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Vegetables are essential for daily nutrition, supplying vital nutrients such as vitamins, organic acids, and mineral salts necessary for human development As a member of the World Trade Organization (WTO), Vietnam has access to a market of over 5 billion consumers, representing 95 percent of global trade value Despite being a major agricultural export for the country, Vietnam holds only a 0.2% share of the global vegetable market, valued at approximately 603 billion USD per year, indicating significant room for growth.
Vietnam's agricultural products face significant challenges in the global market, particularly concerning quantity, quality, pricing, and food safety, with food safety being the most pressing issue To meet international standards, Vietnamese agricultural products must obtain "Good Agricultural Practices" (GAP) certification, ensuring their safety and hygiene for global consumers The current market struggles with product consumption and competitiveness amid international economic integration, making product quality a crucial factor Adopting VietGAP manufacturing standards can enhance product quality by ensuring comprehensive food safety checks throughout the entire production process, from field preparation to storage and pesticide management.
According to the 2003 FAO document, Good Agricultural Practices (GAP) encompass farming processes that promote environmental, economic, and social sustainability, ultimately enhancing the safety and quality of food and agricultural products Each country typically has its own set of guidelines and standards for implementing GAP.
Page 2 a different set of standards, principles and regulations for the implementation of GAP, Vietnam is called VietGAP and the European region is put up as GlobalGAP.[1]
When using food, we face health hazards Can be classified into three hazard groups:
Biological threats, including bacteria and viruses, are significant contributors to food-borne illnesses that can severely impact human health, leading to conditions such as diarrhea, dysentery, cholera, and acute hepatitis These threats not only jeopardize human health but also compromise food quality, resulting in spoilage, shrinkage, and deterioration of products, ultimately leading to food poisoning and various diseases.
Chemical hazards, including heavy metals, pesticides, and toxic chemicals, pose significant health risks and are linked to serious diseases such as diabetes, heart disease, and cancer These harmful substances are often found in livestock feed and plant sources, highlighting the importance of addressing chemical exposure in our food supply.
- Physical hazards: (glass, twigs, needles ) can occur at any stage in the manufacturing process, can cause serious damage to the health of consumers
Safe food or clean food helps to reduce the risk.
THE ROLE AND URGENCY OF PLASMA IN THE FOOD INDUSTRY 2
Food preservation plays a crucial role in maintaining product quality Cold plasma technology is an innovative method that offers fast and efficient preservation with minimal impact on quality This technique is currently being researched in various countries, including Vietnam.
When life is increasingly high, consumers increasingly tend to require offered products with the best quality, both in terms of color, taste and nutrition in particular
To reduce the effects of high temperatures on food quality and nutrition, as well as to prevent alterations in physical and chemical properties that can affect taste, people often resort to methods such as room temperature storage, gamma irradiation, beta irradiation, pulsed electric fields, ultrasound, ozone treatment, ultraviolet (UV) light, and high-pressure processing However, these techniques generally require significant investment and have limited applications.
Page 3 solid products such as vegetables, meat and fish This is an opportunity for preservation method cold plasma.
SOME METHODS OF CLEANING AND DISINFECTION VEGETABLES
The sterilization
To ensure the destruction of harmful bacteria, it is essential to disinfect vegetables and fruits before use or distribution to households This can be achieved through physical or chemical sterilization methods.
1.3.1.1 Physical methods: a Disinfection by UV radiation: Ultraviolet radiation is electromagnetic radiation with wavelengths between 4 - 400 nm, have the effect of altering the DNA of the bacterial cell 254nm wavelength ultraviolet disinfection effect high To ensure good food disinfection must have sufficient contact time One way to take advantage of natural ultraviolet rays of the sun that is In these areas it is possible to heat foods such as vegetables and fruits in the sun for at least 30 minutes This simple method can kill bacteria in food can have under the effect of ultraviolet sun but economically inefficient and impractical.[2]
Page 4 b Disinfection by ultrasound: ultrasonic flow intensity ≥ 2W / cm2, in about 5 minutes contact time with the ability to kill entire microorganisms on food c Sterilized by cold plasma technology :
Cold plasma processing offers an effective method for the gentle decontamination of food surfaces and packaging materials Wageningen Food & Biobased Research is at the forefront of this technology, developing test units that demonstrate the successful inactivation of microorganisms.
