Gas plasma as alternative to chlorine for washing water sanitation

Chlorine or other sanitizers are currently used in the washing practices of fresh-cut produce to reduce pathogens risk and microbial spoilage on its surface, however the surviving bacteria can grow during storage reducing the efficacy of sanitation treatments. Despite the common idea that sanitizers are used to reduce the microbial load of produce, their main mission is to maintain the microbial quality of the water by avoiding cross-contamination.

The increasing concern for the presence of chlorine toxic residues in fresh-cut produce when the proper chlorine level in washing water is exceeded and the ban of chlorine for fresh cut produce sanitation introduced in Germany and Switzerland have prompted the research to develop new sanitation alternatives.

The ionised gas, named gas plasma, is one of the new techniques that are explored in the food scenario. Italian scientists at University of Bologna have investigated the decontamination efficacy of the atmospheric gas plasma generated by a DBD (dielectric barrier discharge) device with parallel plates placed on a batch of deionised water and explored, for the first time in the literature, the role of vegetable substrates in the treatment performances.

The efficacy of gas plasma treatment was evaluated against a mix of Listeria monocytogenes strains and a mix of Escherichia coli O157 and O26 shigatoxing-producing strains artificially inoculated in deionised water or on the surface of fresh-cut celery and radicchio (red chicory, Chicorium intybus). Inoculated deionised water was treated for 10, 20, 40 and 60 min with gas plasma; inoculated fresh-cut vegetables were submerged with deionised water and treated for 30 or 60 min. The microbiological analyses were performed on deionised water, celery pieces and radicchio leaves immediately after treatments (30 and 60 min) and after a further 5 days of storage at 4°C and 80% RH.

The full study is available on line since September 2015 at:

Results showed that after 40 min of gas plasma treatment the numbers of viable target bacteria detected in the deionised water samples were < 1 log CFU/ml, corresponding to a reduction higher than 6 Log CFU/mL, while the presence of vegetables in water reduced the efficacy of gas plasma treatment in inactivating pathogens (reduction up to 2.5 and 3.7 Log CFU/cm2 for L. monocytogenes and E. coli, respectively). The high level of soil particles or organic matter in wash water can represent possible limitations to gas plasma technology.

Scientists conclude that in relation to the vegetable decontamination, the efficacy of gas plasma depends on specific microorganism, kind of vegetable, treatment time and storage duration. A more pronounced bactericidal effect was observed in radicchio leaves (up to -3.7 log cfu/cm2) compared to the fresh-cut celery pieces (up to -0.57 log cfu/g). However, the treatment accelerated the quality losses in radicchio leaves during storage. For a possible application of this technique a balance between sanitisation benefits and nutritional and toxicological aspects should be considered. This study demonstrates that the technique provides a first overview to investigate the possibility to sanitize wash water in a discontinuous (batch) system process.

Source: Annachiara Berardinelli, Frederique Pasquali, Chiara Cevoli, Marcello Trevisani, Luigi Ragni, Rocco Mancusi, Gerardo Manfreda, 'Sanitisation of fresh-cut celery and radicchio by gas plasma treatments in water medium', January 2016, Postharvest Biology and Technology, Vol. 111, pages 297–304.

Chiara Cevoli
Department of Agricultural and Food Sciences
Alma Mater Studiorum, University of Bologna

Via Fanin 50, 40127 Bologna, Italy

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