The core of Nisin's microencapsulation technology

The core of Nisin microencapsulation technology lies in forming micron-sized particles through wall material encapsulation, achieving "isolation from external interference to improve stability + controlled release rate to enhance long-term antimicrobial efficacy." It is a key solution to address Nisin’s shortcomings, such as susceptibility to environmental factors and short action cycle. The specific technical details and research focuses are as follows:

I. Core Objectives of Microencapsulation Technology

Enhancing Environmental Stability: Nisin is inherently sensitive to acid, alkali, high temperatures, and enzymatic hydrolysis. Microcapsule wall materials can isolate interfering factors such as oxygen, moisture, and gastric acid, reducing activity loss during processing or storage.

Achieving Sustained-Release Antimicrobial Effects: The barrier effect of wall materials controls Nisin’s release rate, avoiding rapid concentration drops and extending the antimicrobial cycle to meet the long-term preservation needs of food.

Improving Application Compatibility: Reduces interactions between Nisin and other food components (e.g., proteins, metal ions) while masking its mild odor, without affecting food sensory quality.

Enhancing Targeting: Wall materials are designed for specific scenarios (e.g., intestinal antimicrobial, targeted food preservation), enabling precise release of Nisin at target sites to improve efficacy.

II. Mainstream Microencapsulation Preparation Technologies and Characteristics

1. Spray Drying (Industrial Mainstream Method)

Using water-soluble wall materials (e.g., maltodextrin, gum arabic, gelatin) as carriers, Nisin aqueous solution is mixed with wall material solution, then atomized into fine droplets via a spray dryer. Rapid drying in high-temperature airflow forms microcapsules. This technology features simple operation, low production cost, and suitability for large-scale production. Microcapsules have a particle size of 1–10μm with an encapsulation efficiency of 70%–85%. Drying temperatures must be controlled (inlet air: 120–150°C, outlet air: 60–80°C) to avoid Nisin activity loss due to high heat; adding plasticizers (e.g., glycerol) can improve wall material compactness.

2. Complex Coacervation (High Encapsulation Efficiency Method)

Two oppositely charged wall materials (e.g., gelatin and gum arabic, chitosan and sodium alginate) undergo electrostatic interactions at specific pH values, forming a coacervate phase that encapsulates Nisin. This method achieves high encapsulation efficiency (85%–95%) with dense microcapsule structures and excellent sustained-release performance. Particle sizes are controllable at 2–5μm, making it suitable for scenarios requiring high stability and sustained release (e.g., functional foods, long-term preservation products). Limitations include sensitive process conditions (requiring precise control of pH, wall material ratio, and temperature), higher production costs than spray drying, and slightly greater difficulty in large-scale production.

3. Emulsion Cross-Linking (Environment-Resistant Method)

First, Nisin aqueous solution is dispersed in an oil phase (e.g., soybean oil, paraffin oil) to form a W/O emulsion. Cross-linking agents (e.g., glutaraldehyde, Ca²⁺) are then added to cross-link and solidify water-phase wall materials (e.g., sodium alginate, chitosan), forming microcapsules. The resulting microcapsules exhibit excellent acid/alkali resistance and enzymatic hydrolysis resistance, remaining stable and releasing Nisin slowly in acidic foods or intestinal environments, with an encapsulation efficiency of 75%–90%. Attention must be paid to emulsion stability to prevent oil-water separation from affecting encapsulation; non-toxic cross-linking agents should be selected to ensure safety for food applications.

4. Freeze Drying (High Activity Retention Method)

A mixed solution of Nisin and wall materials (e.g., β-cyclodextrin, whey protein) is frozen to a solid state, then water is removed by sublimation under vacuum to form porous microcapsules. This method maximizes Nisin activity retention (>90%), making it suitable for heat-sensitive Nisin formulations or high-end functional foods. However, high production costs and long cycles limit large-scale application.

III. Wall Material Selection and Optimization (Key to Stability and Sustained Release)

1. Wall Material Types and Suitable Scenarios

Natural Polysaccharides (maltodextrin, gum arabic, sodium alginate): Widely sourced, high safety, and low cost. Suitable for large-scale production via spray drying, 适配普通食品保鲜。

Proteins (gelatin, whey protein, soy protein isolate): High encapsulation efficiency, excellent sustained-release performance, and inherent nutritional properties. Suitable for functional foods (e.g., infant formula, elderly nutrition).

