Aqueous and gaseous plasma applications for the treatment of mung bean seeds

Martina Darmanin,Renald Blundell,Julia Durek,Susanne Neugart,Ruben Gatt,Antje Fröhling,Oliver Schlüter,Monika Schreiner,Sara Bußler,Vasilis P Valdramidis

doi:10.1038/s41598-021-97823-1

Abstract

Sprouts are particularly prone to microbial contamination due to their high nutrient content and the warm temperatures and humid conditions needed for their production. Therefore, disinfection is a crucial step in food processing as a means of preventing the transmission of bacterial, parasitic and viral pathogens. In this study, a dielectric coplanar surface barrier discharge (DCSBD) system was used for the application of cold atmospheric plasma (CAP), plasma activated water (PAW) and their combination on mung bean seeds. Germination assessments were performed in a test tube set-up filled with glass beads and the produced irrigation water. Overall, it was found that the combined seed treatment with direct air CAP (350 W) and air PAW had no negative impact on mung bean seed germination and growth, nor the concentration of secondary metabolites within the sprouts. These treatments also reduced the total microbial population in sprouts by 2.5 log CFU/g. This research reports for first time that aside from the stimulatory effect of plasma discharge on seed surface disinfection, sustained plasma treatment through irrigation of treated seeds with PAW can significantly enhance seedling growth. The positive outcome and further applications of different forms, of plasma i.e., gaseous and aqueous, in the agro-food industry is further supported by this research.

Highlights

Being a significant source of amino acids, proteins, fibre, enzymes, vitamins and minerals fundamental to human health[13], sprouts naturally contain a number of bioactive compounds, known as phytochemicals[16]
Among the different plasma sources cited in the literature, the dielectric barrier discharge (DBD) gains attention as it allows for homogeneous cold atmospheric plasma (CAP) treatment of large volumes that is ideal for seed treatment[28]
Preceding the combined CAP and plasma activated water (PAW) treatment of mung bean seeds, experimental assessment was performed on the CAP and PAW treatments individually

Summary

Introduction

Being a significant source of amino acids, proteins, fibre, enzymes, vitamins and minerals fundamental to human health[13], sprouts naturally contain a number of bioactive compounds, known as phytochemicals[16]. The use of air as a process gas is a common trend for cold plasma application on sprouts, notably due to the presence of O2 and N 2, the parent molecules of reactive oxygen and nitrogen species (RONS) that function as the prime antimicrobial a gents[29], with an additional impact on enhancing seed g ermination[30]. These may include nitrogen oxides ( NO· and N Ox), peroxynitrite ( ONOO−), atomic oxygen (O), ozone (O3), singlet oxygen (1O2), superoxide anion (O2−), hydrogen radicals (H·), hydroxyl radicals (OH·) and/or hydrogen peroxide (H2O2)[5]. Ancillary analyses were carried out in order to characterise the reactive species in the plasma activated water and to assess the composition of secondary metabolites in the harvested sprouts

Methods

Results

Conclusion