The cold plasma technique effectively disinfects food products and packaging surfaces using cold gases at temperatures below 40 °C, making it a promising solution for inactivating microorganisms This method is gaining traction in the food industry due to its ability to reach every corner of products, unlike traditional cleaning options that may not be heat-resistant or are costly, such as water cleaning, while avoiding the use of harsh chemicals.
Wageningen Food & Biobased Research has more than 10 years of experience in cold plasma processing, including microbiology, product research, process impact and technology development.[3]
Main applications of cold plasma:
Cold plasma technology offers an effective method for disinfecting packaging materials by inactivating vegetative microorganisms and spores, making it particularly advantageous for temperature-sensitive products compared to traditional heat treatments Additionally, this innovative approach reduces water usage during the disinfection process Since cold plasma is a gas, it can easily treat irregularly shaped packages, such as bottles, unlike other disinfection technologies.
UV or pulsed light where shadowing occurs
Cold plasma technology effectively disinfects food products by inactivating surface micro-organisms, including both vegetative cells and spores This low-temperature treatment preserves food quality while ensuring safety.
Page 5 appearance of the product are minimal Industrial equipment is not available at this moment for both applications Research and development is necessary for scaling up and implementation
In Vietnam, food sterilization commonly involves the use of saline solutions and ozone gas (O3) Saline solution is a popular and easy-to-implement method that effectively kills bacteria, although its bactericidal ability is limited, making it less effective against pesticides and growth stimulants On the other hand, ozone gas is a powerful disinfectant that can eliminate all bacteria in food with just 1 ppm exposure for 10 minutes However, its strong odor and complexity make it less desirable for everyday use, though it is increasingly adopted by wealthier households due to its cost-effectiveness and technological advantages in the food industry.
Some note
Our recent survey indicates that no single system or equipment can achieve perfection in ensuring a safe food supply Instead, it requires a combination of various techniques tailored to different stages of the process to create a comprehensive and effective system.
GOALS OF THE SUBJECT
Common purpose
Research on plasma technology for cleaning and disinfecting vegetables aims to develop an innovative system that ensures food safety while conserving energy This technology is designed to provide fresh food sources, prioritizing consumer health and safety.
Detail purpose
About quality: vegetable, fruits after treatment will achieve the standards for community use
About design: the system is designed and arranged to do bring the use of convenience and comfort
About aesthetics: the products must be beautiful, refined
About Structure: the system is arranged logically for easy repair and installation
Economic Value: Help improve food safety ensures hygienic food safety
In terms of community development: Will help to society have clean food source leads to minimize the risk of disease to the community
To enhance environmental protection, it is crucial to avoid the use of burning systems and fully transition to electric-powered conveniences, as this can significantly reduce the pollution caused by waste gases emitted during operation.
In terms of sustainable building: maintenance, simple operation 304 stainless steel materials used should be durable, hard to damage So that the system will survive long with time.
THE SCIENTIFIC AND PRACTICAL SIGNIFICANCE OF THE
Scientific significance
This article reviews the efficiency of plasma processing in cleaning and sterilizing microorganisms on various vegetables, laying the groundwork for further research on different fruits It suggests new development directions for the food industry aimed at enhancing the quality and value of agricultural products in Vietnam.
Practical significance
A new treatment method is gaining significant attention in scientific research, emphasizing the need for thorough investigation and innovation This approach aims to enhance food processing by providing a highly efficient, safe, and environmentally friendly sterilization solution.
THE OBJECT AND SCOPE OF THE STUDY
Object of the study
The research has led to the development of a highly automated machine designed for efficient water production with minimal capacity This innovative machine allows for precise adjustments in volume and flow velocity, making it ideal for fruit and vegetable sterilization Its user-friendly design ensures easy installation and disassembly, facilitating convenient transportation.
