Generation of plasma functionalized water : antimicrobial assessment and impact on seed germination

Abstract

Chemical methods are still considered as mainstay in the agro-food sector to improve the safety of seeds and reduce crop losses. Atmospheric plasma to produce functionalised water is emerging as a sustainable alternative for this. Microbial contamination of food remains an imminent food safety challenge, more-so as consumer interest shifts to minimally processed, natural, “healthy”, inexpensive and convenient food. Sprouts fall under this category and have been associated with numerous outbreaks of foodborne illness. This study aimed to evaluate: (i) the effectiveness of plasma activated water (PAW) on the germination capacity of mung bean seeds and (ii) the antimicrobial capacity of PAW. A specially designed set-up composed of two electrochemical cell was used to produce two different types of PAW, by surface plasma discharge ignited from copper cathode and copper anode, respectively. The germination capacity of mung bean seeds was assessed over 96 h incubation in the dark at 25 °C. The antimicrobial capacity of PAW was assessed against 6 h exposure to Escherichia coli NCTC 12900. The anodic PAW (rich in NO3 −) indicated a drastically higher amount of ionic conducting species than the cathodic PAW (rich in NO2 −). Both air PAWs possessed outstanding antimicrobial activity against E. coli strains (> 6 log CFU/mL reduction), while germination and growth of mung bean seeds irrigated with the cathodic PAW was similar to the control. Plasma functionalised water has the potential to be applied on irrigation - hydroponic applications ensuring seed safety and avoiding any negative impact on germination.