The preservative effect of Nisin in food for the elderly

As a special dietary category designed for the physiological characteristics of the elderly, elderly food requires preservation technologies that balance safety, effectiveness, and applicability. The elderly have weakened digestive functions and reduced immunity, resulting in lower tolerance to chemical preservatives in food, while demanding higher retention of nutrients and better texture/taste. Nisin (lacticin), a natural antimicrobial peptide, exhibits advantages such as non-toxicity, targeted antibacterial spectrum, easy degradation, and no impact on food flavor, aligning with the core demand of "safety first, mild preservation" for elderly food. This article systematically analyzes the preservative value and practical pathways of Nisin in elderly food from the aspects of its antibacterial mechanism, adaptability to elderly food preservation pain points, application scenarios, and optimization strategies.

I. Core Antibacterial Properties of Nisin and Adaptability to Elderly Food Preservation

1. Antibacterial Mechanism and Characteristics of Nisin

Nisin is a cationic antimicrobial peptide produced by Lactococcus lactis, with a molecular weight of approximately 3.5 kDa. Composed of 34 amino acid residues, it contains 5 lactone ring structures formed by thioether bonds. Its antibacterial mechanism is highly specific:

It targets the cell membrane of Gram-positive bacteria, binds to lipid II (a peptidoglycan synthesis precursor) on the bacterial cell membrane, and forms transmembrane pores, leading to the leakage of potassium ions, protons, and other substances inside the bacteria, ultimately causing bacterial lysis.

It inhibits bacterial peptidoglycan synthesis, blocks cell wall repair and proliferation, and exhibits particularly significant inhibitory effects on bacteria in the logarithmic growth phase.

Its antibacterial spectrum focuses on common pathogenic and spoilage bacteria in food, including Staphylococcus aureus, Listeria monocytogenes, Clostridium botulinum, and Bacillus subtilis, enabling precise inhibition of pathogenic bacteria that are prone to causing infections in elderly food.

The natural characteristics of Nisin are highly compatible with the needs of elderly food:

High Safety: As a GRAS (Generally Recognized as Safe) substance, it has been approved for food preservation in many countries worldwide. After human ingestion, it can be degraded into amino acids by digestive proteases, with no residues or toxicity, and will not burden the fragile metabolic system of the elderly.

Good Thermal Stability: It is heat-resistant under acidic conditions (pH 2~6), retaining more than 80% of its activity after sterilization at 121℃. It is compatible with food processing technologies and does not affect the thermal sterilization process of elderly food.

No Flavor Interference: It has no off-odor and does not alter the original flavor and texture of elderly food, meeting the sensitive taste requirements of the elderly.

Strong Synergism: It can act synergistically with natural preservatives such as organic acids, plant extracts, and probiotics to broaden the antibacterial spectrum, enhance preservation effects, and reduce the dosage of a single preservative.

2. Preservation Pain Points of Elderly Food and Solutions by Nisin

Due to characteristics such as raw material selection, processing technologies, and consumption scenarios, elderly food faces unique preservation challenges, which Nisin can address specifically:

Pain Point 1: Nutrient-Rich Raw Materials Prone to Pathogen Growth: Elderly food is often based on high-protein, high-carbohydrate, and high-moisture raw materials (e.g., dairy products, soy products, grains, meat). Such raw materials are prone to becoming growth substrates for pathogenic bacteria such as Staphylococcus aureus and Listeria monocytogenes, posing a high infection risk for the elderly. Nisin can inhibit more than 99% of these Gram-positive pathogenic bacteria, effectively reducing food safety risks.

Pain Point 2: Mild Processing with Incomplete Sterilization: To retain nutrients and easily digestible textures, the thermal sterilization intensity of elderly food is usually lower than that of ordinary food, leading to the survival of some heat-resistant spoilage bacteria (e.g., Bacillus subtilis) and shortening the shelf life. Nisin can act as an "auxiliary bactericidal factor" to supplementally inhibit residual bacteria after mild sterilization, extending the food shelf life.

Pain Point 3: Low Tolerance to Chemical Preservatives: The liver and kidney functions of the elderly decline, resulting in reduced metabolic capacity for chemical preservatives such as sodium benzoate and potassium sorbate. Long-term intake may cause adverse reactions. As a natural antimicrobial peptide, Nisin can replace or reduce the dosage of chemical preservatives, aligning with the development trend of "clean labels" for elderly food.

