The effect of using Nisin in combination with tea polyphenols

Nisin, a natural bacteriocin, exhibits potent inhibitory effects against Gram-positive bacteria (e.g., Staphylococcus, Streptococcus). Tea polyphenols, plant-derived polyphenolic compounds, possess broad-spectrum antibacterial, antioxidant, and quality-preserving properties. When used in combination, these two substances leverage three core advantages—"complementary antibacterial spectra, synergistic mechanisms of action, and superimposed functional effects"—to overcome the limitations of single-component use. They demonstrate far superior efficacy to individual components in food preservation, quality maintenance, and functional enhancement, providing a typical solution for the efficient application of natural food additives.

I. Core Effect 1: Synergistic Antibacterial Action – Broadening Antibacterial Spectrum and Enhancing Inhibitory Strength

The combination of Nisin and tea polyphenols first addresses the drawbacks of single-component use (narrow antibacterial range, high-dose dependence). Through synergistic mechanisms, it achieves a "1+1>2" antibacterial effect, covering most pathogenic and spoilage-causing bacteria in food.

(I) Complementary Antibacterial Spectra: From "Single Target" to "Full Coverage"

Nisin’s antibacterial range is limited to Gram-positive bacteria, with almost no effect on Gram-negative bacteria (e.g., E. coli, Salmonella) or fungi (e.g., yeast, molds). In contrast, tea polyphenols (especially catechins) exhibit broad-spectrum antibacterial activity, inhibiting both Gram-negative bacteria and fungi. Their combination achieves comprehensive coverage of antibacterial spectra:

In meat products (e.g., chilled meat, sausages): Using 0.2 g/kg Nisin alone only inhibits Gram-positive bacteria such as Listeria monocytogenes and is ineffective against E. coli and Pseudomonas (which cause meat spoilage). After combining with 0.1 g/kg tea polyphenols, not only does the inhibition rate of Listeria increase from 85% to 99%, but the growth rate of E. coli and Pseudomonas is also reduced by over 80%, extending the refrigerated shelf life of meat from 7 days to 15 days.

In baked goods (e.g., bread): Nisin is ineffective against lactic acid bacteria (which cause bread staling), while tea polyphenols have weak inhibitory effects on molds (e.g., Penicillium). Their combination (0.15 g/kg Nisin + 0.08 g/kg tea polyphenols) inhibits both lactic acid bacteria and Penicillium, delaying bread staling by 5 days and reducing mold contamination rate from 25% to below 5%.

(II) Synergistic Mechanisms: From "Single Attack" to "Multi-Target Destruction"

Nisin and tea polyphenols have fundamentally different antibacterial mechanisms. When combined, they attack microorganisms at multiple targets, significantly enhancing inhibitory strength and reducing the risk of bacterial resistance:

Nisin’s mechanism: Destroys the cell membrane of Gram-positive bacteria by binding to lipid II (a precursor for cell wall synthesis) on the bacterial membrane, forming transmembrane pores. This disrupts intracellular osmotic balance and causes leakage of cellular contents, ultimately leading to bacterial lysis.

Tea polyphenols’ mechanism: Multi-target interference. On one hand, they damage the integrity of bacterial cell membranes (binding to membrane proteins and altering membrane permeability), assisting Nisin in forming more transmembrane pores. On the other hand, they inhibit key bacterial enzymes (e.g., DNA polymerase, respiratory chain enzymes), blocking microbial metabolism and proliferation.

In vitro experiments show:

The minimum inhibitory concentration (MIC) of 0.1 g/L Nisin alone against Staphylococcus aureus is 25 μg/mL.

The MIC of 0.05 g/L tea polyphenols alone is 50 μg/mL.

After combination, the MIC decreases to 8 μg/mL Nisin + 15 μg/mL tea polyphenols, improving antibacterial efficiency by 3–4 times.

Furthermore, no significant bacterial resistance is observed after 10 consecutive subcultures, whereas bacteria treated with Nisin alone develop resistance by the 5th subculture.

