article · Journal of Physics D Applied Physics
Using plasma-activated water alongside mild heating provides an effective method for decontaminating Bacillus cereus spores on japonica rice grains. Combining plasma-activated water with temperatures of 40 °C and 55 °C achieved microbial spore reductions of 1.54 and 2.12 log10 CFU per gram respectively after a 60-minute exposure. This performance significantly exceeded the 0.72 log10 reduction produced by plasma-activated water on its own. Laboratory assays demonstrated that the combined approach damaged the multilayered protective envelope of the spores, triggering the release of internal proteins, nucleic acids, and dipicolinic acid. Electron microscopy verified structural disruption to the spore exterior and resulting leakage of intracellular contents. Furthermore, tests on the cooked rice confirmed that this treatment caused no detrimental changes to texture or sensory characteristics, showing compatibility with grain preservation.
Bacterial spores such as Bacillus cereus are notoriously resilient and can survive standard cooking, presenting persistent food safety risks in staple crops. Developing gentle decontamination methods that eliminate spores without degrading food quality is essential. Because this method operates at mild temperatures and leaves rice texture intact, it provides an alternative to intense heat or chemical treatments that can spoil grain quality.
This research represents applied, laboratory-tested technology of interest to rice millers, grain storage facilities, and food safety processors. It demonstrates a practical method to lower microbial loads on raw grain while preserving end-product quality. Commercial adoption remains at an early stage, as moving beyond laboratory trials will require developing continuous, high-volume processing equipment and reducing the 60-minute contact time to match the throughput demands of industrial grain facilities.
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Abstract This study applied the combination of plasma-activated water (PAW) and mild heat (40 °C and 55 °C) for the decontamination of Bacillus cereus spores in rice ( Oryza sativa L. ssp. japonica ). In this study, PAW combined with 40 °C and 55 °C (PAW-40 and PAW-55) achieved 1.54 and 2.12 log 10 CFU g −1 reductions of B. cereus spores in rice after 60 min exposure, which was significantly higher than the inactivation level (0.72 log 10 CFU g −1 ) induced by PAW treatment alone. The assays for the leakage of intracellular contents (nucleic acids, proteins, dipicolinic acid-DPA) and the propidium iodide (PI) fluorescence probe confirmed that the combination of PAW and mild heat caused significant damages on the intact multilayered structure of B. cereus spores than the individual PAW did. The application of scanning electron microscope (SEM) and transmission electron microscope (TEM) provided a direct observation for the visible disruption of external structure and leakage of intracellular components caused by the combination of PAW and mild heat. Besides, the combination of PAW and mild heat caused no adverse effect on the texture and sensory qualities of the rice after cooking. These findings provide some knowledge for the application of PAW combined with mild heat for the decontamination of spores in rice.
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DOI: 10.1088/1361-6463/ab573a
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