The preservative effect of Nisin compounded with spice extract

The combination of Nisin and spice extracts achieves a synergistic fresh-keeping effect. It not only broadens the antibacterial spectrum (covering Gram-positive bacteria, some Gram-negative bacteria, and fungi) but also extends the shelf life, reduces the dosage of chemical preservatives, and endows food with natural flavor. This aligns with the "safety, naturalness, and low residue" requirements of green food, showing significant application advantages in meat products, dairy products, fruit and vegetable products, and other fields.

I. Core Advantages of the Combination: Synergistic Enhancement to Compensate for Shortcomings of Single Preservatives

The combination of Nisin (a natural antimicrobial peptide) and spice extracts (e.g., cinnamon, clove, rosemary extracts) essentially addresses the application limitations of single preservatives through three dimensions: "complementary mechanisms of action," "overlapping antibacterial spectra," and "improved stability." The specific advantages are as follows:

(I) Complementary Mechanisms of Action: From "Single Target" to "Multi-Target Attack"

Nisin inhibits bacteria by disrupting the cell membrane of Gram-positive bacteria (forming transmembrane pores and causing leakage of intracellular substances), but has weak effects on Gram-negative bacteria (e.g., E. coli, Salmonella) and fungi (e.g., Penicillium, yeast). In contrast, active components in spice extracts (e.g., cinnamaldehyde in cinnamon, eugenol in cloves, rosmarinol in rosemary) inhibit bacteria through multiple mechanisms:

Destroying the integrity of bacterial cell walls (e.g., cinnamaldehyde dissolves the lipopolysaccharide layer of Gram-negative bacteria);

Inhibiting bacterial enzyme activity (e.g., eugenol inhibits dehydrogenase in the bacterial respiratory chain);

Damaging fungal cell membranes (e.g., rosmarinol increases the permeability of fungal cell membranes, leading to leakage of contents).

After combination, they can act on multiple targets of microorganisms (cell membranes, enzyme systems, genetic materials, etc.), significantly improving antibacterial efficiency. For example, using 0.05 g/kg Nisin alone has almost no inhibitory effect on E. coli, but when combined with 0.2 g/kg cinnamon extract, the inhibition rate of E. coli can reach over 90%, achieving a "1+1 > 2" synergistic effect.

(II) Broadened Antibacterial Spectrum: Covering More Spoilage and Pathogenic Bacteria

Single Nisin is only effective against Gram-positive bacteria (e.g., Staphylococcus aureus, Listeria monocytogenes, Clostridium botulinum) and cannot combat common Gram-negative bacteria (e.g., E. coli in fruits and vegetables, Salmonella in meat products) and fungi (e.g., yeast in bread, Penicillium in fruits) in food. However, most spice extracts have broad-spectrum antibacterial properties, and their combination with Nisin achieves "full coverage" of the antibacterial spectrum:

Meat products: The combined system can simultaneously inhibit Listeria (Gram-positive bacteria), Salmonella (Gram-negative bacteria), and biofilm-forming yeast, avoiding "cross-contamination" and "surface mold growth" during low-temperature storage.

Fruit and vegetable products: It can inhibit Pectobacterium (Gram-negative bacteria, causing soft rot), Penicillium (fungi, causing mold), and lactic acid bacteria (causing spoilage due to excessive fermentation), solving the problems of "fast rotting" and "flavor deterioration" in fruits and vegetables.

(III) Improved Stability: Enhanced Processing and Storage Performance

Nisin is easily inactivated under high temperature (>121°C), strong acidity (pH < 2), or in protease-containing environments (e.g., in fermented dairy products, proteases produced by lactic acid bacteria may degrade Nisin). In contrast, spice extracts (e.g., rosmarinol in rosemary extract) have antioxidant properties, which can inhibit protease activity, reduce the damage of free radicals to Nisin, and maintain high stability themselves under high temperature and acid-base conditions (e.g., cinnamaldehyde retains 80% of its activity after high-pressure sterilization at 121°C). For example, in high-temperature sterilized sauced beef, using 0.05 g/kg Nisin alone results in only 60% activity retention after sterilization; when combined with 0.1 g/kg rosemary extract, the activity retention of Nisin increases to 90%, and the shelf life of sauced beef extends from 15 days to 28 days, while avoiding flavor loss caused by high temperature.

II. Typical Application Scenarios: Fresh-Keeping Effect and Process Adaptability of the Combined System

The combination ratio and addition method of Nisin and spice extracts need to be adjusted according to the spoilage characteristics and processing technology (low/high temperature, acidic/neutral) of food categories (meat products, dairy products, fruit and vegetable products) to achieve the best fresh-keeping effect.

(I) Meat Products: Inhibiting Pathogens and Delaying Lipid Oxidation

The main spoilage problems of meat products (e.g., low-temperature ham, sausages, cured meat) include contamination by Gram-positive bacteria (Listeria), lipid oxidation (producing a rancid taste), and mold growth. The combined system can specifically address these issues:

Combination scheme: 0.03–0.05 g/kg Nisin + 0.1–0.3 g/kg cinnamon extract (or clove extract), added via "injection" (for ham) or "marination" (for sausages).

Fresh-keeping effect: During storage at low temperature (0–4°C), the period for ham to meet the total bacterial count standard (≤10⁴ CFU/g) extends from 15 days to 30 days, with no Listeria detected. Meanwhile, the antioxidant property of cinnamon extract reduces the lipid oxidation value (TBARS) by 40%, avoiding rancidity.

