Natamycin is the only bio antifungal compound used in foods

Natamycin as a Cheese Preservative

Use on the surfaces of cheeses is the largest application for natamycin. Experience has shown that it is most effective if it is evenly applied at sufficient concentration (0.6–1 mg/ g). The three main methods of surface treatment are spraying the surface of the cheese with a natamycin suspension, dipping or showering the cheese in a suspension, and applying natamycin in a polyvinyl acetate suspension coating to the cheese surface.

Suitable spraying equipment is critical to successful application of natamycin onto the cheese surface. A number of companies specialize in such equipment. Suspensions of natamycin can support the growth of bacteria over time, and to prevent this, 8–10% salt can be added to the suspension.

For shredded cheese, pneumatically driven spray guns are recommended to spray the shredded cheese as it is being tumbled, thus ensuring homogenous application to the surface. It is essential that the spraying system is well main[1]tained, with properly designed spray nozzles positioned correctly in the spraying drum. The recommended concentra[1]tions of the natamycin suspension are 1250–2500 mg/l. The suspension should be sprayed at approximately 6l /ton to achieve a target level of 7–15 mg kg natamycin on the cheese shreds. Due to its low solubility, it is important to keep natamycin preparations in suspension by stirring or agitation; otherwise, it will gradually settle out. Successful application of natamycin onto shredded cheese can delay or protect against yeast and mold spoilage in modified atmosphere packs that acquire leaks (a common problem) and also extend the shelf life of the product once the pack has been opened.

Natamycin can be used in the production of blue cheese to prevent excessive development of the mold, Penicillium roqueforti, on the cheese surface. The desirable level of natamycin on the cheese surface is 12 mg/ cm2 or more. This can be achieved by using shower-type saturation spraying with natamycin preparation (as a 1250–2500 mg/l natamycin suspension) using a recirculation system to optimize economical use and keep the natamycin preparation in suspension. Blue cheeses can be treated with natamycin either before or after punching (piercing). Treated cheeses have been shown to have superior interior blue mold development compared with untreated cheese where undesirable surface growth can block the opening of the punch hole, limiting oxygen availability.

The best way to treat cheese blocks is by using spray equipment that employs spinning disc technology or pneumatically driven nozzles. A very fine even spray should be applied to all six surfaces of the block of cheese in conjunction with a moving conveyor belt system. Excess spray suspension can be recirculated for further use. As mentioned, the addition of 8–10% salt is recommended for such use to prevent bacterial growth during prolonged run times. Block cheeses also can be treated by simple dipping into natamycin suspensions for a few seconds. Use of natamycin combined with polymers can increase the adherence of the natamycin to the cheese surface. Cheeses treated with natamycin must be allowed to dry before packing or wax coating. Many cheeses are susceptible to unsightly surface growth of molds during ripening. Ripening typically takes place at 10 C or above, with the cheeses stored on large shelves in large ripening rooms. Cheeses, such as parmesan, require a long ripening period and during this period can be subject to mold contamination and subsequent spoilage. Polyvinyl acetate (PVA) and water-based emulsion coatings are plastic-type coatings in liquid form that dry on the surface of the cheese to form a protective film. The film can be removed at the end of the ripening period. PVA coatings that contain natamycin preparations are commercially available from coating manu[1]facturers. The natamycin content of the coating ranges from 250 to 1000 mg/kg. The coating can be applied to the cheese surface by dipping, spraying, or painting either manually or mechanically. Often several coats are applied at regular intervals during ripening, the cheese being turned at regular intervals to achieve thorough and complete protection.

Various feta-type cheeses are often soaked or stored in brine (8–20% salt). Salt-tolerant (halophilic) yeasts and molds are a potential spoilage problem. Natamycin added to the brine  will prevent or delay their growth. Natamycin at concentrations of 10–30 mg/ g can be mixed into soft cream cheeses and cottage cheese dressings to provide protection against yeast and mold spoilage.

Natamycin for Fermented Sausages

Fermented sausages are prepared by stuffing casings with ground meat and fat inoculated with an acidifying bacterial starter culture or allowing natural contaminant fermenting organisms to grow. A wide variety of cured or fermented sausages are popular with consumers in many countries. Fermented sausages are popular in mainland Europe. Examples include Bresaola, Morttadella, Salami, Pastirma, Pepperoni, Saucisson Sec, and Summer Sausage. The fermentation process can last for variable periods of time ranging from 1 day to 1 month at 15–25 C depending on the size and type of sausage.

