Field of the Invention

Engineering science in parts concerning plasma-activated water machines for washing away residual chemicals and microorganisms in vegetables and fruits

Background of the Invention

Most applied plasma technologies emphasize the use of cold or non-thermal plasma (NTP) technologies to eradicate and reduce microorganism contamination in foods and other agricultural products. Examples of applications of cold oxygen plasma to eradicate microorganisms in vegetables and fruits can be found in lettuce (Fernandez and Thompson, 2012; Jahid et al., 2014), mangoes, melons (Pemi et al., 2008), apples and cantaloupes (Critzer et al., 2007), strawberries (Ma et al., 2015) and mushrooms (Xu, Tian, Ma, Liu & Zhang, 2016). This is consistent with Niemira (2014) who stated that non-thermal plasma is an effective process for flexibility in combating microorganisms to reduce the number of microorganisms causing diseases in humans such as E. coli O157:H7, Salmonella, L. monocytogenes, S. aureus and Shigella spp.

Schluter and Frohling (2014) reported that the use of non-thermal plasma systems was an interesting option for reducing contamination in food processing of foods with a surface temperature below 45 degrees Celsius, because heat causes sensitive effects on food ingredients such as protein denaturation and changes in physiology activities. Thus, the application of plasma technology to packaged foods can reduce contamination in food and containers.

Wang et al. (2012) studied the use of atmospheric pressure plasma systems to inhibit Salmonella in fresh-cut vegetables and fruits by analysing coloration and nutritional values before and after giving the plasma treatment and found vegetables and fruits run through plasma for two minutes for changes to chemical quality such as Vitamin C content and physical quality such as slight changes in coloration. Fresh-cut vegetables and fruits remained acceptable to consumers and plasma was able to reduce Salmonella in carrots, cucumbers, and pears by 90%, 80% and 80%, respectively.

Kima et al. (2014) studied effects on the use of dielectric barrier discharge plasma (DBD) on breast milk quality and microorganism safety and found plasma-treated breast milk to have better quality and microorganism safety than breast milk which was not plasma-treated. In addition, pH, coloration, and oxidation of breast milk were found to have slightly changed only.

Leipold et al. (2011) studied the application of atmospheric pressure plasma systems in reducing contamination by Listeria monocytogenes, which is a cause of listeriosis found in plants and food. By culturing on slides and containing slides in a sealed LDPE bag, the volume of air in the bag comprises argon (97.5%) and oxygen (2.5%). After passing through dielectric barrier discharge (DBD) plasma, use of plasma on a sealed LDPE bag containing slides contaminated by bacteria for 15 minutes was found to be able to reduce the number of bacteria by 6 logs.

Rod et al. (2011), who studied the effects of using atmospheric non-thermal plasma to reduce Listeria bacteria quantities and changes to ready-made food quality, found atmospheric non-thermal plasma to be able to reduce microorganism contamination in food before packaging, despite oxidation in certain types of food. Phan et al. (2017) found the use of plasma to have effects causing minor changes in Nam Dok Mai mango quality.

Furthermore, research reports on the use of cold or non-thermal plasma (NIP) to eradicate chemical residues in agricultural products showed most research to prefer synthesizing hydroxyl radicals to cause reactions to disinfect microbes and breakdown organic molecule because cold or non-thermal plasma’s efficiency in causing reactions is the second highest after fluorine (F2).

Bai et al. (2009) and Jiang et al. (2014) studied the condition of cold or non-thermal plasma. Molecules of chemical residues are separated from one another by plasma energy. In 2014, Misra et al. studied the application of DBD plasma to eliminate chemical residues in strawberries and found DBD plasma to mostly be able to reduce azoxystrobin, cyprodinil, fludioxonil and pyriproxyfen.

