Nisin's 3D printing application

The core of Nisin’s 3D printing applications lies in "customized carriers + precise controlled release." By combining Nisin with edible materials via 3D printing technology, preservative structures with tailored shapes and release rates are fabricated to achieve targeted, long-acting food preservation. This addresses issues of uneven distribution and limited efficacy in traditional preservative use.

I. Design of 3D Printing-Compatible Nisin Composite Systems

1. Selection of Edible Printing Materials

Matrix Materials: Priority is given to edible polymers such as gelatin, sodium alginate, chitosan, and starch. These materials exhibit excellent printability (suitable gelation and fluidity) and act as sustained-release carriers for Nisin. Among them, chitosan shows the best synergy: its cationic properties form stable complexes with Nisin (an anionic polypeptide), enhancing Nisin stability.

Auxiliary Materials: Plasticizers like glycerol and polyethylene glycol are added to improve material flexibility and prevent post-formation brittleness. Emulsifiers such as Tween 80 enhance Nisin’s dispersion uniformity in the matrix, avoiding local over-concentration or deficiency.

2. Optimization of Composite Formulations

Nisin Dosage: Based on food preservation needs, Nisin is added at 0.05%–0.2% (relative to total mass of printing materials), corresponding to a final concentration of 500–2000 IU/g in preservative structures. This effectively inhibits Gram-positive bacteria (e.g., Staphylococcus aureus, Clostridium botulinum) while complying with GB 2760 standards (maximum allowable use in food ≤0.5 g/kg).

Material Ratios: A gelatin-sodium alginate composite matrix (3:1 mass ratio) with 0.1% Nisin + 5% glycerol achieves >95% print success rate and stable Nisin sustained release. A chitosan-starch system (2:3 mass ratio) is suitable for preserving acidic foods, enhancing Nisin’s antimicrobial activity.

II. Customized 3D-Printed Preservative Structures and Functions

1. Structure Customization for Specific Scenarios

Film Type: 0.1–0.3 mm thick edible films are printed to coat meat or fruits/vegetables, forming an antimicrobial protective layer via slow Nisin release, extending shelf life by 2–3 times. For example, cold fresh meat surfaces treated with such films inhibit bacterial proliferation, extending shelf life from 3–5 days to 7–10 days.

Microcapsule/Microsphere Type: 100–500 μm microcapsules containing Nisin are printed and added to liquid foods (e.g., beverages, sauces) or semi-solid foods (e.g., yogurt, salad dressings). This prevents direct reaction between Nisin and food components, ensuring continuous antimicrobial release throughout the shelf life.

Special-Shaped Scaffold Type: Mesh scaffolds matching the shape of fragile foods (e.g., strawberries, blueberries) are printed to enclose the food, creating a three-dimensional antimicrobial environment. This protects against physical damage while ensuring uniform Nisin distribution around the food, meeting preservation needs of delicate fruits.

2. Customized Controlled Release Functions

Rapid Release Type: Low-crosslinking gelatin matrices with 30%–40% porosity are used for short-term preservation (1–3 days) of ready-to-eat foods. Over 80% of Nisin is released within 12 hours, rapidly inhibiting initial bacterial growth.

Long-Acting Sustained Release Type: High-crosslinking sodium alginate-chitosan composites or lipid-added (e.g., beeswax) bilayer structures extend Nisin release to 7–14 days, suitable for longer-shelf-life foods (e.g., pastries, cooked meat products) to prevent late-stage bacterial rebound.

Responsive Release Type: pH-sensitive components (e.g., carboxymethyl cellulose) are incorporated into printing materials. For acidic foods (e.g., pickles, fruit juices), Nisin is released only under specific pH conditions, reducing unnecessary consumption and improving preservation efficiency.

III. Optimization of 3D Printing Process Parameters

1. Key Process Parameter Control

Printing Temperature: Adjusted by matrix type: 25–35℃ for gelatin systems and 20–25℃ (room temperature) for sodium alginate systems. High temperatures are avoided to prevent Nisin inactivation (Nisin is heat-stable but loses activity under prolonged heating above 100℃).

Nozzle Diameter and Printing Speed: 0.4–0.8 mm nozzles with 5–10 mm/s printing speeds ensure precision while preventing nozzle clogging. Layer thickness is set to 0.1–0.2 mm to enhance structural density and control Nisin release rate.

Post-Processing: Printed structures undergo freeze-drying (-40℃, 12 hours) or hot air drying (40℃, 6 hours) to remove moisture, fix structures, and enhance Nisin stability in the matrix. Final moisture content is controlled at 10%–15%.

2. Process Adaptability Optimization

For High-Moisture Foods: Printed structures are coated with hydrophobic layers (e.g., beeswax-modified coatings) to reduce erosion from food moisture and maintain controlled release.

For High-Fat Foods: Hydrophobic printing materials (e.g., modified starch) are used to prevent Nisin encapsulation by fats, ensuring antimicrobial efficacy.

IV. Application Scenarios and Preservation Effects

1. Meat and Aquatic Product Preservation

Cold Fresh Meat: Edible printed films inhibit Clostridium botulinum and Listeria in synergy with chitosan. Under 4℃ refrigeration, shelf life extends from 3 days to 8–10 days with no significant odor or color changes.

Fish and Shrimp Products: Printed microcapsules added to surimi products release Nisin slowly, inhibiting spoilage bacteria (e.g., Pseudomonas). Frozen storage shelf life extends by 30%–40% while preserving texture.

2. Fruit and Vegetable Preservation

Berries (Strawberries, Blueberries): Mesh scaffolds create breathable antimicrobial environments, preventing mechanical damage and inhibiting mold (e.g., Botrytis cinerea). Shelf life extends from 1–2 days to 3–4 days at room temperature, or 7–10 days under refrigeration.

Root Vegetables (Carrots, Potatoes): Printed films coat cut surfaces or sustained-release patches are applied to inhibit oxidative browning and bacterial contamination, extending storage by 2–3 times.

3. Pastry and Cooked Food Preservation

Pastries: Edible decorative pieces (e.g., flowers, letters) containing Nisin serve as both decoration and slow-release antimicrobial agents, inhibiting mold (e.g., Penicillium, Aspergillus). Room temperature shelf life extends from 3–5 days to 7–10 days.

Cooked Meats (Sausages, Braised Products): Printed films or sustained-release granules in packaging inhibit heat-resistant bacteria (e.g., Clostridium botulinum) without added chemical preservatives, meeting "natural preservation" demands.

V. Advantages and Challenge Mitigation

1. Core Advantages

Customization: Structures can be precisely designed in shape, size, and release rate based on food geometry, shelf life, and storage conditions, adapting to diverse needs.

Safety: Nisin is a natural food preservative (GRAS-certified), and edible printing materials are non-toxic. Preservative structures are edible, eliminating residue risks.

Efficiency: Uniform Nisin distribution and controlled release improve preservation efficacy by 30%–50% compared to traditional coating/spraying methods, while reducing Nisin usage.

2. Challenges and Solutions

Print Precision and Formability: Low-viscosity materials prone to deformation can be stabilized by increasing matrix concentration (e.g., gelatin to 15%–20%) or adding crosslinkers (e.g., calcium chloride).

Nisin Activity Retention: Optimize printing temperature (≤35℃) and post-processing, avoid prolonged high-temperature exposure, or pre-encapsulate Nisin in microcapsules to enhance thermal stability.

Cost Control: Use low-cost 3D printing technologies (e.g., fused deposition modeling) for mass production and cheap matrix materials (e.g., starch, gelatin) to reduce manufacturing costs.