Dielettric barrier atmospheric cold plasma for microbial inactivation in water suspensions, fresh fruit and juice

Aim: The main objective of this study was to evaluate the efficacy of dielectric barrier discharge atmospheric cold plasma (DBD-ACP) for the inactivation of Escherichia coli and Bacillus subtilis on different food matrices, including microbial water suspensions, fresh apples, and apple juices. This work aimed to assess the influence of key processing parameters—namely, applied voltage and treatment duration—on microbial inactivation efficiency. Escherichia coli OP50 and Bacillus subtilis were selected as representative Gram-negative and Gram-positive bacteria, respectively, to evaluate the potential of this non-thermal, environmentally sustainable technology for improving the microbial safety and shelf life of fresh produce and fruit-derived products. Method: CP treatments were performed using a dielectric barrier discharge (DBD) system consisting of two plate stainless steel electrodes separated by a dielectric material. Plasma was generated at two different voltages (25 kV and 15 kV) in atmospheric conditions. Microbial suspensions of Escherichia coli OP50 and Bacillus subtilis (both at 10⁷ CFU/mL) were prepared in sterile water and treated in a sealed container using DBD cold plasma for varying durations (2.5, 5, 7.5, 10, and 15 minutes). The treatment was extended to fresh apples and apple juice inoculated with the same microbial strains, applying the same voltage and exposure time ranges Results: Complete inactivation of both microorganisms was observed under specific conditions. At 25 kV, total inactivation of both bacterial strains was achieved at all treatment times. At 15 kV, B. subtilis was inactivated within 2.5 to 10 minutes, whereas E. coli was effectively inactivated between 5 and 10 minutes. On the food matrix, at the lowest applied voltage of 15 kV, the E. coli load (initially 10⁵ CFU/g) dropped below the limit of detection after both 5 and 2.5 minutes of treatment. Conclusion: In all matrices, a reduction in microbial load was observed, demonstrating the effectiveness of DBD cold plasma as a non-thermal microbial inactivation method suitable for fresh produce and liquid foods.