Applications of plasma technology in agricultural produce is preferably in the form of plasma water due to plasma water does not affect produce color, shape, or other properties, while there are many models for synthesizing hydroxyl radicals to obtain enough for chemical decomposition. One of the models preferred is plasma jets. From examining relevant works, works which applied for protection concerning synthesis of hydroxyl radicals with jet discharge preferred discharge via gaseous mediums such as helium, argon, and air, etc., by directly spraying plasma on material surfaces or by spreading plasma via various types of membranes.

Australian patent publication no. AU2020101313A4 describes plasma jets for maintaining vegetable and fruit freshness that use air in the plasma production process without using water via positive and negative electrodes arrayed in a perpendicular manner whereby the other side of electrodes are connected to insulation to create a space for releasing electrical charges. This method can eradicate pesticide residues on vegetable and fruit surfaces along with sterilizing bacteria without damage to the quality of agricultural products.

United States patent publication no. US20200325049 Al describes a small modular surface devices with small in-built modules for eradicating air contamination and eradicating contamination at internal surfaces through a technical process of producing plasma at the surface of electric barriers (DBD) from the environment for eliminating contamination and destroying ethylene gas, which causes premature ripening, including adaptations for causing oxidation at the surface and/or atmosphere of containers. This process comprises connections between power distribution units and loads comprising the transformer conductor; the capacitor parallel to the transistor with inductors and capacity of capacitors set according to the resonance frequency of conversion connected to voltage load and adjustments to capacitor capacity to adjust power amp impedance when the impedance of the load changes. Loads are driven by power distribution units to create ozone comprising ozoneproducing plasma actuators and circuits engraved in plasma actuators which allow water to come into contact with ozone.

Thai patent publication no. 2001000977 describes the system for producing plasma at sub- atmospheric pressures produces plasma with high quantities of active hydrogen peroxide continually for production and functional benefits. The system consists of a high-voltage electricity generation part alternated by radio frequencies, a plasma production part, and a production room pressure control part. The high-voltage electricity generation alternated by radio frequencies part has a generator which uses 500-1,000 watt electricity. The electricity is sent to the plasma production part at the surface comprising dielectric plasma nozzles with an electrode diameter-to-glass tube interior diameter ratio of 1 :2-5 where the lower ends of electrodes have an appropriate distance from the end of the glass tube and an appropriate distance from the surface to the end of the glass tube and production room pressure is controlled within a range of 125-500 Torr.

United states patent publication no. US20160016142A1 describes a device for producing and injecting electrically charged air into a flowing water system whereby plasma release has no direct contact with flowing water and flowing water is separated from plasma by a volume gap. The resultant activated water may be used for industrial cleaning. This device consists of a body connected to electrical grounding, a digital or analog interface and a power source, an air pump for bringing air through the plasma chamber to cause ionization, a water pump which brings water through the reservoir, a plasma chamber where air molecules are separated into electrically charged air in the volume space underneath the plasma chamber, a reservoir with an inlet for untreated water, an outlet for activated water and a mixing device.

Furthermore, Chinese patent publication no. CN110235932A describes a plasma processing device for sterilizing and preserving fruits which produces plasma between positive and negative electrodes in a cross-shaped arrangement. The surface on the opposite side is connected to insulation to create a discharge space. When the power distribution source is open, the electrode set produces plasma, which is blown to fresh vegetables and fruits until the specified time is reached, in which case the fruit sterilization and preservation process is considered complete.

According to the abovementioned information, devices and equipment with different plasma production functions have been found to be based on different components and functional objectives. The inventor developed plasma production via an air medium with liquid solutions capable of decomposing residual agricultural chemicals and suppressing microorganism growth in the process of cleaning agricultural produce along with sterilization with UVC light in the same device, which enhances efficiency in washing residual chemicals and microorganisms from vegetables and fruits.

