Abstract
Abstract: Plasma-activated water (PAW) has widely been accepted and proven to have broad-spectrum bactericidal properties. It can also effectively kill microorganisms on fresh foods, further inhibiting spoilage. The emerging low-temperature PAW sterilization has presented great potential for application in food production and safety control. However, the systematic design of PAW generating equipment is still lacking in recent years. In this study, a piece of novel equipment to produce low-temperature PAW was developed using the plasma generation via dielectric barrier discharge, in order to improve the level of PAW equipment development and application. The system of this equipment included the components of dielectric barrier discharge, ventilation channels of heat dissipation, flow channels of activated water, and the high-voltage alternating current power supply. The components of dielectric barrier discharge were composed of a cylindrical high-voltage discharge electrode and a flat-shaped low-voltage discharge electrode in an upper-down parallel configuration with the uniform gas gap. Among them, the flowing water film was integrated to be used as the low-voltage electrode, thereby realizing the uniform plasma generation, particularly for the continuous and stable production of activated water. Furthermore, the heat dissipation of high-voltage discharge electrode was employed two bidirectional-countercurrent ventilation channels inside and outside the electrode tube. A typical Alternating Current-Direct Current-Alternating Current (AC-DC-AC) structure was also designed as the power circuit of a high-voltage alternating current power supply, further to realize the energy supply of thee dielectric barrier discharge. In addition, the control circuit was utilized to monitor and adjust the operational parameters, such as frequency, voltage, and current. Some structural and working parameters of equipment were designed to be continuously adjustable within a certain range, including the inclination angle of stainless-steel plate for water flow, the air gap between the high-voltage discharge electrode and the stainless-steel plate, water flow rate, discharge power, and discharge voltage, in order to meet the diversified requirements for the application of plasma-activated water. Furthermore, an experiment was performed on the PAW equipment to verify the effect of PAW treatment on the vegetables. The fresh-cut potato slices were simulated to be infected with Escherichia coli before the PAW sterilization cleaning and preservation. An optimal sterilization rate was (98.65±0.59)% for the sterilizing of PAW on Escherichia coli in the potato slices, in which the water flow was 600 mL/min, the air gap was 10 mm, the mass ratio of material to activated water was 1:20, the power supply voltage was 137.4 V, and the sterilization time was 4.72 min. More excellent performance was achieved under the optimal condition than before, thereby greatly contributed to relatively higher hardness, lower color difference, lower relative conductivity, lower soluble solid content, and lower decay rate in the bacteria-contaminated potato slices during storage. After 24 d of storage, the bacteria-infected potato slices without cleaning, with distilled water cleaning, and with PAW cleaning achieved a hardness of (3.01±0.84), (3.54±0.81), (4.70±0.48) N, respectively, a color difference of 22.08±1.05, 13.21±1.43, 7.35±0.81, respectively, a relative conductivity of (28.00±6.43)%, (26.72±2.07)%, (17.19±2.26)%, respectively, a soluble solid content of (6.850±0.120)%, (5.430±0.006)%, (3.080±0.006)%, respectively, and a decay rate of (87.04±1.63)%, (76.32±1.60)%, (52.09±1.41)%, respectively, indicating better advantages of sterilization and preservation. This finding can provide a sound reference on the development and industrial application for the sterilization technology of plasma-activated water.
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