II. Core Effect 2: Synergistic Antioxidation – Delaying Oxidative Deterioration of Food

Beyond antibacterial activity, the strong antioxidant properties of tea polyphenols and the stability of Nisin synergize to effectively delay oxidative deterioration of food (especially high-fat, oxygen-sensitive foods), maintaining color, flavor, and nutritional quality.

(I) Inhibiting Lipid Oxidation – Extending Shelf Life of High-Fat Foods

Oxidative deterioration of high-fat foods (e.g., fried foods, nuts, edible oils) primarily stems from lipid peroxidation. Tea polyphenols inhibit this process by scavenging free radicals and chelating metal ions (e.g., Fe²⁺, Cu²⁺), while Nisin reduces reactive oxygen species (ROS) production by inhibiting oxygen-dependent microorganisms (e.g., certain aerobic bacteria). Their combination enhances antioxidant efficacy:

In fried potato chips: Adding 0.05 g/kg tea polyphenols alone reduces the peroxide value (POV, an indicator of lipid oxidation) of chips from 8.5 meq/kg to 5.2 meq/kg after 30 days of storage. Combining with 0.03 g/kg Nisin further lowers the POV to 3.1 meq/kg, significantly reducing the rancid smell (oxidative off-odor) and improving sensory scores (color, flavor) by 20% compared to the single-component group.

In walnut storage: Nisin alone has no significant inhibitory effect on walnut oxidation. Using 0.1 g/kg tea polyphenols alone reduces the acid value (AV, an indicator of oil hydrolysis and rancidity) of walnuts from 4.0 mg KOH/g to 2.8 mg KOH/g after 60 days of storage. After combination, the AV decreases to 1.9 mg KOH/g, significantly improving walnut crispness and original flavor retention, while simultaneously reducing mold contamination rate from 18% to 3%.

(II) Protecting Pigments and Vitamins – Maintaining Food Nutrition and Appearance

Natural pigments in food (e.g., myoglobin in meat, chlorophyll in fruits/vegetables) and vitamins (e.g., vitamin C, vitamin E) are easily oxidized and destroyed, leading to discoloration and nutrient loss. The combination of Nisin and tea polyphenols specifically protects these components:

In chilled meat preservation: Oxidation of myoglobin turns meat color from bright red to brown (due to metmyoglobin formation). Tea polyphenols inhibit myoglobin oxidase activity, while Nisin inhibits bacterial growth (bacterial metabolism accelerates myoglobin oxidation). When used together (0.2 g/kg Nisin + 0.1 g/kg tea polyphenols), the metmyoglobin content of chilled meat stored at 4°C for 12 days decreases from 45% to 18%, extending the bright red period by 5 days. Additionally, the retention rate of vitamin B₁ increases from 55% to 80%.

In fruit juices (e.g., apple juice): Tea polyphenols scavenge free radicals in juice to protect vitamin C from oxidation, while Nisin inhibits lactic acid bacteria in juice (preventing fermentation and spoilage). After combination (0.08 g/kg Nisin + 0.05 g/kg tea polyphenols), the retention rate of vitamin C in apple juice stored at room temperature for 7 days increases from 40% to 72%, and the browning degree (indicating juice discoloration) decreases from 0.8 to 0.3, minimizing flavor differences from freshly squeezed juice.

III. Core Effect 3: Improving Food Quality – Reducing Side Effects of Single Components

The combination of Nisin and tea polyphenols not only "enhances efficacy" but also "reduces harm." Through mutual regulation, it minimizes taste and flavor side effects of single components while improving food processing adaptability.

(I) Masking Off-Flavors – Enhancing Sensory Acceptance

High-dose Nisin (>0.3 g/kg) imparts a slight bitter or metallic taste to food, while tea polyphenols (especially ester-type catechins) have a certain astringency. Their combination reduces off-flavor perception through flavor complementarity:

In dairy products (e.g., pasteurized milk): Adding 0.3 g/kg Nisin alone causes a distinct bitter taste in milk, with a sensory acceptance score of only 65. After combining with 0.1 g/kg tea polyphenols, the bitterness intensity decreases by 40%, astringency is negligible, and the sensory acceptance score rises to 88. Additionally, the shelf life of milk extends from 7 days to 14 days, with no curdling or souring.

