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The ability of atmospheric pressure glow discharges (APGD) to inactivate microorganisms has been demonstrated in a number of previous studies. However, most of this work has been performed using microorganisms that do not form biofilms and with the microorganisms supported on abiotic surfaces that discourage cell growth. When microorganisms attach to the surface of a food, they can extract nutrients from the food and proliferate at the surface. Often this growth takes the form of biofilms which comprise three-dimensional (3-D) networks of polysaccharides that attach microorganisms to surfaces and serve to protect them from external stresses; fresh foods, such as salad crops, frequently harbor biofilms. We believe that the use of APGD offers a potential for inactivating microorganisms on the surface of fresh foods that cannot be readily treated by other methods without inducing unacceptable changes to these foods. As a first step toward a full evaluation of the viability of the APGD technology for food safety control, we consider in this paper two key issues, namely: 1) whether atmospheric glow discharges can inactivate biofilm-forming microorganisms and 2) whether plasma treatment causes significant discoloration to food surfaces. Using the biofilm-forming bacterium Pantoea agglomerans and bell peppers (Capsicum annuum) as a typical example of plant tissue, we show that atmospheric He-[O.sub.2] plasmas can be effective inactivation agents without causing unacceptable levels of discoloration to the peppers, and that furthermore they are superior to the use of low-pressure ultraviolet sources. Index Terms--Atmospheric glow discharges, biofilm, decontamination, food-borne microorganisms, food surfaces, inactivation, sterilization.

To further enhance biopreservation of meat products, the antilisterial effect of the newly described protective culture Leuconostoc carnosum 4010 and its bacteriocins, leucocins 4010, was examined in the presence of sodium chloride and sodium nitrite in a solid matrix using a structured gelatin system. Interaction between Listeria monocytogenes 4140 and Leuc. carnosum 4010 or the leucocins 4010-resistant mutant L. monocytogenes 4140P showed that the inhibitory effect of Leuc. carnosum 4010 in the gelatin system was caused by the production and activity of leucocins 4010. The presence of sodium chloride (2.5% w/v) and sodium nitrite (60 mg/l) reduced the antilisterial effect of Leuc. carnosum 4010 in the structured gel system compared to the use of Leuc. carnosum 4010 alone. Investigations carried out at 10 degrees C showed that the lag phase of L. monocytogenes 4140 in the presence of Leuc. carnosum 4010 was reduced from 71 to 58 h by the addition of sodium chloride and to 40 h by the addition of sodium nitrite. Addition of sodium chloride increased the maximum specific growth rate of L. monocytogenes 4140 in the presence of Leuc. carnosum 4010 from 0.02 to 0.06 h(-1), whereas no change was observed by the addition of sodium nitrite. Compared to the antilisterial effect of leucocins 4010 alone, the addition of sodium chloride (2.5%, w/v) decreased the antilisterial effect at high concentrations of leucocins 4010 (5.3 and 10.6 AU/ml) as measured after 11 days of incubation at 10 degrees C. In gels with added leucocins 4010, the most pronounced reduction in growth of L. monocytogenes 4140 was observed at the highest concentration of leucocins 4010 (10.6 AU/ml) together with sodium nitrite (60 mg/l). More detailed information on the lag phase and the maximum specific growth rate of single colonies of L. monocytogenes 4140 in the presence of leucocins 4010 was obtained using microscopy and image analysis. No pronounced difference in the growth of single colonies was observed in the gel system. Real-time measurements of colony growth at 10 degrees C in the gelatin matrix showed that the growth inhibiting effect of leucocins 4010, including a longer lag phase as well as a lower maximum specific growth rate for L. monocytogenes 4010, was negated in the presence of 2.5% (w/v) sodium chloride.