Nisin is compounded with sodium lactate

Roast meat is prone to quality deterioration during storage, including microbial spoilage, moisture loss, and lipid oxidation—leading to dry/tough texture, bland flavor, and even rancidity. The combination of nisin (a natural antimicrobial peptide) and sodium lactate (a humectant preservative) delivers more than just additive effects. Through synergistic "antibacterial-humectant-antioxidant" actions, it inhibits spoilage while protecting roast meat’s texture and flavor at the molecular level, providing an efficient solution to extend shelf life and maintain eating quality.

I. Mechanisms for Texture Protection in Roast Meat: Locking Moisture and Stabilizing Proteins

The texture properties of roast meat (e.g., tenderness, elasticity) depend primarily on the integrity of muscle protein structure and moisture retention. The combined system reduces texture deterioration through dual actions, keeping roast meat tender even after storage.

(I) Sodium Lactate: Building a "Moisture-Locking Network" to Reduce Moisture Loss

Sodium lactate contains hydroxyl and carboxyl groups that form stable hydrogen bonds with bound water and muscle proteins in roast meat. Acting like a "scaffold," it traps moisture within the meat tissue, minimizing evaporation or exudation of free water.

Under regular storage (4°C for 10 days), roast meat without additives loses 12%–15% moisture, resulting in dry, tough texture. The combined group with 2 g/kg sodium lactate reduces moisture loss to 5%–7%, with bound water content increasing from 60% to over 75%. The meat remains moist to the touch and does not cause a "dry choking sensation" when chewed.

For frozen storage (-18°C), sodium lactate also inhibits ice crystal formation—preventing ice crystals from rupturing muscle cells (which causes moisture loss during thawing). After thawing, the meat’s hardness increases by only 20% compared to fresh roast meat, far lower than the 50% increase in the non-added group.

(II) Nisin: Assisting Protein Structure Stabilization to Avoid Excessive Hardening

As a peptide, nisin binds to myofibrillar proteins (the core component of meat elasticity) in roast meat. It inhibits aggregation and denaturation of these proteins during low-temperature storage, maintaining structural flexibility.

Texture Profile Analysis (TPA) shows: After 10 days at 4°C, the hardness of non-added roast meat increases from 2200 g to 4500 g, with chewiness rising by 130%. In the combined group (0.2 g/kg nisin + 2 g/kg sodium lactate), hardness only increases to 2800 g, and chewiness rises by 30%. When biting down, the meat still retains elastic feedback rather than a "dry, tough" texture.

Differential Scanning Calorimetry (DSC) validation: The denaturation temperature of myofibrillar proteins in the combined group increases from 58°C to 62°C. This means proteins are less likely to denature due to temperature fluctuations during storage, preserving the "tenderness foundation" of roast meat at the molecular level.

II. Mechanisms for Flavor Preservation in Roast Meat: Inhibiting Oxidation and Reducing Off-Flavors

The roasted, meaty flavor of roast meat comes from heat-generated volatile compounds (e.g., aldehydes, sulfur-containing compounds). During storage, lipid oxidation and microbial metabolism destroy these flavor compounds and produce off-flavors (e.g., rancidity, gaminess). The combined system stabilizes flavor through "flavor protection" and "off-flavor inhibition."

(I) Sodium Lactate: Chelating Metal Ions to Block Lipid Oxidation

Metal ions (e.g., Fe²⁺, Cu²⁺) in roast meat are key "catalysts" for lipid oxidation. The lactate ions in sodium lactate chelate these ions, inactivating their catalytic ability and reducing the production of rancid compounds (e.g., malondialdehyde, MDA).

After 10 days at 4°C, the MDA content of non-added roast meat reaches 1.2 mg/kg, with a distinct rancid odor. The combined group has an MDA content of only 0.35 mg/kg, with almost no detectable rancidity. Gas Chromatography-Mass Spectrometry (GC-MS) analysis shows that 75% of roast meat’s characteristic roasted flavor compounds (e.g., 2-pentylfuran, hexanal) are retained, so the meat still tastes "freshly roasted."

(II) Nisin: Inhibiting Microorganisms to Reduce Off-Flavor Metabolism

Microorganisms (e.g., Pseudomonas, Staphylococcus aureus) decompose proteins during growth, producing off-flavor compounds such as amines (e.g., trimethylamine) and sulfides. Nisin specifically inhibits these Gram-positive bacteria, reducing off-flavor production at the source.