In plant-based protein drinks (e.g., soy milk): Adding tea polyphenols alone intensifies the astringency of soy milk. Combining with low-dose Nisin (0.05 g/kg) reduces astringency perception; meanwhile, the beany flavor of soy milk (partially caused by bacterial metabolism) is alleviated by Nisin’s antibacterial effect, resulting in a cleaner overall flavor.

(II) Enhancing Processing Stability – Adapting to Complex Processes

Nisin is prone to inactivation under high temperatures and acidic conditions (e.g., high-temperature sterilization causes 30%–50% loss of Nisin activity). The antioxidant properties of tea polyphenols protect Nisin from oxidative degradation, improving its stability in complex processing:

In canned food (e.g., mushroom cans): Sterilization at 121°C for 30 minutes causes 45% loss of Nisin activity when used alone, significantly reducing antibacterial efficacy. After combining with tea polyphenols (0.2 g/kg Nisin + 0.1 g/kg tea polyphenols), the loss of Nisin activity decreases to 15%. After 6 months of room-temperature storage, the total bacterial count in cans remains <100 CFU/g, far lower than the 500 CFU/g in the single-Nisin group.

In acidic foods (e.g., pickles): Environments with pH < 4.0 accelerate Nisin degradation; only 30% of Nisin activity remains after 10 days of fermentation when used alone. After combining with tea polyphenols, the activity retention rate of Nisin increases to 65%. Additionally, tea polyphenols inhibit nitrite formation during pickle fermentation (reducing nitrite content from 20 mg/kg to 8 mg/kg), improving food safety.

IV. Typical Application Scenarios and Recommended Formulation Parameters

The synergistic efficacy of Nisin and tea polyphenols varies by food type and processing technology. Formulation ratios and dosages need optimization based on specific scenarios. Below are application cases for typical food categories, providing references for practical production:

(I) Meat Products: Chilled Meat, Sausages

Formulation ratio: 0.15–0.2 g/kg Nisin + 0.08–0.12 g/kg tea polyphenols

Core efficacy: Antibacterial (inhibiting Listeria, E. coli), antioxidant (delaying myoglobin oxidation and lipid oxidation); extends refrigerated shelf life by 2–3 times and bright red period of meat by 5–7 days

Application method: Spraying or soaking (0.2% formulation solution) after slaughter, or direct addition during sausage chopping

(II) Dairy Products: Pasteurized Milk, Yogurt

Formulation ratio: 0.05–0.1 g/kg Nisin + 0.03–0.05 g/kg tea polyphenols

Core efficacy: Inhibits excessive growth of lactic acid bacteria (preventing over-acidification of yogurt), protects milk proteins from oxidation; extends shelf life by 1–2 times with no significant off-flavors

Application method: Added after pasteurization and before filling to avoid high-temperature inactivation

(III) Fruits, Vegetables, and Their Products: Fresh Fruits/Vegetables, Fruit Juices

Formulation ratio: 0.08–0.12 g/kg Nisin + 0.05–0.08 g/kg tea polyphenols

Core efficacy: Inhibits molds (e.g., Penicillium, Botrytis), protects vitamin C and pigments; extends refrigerated shelf life of fresh fruits/vegetables by 3–5 days and reduces juice browning by over 50%

Application method: Soaking fresh fruits/vegetables (0.1% formulation solution, 10-minute soak), or direct addition after juice extraction

The combination of Nisin and tea polyphenols achieves an upgrade from "single-component preservation" to "multi-dimensional freshness maintenance" through synergistic antibacterial, antioxidant, and quality-enhancing effects. It not only expands the application scope of natural food additives but also addresses limitations of single components (narrow antibacterial spectrum, easy development of resistance, flavor side effects). Against the backdrop of increasing demand for food safety and naturalization, this formulation has become a preferred preservation technology in meat products, dairy products, fruits, vegetables, and their processed goods.