Advantage: It replaces traditional nitrite (reducing dosage from 50 mg/kg to <20 mg/kg), lowers the risk of nitrosamine formation, and endows meat products with a light cinnamon aroma, improving flavor acceptance.

(II) Dairy Products: Inhibiting Heat-Resistant Bacteria and Extending Shelf Life

The main spoilage bacteria of dairy products (e.g., fresh milk, yogurt, cheese) are heat-resistant Gram-positive bacteria (e.g., Bacillus cereus, mutant strains of Streptococcus thermophilus) and yeast. The combined system can adapt to low-temperature and fermentation processes:

Fresh milk scenario: 0.02–0.03 g/kg Nisin + 0.05–0.1 g/kg rosemary extract, added before pasteurization (65°C for 30 minutes). Fresh-keeping effect: During storage at 0–4°C, the shelf life of fresh milk extends from 7 days to 14 days, with Bacillus cereus content <10 CFU/mL. Additionally, the antioxidant property of rosemary extract reduces vitamin C loss (retention rate increases from 70% to 90%).

Yogurt scenario: 0.01–0.02 g/kg Nisin + 0.05 g/kg clove extract, added after fermentation. Fresh-keeping effect: During storage at 2–6°C, the yeast growth period of yogurt extends from 21 days to 35 days. Meanwhile, the flavor of clove extract masks the slight sour taste that may occur during fermentation, improving taste.

(III) Fruit and Vegetable Products: Preventing Soft Rot and Mold

The main spoilage problems of fruit and vegetable products (e.g., fresh-cut lettuce, strawberries, pickles) include bacterial soft rot (Pectobacterium), fungal mold (Penicillium, Botrytis cinerea), and enzymatic browning (e.g., browning of cut apples). The combined system can be added via "soaking" or "spraying":

Fresh-cut lettuce scenario: 0.02 g/kg Nisin + 0.1 g/kg rosemary extract, prepared into an aqueous solution to soak lettuce for 5 minutes. Fresh-keeping effect: During storage at 4°C, the period for lettuce to meet the total bacterial count standard extends from 3 days to 7 days, with no Pectobacterium detected. Meanwhile, rosemary extract inhibits polyphenol oxidase activity, reducing browning rate by 50% and maintaining the fresh green color of lettuce.

Strawberry scenario: 0.015 g/kg Nisin + 0.08 g/kg cinnamon extract, sprayed and air-dried. Fresh-keeping effect: During storage at 4°C, the mold rate of strawberries decreases from 80% on day 5 to 20% on day 10. Additionally, the aroma of cinnamon extract masks the "fermentation taste" that may occur during strawberry storage, maintaining the fruit aroma.

III. Combination Ratio and Process Control: Keys to Maximizing Fresh-Keeping Effect

The fresh-keeping effect of the Nisin-spice extract combination is not "the higher the ratio, the better." The optimal ratio must be determined through orthogonal experiments, and the addition process must be controlled to avoid loss of active components or flavor conflicts.

(I) Optimization of Combination Ratio: Adjust According to Food Category

High-risk foods (e.g., low-temperature meat products, sterile dairy products): The ratio of Nisin to spice extract can be controlled at 1:3–1:5 (e.g., 0.05 g/kg Nisin + 0.2 g/kg cinnamon extract) to ensure antibacterial strength.

Low-risk foods (e.g., fresh-cut fruits and vegetables, baked goods): The ratio can be adjusted to 1:1–1:2 (e.g., 0.02 g/kg Nisin + 0.03 g/kg rosemary extract) to ensure fresh-keeping effect while avoiding excessive spice flavor.

Precautions: The addition amount of spice extracts should not be too high (e.g., >0.5 g/kg), otherwise it may produce "spicy taste" or "bitter taste" (e.g., excessive clove extract causes bitterness in dairy products), affecting food sensory quality.

(II) Key Points of Process Control

Addition timing: For high-temperature processed foods (e.g., sterilized meat products, canned foods), the combined system must be added "before sterilization" to avoid inactivation of active components by high temperature. For low-temperature processed foods (e.g., yogurt, fresh-cut fruits and vegetables), it can be added "in the later stage of processing" to reduce interactions between active components and other raw materials.

Dissolution and dispersion: Nisin is easily soluble in water, while spice extracts (e.g., cinnamaldehyde) are easily soluble in ethanol. When combining, spice extracts can first be dissolved in a small amount of food-grade ethanol, then mixed with Nisin aqueous solution to ensure uniform dispersion (avoiding uneven flavor caused by local high concentration).

pH adaptability: Nisin has the best activity at pH 5–7, and spice extracts (e.g., cinnamaldehyde) are more stable under acidic conditions. Therefore, the combined system is suitable for foods with pH 4–7 (e.g., meat products, neutral dairy products). If the food pH < 4 (e.g., high-acid fruit juice), the addition amount of Nisin should be appropriately increased (by 20%–30%) to compensate for activity loss caused by acidity.

The fresh-keeping effect of the Nisin-spice extract combination essentially relies on "complementary mechanisms, broadened spectrum, and improved stability" to achieve synergistic enhancement. It not only solves the problems of narrow antibacterial spectrum and poor stability of single preservatives but also reduces the dosage of chemical preservatives, aligning with the development trend of green food. In practical applications, the combination ratio and addition method should be optimized according to the spoilage characteristics and processing technology of food categories to ensure fresh-keeping effect while considering food flavor and sensory quality. In the future, with the advancement of purification technology for natural spice extracts (e.g., improving the purity of active components and reducing off-flavors), the application prospects of this combined system in high-end food and organic food will be further expanded.