Post-harvest decontamination of rocket leaves through plasma activated water (PAW): effects on quality and shelf-life

Ready-to-eat vegetables offer great advantages to consumers due to their nutritional value and convenience, although they are an ideal substrate for microbial growth. Rocket (E. sativa) is appreciated by consumers for its pleasant bitter flavor and its high content of vitamins C and K, Calcium, fibers and glucosinolates. The major post-harvest problems of rocket are wilting, senescence and microbial spoilage which limits its shelf-life. Also decontamination from pathogenic microorganisms is a critical aspect for food safety. In the food industry, fresh rocket is usually washed with chlorine sanitizers (e.g. NaOCl, ClO2) to limit degradative processes and the microbial growth. However, this procedure releases on the rocket leaves several by-products including chloramines which are potentially harmful to human health. Plasma Activated Water (PAW), obtained by exposing water to cold plasma discharges, could be an alternative method for the decontamination of fresh rocket. In this contest, the aim of this study was to use PAW for the decontamination of fresh rocket leaves to extend their shelf-life without affecting their quality characteristics. PAW was generated with distilled water exposed to a Microsecond Pulsed Corona device for 4 minutes. Subsequently, rocket leaves were washed with PAW for 2, 5, 10 and 20 min then dried and finally stored at 4°C up to 10 days in PP bags under ordinary atmosphere. The load of spoilage microbiota on rocket salad treated with PAW was compared to those washed with sodium hypochlorite solution (100 ppm). Also, the effects of PAW washing on product quality traits were evaluated by measuring pH, color parameters and the content of some bioactive compounds. Data showed that PAW resulted in an immediate reduction of 1-1.5 log CFU/g for the target microbial groups. Sodium hypochlorite, which is the reference sanitizer, exhibited a similar efficacy to the PAW against mesophilic and psychrotrophic bacteria, while its activity against Enterobacteriaceae was higher than PAW. During storage at 4°C, cell loads of the spoilage microbiota increased suggesting that survivors were able to repair Second International Conference on Advances in Plasma Science and Technology (ICAPST), 2021, Coimbatore, India ISBN 978-93-90853-30-4 | ICAPST’21| 69 damages. However, the same trend was detected also for rocket samples washed with sodium hypochlorite. Moreover, minimal variations in the qualitative parameters were observed. Overall, these results showed that PAW can be a promising innovative post harvest treatment to preserve perishable foods such as ready to eat vegetables. The present work is part of the research activities developed within the project “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 – PRIN Progetti di Ricerca di Rilevante Interesse Nazionale, Bando 2017.