encapsulation efficiency of 75%-80%, with stability in acidic beverages for >3 months.

3. Ion Gelation Method (Chemical Crosslinking)

Principle: Use polysaccharide wall materials (e.g., sodium alginate, chitosan) to form a gel network with metal ions (e.g., Ca²⁺) or acid/base reactions, encapsulating Nisin.

Advantages: Prepared under mild conditions (room temperature, neutral pH) to avoid Nisin activity loss. For example, sodium alginate-calcium chloride gel microcapsules applied in dairy products resist gastric acid degradation and release Nisin in the intestine due to reduced Ca²⁺ concentration, combining anti-corrosion with intestinal antibacterial effects.

4. Layer-by-Layer Self-Assembly (Nanoscale Embedding)

Principle: Alternately deposit oppositely charged polymers (e.g., chitosan-sodium alginate) on the Nisin surface to form multi-layer nanoscale walls.

Characteristics: High embedding precision, controllable wall thickness (nanoscale), and pH-responsive release (e.g., chitosan protonation in acidic environments swells capsules to release Nisin), suitable for acidic juices, pickles, etc.

III. Specific Application Scenarios in Foods

1. Dairy Anti-Corrosion (Yogurt, Cheese)

Application Advantage: Free Nisin is easily degraded by proteases in dairy products, while microencapsulation resists milk proteases (e.g., rennin). For example, chitosan-sodium alginate microencapsulated Nisin added to cheese retains 65% activity after 30 days of storage at 4℃, versus only 20% for free Nisin, effectively inhibiting thermophilic Streptococcus contamination.

2. Meat Product Preservation (Sausages, Ham)

Technical Value: The complex matrix of meat products can cause non-specific binding of Nisin to proteins/fats, avoided by microencapsulation. For instance, Nisin-maltodextrin microcapsules prepared by spray drying added to sausages release slowly under refrigeration, controlling total bacterial count below 10³ CFU/g for 21 days (free Nisin only maintains 10 days) while avoiding flavor changes from traditional addition.

3. Anti-Corrosion of Acidic Beverages and Juices

Controlled Release Application: In pH 3.0-4.5 beverages, microencapsulated Nisin achieves rapid release via acid-soluble walls (e.g., polyacrylic resin-embedded microcapsules swell in acidic conditions, releasing 80% Nisin within 2 hours), efficiently inhibiting yeasts and molds. This avoids Nisin inactivation from electrostatic binding to polyphenols in low-pH beverages.

4. Baked Goods (Bread, Cake)

High-Temperature Resistance Application: High temperatures (180-220℃) during baking easily inactivate Nisin, but microencapsulation protects activity via wall material thermal insulation. For example, microcapsules with whey protein-dextran composite walls added to bread retain 40% Nisin activity after baking (free Nisin is almost completely inactivated), continuously releasing during storage to inhibit heat-resistant Bacillus and extending shelf life by 5-7 days.

IV. Technical Challenges and Development Trends

Challenges:

Microencapsulation may reduce Nisin's antibacterial efficiency (e.g., decreased contact efficiency with bacteria), requiring optimization of wall pore size or surface modification (e.g., grafting antibacterial peptides) for enhanced targeting.

Safety of some wall materials (e.g., synthetic polymers) needs further verification.

Trends:

Developing biodegradable composite wall materials with both antibacterial and nutritional functions (e.g., chitosan-probiotic co-encapsulation) or responsive intelligent microcapsules (e.g., temperature/pH dual-responsive release) to adapt to diversified food processing needs.

Nisin microencapsulation technology breaks through its natural limitations via dosage form innovation, expanding application in complex food systems while maintaining high antibacterial activity, providing an important direction for green anti-corrosion technology development.