The anti-mold effect of Nisin in baked goods

Nisin, a natural antibacterial peptide derived from lactic acid bacteria fermentation, is traditionally known for its core antibacterial spectrum focusing on Gram-positive bacteria (such as staphylococci, streptococci, and spore-forming bacteria). However, in baked goods—especially products like cakes and bread that are highly susceptible to mold contamination—Nisin can exert indirect or synergistic anti-mold effects through adaptation to food system characteristics and process optimization. Its core value lies in inhibiting mold growth, delaying spoilage, thereby significantly extending product shelf life, while aligning with consumers’ demand for "natural preservation."

I. The Nature of Mold Contamination in Baked Goods

Cakes and bread, characterized by high moisture content (bread: ~30%–40%; cakes: ~20%–35% due to added eggs, milk, etc.), abundant carbohydrates (starch, sugar), and proteins (flour, egg whites), serve as ideal "culture media" for molds. Common molds contaminating baked goods include Penicillium (e.g., Penicillium chrysogenum), Aspergillus (e.g., Aspergillus oryzae), and Rhizopus (e.g., Rhizopus stolonifer). Under suitable temperatures (20–30℃) and humidity, these molds typically germinate hyphae within 3–7 days after the products are baked. They not only form visible mold spots on the surface (e.g., blue-green or white spots) but may also produce harmful mycotoxins (e.g., patulin), rendering the products inedible.

Traditional methods to extend the shelf life of baked goods mostly rely on chemical preservatives (e.g., calcium propionate, potassium sorbate) or physical means (e.g., vacuum packaging, low-temperature refrigeration). However, chemical preservatives often trigger consumers’ concerns about "food additives," while low-temperature refrigeration increases storage and transportation costs. Nisin, with its natural origin, has become an ideal alternative or supplementary option to traditional preservation methods, particularly demonstrating unique advantages in synergistic anti-mold effects.

II. Anti-Mold Effects of Nisin in Bread

In bread, nisin’s anti-mold effects are primarily achieved through "indirect inhibition" and "synergistic enhancement":

Indirect inhibition by suppressing mold-associated bacteria: During bread making, yeast fermentation produces small amounts of organic acids (e.g., lactic acid, acetic acid), maintaining the dough’s pH at a weakly acidic range (5.0–6.0). While this environment moderately inhibits mold growth, it is insufficient to prevent mold proliferation over the long term. When nisin is added to bread dough (typically at 0.001%–0.005%), its core function is not to directly kill molds but to inhibit "mold-associated bacteria" (e.g., certain Gram-positive saprophytic bacteria) that may exist in bread. This reduces the production of "mold-promoting substances" (e.g., small-molecule peptides, organic acid derivatives) from bacterial metabolism, thereby weakening the germination drive of molds.

Slow release to form an antibacterial microenvironment: Nisin can form mild complexes with natural components in bread (e.g., gluten in flour) and be slowly released into the food matrix, creating an "antibacterial microenvironment" inside the bread that delays the spread of mold hyphae.

Synergistic enhancement with traditional anti-mold agents: Nisin exhibits significant synergy with traditional anti-mold agents such as calcium propionate. Calcium propionate inhibits mold growth by altering intracellular osmotic pressure, while nisin disrupts the integrity of mold cell membranes, enhancing the penetration efficiency of calcium propionate into cells. Their combined use can improve anti-mold effects by 30%–50%, extending bread’s shelf life from the conventional 3–5 days to 7–12 days.

For example, in whole-wheat bread, using calcium propionate alone results in a shelf life of approximately 5 days. However, when combined with 0.003% nisin, even under room temperature storage (25℃), mold spots are effectively prevented, and the shelf life can be extended to over 10 days—without significantly affecting the bread’s texture (e.g., softness) or flavor (e.g., wheat aroma).