Scope study
Research and development modeling sterilized vegetables, fruit using cold plasma technology at low temperature in the pressure environment After the test run,
Page 8 improvement and optimization of mechanical components, automatically will be extended application of technology, commercialization of products to meet the needs of large enterprises.
RESEARCH METHODS
Methodological basis
The document analysis method employed qualitative analysis techniques, utilizing the latest scientific research on plasma technology published in both international and Vietnamese scientific journals Key insights were drawn from scientific reports presented at international conferences and major reference works, notably those by Associate Professor Dr Tran Ngoc Đam, which significantly contributed to our study Additionally, an actual survey was conducted through experiments on the sterilization of vegetables and fruits, leading to valuable evaluations We also consulted food sterilization machines that utilize plasma technology, examining their structural similarities and market prices.
American scientists have introduced a groundbreaking food preservation technology that utilizes freezing plasma gas, ensuring high safety standards This innovative method involves a continuous flow of air and a TV tape running through the food, effectively eliminating bacteria while also reducing production costs Prior to the announcement of this gas plasma preservation technique, microbiologists were already exploring its potential benefits.
Brendan Niemira and engineer Joseph Sites from a research center in the Eastern United States conducted tests on heavily infested Golden Delicious apples Their findings confirm that frozen plasma gas is effective as a powerful bactericide without damaging the preserved products Additionally, increasing the gas projection, air flow speed, or gas flow profiles enhances bactericidal efficiency, thereby improving food safety.
Plasma Sources
Recent advancements in plasma treatments have transitioned from vacuum conditions to atmospheric pressure systems, significantly lowering costs and enhancing treatment speed for industrial use The ability to generate non-thermal plasma discharges at atmospheric pressure simplifies and reduces the expense of the decontamination process While most commercially available cold plasma devices were initially designed for biomedical research, they may require customization for food applications A commonly used non-thermal plasma (NTP) system is the barrier glow discharge, which could be utilized in an industrial setup where food is passed through the discharge for effective microbial decontamination.
The plasma pen or jet configuration utilizes a directed stream of gases for treatment purposes Biozone Scientific has innovated a method for producing cold oxygen plasma (COP) by exposing air to high-energy conditions.
UV light with an effective radiation spectrum between 180 nm and 270 nm
Cold gas plasma consists of various components, including positive and negative ions, free radical molecules, electrons, UV photons, and ozone The Duo-Plasmaline is a plasma source that is linearly extended and is activated using microwaves at a frequency of 2.45 GHz under specific pressure conditions.
The Plasmodul is an innovative microwave sustained low-pressure plasma reactor designed around the Duo-Plasmaline principle, allowing for easy scalability in industrial applications This advanced plasma treatment system operates effectively at pressures below 1000 Pa and is ideal for large area plasma treatment Its capabilities make it suitable for surface treatment of foods and processing surfaces on an industrial scale.
In 2010, Kim et al introduced a cold plasma jet that operates at 20 kHz AC under atmospheric pressure, highlighting the adaptability of plasma systems through the selection of various gases or gas mixtures Ongoing advancements in current plasma technologies and the development of new equipment aimed at treating actual food systems are expected to capture the interest of researchers and engineers in the near future.
A novel dielectric barrier discharge method shows promise for treating various foods by utilizing high voltage electrodes in contact with food packaging This technique requires only 40-50 W of power to ionize air within a 4 L re-sealable LDPE bag, generating reactive molecules while maintaining low product surface temperatures Treatment times for reducing spores or bacteria vary based on factors such as product loading, packaging material, gas composition, and electrode configuration The ionization process has been successfully applied to multiple packaging materials, including cardboard, glass, LDPE, HDPE, PETE, polystyrene, rubber, and tygon Furthermore, advancements in system scale-up allow for the treatment of air-filled packages with electrode gaps of up to 10 cm and rapid processing times.
