E. coli growth may be inhibited by tomato-based edible film

The results of new research, published in the Journal of Food Science,​ show that carvacrol-containing tomato-based edible films inactivated the virulent pathogen E. coli ​O157:H7 and the inactivation was related to the carvacrol levels in films.

Researchers from the Agriculture Research Service (ARS) of the US Department of Agriculture (USDA) and the Western Regional Research Centre, Processed Foods said that antimicrobial assays of tomato films indicated that optimum antimicrobial effects occurred with carvacrol levels of approximately 0.75 per cent added to tomato purees before film preparation.

They said that the aim of the study was to evaluate the antimicrobial activities, storage stabilities and the physical–chemical–mechanical properties of edible films made from tomatoes containing carvacrol, the main constituent of oregano oil.

Edible polymers​

The authors claim that edible films containing plant antimicrobials are gaining in importance as potential treatments for extending product shelf life and reducing the risk of pathogen growth on contaminated food surfaces.

They said that edible tomato films containing antimicrobials may have multiple benefits: “Consumption of tomatoes, tomato products and isolated bioactive tomato ingredients is reported to be associated with lowered risk of cancer, heart disease, diabetes and hypertension.”​

Film formation​

The antimicrobial activities against E. coli ​O157:H7 and the stability of carvacrol were evaluated during the preparation and storage of tomato-based films made by two different casting methods, continuous casting and batch casting, according to the authors.

Hot break tomato puree was the primary ingredient in all tomato based film forming solutions, said the authors.

They said that high methoxyl pectin 1400 was added to increase film strength and carvacrol was incorporated into tomato puree solutions before the film casting stage at concentrations of 0, 0.5, 0.75, 1.0 and 1.5 per cent.

Results​

‘E. coli O157:H7 grew normally on agar plates with films lacking carvacrol incubated at 35°C for 24 or 48 hours. By contrast, no growth was observed on the plates around the film discs containing 0.75 per cent or 1 per cent carvacrol.​

“The extent of bacterial growth inhibition increased as the per cent of carvacrol in the films was increased,” ​claims the team.

The results also showed that films prepared by continuous casting are preferable for large scale use than those prepared by batch casting.

The researchers said that further studies are currently underway to test the effectiveness of other fruit and vegetable films against contaminated meat.

Source: Journal of Food Science ​Published online ahead of print - doi: 10.1111/j.1750-3841.2008.00892.xAntibacterial activity against E. coli 0157:H7, physical properties, and storage stability of novel carvacrol-containing edible tomato films​Authors: W.X. Du, C. W. Olsen, R. J. Avena-Bustillos, T.H. McHugh, C.E. Levin, M Friedman