Storage points and precautions for Nisin

As a natural antimicrobial peptide food additive, the activity of nisin is easily affected by environmental factors. Rational storage and usage management are crucial to ensuring its antimicrobial efficacy and avoiding safety risks. Specific key points can be elaborated from the dimensions of storage condition control, usage operation specifications, and safety protection:

I. Core Storage Points: Focusing on "Maintaining Activity" and "Preventing Contamination"

1. Control Temperature and Avoid High-Temperature Exposure

The active components of nisin are sensitive to high temperatures. Prolonged exposure to high-temperature environments (e.g., above 40°C) can lead to a significant decline in its antimicrobial activity, or even complete inactivation. Therefore, it should be stored in a cool and dry environment, with an ideal storage temperature of 15–25°C. It is strictly prohibited to place nisin near heat sources (e.g., stoves, radiators, windowsills exposed to direct sunlight) or store/transport it in high-temperature environments for a long time (e.g., in an unshaded car compartment in summer). For long-term storage (over 6 months), it is recommended to seal and store nisin under refrigeration at 2–8°C to maximize the retention of its activity.

2. Isolate Moisture to Prevent Dampness and Caking

Nisin (especially in powdered form) has a certain hygroscopicity. It tends to cake when in contact with moisture in the air, which not only affects the uniformity of subsequent weighing and dissolution but also may cause degradation of active components due to local dampness. During storage, ensure the packaging is intact and use containers with strong sealing properties (e.g., original aluminum foil packaging bags, sealed jars with silica gel desiccants). Immediately reseal the bag or jar opening after each use to avoid prolonged exposure to the air. Meanwhile, the relative humidity of the storage environment should be controlled below 60%, and Nisin should not be stored together with materials with high moisture content (e.g., salt, sucrose, and other moisture-absorbing raw materials) to prevent cross-hygroscopicity.

3. Store Away from Light to Prevent Photooxidation

Ultraviolet rays and strong light can accelerate the oxidative degradation of nisin, destroy its polypeptide structure, and reduce its antimicrobial activity. Therefore,nisin should be stored in opaque containers (e.g., brown glass bottles, light-shielding plastic jars) or with the light-shielding layer of the original packaging (e.g., aluminum-plastic composite film) kept intact. Avoid placing it in transparent containers or areas exposed to direct sunlight or strong light, and do not use transparent packaging bags for repackaging and storage.

4. Classified Storage to Avoid Cross-Contamination

As a food additive, nisin should be stored separately from food raw materials and other additives. It is strictly prohibited to mix it with toxic and harmful substances (e.g., pesticides, chemical reagents, detergents) to prevent cross-contamination caused by packaging damage or leakage. At the same time, it should be isolated from materials with volatile odors (e.g., spices, organic solvents) to avoid absorbing odors and affecting the safety of its subsequent application in food.

II. Key Points for Usage and Management: Focusing on "Precise Application" and "Safety Protection"

1. Accurate Weighing to Control the Addition Dosage

The antimicrobial effect of nisin is dose-dependent. Excessive addition not only provides no additional preservative effect but also increases food production costs and may even cause mild gastrointestinal irritation to some people (e.g., those with sensitive constitutions). Insufficient dosage, on the other hand, fails to achieve the expected antimicrobial effect and may lead to food spoilage. During use, the minimum effective dosage (usually 50–200 mg/kg of food) should be determined based on the type of food (e.g., infant complementary foods, dairy products, meat products), processing technology (e.g., heat treatment intensity, shelf-life requirements), and with reference to national standards or product instructions. Weighing tools with appropriate precision (e.g., electronic analytical balances with a precision of no less than 0.001 g) should be used to avoid dosage deviations caused by empirical estimation.