Action of Plasma on microorganisms
Fig1.1: Action of plasma on microogranisms (source: the internet)
Action on cell components and functions
The sterilizing properties of plasma were first introduced in the late 1960s, with a patent granted in 1968 and initial research on oxygen plasma conducted in 1989 Extensive studies have since explored the mechanisms by which plasma agents inactivate microbes, demonstrating their lethal effects through interactions with biological materials Notably, Nelson and Berger (1989) highlighted the efficacy of O2 plasma as a potent biocide against bacteria Plasma treatment has proven effective in inactivating a diverse array of microorganisms, including spores and viruses Additionally, the effects of plasma can be selectively tuned to target pathogenic organisms while preserving host tissues, allowing for the activation of different pathways in various organisms.
Low-pressure oxygen plasma effectively degrades lipids, proteins, and DNA in cells, primarily due to the reactive species generated during the process These species, including reactive oxygen and nitrogen compounds such as O•, O2, O3, OH•, NO•, and NO2, are known for their oxidative effects on microbial cell surfaces Notably, atomic oxygen serves as a potent sterilizing agent, exhibiting an oxidation rate at room temperature that is approximately 106 times greater than that of molecular oxygen.
Reactive oxygen species (ROS) significantly impact the unsaturated fatty acids in the lipid bilayer of cell membranes, hindering the transport of biomolecules The double bonds in unsaturated lipids are particularly susceptible to ozone attacks, making membrane lipids more vulnerable due to their exposure on the bacterial cell surface This exposure allows them to be targeted by strong oxidizing agents Additionally, both cell proteins and spores are at risk of denaturation and leakage from ROS effects Furthermore, the oxidation of amino acids and nucleic acids can lead to changes that may result in microbial death or injury.
Micro-organisms in plasma experience intense bombardment by radicals, leading to surface lesions that living cells cannot repair quickly enough This phenomenon, known as "etching," may account for the rapid destruction of cells observed in many cases Additionally, the rupture of cell walls has been documented by researchers Laroussi et al (2003) and Mendis et al.
In 2002, research indicated that electrostatic forces arise from the accumulation of charges on the outer surface of cell membranes A study by Hong et al revealed morphological changes in E coli cells when exposed to atmospheric plasma at 75W for 2 minutes, as observed through electron microscopy.
Clearly revealed that the treated cells had severe cytoplasmic deformations and leakage of bacterial chromosome These observations demonstrate the loss of viability of bacterial cells after plasma treatment
An analogy can be made between plasma and pulsed electric fields regarding their effects on cell membranes Research shows that pulsed electric fields induce electroporation, and plasma appears to operate similarly by creating perforations in the membranes of microorganisms Moreover, humid air plasma not only generates pores but also significantly acidifies the surrounding medium.
Role of UV photons and charged particles
The production of UV photons of different wavelengths has been proposed to be involved in dimerizing the thymine bases of DNA including that of spores The role of
A detailed review by Boudam et al (2006) examined the role of UV photons in bacterial death during plasma treatment Recent research by Roth et al (2010) demonstrated that UV-C radiation, when isolated from reactive particles and specific spectral fractions, is the most effective agent for inactivating spores in plasma treatments.
Ultraviolet (UV) photons have a limited impact on atmospheric pressure glow discharge (APGD) due to their absorption by gas atoms and molecules, as noted by Vleugels et al (2005) Research by Lu et al (2009) demonstrated that charged particles contribute minimally to bacterial inactivation when using He/N2 (3%) as the working gas, compared to He/O2 (3%) Their findings indicate that heat and UV radiation have negligible effects on the inactivation process This aligns with earlier results from Perni et al (2007), who utilized optical emission spectroscopy to show that oxygen atoms are the primary contributors to plasma inactivation, with UV photons playing a minor role.
OH radicals, singlet oxygen metastables and nitric oxide Thus, a contradiction over the
Page 14 role of UV photons in plasma exists and future studies must be directed to get a clear picture.