Pain Point 4: Soft Food Texture Prone to Microbial Invasion: Most elderly food is in paste, semi-liquid, or soft forms (e.g., nutritional paste, soft bread, ready-to-eat porridge), with large surface area and high water activity, making it vulnerable to microbial contamination. Nisin can be uniformly dispersed in the food matrix to form a continuous antibacterial environment, inhibiting the proliferation of microorganisms on the surface and inside the food.

II. Preservative Applications of Nisin in Major Elderly Food Categories

1. Elderly Dairy Products (Nutritional Milk, Yogurt, Cheese, Whey Protein Products)

Elderly dairy products are high-protein, high-moisture foods, prone to contamination by Staphylococcus aureus, Listeria monocytogenes, Streptococcus, etc. Fermented foods such as yogurt may undergo flavor deterioration due to miscellaneous bacterial contamination.

Application Scenarios: Adding 100~200 IU/mL Nisin to pasteurized milk and modified milk can extend the shelf life from 7 days to 14~21 days, while inhibiting the proliferation of heat-resistant spore-forming bacteria to avoid milk coagulation and off-odor.

In yogurt production, Nisin can be added after fermentation (50~100 IU/mL) to inhibit contamination by yeasts, molds, and other miscellaneous bacteria, extending the refrigerated shelf life of yogurt to 21~28 days without affecting the activity of probiotics in yogurt.

In elderly cheese, whey protein bars, and other products, adding 150~300 IU/mL Nisin can effectively inhibit the growth of Clostridium botulinum and Staphylococcus aureus, reduce spoilage risks, and retain the soft texture and nutrients of the products.

2. Elderly Cereals and Staple Foods (Nutritional Porridge, Soft Bread, Ready-to-Eat Noodles, Rice Paste)

Such foods have high moisture content and rich starch, making them prone to mold, yeast, and spore-forming bacteria growth, leading to mold, caking, and rancidity.

In ready-to-eat nutritional porridge (e.g., mixed grain porridge, vegetable porridge), adding 80~150 IU/mL Nisin combined with vacuum packaging and mild sterilization (90℃, 10 min) can extend the room-temperature shelf life from 3 months to 6 months without affecting the viscosity and digestibility of the porridge.

In fermented staple foods such as elderly soft bread and steamed buns, Nisin can be used synergistically with calcium propionate (a natural preservative) (50~100 IU/g Nisin + 0.1% calcium propionate) to inhibit the growth of surface molds (e.g., Penicillium, Aspergillus) and internal spore-forming bacteria, extending the shelf life to 7~10 days while avoiding off-odors caused by excessive chemical preservatives.

In powdered elderly foods such as rice paste and lotus root starch, adding 50~80 IU/g Nisin can inhibit the proliferation of heat-resistant spore-forming bacteria during storage, preventing stratification and rancidity after reconstitution, and extending the shelf life of dry powder to more than 12 months.

3. Elderly Meat and Soy Products (Soft Sausages, Ready-to-Eat Dried Tofu, Tofu Pudding)

Most elderly meat products adopt low-fat, low-salt, and soft processing technologies. Soy products are rich in protein and moisture, both of which are prone to contamination by pathogenic and spoilage bacteria.

In elderly soft sausages (e.g., chicken sausages, fish sausages), adding 150~250 IU/mL Nisin combined with low-temperature sterilization (72℃, 30 min) can inhibit the growth of Clostridium botulinum and Staphylococcus aureus, extending the refrigerated shelf life to 15~20 days while retaining the tenderness and digestibility of the sausages.

In ready-to-eat dried tofu, shredded tofu, and other soy products, adding 100~180 IU/mL Nisin can inhibit the proliferation of Bacillus subtilis and Escherichia coli (needing synergy with organic acids), avoiding stickiness and off-odor of soy products, and extending the room-temperature shelf life to 10~15 days.

In fresh tofu pudding, soybean milk, and other ready-to-eat soy products, adding 50~100 IU/mL Nisin can effectively inhibit the growth of Gram-positive bacteria, reduce the spoilage rate in high-temperature summer environments, and extend the consumption window to 8~12 hours.

