Evaluating the synergistic efficacy of cold plasma technology on microbial inactivation and seed germination

Abstract

Chemical methods are still considered the mainstay in the agro-food sector to improve the safety of seeds and reduce crop losses. Microbial contamination of food remains an imminent challenge, more-so as consumer interest shifts to minimally processed, natural, “healthy”, inexpensive and convenient food. Sprouts fall under this category and their consumption is an increasing trend in Western diets. However, sprouts are prone to microbial contamination and have been associated with numerous outbreaks of foodborne illness. The application of cold atmospheric plasma is an emerging sustainable alternative for improving the safety of seeds and food with additional potential in enhancing product yield. This study aimed to evaluate: (i) the effectiveness of plasma activated water (PAW) and combinations of cold atmospheric plasma and PAW on the germination capacity (germination percentage, growth rate and growth performance) of mung bean seeds; (ii) the antimicrobial capacity of different types of PAW and (iii) the decontamination efficiency of the combined plasma treatments on mung bean sprouts. An in-house manufactured electrochemical cell was used for surface plasma activation of water and a diffuse coplanar surface barrier discharge plasma system was used for the combined CAP treatment of seeds and the formation of PAW. A test-tube setup was designed to assess the germination capacity of mung bean seeds 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 and E. coli DSM 1116. Microbial populations on combined plasma treated mung bean sprouts were measured every 24 h. Results showed no significant inhibitory effect from either PAW or combined CAP and PAW treatments on seed germination and growth capacity of sprouts, when compared to the control. Air PAW possessed outstanding antimicrobial activity against both E. coli strains (>6 log CFU/mL reduction) when compared to the control and other PAW produced in nitrogen and 80% carbon dioxide and 20% oxygen. Sprouts grown from the combined CAP (air) and PAW (air) treatment of seeds demonstrated enhanced control over the natural microbiota of sprouts during 96 h incubation. This study demonstrated effective disinfection properties of PAW (air) treatment without inhibiting the germination and growth capacity of mung bean seeds.