STRUCTURE PROJECTS
The structure of the graduation thesis consists of 6 chapters:
Chapter 2: Overview of research topics
Chapter 5: Proposed technology / Calculation, design
Chapter 6: Production Test / Experimental evaluation
OVERVIEW OF SUBJECT
INTRODUCTION OF PLASMA
Page 15 a - Natural plasma b - Artificial plasma
Fig 2.1: Plasma beams (source: the internet)
Plasma is an ionized gas composed of free ions, electrons, and neutral atoms or molecules It can be categorized based on various criteria, including temperature and degree of ionization Specifically, plasma is divided into two main types: low-temperature plasma and high-temperature plasma, depending on the temperature levels and the relationship between plasma wave velocities and electron temperatures.
Low temperature plasma (3000-70000 C) is divided into two branches:
1 Unbalanced thermal plasma (cold plasma): low pressure, temperatures much greater electron temperature Ion For example: fluorescent bulbs, discharge luminescence, etc
2 Plasma thermal balance: atmospheric pressure, electron temperature equal to the ion temperature For example: electric arc, plasma torch, etc
High temperature plasma (> 70,000 - several billion degrees): accounting for 99% of the universe, for example: sun, stars, galaxies, hydrogen bombs, thermonuclear reactions
Fig 2.2: The physical conversion according to temperature(source: the internet)
Plasma is recognized as the fourth state of matter, alongside solid, liquid, and gas For instance, when ice (solid) is heated, it transforms into water (liquid), and further heating causes it to evaporate into gas As temperatures rise even more, electrons are stripped from atoms, resulting in positively charged ions and free-moving electrons This process, known as ionization, occurs when high temperatures accelerate the release of electrons from gas atoms, leading to the formation of ionized gas, or plasma.
The plasma state can be achieved not only through high temperatures but also by using UV rays, X-rays, and beta rays, which effectively transform gas into plasma This state is characterized by the presence of charged particles, allowing plasma to conduct electricity within an electromagnetic field.
Page 17 may be the environment through chemical reactions stimulated and emit electromagnetic radiation in many different wavelengths.[8]
Plasma technology utilizes electrical energy to create an ionization environment, resulting in the formation of both hot (thermal) and cold (non-thermal) plasma Hot plasma is generated at high temperatures and pressures, while cold plasma forms at normal pressure or in a vacuum with less energy Despite their differences, both types of plasma consist of ionized gas, including photons, ions, and free electrons This technology effectively increases the kinetic energy of these particles, allowing for quick, safe, and economical processing of materials.
Cold plasma has demonstrated a significant inhibitory effect on various microorganisms, including spores and viruses When directed at surfaces contaminated with mold and bacteria, the kinetic energy from electrons and ions, along with UV rays generated during plasma creation, bombards the cell walls of these pathogens This process leads to heightened oxidative stress, resulting in the disruption of DNA structure and the breakdown of cell walls, ultimately damaging and irreversibly killing bacteria, fungi, and viruses.
Cold plasma has potential applications for disinfection of raw materials, dried nuts and packaging materials, in the food industry
APPLICATION OF COLD PLASMA IN FOOD STERILIZATION
Fig 2.3 Application of cold plasma in food sterilization (source: the internet)
Nonthermal plasma (NTP) technology is highly effective for decontamination in food processing due to its energetic plasma species It offers diverse applications in the food industry, including the dry disinfection of surfaces of meat, poultry, fish, and fresh produce, as well as granular foods like dried milk and spices With the recent ban on ethylene oxide gases, NTP presents a promising solution for sterilizing particulate foods Additionally, NTP has proven successful in surface sterilization of packaging materials and enhancing their properties Recent studies have shown NTP's efficacy in inactivating microorganisms on various abiotic surfaces, such as glass and synthetic membranes, making it a valuable tool for food safety.
2.2.2 Treatment of raw and dried produce
Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes and Enterococcus faecalis are general food-borne pathogens that cause
Page 19 severe diseases and in some cases even death Raw agricultural produce has frequently been implicated in disease outbreaks Any treatment applied to ensure the microbiological safety of a food must be selected so as to minimize changes to its sensory, nutritional and functional properties.[9]
Traditional sterilization methods like heat, chemical solutions, and gases (such as ethylene oxide and hydrogen peroxide) are commonly used for disinfecting surfaces of fruits, spices, and nuts, but these methods can be time-consuming, damaging, and may leave toxic residues In contrast, cold plasma technology presents a promising alternative for pathogen inactivation, effectively reducing microbial load on fresh produce while preserving its nutritional and essential qualities.
