Use plant antimicrobial carvacrol in edible apple films for antibacterial activity against E. coli O157:H7.

E.coli O157:H7 is responsible for the majority of human illnesses attributed to Escherichia coli. A need exists to discover new, food-compatible ways to protect foods against this and other pathogens. Edible films made from fruits or vegetables containing plant essential oils have the potential to be used commercially to protect food against contamination by pathogenic bacteria and fungi.

With this in mind, USDA-ARS scientists evaluated the antimicrobial activities as well as the storage stability and physical properties of apple-based films containing carvacrol, the main component of oregano oil. The antimicrobial activity against E. coli O157:H7 and the stability of carvacrol were evaluated during the preparation and storage of apple-based films made by two different casting methods, continuous casting and batch casting.

The scientists undertook physico-chemical and antimicrobial assays of films, as well as an HPLC analysis of film extracts after samples had been stored at 5 C and 25 C. The assays and extract analysis showed that carvacrol worked best antimicrobially when it was added at about a 1% level to apple purees prior to film preparation. Also, carvacrol in the films and the film weight remained unchanged over a storage period of up to seven weeks. In addition, the casting methods affected the concentrations of carvacrol, bactericidal activity and the physical properties of the films. Adding carvacrol to the purees used to prepare the films reduced the water vapor and oxygen permeability of the films.

The results indicate that carvacrol has a dual benefit. It can be used to both impart antimicrobial activities and to enhance the barrier properties of edible films. This research will help you relate the compositional and physico-chemical properties of apple films containing volatile plant antimicrobials to their use in foods. Additional studies are needed to demonstrate the potential of these films to reduce the human pathogen burden of foods.

Further information. Wen-Xian Du, USDA-ARS Western Regional Research Center, Processed Food Research, Room 1105, 800 Buchanan St., Albany, CA 94710; phone: 510-559-6148; fax: 510-559-5818; email: wen-xian.du@ars.usda.gov.

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