4. Elderly Nutritional Supplements (Protein Powder, Nutritional Paste, Meal Replacement Powder)

Such foods are mostly in high-protein, high-nutrient-density powder or semi-liquid forms, prone to deterioration due to microbial contamination, affecting the nutritional intake of the elderly.

In elderly protein powder (whey protein, soybean protein), adding 60~100 IU/g Nisin can inhibit the growth of heat-resistant spore-forming bacteria and molds during storage, avoiding caking and off-odor of protein powder, and extending the shelf life to 18 months.

In elderly nutritional paste (e.g., walnut paste, black sesame paste, vegetable nutritional paste), adding 80~120 IU/mL Nisin combined with spray drying technology (Nisin added after drying) can inhibit the rapid proliferation of microorganisms after reconstitution, while retaining nutrients (e.g., vitamins, minerals) from being destroyed.

In meal replacement powder products, Nisin can be used synergistically with probiotics (e.g., Bifidobacterium), inhibiting harmful bacterial contamination without affecting probiotic activity, and ensuring the balance of intestinal flora in the elderly.

III. Optimization Strategies and Precautions for Nisin Application in Elderly Food

1. Core Strategies for Optimizing Application Effects

(1) Construction of Synergistic Preservation Systems

Nisin has weak inhibitory effects on Gram-negative bacteria and requires high concentrations when used alone. Therefore, synergistic systems need to be constructed:

Synergy with Organic Acids: Citric acid, lactic acid, malic acid, etc., can lower the food pH value, enhance the antibacterial activity of Nisin (improving Nisin stability and cell membrane penetration under acidic conditions), and inhibit Gram-negative bacteria. For example, adding 0.1% citric acid + 100 IU/mL Nisin to elderly ready-to-eat porridge improves the antibacterial effect by 40% compared to single Nisin use.

Synergy with Plant Extracts: Natural substances such as tea polyphenols, rosemary extract, and ε-polylysine can broaden the antibacterial spectrum, synergizing with Nisin to inhibit molds, yeasts, and Gram-negative bacteria. For example, adding 50 IU/g Nisin + 0.05% tea polyphenols to elderly soft bread improves the mold inhibitory effect by 50% compared to single Nisin use.

Combination with Physical Preservation Technologies: Vacuum packaging, modified atmosphere packaging (MAP), and low-temperature storage can reduce oxygen content, delay microbial growth, and synergize with Nisin to extend the shelf life. For example, elderly meat products using vacuum packaging + 150 IU/mL Nisin + 4℃ refrigeration have a shelf life twice as long as ordinary refrigeration.

(2) Precise Dosage Control and Addition Method Optimization

Dosage Control: Adjust Nisin dosage according to food type, water activity, and processing technology to avoid excessive addition (though non-toxic, it may affect the intestinal flora of some sensitive groups). Generally, the addition amount is 50~200 IU/mL for liquid elderly food (milk, porridge, soybean milk) and 50~300 IU/g for solid food (bread, protein powder, dried tofu), which must comply with the limits specified in GB 2760 National Food Safety Standard for the Use of Food Additives.

Addition Method: For elderly food with poor thermal stability (e.g., yogurt, cold-processed meat products), Nisin should be added in the late processing stage (after sterilization) to avoid high-temperature inactivation. For powdered food (protein powder, meal replacement powder), Nisin can be uniformly mixed with raw material dry powder before packaging. For liquid food, Nisin can be dissolved in a small amount of sterile water and slowly added with stirring to ensure uniform dispersion.

(3) Adaptation to Elderly Food Processing Technologies

Avoid Strong Alkaline Environments: Nisin stability decreases and is prone to degradation and inactivation in environments with pH＞7. During elderly food processing, the pH should be controlled within the range of 4~6.5, avoiding excessive addition of alkaline raw materials (e.g., sodium bicarbonate).

Reduce Metal Ion Interference: High concentrations of metal ions such as Ca²⁺ and Mg²⁺ may bind to Nisin, reducing its antibacterial activity. If mineral supplements are added to elderly food, the metal ion concentration should be controlled, or mineral forms compatible with Nisin (e.g., chelated forms) should be selected.

Optimize Sterilization Synergy: Adopt a combined process of "mild sterilization + Nisin assistance" to ensure sterilization effects while reducing the destruction of nutrients by thermal processing, aligning with the "high nutrition, easy digestion" requirements of elderly food.