Summary of the Invention The plasma activated water system, which comprises of a plasma discharge tube, a UVC light bulb, an air pump, a water pump, a high voltage transformer, and a touch screen control system, is a device used to remove chemical residues and microorganisms from vegetables and fruits. The water and air that enters the device through the water and air inlets are activated with high voltage electricity when they enter the plasma discharge tube, resulting in plasma ionization by pinhole plasma jet technique. The resulting plasma is collected in a plasma activated water container and pushed back into the plasma machine after dissolving and mixing with the tap water flowing to the water outlet. As a result, the plasma activated water is circulating. The plasma activated water performs more effectively and efficiently when used in conjunction with a UVC light bulb to remove the chemical residues and slow microbial growth in vegetables and fruits. The purpose of this invention is to increase options for eradicating residual chemicals and inhibiting microorganism growth in vegetables and fruits effectively by using plasma-activated water and UVC sterilization to increase health safety from residual chemicals while extending vegetable and fruit storage life.

Brief Description of the Drawings Figure 1 - Sample image of the plasma-activated water machine

Figure 2 - Sample image of a part of the plasma-activated water machine

Figure 3 - Graph of determination results of chemical residues decomposition efficiency of the plasma-activated water machine

Detailed Description of the Invention Figure 1 and Figure 2 show sample images of the plasma-activated water machine for washing away residual chemicals and microorganisms in vegetables and fruits comprising a body which is opaque from every side and made from materials resistant to chemical corrosion and capable of withstanding heat at 50 degrees Celsius and up such as Stainless 304 or ABS plastic, etc. The plasma- activated water production system is divided into four parts consisting of the high-voltage power supply unit, the plasma-activated water unit which produces plasma-activated water from the plasma discharge tube, the air and/or gas distribution unit and the touch screen control system.

The water container (2) comprises and may include a part for receiving external water to activate plasma capable of connection to the external water inlet, which may be connected to a water tank, a faucet, or a filter, etc., and a part for discharging water functioning to discharge plasma- and UVC-activated water for use. Water contained in the water container (2) will flow into the water pump (1) at a rate of 1-5 liters per minute. Water flow rates can be set with the touch screen control system (9). Water is controlled to flow into the water inlet (3b) of the plasma discharge tube (3). Furthermore, when electricity is discharged from a 15 -kilovolt high-voltage direct current transformer (8) connected to the negative electrodes (3c) at the center of the plasma discharge tube (3) and the positive electrodes (3g) at one end of the plasma discharge tube (3), air from the air pump (4) connected the air pressure regulator (7) is arranged to function with the gas storage tank (5) connected to the gas pressure regulator (6) where gases for use in the plasma discharge tube (3) can be selected from argon, nitrogen, oxygen or hydrogen, either singularly or a combination thereof. The gas is sent into the gas inlet (3f) of the plasma discharge tube (3) with a flow rate of 1-25 liters per minute.

When air and/or gas receive high-voltage direct current electricity, energy is converted into plasma and electrical charge particles comprising free radicals of reactive oxygen species (ROS) such as hydroxyl radicals and free radicals of reactive nitrogen species (RNS) such as nitrate (NO3‘) and nitrite (NO2’), etc., are released through pinholes (3h) into the plasma discharge tube (3). This plasma is then dissolved to blend in water flowing into the plasma discharge tube (3), converting water into plasma-activated water which flows to the water outlet (3 a) into the water container (2). The plasma- activated water is then continually circulated in the plasma discharge tube (3) until the specified plasma-activated water discharge time is complete. Time settings for plasma-activated water production can be set by using the touch screen control system (9) in a range of 1-60 minutes.

The plasma discharge tube (3) is a hollow cylinder with two layers made from insulation materials with insulating properties capable of withstanding heat and acid corrosion such as glass, quartz or other materials. The outer cylinder (3d) has a diameter of 2.5-3.0 centimeters and a length of 15-20 centimeters. One lower side of the cylinder has a water inlet (3b) and the other lower side has a water outlet (3a). The connector to the negative electrodes (3c) is at the center of the outer cylinder. These three have a similar distance from one another. The preferred distance between these three spaces has been set at five centimeters equally. The interior of the plasma discharge tube comprises the inner cylinder (3e) with a diameter of 0.8 centimeter and a length of 20-25 centimeters. The inner cylinder is covered by the outer cylinder and has an appropriate distance between the inner and outer cylinders of the tube at 0.3-1 centimeter. One end of the inner cylinder includes the positive electrodes (3 g).

