Effects of Nonthermal Plasma Treatment on Decontamination and Sprouting of Radish (Raphanus sativus L.) Seeds

Abstract

Sprout-related foodborne disease outbreaks are increasingly becoming a concern for food safety. The primary sources of microbial contamination in ready-to-eat sprouts are contaminated seeds, which are improperly disinfected prior to sprouting. In recent years, the application of nonthermal plasmas for seed decontamination is increasingly being investigated as a substitute to regular pre-germination treatments. The present study was intended to evaluate the potentiality of corona discharge plasma jet (CDPJ) for decontaminating microorganisms on radish seeds and to determine the plasma exposure effects on the seed germination as well as physicochemical properties of sprouts grown from the CDPJ-treated seeds. Microbial contaminants, namely, aerobic bacteria, Bacillus cereus, Escherichia coli, Salmonella spp., and molds and yeast were detected in the seeds. All the microorganisms found in the seed samples were reduced in the range of 1.2-2.1 log CFU/g upon treatment using the CDPJ for 3 min. Pseudo-first-order kinetics provides the best fit to the microbial inactivation patterns. The plasma seed treatment for up to 2 min showed beneficial effects on seed germination rate and growth of seedlings. Compared to untreated controls, sprouts grown from the CDPJ-treated seeds exhibited no significant changes in the levels of moisture (mean range 85.45-87.51%), reducing sugars (0.547-0.550%), total phenolic content (6.14-6.29 mu g GAL/g), and DPPH radical scavenging activity (78.03-78.60%). Sensory characteristics of radish sprouts grown from the plasma-treated (up to 2 min) seeds were not significantly different from controls. In conclusion, the CDPJ treatment of radish seeds for 2 min not only decreased the seed microbial counts but also led to the improvement of their germination rate and seedling growth, without negatively affecting the physicochemical and sensory properties of their corresponding sprouts.