Nisin in baked goods

As a natural biological preservative, nisin finds applications in baked goods to exert anti-corrosion effects while potentially influencing product texture. Its mechanism and efficacy are regulated by multiple factors, as detailed below:

I. Anticorrosion Efficacy in Baked Foods

1. Anticorrosion Mechanism and Antibacterial Spectrum

Nisin, a polypeptide produced by Streptococcus lactis, inhibits Gram-positive bacteria (e.g., Bacillus, Listeria, Staphylococcus aureus) by disrupting microbial cell membrane integrity and inhibiting cell wall synthesis. It notably delays the growth of common spoilage bacteria (e.g., Bacillus cereus) in baked goods. However, it shows weak inhibition against Gram-negative bacteria, yeasts, and molds, thus often requiring synergistic use with other preservatives (e.g., calcium propionate, potassium sorbate) or antibacterial measures (e.g., low water activity, sealed packaging) to broaden the anticorrosion spectrum.

2. Application Effects in Different Baked Foods

Bread: In traditional yeast-fermented bread, Nisin suppresses acidification and mold growth caused by microbial contamination, extending shelf life by 1–2 days. For example, adding 0.02–0.05 g/kg nisin significantly reduces the count of heat-resistant spores without affecting yeast fermentation activity (nisin is highly stable under acidic conditions, and the dough pH of bread typically ranges from 5.0 to 6.0, suitable for its action).

Cakes and Pastries: These products have high sugar content and water activity (Aw), making them prone to mold contamination. Studies show that adding 0.03 g/kg nisin to cream cakes combined with low-temperature storage (4°C) delays mold growth by 3–5 days, with no obvious impact on color and flavor.

Frozen Baked Foods: Microbial activity decreases during freezing, but reproduction may resume after thawing. Adding nisin (0.05–0.1 g/kg) inhibits spore resuscitation after thawing, and vacuum packaging extends the shelf life of frozen bread to 15–20 days.

3. Key Factors Affecting Anticorrosion Efficacy

pH and Heat Treatment: Nisin is stable and highly active under acidic conditions (pH ≤ 5.5). At pH > 6.0, its structure is prone to degradation by proteases, reducing activity. High temperatures (180–220°C) during baking cause partial inactivation of nisin, but 30%–50% activity remains after short-term heat treatment (e.g., 20–30 minutes of bread baking), sufficient to inhibit residual microbial growth.

Dosage and Synergy: The effective dosage of Nisin is typically 0.01–0.1 g/kg. Excessive use may increase costs and negatively affect texture. Compounding with acidic substances like citric acid or vitamin C enhances nisin activity by lowering system pH; synergizing with natural bacteriostatic agents like tea polyphenols or chitosan compensates for its insufficient inhibition of molds.

II. Influence on the Texture of Baked Foods

1. Effects on Dough Rheological Properties

Dough Ductility and Elasticity: Low-dose nisin (≤ 0.05 g/kg) has no significant impact on the formation of wheat flour dough gluten networks, as nisin has a small molecular weight (approximately 3.5 kDa) and hardly interacts with gluten proteins. However, high doses (> 0.1 g/kg) may slightly reduce dough ductility through water competition or weak ionic effects, leading to decreased gas retention during proofing and slightly smaller bread volume.

Fermentation Characteristics: Nisin has extremely weak inhibitory effects on yeast (yeast is a fungus, and nisin mainly targets bacteria), so normal dosages do not affect dough fermentation rate or gas production, and bread puffiness remains basically unaffected.

2. Specific Effects on Finished Product Texture

Bread Texture: Appropriate nisin (0.03–0.05 g/kg) slightly reduces bread hardness and chewiness, possibly due to its inhibition of certain acid-producing bacteria, reducing the softening effect of organic acids on gluten proteins. For example, studies show that toast bread with nisin has a hardness 10%–15% lower than the control group after 3 days of storage, with a softer texture.

Cake Texture: In sponge cakes, nisin addition has little effect on batter viscosity and whipping stability, but excessive amounts (> 0.08 g/kg) may cause slightly loose internal structures and uneven pore distribution, possibly due to nisin disrupting the gel network of some egg proteins.

Anti-aging Effect: Nisin indirectly delays the aging process of baked goods by inhibiting microbial reproduction. For instance, bread with nisin shows reduced starch retrogradation rate and better water retention during storage, extending the softness period.

III. Precautions for Practical Applications

Dosage Control: Reasonably adjust the nisin dosage (usually ≤ 0.1 g/kg) according to the type of baked food and microbial risk to avoid texture deterioration caused by excess.

Construction of Synergistic Anticorrosion Systems: For microorganisms insensitive to nisin, such as molds, combine with natural bacteriostatic components (e.g., natamycin) or improved packaging technologies (e.g., nitrogen-filled packaging) to achieve broad-spectrum anticorrosion.

Process Adaptability: When adding nisin before baking, pay attention to adjusting the pH of dough or batter (e.g., adding a small amount of citric acid) to maintain its activity. For products requiring long-term high-temperature baking (e.g., cookies), consider spraying nisin solution after cooling to reduce thermal inactivation.

Conclusion

Nisin serves as an efficient and safe biological preservative in baked foods, significantly inhibiting spoilage caused by Gram-positive bacteria while optimizing product texture (e.g., bread softness, cake structure) at reasonable dosages. Future research could focus on compounding nisin with other natural bacteriostatic agents and improving its thermal stability through microencapsulation technology to further expand application scenarios in the baking sector.