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The Cheese Corner

Natamax™: Use as an Antimycotic Preservative on Cheese

Natamax™ is the commercial preparation of natamycin. Natamycin previously was sometimes known as pimaricin, which is a polyene macrolide antimycotic produced by the actinomycete Streptomyces natalensis and other closely related Streptomyces spp. Bacteria. Natamycin shows antimicrobial activity against yeasts and molds but has no antimicrobial activity against bacteria. Such an antimicrobial spectrum has resulted in the development of commercial preparations of natamycin as preservatives in bacterial fermented foods such as cheese and sausages, preventing mold growth, but not affecting the bacterial fermentation or ripening of the food.

Origin and History of Natamycin

Natamycin was first discovered in 1955 in a culture filtrate of the actinomycete bacterium Streptomyces natalensis. This organism was isolated from a soil sample from the Natal Province in South Africa, hence the name natamycin. The potential use of natamycin as a food preservative was first demonstrated on the surface of soft fruits. Since then, other applications have been developed, including surface treatment of cheese and fermented sausages, yogurt, soft cheeses, fruit juices and in wine.

Natamycin has a wide regulatory approval status throughout the world. In the USA it is approved in cheese at a maximum permitted level of 20 mg/kg (20 ppm).The safety and no or low toxicology of natamycin and its safe use as a food preservative were confirmed in 2003 by the publication by JECFA of Natamycin Toxicological Monograph (www.inchem.org/documents/jecfa/jecmono/v48je06.htm).

Commercial preparations are produced by fermentation of sugar-based substrates by Streptomyces natalensis. Natamycin is then recovered by extraction and filtration, and then it is spray dried. The commercial preparations made by DuPont Nutrition & Health are as follows:

  • Natamax™ - a blend of 50% natamycin with lactose for use mainly for dairy applications.
  • Natamax Salt – a blend with salt used mainly for cheese and brine water applications
  • Natamax SF – a concentrated blend containing 87% effective natamycin. Lower use level.
  • Natamax B-Plus - designed specifically for better solubility for use in spray applications

Structure and physical and chemical properties

Natamycin is a polyene macrolide antimycotic with a molecular weight of 665.7 Daltons and the empirical formula C33H47NO13. As a dry powder it can be stored for several years with minimal loss of activity. Natamycin stability is adversely affected by oxidants, chlorine, heavy metals and extreme pH values

Natamycin has low solubility in water (approximately 40ppm). This low solubility is an advantage for the surface treatment of food for it will stay on the surface where it is needed, instead of migrating into the food. Natamycin has numerous advantages over other antimycotic preservatives such as sorbate and these are summarized in Table 1 below. These advantages make it very effective as a food preservative.

Natamycin K Sorbate
Natural Chemical
Fungicidal Fungi static
No effect on bacteria Bactericidal
No migration into food Penetrates into food
No flavor Bitter flavor and “back of throat burn”
Effective at 1-40 mg/kg Effective at 1000-2000 mg/kg
Effective at pH range 3-9 Effective only at acidic pH

Mode of action and antimicrobial activity

Natamycin acts by combining with ergo sterol and other sterols present in the cell membranes of yeasts and vegetative mycelium of molds resulting in enzyme inhibition and preventing cell division. Ergo sterol is not found in cell membranes of bacteria, which explains why bacteria are not sensitive to natamycin. Less is known about the mode of action of natamycin against mold spores but it is thought to inhibit their germination. There are no reports of development of resistance to natamycin in vivo. Studies undertaken in cheese factories that have used natamycin for several years showed no increase in the levels of natamycin-resistant yeasts and molds compared to similar factories not using natamycin.

Most molds are sensitive to natamycin at concentrations of 40 ppm or less and yeasts are even more sensitive with minimum inhibitory concentrations of 5 ppm or less.

Application of natamycin as a cheese preservative

The three main methods of surface treatment are 1) spraying the surface of the cheese with a natamycin suspension, 2) dipping the cheese in a suspension, 3) applying natamycin in a polyvinyl acetate (PVA) 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 used in such systems can support the growth of bacteria over time; to prevent this 8-10% salt should be added to the suspension.

For shredded cheese, pneumatically driven spray guns are recommended to spray the shredded cheese while it is being tumbled, thus ensuring homogenous application of the natamycin onto the surface. It is essential that the spraying system is well maintained, with properly designed spay nozzles positioned correctly in the tumble drum. The recommended concentrations of the natamycin suspension are 2500 - 5000 mg/l as Natamax™ or Natamax™ salt. The Natamax ™ suspension should be sprayed at a rate of approximately 6 liters per ton to achieve a target level of 14 - 30 mg/kg Natamax ™ on the cheese shreds. Due to its low solubility it is important to keep Natamax™ in suspension by stirring or agitation otherwise it will gradually fall out of suspension, resulting in poor application onto the cheese. Successful application of Natamax ™ on to 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 also be used in the production of blue cheese by preventing excessive development of the mold Penicillium roqueforti on the cheese surface. The desirable level of Natamax™ required on the surface is 12 mg /cm2 or more. This can be achieved by using shower- type saturation spraying with Natamax™ (as a 2500-5000 mg/ liter suspension) using a re-circulation system to optimize economical use and keep Natamax™ in suspension. Blue cheeses can be treated with Natamax™ either before or after punching (piercing). Treated cheeses have been shown to have superior interior blue mold development compared to 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. This achieves the most economic, even and complete distribution of the Natamax™ onto the surface. A very fine and even spray should be applied to all surfaces of the blocks in conjunction with a moving conveyor belt system. Excess spray suspension in the spinning disc system can be re-circulated for further use. As mentioned earlier, addition of 8-10% salt is recommended for such use as to prevent bacterial growth during prolonged production run times.

For block cheese, natamycin can also be applied by dipping the cheese. Simple dipping in Natamax™ suspensions for a few seconds can ensure adequate deposition of natamycin, preventing mold growth on the cheese surface.

Painting cheese suspensions with Natamax ™ or Natamax™ Cheese Gel onto the surface of cheese using a brush is also an effective method of application and can be used in small-scale farmstead type operations. Cheeses treated with natamycin suspensions must be allowed to dry before packing or wax coating.

Many cheeses are susceptible to unsightly surface mold growth during ripening. Ripening typically takes place at temperatures of 50 °F and above, with the cheeses stored on open shelves in large ripening rooms. Polyvinyl acetate (PVA), water based emulsion coatings are plastic type coatings in liquid form that dry on the cheese surface to form a protective skin. They can be removed at the end of the ripening period. PVA coatings containing Natamax™ to prevent surface mold are available from coating manufacturers. The Natamax™ content of the coating ranges from 500-2000 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.

When used in soft cheeses Natamax™ can be mixed into the curd at the same time as when the salt is added. 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. Natamax™ added to brine at 20 – 40 mg/l will prevent their growth. Natamax™ at concentrations of 10-30 mg/kg can be mixed into soft cream cheese and in cottage cheese dressings to provide protection against yeast and mold spoilage in these types of fresh cheese products.

Natamax™ can also be used as a preservative often as a replacement for potassium sorbate or sorbic acid in processed cheese spreads and slices. The Natamax™ is added to the cheese blend prior to the melt process. The target concentration in the final product is typically 15-25 mg/kg.

Technical service and customer support

The DuPont technical support team offers customers the following technical support when using Natamax:

  • Technical advice
  • Support for trials – including site visits and product formulation
  • Analysis of cheese for natamycin levels
  • Storage studies examining the retention of natamycin at different temperatures
  • Analysis of spoilage microflora
  • Natamycin sensitivity testing