Recent FDA regulations mandate that food processors achieve a 5 log reduction in resistant pathogens in their products Research from CSIRO in Australia has shown that cold plasma treatment can also achieve up to a 5 log10 reduction of microorganisms in just a few seconds.
Cold plasma ions can effectively penetrate complex surfaces, making them a superior surface treatment compared to UV light, particularly for irregular or cracked surfaces found on various foods like seeds and meat This technology has successfully decontaminated seeds, including tomato, wheat, bean, chickpea, soybean, barley, oat, rye, lentil, and corn, reducing contamination from Aspergillus parasiticus 798 and Penicillium sp to below 1% of initial levels, depending on treatment duration Treatment times ranged from 30 seconds to 30 minutes, utilizing a custom-designed low-pressure cold plasma (LPCP) prototype unit operating under vacuum with air and SF6 gases.
The study indicates that plasma treatment has minimal impact on the food quality of wheat and beans, with only marginal changes observed Importantly, the seeds remained viable after undergoing plasma processing.
A study on E coli 12955, a non-pathogenic surrogate for Salmonella spp., demonstrated a reduction exceeding 4 log CFU/ml when inoculated onto almonds This sterilization was accomplished by positioning the almonds in a 10-mm gap between two plasma discharge electrodes and applying treatment for 30 seconds at 25 kV and 2 kHz.
In 2008, a study demonstrated that cold plasma generated in a gliding arc significantly reduced viable populations of Salmonella and E coli O157:H7 on apple surfaces The researchers observed reductions of 2.9 to 3.7 log CFU/ml for Salmonella Stanley and 3.4 to 3.6 log CFU/ml for E coli Notably, the highest air flow rate of 40 liters per minute was found to be the most effective in achieving these results.
2.2.3 Control of biofilms and decontamination of processing surfaces
Microorganisms thrive in biofilms, which provide a nutrient-rich environment and protection from external stresses like plasma species attacks This article reviews the mechanisms of biofilm formation, their detrimental effects, and control strategies Biofilms pose significant challenges in various sectors of the food industry, including brewing, dairy processing, fresh produce, poultry, and red meat processing.
Plasma technology offers promising solutions for addressing biofilm formation on processing surfaces A US patent by Denes et al (2000) details a method for passivating bacterial biofilm surfaces through cold-plasma treatments The patent asserts that treating contaminated food processing surfaces with oxygen plasma not only sterilizes the area but also transforms the biological contamination into a form that resists further bacterial adhesion This process effectively cleans and sterilizes the uncovered areas of the substrate, enhancing overall hygiene in food processing environments.
The inventors proposed a second step involving plasma treatment to facilitate the deposition of an anti-fouling film that creates macromolecular networks on the substrate, enhancing resistance to bacterial adhesion Vleugels et al (2005) demonstrated a significant reduction in biofilms formed by Pantoea agglomerans on synthetic membranes, achieving a two-log reduction in just 10 minutes Notably, the exposure to glow discharge plasma resulted in minimal color change in red, green, and yellow bell pepper samples.
Abramzon et al (2006) demonstrated that a 100W RF high-pressure cold plasma jet can achieve nearly 100% eradication of Chromobacterium violaceum cells within four-day-old biofilms Their research indicates that various kinetic stages of inactivation occur, suggesting multiple mechanisms at play, potentially influenced by different plasma species and their synergistic effects.