2. Standardized Dissolution to Ensure Uniform Dispersion

Direct addition of nisin powder to food may result in uneven dispersion, leading to local high or low concentrations (which affects the preservative effect). Therefore, nisin should be dissolved first before addition. For dissolution, it is recommended to use neutral or weakly acidic aqueous solutions (e.g., distilled water, normal saline, with a pH of 5.0–7.0). Strongly acidic (e.g., concentrated hydrochloric acid, citric acid solution) or strongly alkaline (e.g., sodium hydroxide solution) solvents should be avoided to prevent damage to its polypeptide structure. During dissolution, gentle stirring can be used (avoid violent stirring that generates a large amount of foam, which affects subsequent addition) to ensure nisin is completely dissolved. Then, it should be slowly added to food raw materials and further stirred uniformly. Especially for high-viscosity foods (e.g., sauces, thick soups), the stirring time should be extended to prevent local precipitation.

3. Pay Attention to Compatibility Contraindications and Avoid Use with Antagonistic Substances

Some substances may interact with nisin and reduce its antimicrobial activity, so simultaneous addition should be avoided:

Metal ions (e.g., Fe³⁺, Cu²⁺, Zn²⁺): These ions may combine with nisin to form complexes, inhibiting its antimicrobial function. If food requires the addition of nutritional fortifiers containing such ions (e.g., ferrous gluconate, copper sulfate), nisin should be added separately (with an interval of at least 30 minutes), or the pH value can be adjusted or chelating agents (e.g., EDTA) added to reduce the impact of ions.

Surfactants (e.g., certain emulsifiers, detergent residues): These may destroy the spatial structure of Nisin. Therefore, it is necessary to ensure that processing equipment is thoroughly cleaned to avoid detergent residues.

Protease substances (e.g., trypsin, papain): These can degrade the polypeptide chain of nisin. Thus, in foods containing proteases (e.g., fermented dairy products, enzymatically hydrolyzed meat products), the timing of nisin addition should be controlled (e.g., added after protease inactivation).

4. Conduct Safety Protection to Avoid Direct Contact

Although nisin has high safety and no obvious toxicity, long-term or large-scale direct contact with its powder may cause mild irritation to the respiratory tract and skin:

During operation, it is recommended to wear disposable gloves to prevent the powder from sticking to the skin (rinse with clean water immediately if contact occurs).

If a large amount of nisin needs to be weighed or dissolved, a dust mask should be worn to prevent inhaling the powder and causing discomfort such as coughing or sneezing.

At the same time, avoid the powder entering the eyes. If it accidentally gets into the eyes, rinse immediately with a large amount of normal saline, and seek medical attention if necessary.

5. Record and Traceability to Ensure Compliant Management

A complete recording system should be established during storage and use, including nisin’s procurement information (manufacturer, batch number, production date, shelf life), storage conditions (temperature and humidity records), and usage records (date of use, food name, addition dosage, operator). This facilitates traceability in case of quality problems (e.g., food preservative failure, reduced activity) and also complies with the compliance requirements for food additive use (e.g., provisions on additive traceability in national food safety standards).

III. Shelf-Life Management: Conduct Timely Inspections and Avoid Expired Use

The shelf life of nisin is usually 12–24 months (subject to the label on the product packaging). During storage, its condition should be inspected regularly:

First, check whether the packaging is intact (for damage or leakage). If the packaging is damaged, seal it immediately or transfer it to a new sealed container, and prioritize its use.

Second, observe the appearance: powdered nisin should be a white or light yellow uniform powder, without caking, discoloration, or odor. If caking occurs (that cannot be dispersed by gentle pressing), the color darkens (e.g., turns brown), or an abnormal odor is produced (e.g., sourness, mustiness), it indicates that nisin may have become damp, oxidized, or deteriorated. In such cases, its use should be stopped immediately to avoid affecting food quality and safety.

Third, 1–2 months before the expiration date, evaluate the activity of the remaining nisin in advance (its antimicrobial effect can be tested through small-dose experiments). If the activity decreases significantly, replace it with a new batch of products in a timely manner.