The positive electrodes (3g) and the negative electrodes (3c) are wires made from other materials with properties of induction and resistance to corrosion such as stainless steel with a diameter of 0.5-2 millimeters and a length of 5 centimeters and 20 centimeters, respectively. The space between both electrodes is the discharge area. When electricity is discharged in the plasma discharge tube (3), electricity is transformed by air or gas from the gas inlet (3f) at the other end of the inner cylinder into plasma.

Plasma is distributed through 5 pinholes (3h) of the inner cylinder of the plasma discharge tube (3) with diameters of 0.5-1.5 millimeters. Each pinhole (3h) has an appropriate distance from the others at 2 centimeters. The central pinhole is located at the position of the negative electrodes (3c). The produced plasma permeates the inner (3e) and outer (3d) cylinders of the plasma discharge tube to mix with water flowing in at the water inlet (3b), transforming the water into plasma-activated water, which flows through the water outlet (3 a) into the water container (2) and is continually circulated into the plasma discharge tube until the specified discharge time is complete. The unit for producing plasma-activated water from the plasma discharge tube (3) comprises at least one plasma discharge tube (3) and has an appropriate plasma-activated water production rate of one plasma discharge tube (3) per 5 liters of water, which can produce hydroxyl radicals at 10-30 ppm in 60 minutes. If the number of plasma discharge tubes (3) is increased, this will increase hydroxyl radical production capacity. Because hydroxyl radicals decompose quickly and do not have a long storage life, hydroxyl radical production must be at sufficient concentrations for residual chemical decomposition.

The plasma machine is mounted with at least one UVC light bulb (11) for preparing plasma- activated water. When ultraviolet light from the UVC light bulb is spread in plasma-activated water containing dissolved hydroxyl radicals, oxygen atoms will breakdown into charges and react with various free radicals in plasma-activated water, converting the free radicals into hydroxyl radicals and increasing hydroxyl radical concentrations, which enhances efficiency of plasma-activated water in eradicating residual chemicals in agricultural produce.

Figure 3 shows a graph of determination results of chemical residues decomposition efficiency of the plasma-activated water machine. Chemical residues decomposition efficiency of plasma-activated water produced from the plasma machine in randomly selected vegetable and fruit samples were from plasma-activated water produced by applying optimal condition with a discharge time of 60 minutes, a water flow rate of 140 liters per hour and an air flow rate of 3 liters per minute. Hydrogen peroxide concentrations were determined at 32.12 +1.63 ppm.

The randomly selected fruit sample was tangerines. Tangerines had residual malathion and profenofos chemicals before washing at 0.41 + 0.14 mg/kg and 0.09 + 0.03 mg/kg, respectively.

When tangerines were washed with plasma-activated water produced under the above-mentioned conditions by soaking for 15 minutes, plasma-activated water was found to have reduced malathion and profenofos content to 0.08 + 0.01 mg/kg and 0.04 + 0.01 mg/kg or reductions of 80.49% and 55.56%, respectively. When compared to tangerines washed with tap water by soaking for an equal amount of time, the method was found to have reduced malathion and profenofos content to 0.26 + 0.02 mg/kg and 0.06 + 0.002 mg/kg or reductions of 36.59% and 33.34%, respectively.

According to this result, plasma-activated water was found to be significantly effective in reducing malathion and profenofos at a reliability level of 95 percent. In addition, malathion and profenofos levels were found to be lower than the standard maximum residual limit (MRL) specified by the National Bureau of Agricultural Commodity and Food Standards, Ministry of Agriculture and Agricultural Cooperatives, at no more than 7 mg/kg for malathion in tangerines and no more than 0.1 mg/kg of profenofos in tangerines.

Best Mode of the Invention

As described in Detailed Description of the Invention