In non-added roast meat stored for 10 days, trimethylamine content reaches 5.2 mg/kg, with a strong gamy odor. The combined group has a trimethylamine content of only 0.8 mg/kg, and sensory evaluation gives it a "rich meat flavor" score of 7.8/10—far higher than the 4.2/10 of the non-added group. Additionally, the retention rate of umami compounds (e.g., glutamic acid, inosinic acid) increases by 30%, making the meat taste more "savory."

III. Practical Applications of the Combined System: Parameter Optimization and Scenario Adaptation

To maximize the efficacy of the combined system, parameters must be adjusted based on roast meat type and processing technology to avoid flavor interference and adapt to industrial production.

(I) Combination Ratio: Adjusting for Roast Meat Type

High-fat roast meat (e.g., pork belly, beef skewers): High risk of lipid oxidation requires a higher sodium lactate ratio (2.5–3 g/kg) with nisin maintained at 0.2 g/kg to enhance antioxidant effects and prevent rancidity.

High-protein, low-fat roast meat (e.g., chicken breast, lean pork): Prone to dryness; sodium lactate is controlled at 1.5–2 g/kg (to avoid excessive saltiness), and 0.1% vitamin C can be added to assist moisture retention, with nisin at 0.15–0.2 g/kg.

Seasoned roast meat (e.g., marinated roast meat): If salt is already added, sodium lactate is reduced to 1–1.5 g/kg to prevent saltiness overlap, with nisin at 0.2 g/kg.

(II) Addition Timing: Avoiding High Temperatures to Preserve Activity

Nisin is easily inactivated at temperatures >80°C, so it is recommended to add it during the marination stage (low temperature <10°C for 2–4 hours). This allows the combined ingredients to penetrate the meat interior with the marinade, exerting deep antibacterial effects while avoiding high-temperature damage. If not added during marination, it can be sprayed on the roast meat surface when cooled to 40–50°C to form a "protective film" that inhibits surface microorganisms.

(III) Storage Coordination: Vacuum Packaging + Low Temperature for Doubled Efficacy

Combining the system with vacuum packaging (to isolate oxygen) further reduces lipid oxidation: After 15 days at 4°C, MDA content can drop to 0.28 mg/kg, and total bacterial count remains <10³ CFU/g. For frozen storage at -18°C, shelf life can extend to 3 months, with almost no difference in texture or flavor after thawing—suitable for large-scale production by prepared meal enterprises.

IV. Core Advantages and Precautions

(I) Advantages: Natural, Efficient, and Low-Cost

Natural safety: Nisin is produced by lactic acid bacteria fermentation, and sodium lactate can be extracted from milk or beets. Both are FDA-certified "GRAS" (Generally Recognized as Safe) substances, eliminating concerns about chemical preservative residues and meeting consumer demand for "natural, additive-free" products.

Cost-effectiveness: The addition cost per kilogram of roast meat is only ~0.07 yuan (based on 2 g/kg sodium lactate + 0.2 g/kg nisin), much lower than natural extracts like tea polyphenols—suitable for small and medium-sized manufacturers.

(II) Precautions: Avoiding Flavor and Activity Loss

Control sodium lactate dosage: Excessive amounts (>3 g/kg) make roast meat overly salty, masking its original flavor. Adjustments should be made based on salt content.

Avoid high temperatures: Never add nisin directly during roasting to prevent activity loss.

Adapt to pH: Nisin is most active at pH 5.0–7.0. For acidic roast meat (e.g., lemon-flavored), increase nisin dosage to 0.25–0.3 g/kg or adjust pH to above 5.5.

The combination of nisin and sodium lactate leverages dual synergies: "sodium lactate for moisture/texture retention + nisin for antibacterial/protein stabilization" and "sodium lactate for antioxidant + nisin for off-flavor inhibition." It not only solves spoilage issues in roast meat storage but also preserves "tenderness" and "roasted flavor," extending the refrigerated shelf life at 4°C from 5 days to 10–12 days. This natural, low-cost solution adapts to various roast meat processing scenarios, making it the preferred choice for balancing "safety" and "quality" in roast meat preservation.