Cold atmosferic plasma treatment on fresh-cut melon: effects on safety and quality

Non-thermal technologies as Cold Atmospheric Plasma (CAP) could be used to decontaminate and stabilize food products by removing spoilage microorganisms, moulds, and mycotoxins. Additionally, the consumption of ready-to-eat fruits has increased as the frequency of outbreaks and cases of foodborne disease linked to contaminated products. The aim of this work was to analyse the effects of CAP treatments on the native microbiota of fresh-cut melon. Also the effectiveness on products deliberately contaminated with pathogenic microorganisms, i.e. Listeria monocytogenes 56LY, Salmonella enteritidis 155 and Escherichia coli 555, was evaluated. Two alternative chemical regimes were used for the treatments, one with high levels of ozone (O3) and the other with high levels of nitrogen oxides, i.e. NO, NO2, NO3, N2O5 (NOx). Fresh-cut melon samples were exposed to the two gas regimes for different times: 2, 5, 10, 20, 30 minutes and the reduction of spoilage and pathogenic species were evaluated and compared with control sample. Several qualitative aspects such as pH, Brix°, colour and bioactive compounds were also evaluated. Results showed that plasma exposure allowed to achieve reductions of microbial loads up to about 1-1.5 Log CFU/g. Different sensitivities were detected for relevant microbial groups. In particular, lactobacilli and total mesophilic bacteria showed a significative decrease after 20 and 30 minutes of NOx treatment. Significant reductions of over 2 Log CFU/g were determined for the pathogens after 20 and 30 min NOx-treatments, and around 1.5 Log CFU/g for O3-treatment, regardless the pathogenic species and of their contamination levels (⁓ 4 and ⁓5 Log CFU/g). These results suggest that nitrogen oxides are more effective in microbial inactivation than ozone. As far as the effects of CAP treatment on physico-chemical characteristics, Brix° and colour did not show any difference. On the other hand, pH decreased by 1 unit with increasing treatment time for NOx-regime. In conclusion, 20 and 30 min treatments with NOx and 30 minutes with O3 had the strongest inactivation effect. These results allowed to understand and acquire more information in order to scale up this technology for its use in industrial processing. The present work is part of the project “PRIN 2017 -PLASMAFOOD - Study and optimization of cold atmospheric plasma treatment for food safety and quality improvement” founded by MIUR - Ministero dell’Istruzione dell’Università e della Ricerca.