Fermented sausages are prone to spoilage by the growth of yeasts and molds, resulting in unsightly surface mycelium or colonies. During ripening, the pH falls and this reduces the water-holding capacity of the meat, resulting in an increase in surface moisture. This provides ideal conditions for surface mold growth. Later, during wholesale distribution or retail storage, there is further potential for unwanted fungal growth. A wide variety of molds can be implicated in storage, including Aspergillus and Penicillium spp. The recommended dosages for dipping or spraying sausages are 2500–4000 mg/l in water. Thorough agitation is required to keep the natamycin in suspension, and spraying of the sausages must be even and complete. A further method of treating the sausages is to pretreat the casings before stuffing. This can be best achieved by soaking the casing in a 500–1000 mg/l natamycin suspension. It is more effective, however, to treat the sausages after stuffing.

Natamycin as a Yogurt Preservative

Yogurts because of their low pH can be prone to spoilage by yeasts and molds. A preservative is required that has no negative effects on the viability and fermentation performance of the bacterial starter cultures used in yogurt production, but it shows amtimicrobial activity against yeasts and molds. The selective antimicrobial action of natamycin meets this criteria and natamycin is an effective preservative in both set and drinking yogurts. The natamycin can be added to the milk before or after pasteurization at the same time as the inoculation of the starter cultures. The effect of natamycin at concentrations ranging from 0 to 20 mg/l against an inoculated yeast is shown.

Natamycin as a Preservative on the Surface of Baked Goods

Surface mold growth on baked goods, which includes bread, tortillas, muffins, and cakes, restricts the shelf life of these products and can have a significant economic impact. Application of natamycin to the surface of baked goods using fine sprays using either spray gun or spinning disc technology as described has proved to be an effective method in increasing shelf life. As with the surface spraying of cheeses and sausages, it is important that the natamycin be applied evenly to all surfaces. Surface levels of natamycin that have been proved to be effective are 0.5 mg /m2 and above. Natamycin is approved in the United States at levels in bread up to 14 mg/kg , tortillas and English muffins up to 20 mg /g , and cakes and U.S.-style muffins at 7 mg /kg . In China, it can be used on the surface of moon cakes and baked goods when applied by spraying or dipping in a suspension of concentration of 200–300 mg /kg , providing that the residues in the treated product are less than 10 mg /kg.

Natamycin Control of Yeast Spoilage in Wine

Although wine is produced by the fermentative action of yeasts, this same metabolic activity can result in spoilage. Unwanted yeast growth can cause several wine defects: ester taints, volatile acidity, phenolic off-flavors, deacidification, turbidity, and unwanted secondary fermentation of semisweet wines. This spoilage can be caused not only by contaminant yeasts but also by those used for wine fermentation if their growth is unchecked or is restarted by the addition of further nutrients. Yeast spoilage can result in serious economic loss and is a worldwide problem. It is only in South Africa, however, where such use in wine is authorized. In that country, natamycin is allowed in wine, alcoholic fruit beverages, and grapebased liquors at a maximum level of 30 mg/l . Natamycin usually is added after fermentation is completed, the wine has been racked, and free sulfur-dioxide levels have been adjusted to 37 mg/l. The wine is then filtered and natamycin added at 5–10 mg/l before bottling. It is used particularly in semisweet wine to reduce secondary fermentation and can be employed when chemical preservatives, such as sorbate and sulfur dioxide, fail to control the growth of spoilage yeasts. It has been determined that the half-life of natamycin in wine under typical storage conditions is around 20 days.

Natamycin to Control Spoilage of Fruit Juices

Natamycin has been shown to be an effective preservative in both pasteurized and unpasteurized fruit juices, preventing the growth of yeasts and molds. Additional levels typically used are 6–12 mg/l and efficacy in delaying or preventing yeast and mold spoilage is usually superior to sorbate at 1000 mg/l or higher. Furthermore, yeasts and molds are becoming increasingly resistance to sorbate, and the use of high levels of sorbate can have a bad taste effect. Retention of natamycin in orange juice pasteurized at 80 C for 10 min is around 70%.

Potential Applications

Potential applications include uses on the surface of such fruits as strawberries, use in tomato pureé, and use in black olive production to prevent the growth of molds on the surface of the brine during the fermentation process, without interfering with the desired lactic acid bacteria fermentation. Although not a food use, natamycin has been proposed as a selective antifungal agent in microbiological agar media.