Study the application of Nisin in the preservation of seafood

Nisin (nisin), a natural antimicrobial peptide produced by lactic acid bacteria, has attracted much attention in the field of food preservation due to its characteristics of high-efficiency bacteriostasis, no residue, and high safety. Seafood is rich in protein, moisture, and unsaturated fatty acids, which are prone to spoilage caused by microbial contamination and oxidation. Nisin's strong inhibitory effect on Gram-positive bacteria (such as Listeria and Staphylococcus, common seafood spoilage bacteria) makes it a potential seafood preservative. The following outlines the experimental research directions of Nisin in seafood preservation from the aspects of experimental design ideas, key detection indicators, and application effects.

I. Core Ideas of Experimental Design

Experimental research on Nisin in seafood preservation needs to focus on the two goals of "inhibiting the growth of spoilage microorganisms" and "delaying quality deterioration". It usually combines in vitro bacteriostatic experiments with actual sample preservation experiments. The specific design ideas include:

Screening of Nisin concentration gradients

Based on pre-experiments, determine the effective bacteriostatic concentration range (e.g., 0.01~1.0 g/kg), set multiple concentration groups (e.g., 0.1, 0.3, 0.5, 0.8 g/kg) and a control group (sterile water or solution without Nisin). Evaluate the optimal concentration through subsequent indicators — too low a concentration may fail to inhibit microorganisms, while too high a concentration may increase costs or affect the flavor of seafood.

Optimization of treatment methods

Common treatment methods include immersion (soaking seafood in Nisin solution for 5~30 minutes), spraying (directly spraying Nisin solution on the surface), or composite coating (mixing with edible film materials such as chitosan and sodium alginate and then wrapping). Experiments need to compare the effects of different treatment methods on preservation. For example, composite coating can extend the action time of Nisin and reduce its loss during storage.

Simulation of storage conditions

The storage conditions of seafood preservation (temperature, humidity, packaging method) directly affect the effect of Nisin. Experiments need to simulate typical conditions in actual circulation, such as refrigeration (4℃), ice storage (0℃), or low-temperature freezing (-18℃), and set different packaging groups (e.g., vacuum packaging, modified atmosphere packaging) to analyze the stability and preservation effect of Nisin in different environments.

II. Key Detection Indicators and Evaluation Methods

In experiments, multiple indicators are needed to evaluate the preservation effect of Nisin, with core indicators including:

Microbial indicators

Total colony count: Determine the total number of bacteria on the surface or homogenate of seafood by plate counting to evaluate Nisin's ability to inhibit microbial reproduction. If Nisin is effective, the growth rate of total colony count in the experimental group should be significantly lower than that in the control group.

Detection of specific pathogenic bacteria: For common pathogenic bacteria in seafood (such as Listeria and Staphylococcus aureus), use selective culture media or PCR methods for quantitative detection to verify the targeted inhibitory effect of Nisin on target bacteria.

Physicochemical indicators

Total volatile basic nitrogen (TVB-N): Volatile nitrogen-containing substances are produced during seafood spoilage. The TVB-N value is a classic indicator to measure the degree of spoilage (the freshness threshold is usually 30 mg/100g). If Nisin is effective, the increase rate of TVB-N value in the experimental group should be slower.

pH value: Microbial metabolism will cause the pH value of seafood to rise (e.g., the pH of fresh fish is about 6.5~7.0, which can rise to above 7.5 after spoilage). Monitor changes with a pH meter to reflect the spoilage process.

Texture and color: Use a texture analyzer to determine parameters such as hardness and elasticity, and analyze changes in L* (lightness), a* (redness), and b* (yellowness) with a color difference meter to evaluate the protective effect of Nisin on the sensory quality of seafood.

Sensory evaluation

A professional review team scores from aspects such as odor, color, and tissue state (e.g., 9-point scale, below 6 points is unacceptable), and combines with physicochemical indicators to comprehensively judge the effect of extending the preservation period.

III. Experimental Results and Application Potential Analysis

Existing studies have shown that Nisin has significant potential in seafood preservation, but its effect is affected by many factors:

Limitations of single Nisin: Nisin has a weak inhibitory effect on Gram-negative bacteria (such as Escherichia coli and Vibrio), while seafood spoilage often involves the synergistic effect of multiple bacterial groups. Therefore, the preservation effect may be limited when used alone. Experiments have observed that high concentrations of Nisin (e.g., above 0.5 g/kg) have a certain inhibitory effect on some Gram-negative bacteria, but they need to be compounded with other preservatives (such as EDTA and plant extracts) to enhance the effect.

Synergistic effect of composite preservation: Combining Nisin with low temperature, edible films, or other natural bacteriostats (such as lysozyme and carvacrol) can significantly improve the preservation effect. For example, salmon treated with Nisin-chitosan composite coating has a preservation period extended by 3~5 days compared with the control group under 4℃ storage conditions, and both the total colony count and TVB-N value are significantly reduced.

Applicability differences among different seafood: Nisin has a better preservation effect on low-fat, high-protein seafood (such as shrimp and shellfish), while its effect on high-fat fish (such as salmon and tuna) may be affected by fat oxidation. It needs to be used with antioxidants (such as vitamin C) to inhibit both microorganisms and oxidative deterioration.

IV. Research Prospects

The application of Nisin in seafood preservation still needs to solve the following problems:

Improve the inhibitory ability against Gram-negative bacteria, which can be achieved by genetically engineering the structure of Nisin or compounding with cell membrane disruptors;

Optimize the delivery system of Nisin (such as nano-encapsulation technology) to reduce its degradation during processing and storage and extend the action time;

Carry out large-scale application research to verify the stability and economy of Nisin in industrial production, promoting its transition from the laboratory to actual production.

As a natural preservative, Nisin has broad application prospects in seafood preservation, but its effect needs to be maximized through scientific experimental design, multi-dimensional evaluation, and combined with composite preservation technologies.