Natamycin, a polyene macrolide antibiotic, was first isolated in 1955 from a culture of Streptomyces natalensis, a microorganism found in soil from Natal, South Africa. The name natamycin is synonymous with pimaricin, a name used in earlier literature. In the United States, natamycin was approved for use in cheese making as a mold spoilage inhibitor in 1982. Natamycin may be applied to the surface of cuts and slices of cheese by dipping or spraying an aqueous solution containing 200 to 300 ppm. Natamycin does not readily migrate into the cheese and does not adversely affect flavor or appearance.

Natamycin is active against nearly all molds and yeasts but has little or no effect on bacteria or viruses (65). Most molds are inhibited at concentrations of natamycin from 0.5 to 25 /ig/mL. Most yeasts are inhibited at natamycin concentrations from 1.0 to 5.0 /ig/mL. In addition to fungal growth inhibition, natamycin has been shown to inhibit aflatoxin Bj production of Aspergillus flavus and penicillic acid production by Penicillium cyclopium as well as eliminate ochratoxin production by A. ochraceus and patulin production by P. patulum (66).

Several factors affect the stability and resulting anti-mycotic activity of natamycin. While pH has no apparent effect on antifungal activity, it does influence stability of the compound. In the pH range of most food products (pH 5-7), natamycin is very stable. Under normal storage conditions, temperature has little effect on natamycin activity when in neutral aqueous suspension. Sunlight, contact with certain oxidants (eg, organic peroxides and sulfhydryl groups), and heavy metals all adversely effect stability of natamycin solutions or suspensions (67).

Natamycin added in the wash water was effective in increasing the shelf life of cottage cheese up to 13.6 days at 4.4°C (68). Adding natamycin to the cottage cheese dressing was even more effective in extending shelf life. At 500 or 1000 /ig/mL, natamycin delayed mold growth on cheese for up to six months but did not prevent it completely (69). Natamycin was shown to be effective in preserving Italian cheeses with no detrimental effect on ripening (70).

In addition to dairy products, early work on natamycin suggested it might be useful to inhibit fungal growth on fruit products and poultry. Natamycin was shown to be an effective antifungal agent on strawberries, raspberries, and cranberries and in orange juice (71,72). Natamycin, alone and in combination with chlortetracycline, inhibited yeast growth on chicken stored 12 to 15 days at 4.4°C (73).

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