Electron beam irradiation may enhance efficacy of antimicrobial films.

Food irradiation can alter the properties of polymeric materials used in food packaging systems. One alternative is to use polymeric films that contain antimicrobials that increase the radiation sensitivity of microorganisms, minimizing the dose absorbed by the package.

The goal of Texas A&M University scientists was to evaluate the effect of electron beam irradiation on the functional properties of antimicrobial films and to test their effectiveness on fresh-cut romaine lettuce. It appears that antimicrobial packaging systems, combined with low-dose irradiation, could play an important role in ensuring safety by controlling post-processing contamination in prepackaged foods.

Using up to 20 kGy, the investigators irradiated samples of trans-cinnamaldehyde (TC)-coated low-density polyethylene-polyamide films (3% w/w) which had a thickness of 53 aem. Exposing the films to high doses of irradiation and applying a TC-polyamide coating did not affect the films' tensile strength and toughness. Applying irradiation at 20 kGy increased the films' flexibility--percent elongation-at-break, 8.1%--and improved their oxygen and moisture barrier properties (14.2%). Films irradiated at doses higher than those used for food decontamination purposes maintained their functionality.

Then, researchers placed 50 g of fresh-cut romaine lettuce into petri dishes covered with the TC-coated films. The control was not irradiated, but the others were--at 0.5 kGy and 1.0 kGy. All were stored for 14 days at 4 C. The scientists determined total aerobic microbial counts (APCs) and yeast and mold counts (YMCs) throughout the storage period.

Increasing amounts of irradiation caused reductions in APCs and YMCs. The 0.5- and 1.0-kGy treatments decreased initial APCs by 1.2 and 1.5 logs, respectively. No YMCs were observed in the 1.0 kGy-treated samples on the first day of treatment. Irradiation significantly lowered the APCs of lettuce samples by almost 1 log CFU per g compared to the non-irradiated control. Little reduction occurred in YMCs.

Up to 1.0 kGy electron beam irradiation of fresh produce enclosed in antimicrobial films enhanced the inhibition of APCs and YMCs. The antimicrobial activity of the films improved with increased dose level and TC concentration--3% to 10%.

Further information. Maria Elena Castell-Perez, Department of Biological and Agricultural Engineering, Texas A&M University, 306C Scoates Hall, College Station, TX 77843; phone: [phone]; fax: [phone]; email: [e-mail].