Survival of food-borne pathogens has been detected at a level of 105 CFU/cm2 on stainless steel surfaces in a study by Kusumaningrum et al (2003) Deng et al
Cold gas plasmas have demonstrated the ability to denaturize proteins on stainless steel surfaces and effectively remove allergens from food processing equipment Research by Leipold et al (2010) focused on decontaminating a rotating cutting tool in the meat industry using atmospheric pressure dielectric barrier discharge in air, specifically targeting Listeria monocytogenes In their experiment, the knife was inoculated with Listeria innocua, serving as a ground electrode, and achieved a significant 5 log reduction after 340 seconds of plasma treatment, while maintaining a temperature below 300°C This method allows for decontamination during operation, minimizing the risk of cross-contamination between different meat batches, making it increasingly appealing to food manufacturers.
Page 22 investing in the cold plasma technology in order to kill the pathogens in the air and on the surfaces of processing plants.[12]
The United States Environmental Protection Agency's surface water regulations regarding chlorine have prompted poultry and meat industry operators, who consume significant water volumes, to explore technologies for ensuring compliance One promising method involves generating plasma in liquids through high-voltage pulses applied to gas-injected or sparged liquids, particularly for treating wastewater from food industries like poultry wash water This technique combines pulsed electric fields and cold plasma, producing free radicals, free electrons, UV light, acoustic and shock waves, and electric fields at 10-40 kV/cm The application of high-voltage pulses to gas-sparged liquids results in partial discharge activity and ionization of the gas, ultimately leading to the complete breakdown of the gas within the liquid medium.
CLEAN FOOD NORMS
Regulations limit allows microorganisms in vegetables, fruit and vegetable products, fruit ( QCVN 8-1:2011/BYT )( source :The internet )
Microorganis ms limits(In 1g or 1ml of food) (*)
(*) More than 25g or 25ml for Salmonella
THE SYSTEM DISINFECT FOOD BY COLD PLASMA TECHNOLOGY
Cold plasma is a neutral ionized gas made up of charged particles, free electrons, and ions, alongside neutral reactive species like atoms and molecules When this ionized gas is exposed to an electric field, the charged particles are accelerated, leading to collisions with the surrounding atoms and molecules.
Consequences of these collisions are new charged particles (ions, electrons and free radicals)
UV radiation and collisions with heavy ions significantly impact the survival of biological species, such as bacteria and viruses, by causing substantial structural damage to cell membranes Since the sample temperature remains relatively stable during processing, this technology is classified as non-thermal In food applications, there are two primary principles to consider.
Low-pressure plasma is generated in a vacuum chamber known as a plasma reactor, which maintains a pressure of 0.01 to 0.02 MPa This chamber is partially filled with gases such as argon, N2O, N2, or oxygen Plasma can be produced using a radiofrequency field, typically at 13.6 MHz, between two electrodes, or through microwave energy, usually at 2450 MHz, emitted from an antenna.
Atmospheric plasma is generated at ambient pressure (0.1 MPa) by applying a high potential difference between two electrodes in a gas mixture Various methods exist for producing atmospheric plasma.
Radiofrequency plasma (RF plasma), corona discharge plasma, resistive barrier discharge (RBD) plasma, and gliding arc discharge plasma are key technologies in food applications, with RBD and One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) systems showing significant promise In RBD plasma, a high-resistivity material is placed in the discharge gap between a high voltage electrode and a ground electrode connected to a transformer, which limits discharge current and prevents uncontrolled arcing Meanwhile, the OAUGDP system utilizes a gas mixture, such as argon or CF4, blown between two electrodes, where a high potential difference generates a stable glow discharge, effectively creating plasma.
Fig 2.4 Low-pressure plasma sketch; © Pierre Picouet(source: the internet)
Fig 2.5 Atmospheric plasma (RBD discharges) sketch; © Pierre Picouet(source: the internet) o Processing process
Samples are loaded onto a conveyor belt on one side of the machine
The system was initially created for the continuous treatment of food contact materials like conveyor belts; however, its adjustable electrode platform allows food products to pass near the plasma generating apparatus This system can accommodate a maximum height of 30 cm.
After setting the desired height for the product, the plasma is energized and the conveyor belt begins to move, transporting products through the system for a gentle plasma treatment The plasma, indicated by a purple glow on the electrodes, generates reactive species that effectively reach and treat the surfaces of the samples, including hard-to-reach areas often affected by shadowing Once the treatment is complete, the samples are packed and stored for future use.