2. Application Precautions

Compliance Requirements: Strictly follow national food additive use standards. The addition amount of Nisin in elderly food shall not exceed the maximum use limit specified in GB 2760 (e.g., 300 IU/mL in dairy products, 500 IU/mL in meat products).

Labeling Requirements: As a food additive, "Nisin (Lacticin)" should be clearly marked under the "Food Additives" section of elderly food packaging labels, facilitating the elderly and their families to know, while meeting the "clean label" consumer demand.

Adaptability to Special Groups: Nisin has no inhibitory effect on probiotics such as lactic acid bacteria, making it suitable for the elderly with weak intestinal functions. However, elderly people allergic to milk should note that some Nisin products may contain milk-derived impurities, and high-purity Nisin preparations without milk sources should be selected.

Storage Conditions: Nisin preparations should be stored in sealed, light-shielded, and low-temperature (4~25℃) environments to avoid activity loss caused by high temperature and humidity, which affects preservation effects.

IV. Industrial Application Prospects and Future Development Directions

1. Application Prospects

Meeting Safety Demands: The naturalness and non-toxicity of Nisin align with the elderly's safety requirements for food preservatives. It can replace or reduce the dosage of chemical preservatives, lowering the safety risks of elderly food.

Extending Shelf Life and Reducing Losses: By precisely inhibiting spoilage and pathogenic bacteria, the shelf life of elderly food can be extended by 30%~100%, reducing losses during production, transportation, and storage, and lowering enterprise costs.

Facilitating Product Upgrade: The application of Nisin can promote the upgrading of elderly food towards "natural, healthy, and clean label," enhancing product competitiveness and meeting the demand for high-quality elderly food in an aging society.

Broadening Application Scenarios: It can be adapted to various types of elderly food (dairy products, grains, meat products, nutritional supplements) with a wide application range and great industrialization potential.

2. Future Development Directions

(1) Development of High-Purity, Customized Nisin Preparations

Develop high-purity Nisin preparations without milk sources and allergens, suitable for elderly people allergic to milk.

Target the characteristics of different elderly foods (e.g., pH, water activity, raw material composition), develop customized composite preservatives (e.g., special formulas of Nisin + organic acids + plant extracts), improving application convenience and effects.

(2) R&D of Sustained-Release Nisin Preparations

Use microencapsulation, nanocarrier, and other technologies to prepare sustained-release Nisin preparations, controlling the release rate of Nisin in food to achieve long-term preservation and reduce addition amount.

Sustained-release preparations can protect Nisin from being destroyed during processing, adapting to more elderly foods with complex processing technologies.

(3) Deepening Mechanism Research and Expanding Applications

Conduct in-depth research on the antibacterial mechanism of Nisin in complex matrices of elderly food, clarify its interactions with nutrients and microbial flora, and optimize application schemes.

Explore the synergistic effects of Nisin with functional ingredients such as probiotics and dietary fiber, developing elderly food with both preservation and intestinal health functions.

(4) Standardization and Regulation Construction

Establish standardized process parameters and detection methods for Nisin application in elderly food, ensuring product quality stability.

Strengthen consumer education, popularize the natural properties and safety of Nisin, eliminate misunderstandings about "additives," and promote its wide application in elderly food.

As a natural antimicrobial peptide, Nisin has irreplaceable value in the preservation of elderly food due to its high safety, precise antibacterial activity, and no flavor interference. By targeting the inhibition of Gram-positive pathogenic and spoilage bacteria, combined with synergistic preservation strategies, it can effectively address the pain points of elderly food, such as nutrient-rich raw materials, mild processing, and easy spoilage, while meeting the elderly's high requirements for food safety and taste. Currently, Nisin has shown good application effects in multiple categories of elderly food, including dairy products, grain staples, meat products, and nutritional supplements. However, there is still room for improvement in the development of customized preparations, application of sustained-release technologies, and research on mechanisms in complex systems. With the advancement of aging society and the improvement of consumer requirements for elderly food quality, Nisin is expected to become a core natural preservative for elderly food, promoting the development of the elderly food industry towards safety, health, and sustainability, and providing important guarantee for the dietary safety and nutritional health of the elderly.