Composite Wall Materials (polysaccharide + protein, polysaccharide + polysaccharide): Synergize advantages of single wall materials. For example, sodium alginate-chitosan composites enhance acid resistance and compactness; maltodextrin-gum arabic composites balance encapsulation efficiency and production cost.

Functional Wall Materials (e.g., cyclodextrin, polylactic acid): Cyclodextrin improves Nisin’s temperature resistance; polylactic acid is biodegradable, suitable for high-end food or pharmaceutical applications.

2. Key Optimization Points for Wall Materials

The ratio of wall material to Nisin must be reasonable, typically 5:1–20:1. Too low a ratio causes insufficient encapsulation; too high reduces antimicrobial activity per unit mass of microcapsules.

Wall material molecular weight affects sustained release: high-molecular-weight materials (e.g., high-viscosity sodium alginate) form thicker membranes with slower release rates, while low-molecular-weight materials release faster. Selection depends on application needs.

Adding appropriate additives (e.g., plasticizers, emulsifiers) improves film-forming properties and microcapsule stability, reducing the risk of capsule rupture during storage.

IV. Mechanisms and Research Findings for Enhancing Stability and Sustained Release

1. Stability Enhancement Mechanisms

Physical barriers formed by wall materials isolate oxygen, moisture, and external chemicals, preventing damage to Nisin’s molecular structure. For example, in acidic foods, chitosan/sodium alginate composite walls block H⁺ from interacting with Nisin, increasing activity retention by 30%–50% compared to unencapsulated Nisin.

During high-temperature processing, wall materials (e.g., maltodextrin) absorb heat, reducing Nisin’s conformational changes due to heat. After spray drying, Nisin activity retention exceeds 80%, compared to only 40%–60% in unencapsulated groups.

Microcapsules reduce Nisin’s oxidative degradation and moisture-induced agglomeration during storage. After 6 months of room-temperature storage, activity loss in encapsulated groups is <20%, versus >50% in unencapsulated groups.

2. Sustained Release Enhancement Mechanisms

The swelling and degradation rate of microcapsule walls determines Nisin’s release rate. In food storage or human digestive environments, wall materials gradually swell, dissolve, or are enzymatically degraded, enabling slow release of Nisin.

Precise sustained release is achievable by adjusting wall thickness, compactness, or selecting materials with different degradation rates. For example, in refrigerated foods, microcapsules prepared via complex coacervation extend Nisin’s antimicrobial cycle from 7–10 days to 20–30 days.

Targeted sustained release designs allow Nisin release at specific sites. For instance, intestinal-targeted microcapsules remain stable in the stomach (pH 1–3) and release Nisin in the intestine (pH 6–8) after wall dissolution, enhancing intestinal antimicrobial efficacy.

V. Application Scenarios and Research Prospects

1. Main Application Scenarios

Food Preservation: Used in meat products, dairy products, and pastries to extend shelf life. For example, microencapsulated Nisin added to sausages extends room-temperature shelf life from 3–5 days to 10–15 days.

Functional Foods: Added as intestinal antimicrobial components to probiotic foods and meal replacements, exerting sustained antimicrobial and gut-protective effects via controlled release.

Specialty Foods: Adapted for infant formula and elderly nutrition, ensuring Nisin stability while reducing intestinal irritation in vulnerable populations.

2. Future Research Directions

Novel Wall Material Development: Focus on biodegradable, functional materials (e.g., plant extract-modified walls) to enhance microcapsule safety and added value.

Preparation Process Optimization: Develop low-cost, high-efficiency large-scale production technologies to overcome industrialization bottlenecks of methods like complex coacervation.

Precision Sustained Release Design: Customize release rates based on food storage environments or human physiological characteristics to maximize Nisin efficacy.

Safety and Compatibility Studies: Further verify applicability of microencapsulated Nisin in special populations (e.g., infants, the elderly) and compatibility with other food components.

Microencapsulation technology addresses Nisin’s core issues of poor stability and short action cycle through rational wall material selection and preparation processes, significantly expanding its application scenarios. Different preparation technologies have unique advantages: spray drying dominates industrial applications, while complex coacervation or emulsion cross-linking suits high-end scenarios. Future advancements in novel wall materials and process optimization will enable microencapsulated Nisin to play a greater role in food preservation and functional foods, with broad prospects in safe preservation and functional enhancement of specialty foods.