Rapid industrialization and population growth have led to increased food contamination, making it a significant concern in our lives To combat this issue, individuals must adopt various measures to safeguard their family's health, including the use of food sterilizers.
In various regions, food sources are believed to be contaminated with excessive stimulants, prompting many families to invest in food sterilizers for home use As awareness of food safety grows, a significant number of individuals have adopted food sterilizers for long-term protection against potential contaminants.
The challenge of ensuring quality assurance in daily food needs through food sterilizers remains prevalent This article highlights the research and development of household-scale food cold-plasma screening machines, which are also suitable for use in various companies and small enterprises.
THEORETICAL BASIS
Basic definitions
Ionization is the process where an atom or molecule gains or loses electrons, resulting in a positive or negative charge and the formation of ions This process can occur due to collisions with subatomic particles, interactions with other atoms or molecules, or exposure to light Additionally, ion pairs can be formed through heterolytic bond cleavage and substitution reactions Ionization can also happen during radioactive decay via internal conversion, where an excited nucleus transfers energy to an inner-shell electron, causing its ejection.
The trend in ionization energy illustrates the periodic behavior of atoms based on atomic number, as outlined in Mendeleev's periodic table This trend aids in understanding electron arrangement in atomic orbitals without delving into complex wave functions or the ionization process For example, the significant drop in ionization potential following rare gas atoms signifies the onset of a new electron shell in alkali metals Additionally, the local maxima observed in the ionization energy graph, when moving from left to right across a period, reflect the presence of s, p, d, and f sub-shells.
3.1.3 Degrees of ionization a Degrees of ionization
Degrees of ionization is the ratio between the concentration of the particles with the concentration of the gas particles in the environment
The degree of ionization, often referred to as ionization yield, measures the proportion of neutral particles in a gas or aqueous solution that become charged particles In simpler terms, it reflects the ability of an acid or base to ionize A low degree of ionization indicates partial ionization, while a high degree signifies full ionization.
β : Degrees of ionization i n e , : The concentration of particles no : Individual air particle concentrations in the environment plasma has strong ionization : ei eo
Plasma has weakly ionization: ei eo
ei : The effective cross section, characterizing the interaction between the electron with ions
eo : The effective cross section, characterizing the electronic interaction between particles
In view of thermodynamics has two types of plasma and plasma equilibrium is unbalanced:
Equilibrium plasma, also known as isothermal plasma, consists of particles that maintain the same temperature and are electrically neutral In this state, the charged particles are balanced by the ionization process, allowing the plasma to exist without external energy input.
Plasma unbalance, also known as thermal plasma inequality, refers to a state where the plasma is not electrically neutral This condition requires external power for stabilization; without sufficient energy input, the plasma will dissipate Additionally, ionization membranes play a crucial role in maintaining plasma stability.
Plasma is defined as a collection of ions, electrons, and neutral particles that interact with one another and the surrounding radiation field, approaching neutral conditions.
However, this definition is not to say the fundamental properties of plasma, we need to learn more about static display r kT e
N r : The average distance between particles
N=ne+ ni n e : Electron concentration n i : Ion concentrations c Debye radius:
Consider a particle any: there will be a charge layer surrounding spherical particles produced, the thickness of this layer depends on temperature and particle concentrations
The thickness of the exposed layer is crucial for effectively containing a sufficient number of county seals, enabling the production of screens for county schools This concept is related to the Debye radius, which is the radius of the sphere that plays a significant role in this process.
So the charge surrounding the particle layer made of particle shielding on the specified distance
In the general case, the Debye radius is calculated by the formula :
ie ie ie ie ie Z n
For a plasma to exist, the Debye radius must be sufficiently small to enable effective shielding; if the Debye radius is excessively large, the medium cannot be classified as plasma Therefore, plasma must meet specific criteria regarding the size of the Debye radius to maintain its distinct properties.
Satisfy the condition near neutral:
The Debye radius has to be many times smaller than the size of the domain containing that set D