Bacterial isolate from pozol shows antimicrobial activity.

Consumer interest in minimally processed foods with a long shelf life and concerns over ill effects from chemical preservatives have stimulated the search for new natural antimicrobial substances that are effective against foodborne spoilage and pathogenic microorganisms. The potential natural biopreservatives under study include lytic enzymes, plant aniimicrobials and bacteriocins.

Much of the research on bacteriocins has concentrated on those produced by lactic acid bacteria. However, a drawback of using these bacteriocins is their narrow spectrum of activity and their ineffectiveness against Gram-negative bacteria, yeasts and molds. So it appears that there is a demand for natural biopreservatives that can control such bacteria, yeasts and molds. One source of new isolates capable of producing biopreservatives could be indigenous fermented foods that are primarily known only within their countries of origin.

Pozol is an example of such fermented foods. It is an indigenous fermented maize dough that dates back to the Mayan civilization. The Mayans used pozol to combat intestinal disorders and as a poultice for wounds and skin infections. Few have attempted to extensively explore the antagonistic properties of the pozol isolate since its initial isolation in the 1970s, according to researchers at the University of Minnesota (Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, St. Paul, Minnesota 55108).

Minnesota scientists wanted to confirm the identity of the pozol isolate, determine its antimicrobial spectrum, examine the conditions for production of the antagonistic compound and investigate its chemical nature. This information could then possibly be used in assessing the antimicrobial compound as a biopreservative for use in enhancing the safety and extending the shelf life of food products.

From pozol, the scientists isolated a bacterial isolate, designated CS93, capable of producing broad-spectrum antimicrobial compounds effective against Gram-positive and Gram-negative bacteria, yeasts and molds. This strain was phenotypically similar to another pozol isolate that was previously designated as Agrobacterium azotophilium by other investigators. By using biochemical, phenotypic and rRNA sequence analysis, both pozol isolates were identified as members of the genus Bacillus, possibly a variant of Bacillus subtilis.

The antimicrobial compound was initially produced only on a solid medium. Researchers identified the parameters required for its production in broth. The compound was heat-stable (121 C for 15 min), exhibited activity over a wide pH range (pH 3 to pH 11) and was inactivated by pronase E.

The antimicrobial compound was bactericidal and bacteriolytic against Escherichia coli V517, bacteriostatic against Micrococcus luteus and fungistatic against Saccharomyces cerevisiae. The inhibitory compound could possibly serve as a food preservative, researchers indicated.

Further information. L. L. McKay; phone: [phone]; fax: [phone]; email: [e-mail].