Develop novel combinations of natural antimicrobials.

European scientists are looking to improve the quality and safety of foods by developing new combinations of natural antimicrobial systems. Such antimicrobials would reduce the need for traditional physical and chemical food preservation processes.

Some of the natural antimicrobial compounds under investigation include chitosan, nisin, three novel bacteriocins and several plant essential oils or their components, including oregano, sage, mint, dictamus, thymol, carvacrol, carvone, cuminaldehyde, cinnamaldehyde and cymene. Researchers are evaluating the effect of these systems on beer, milk, fresh meat, apple juice, homous, fresh pork sausage, mayonnaise, taramosalata, salmon, boiled rice, potato and cabbage salad.

Preliminary tests indicate that yeast and mold growth may be inhibited in skinless sausages by dipping the product in chitosan. Enzymatic and chemical methods were used to degrade chitosan. The resulting oligomers had improved microbial activity against selected organisms, compared with native chitosan. However, the improvements were not sufficiently significant to warrant further pilot scale tests. Tests with a novel bacteriocin in model systems, representing the general composition of dairy products, indicated that high levels of the compound are needed to inhibit B. cereus at high abuse temperatures. An emulsifier was also necessary, since fat had a negative effect on the bacteriocin.

The essential oils of oregano, mint, dictamus and sage in laboratory media inhibited the growth of S. enteritidis, L. monocytogenes and E. coli O157:H7. Carvacrol was bactericidal to B. cereus in buffer solution at low concentrations. Combinations of carvacrol, cymene, thymol, cuminaldehyde, cinnamaldehyde and carvone did not work well together, except for the combination of cymene and carvacrol.

Future work will concentrate on using combinations of antimicrobials in real food systems.

Further information. S. Roller, School of Applied Science, South Bank University, 103 Borough Rd., London SE1 0AA, England, U.K.; phone: [phone]; fax: [phone]; email: [e-mail].