III. Anti-Mold Application of Nisin in Cakes

In cakes, nisin’s anti-mold application requires adjustments based on the product’s high-sugar and high-fat characteristics, with a focus on "optimizing dispersibility" and "targeted inhibition":

Optimizing dispersibility in high-fat systems: Cake formulations typically contain high proportions of sugar (e.g., sucrose, white granulated sugar, accounting for 50%–100% of flour weight) and fats (e.g., butter, vegetable oil). High sugar creates a hyperosmotic environment that moderately inhibits microbial growth, but high fat reduces the dispersibility of water-soluble preservatives. As a water-soluble antibacterial peptide, Nisin tends to form "aggregates" when directly added to cake batter with high fat content, failing to disperse evenly in the food matrix and thus reducing anti-mold efficacy. In practical applications, nisin is first dissolved in a small amount of warm water or egg white, then gradually added to the batter to ensure uniform distribution in the mixed system of fat, sugar, and flour.

Targeted protection of high-humidity surfaces: During the cooling process of baked cakes, condensation often forms a "water film" on the surface—a high-humidity area prone to mold germination. Spraying a low-concentration nisin solution (e.g., 0.002% aqueous Nisin solution) on the cake surface creates an "antibacterial protective film," directly inhibiting the attachment and germination of mold spores on the surface.

Stabilization by protein complexes to retain activity: Proteins from ingredients such as eggs and milk in cakes can form stable complexes with Nisin, reducing the loss of Nisin’s activity caused by high baking temperatures (typically 160–180℃). Nisin can retain partial activity even after short-term treatment at 121℃, and the moderate-low temperature environment during cake baking is more conducive to preserving its activity.

Through these methods, the shelf life of cakes (e.g., chiffon cakes, sponge cakes) with added nisin can be extended from the conventional 2–4 days to 5–8 days, effectively preventing mold-induced "stickiness and off-odors." For example, in cream cakes, nisin not only inhibits mold growth on the cake base but also helps suppress Gram-positive bacteria that may multiply in the cream, further enhancing overall preservation efficacy.

IV. Practical Application Optimization and Limitations

1. Optimization of Processing and Storage Conditions

In practical applications, nisin’s anti-mold effects in baked goods require comprehensive optimization based on processing technology and storage conditions:

Timing of addition in bread fermentation: To avoid slight inhibition of yeast activity by high-concentration nisin (though yeast has strong resistance to nisin, low-dose addition is more prudent), nisin should not be added during the initial yeast activation stage. It is generally recommended to add it in the late stage of dough kneading.

Rapid cooling of cakes after baking: Cooling cakes quickly (e.g., packaging immediately after cooling to room temperature) reduces the formation of surface water films, complementing nisin’s surface protective effect.

Synergy with physical preservation methods: Combining nisin with physical preservation techniques (e.g., nitrogen-flushed packaging, oxygen absorber packaging) further reduces oxygen content in the food system. Since most molds are aerobic, an oxygen-deficient environment significantly impairs their growth ability, leading to more stable shelf life extension.

2. Limitations and Precautions

Nisin’s anti-mold effect has certain limitations:

Its inhibitory effect on molds is weaker than its bactericidal effect on Gram-positive bacteria, so it cannot replace high-efficiency anti-mold agents alone and is usually used as a "synergistic component" in combination with other preservation methods.

Its activity is easily affected by factors such as pH, salt content, and water activity in baked goods (e.g., activity decreases significantly when pH > 7.0; fortunately, bread and cakes are mostly weakly acidic, ensuring good compatibility).

Therefore, in practical applications, the addition amount and usage of nisin should be adjusted precisely based on product formulations (e.g., sugar-fat ratio, presence of dairy products) and target shelf life. This ensures anti-mold efficacy while avoiding slight bitterness in products caused by excessive addition (Nisin itself has a faint bitter taste, but it barely affects flavor when added within standard limits).

In summary, relying on its natural and safe advantages, nisin demonstrates important auxiliary value in anti-mold protection and shelf life extension of baked goods—especially providing an effective preservation solution for baked products pursuing "clean labels."