Plasma Sterilization Research Articles

Can sterilization of disposable face masks be an alternative for imported face masks? A nationwide field study including 19 sterilization departments and 471 imported brand types during COVID-19 shortages.

Face masks, also referred to as half masks, are essential to protect healthcare professionals working in close contact with patients with COVID-19-related symptoms. Because of the Corona material shortages, healthcare institutions sought an approach to reuse face masks or to purchase new, imported masks. The filter quality of these masks remained unclear. Therefore, the aim of this study was to assess the quality of sterilized and imported FFP2/KN95 face masks. A 48-minute steam sterilization process of single-use FFP2/KN95 face masks with a 15 minute holding time at 121°C was developed, validated and implemented in the Central Sterilization Departments (CSSD) of 19 different hospitals. Masks sterilized by steam and H2O2 plasma as well as new, imported masks were tested for particle filtration efficiency (PFE) and pressure drop in a custom-made test setup. The results of 84 masks tested on the PFE dry particle test setup showed differences of 2.3±2% (mean±SD). Test data showed that the mean PFE values of 444 sterilized FFP2 face masks from the 19 CSSDs were 90±11% (mean±SD), and those of 474 new, imported KN95/FFP2 face masks were 83±16% (mean±SD). Differences in PFE of masks received from different sterilization departments were found. Face masks can be reprocessed with 121 °C steam or H2O2 plasma sterilization with a minimal reduction in PFE. PFE comparison between filter material of sterilized masks and new, imported masks indicates that the filter material of most reprocessed masks of high quality brands can outperform new, imported face masks of unknown brands. Although the PFE of tested face masks from different sterilization departments remained efficient, using different types of sterilization equipment, can result in different PFE outcomes.

Assessment of the possibility of surgical masks re-use after a sterilization process in the pandemic condition of COVID-19

The aim of this study was to explore the possibility to re-use disposable masks in order to prevent excessive waste generation during the pandemic period. The COVID-19 pandemic has caused rapidly increasing waste production resulting from the necessity of common usage of disposable personal protective equipment. This research covers the evaluation of the structure of surgical masks subjected to a threefold steam, gas or plasma sterilization process in order to verify the possibility of their re-use. The results of the study showed that gas sterilization even after three cycles did not cause significant changes in mask structure or air permeability. Hydrogen peroxide plasma sterilization caused significant changes in the structure of layer A after the third cycle of sterilization; nonetheless, it did not influence the air permeability of the mask. A significant reduction in the cover ratio of layers composing surgical masks causes an increase of air permeability in the case of steam sterilization, leading to a reduction of the mechanical ability to prevent the penetration of microorganisms. The reduction in cover ratio limits the filtration efficiency. Surgical masks subjected to threefold gas sterilization can be recommended for re-use. This allows one to use the mask thrice, ensuring safety for users and limiting the mask-waste production to one-third of the volume compared with when the mask is used once. The volume of mask-waste can be reduced with the application of the sterilization process for used masks during the pandemic period. Currently, it is not possible to sterilize all one-use masks, but implementation of this method in hospitals and medical centers is a step in the pro-environmental direction.

A Plasma Reactor for Experimental Investigation of Sterilization Processes: Preliminary Results on Escherichia Coli

Plasma process is a promising physical method for sterilization. Due to the lack of suitable plasma diagnostics, installed in the reactors, a general lack of knowledge happens about the gas-phase chemical composition and the influence of operating parameters. The same lack of knowledge happens in case of gas plasma generated from different gases, candidates for sterilization purposes. The aim of this work is to understand the role of different agents acting in the sterilization process, evaluate the effectiveness of different precursor gases and validate the plasma reactor dedicated. A plasma reactor, equipped with an extended set of plasma diagnostics is dedicated to the understanding the role of different agents of gas plasma sterilization process. A microbiological investigation is carried out to evaluate the efficiency of the steps of the process on cultures of Escherichia coli, using both hydrogen peroxide and argon. The effects on the colonies of Escherichia Coli are assessed in terms of species present in the chamber, acquiring the spectra resulting from the exposure of the Petri dish to sterilization. With regard to the sterilization action of Peroxide and Argon plasma, CFUs are counted for each significant point of the cycle and survival curves are provided. Differences emerge between Peroxide and Argon plasma, for action mechanisms and sterilization time. The survival curves show a more effective sterilizing action of Argon plasma. A validation is necessary by an appropriate statistic and by considering more resistant microorganisms. Reactor will be used to evaluate different precursor gases and microorganisms. The use of non-corrosive and non-irritating gas, such as argon, for sterilization purpose implies a simplification of the plant equipment. It would be possible to remove the components for the vaporization and concentration of peroxide, and to eliminate the management of the boxes containing discarded peroxide, managed to date as hazardous wastes and to reduce significantly the risk for health professionals.

The influence of low-temperature sterilization procedures on piezoelectric ceramics for biomedical applications

Piezoelectric materials are intensively investigated for usage in biomedical applications ranging from in vivo sensors and energy harvesters to implants for bone and neural cell stimulation. Besides the high requirements for reliability and low cytotoxicity, implantable materials must be sterilizable without losing their functionality. In this study, we investigate the impact of low temperature plasma sterilization and the associated cleaning routines on the piezoelectric properties of PZT, BCZT and KNN bulk ceramics. The stability of the piezoelectric response strongly depends on the material system, with BCZT ceramics showing the strongest decline in properties. Several factors were identified to contribute to this reduction of the piezoelectric coefficient, the most important being mechanical stress due to sample handling as well as chemical reactions during cleaning, disinfection and sterilization. The study highlights the importance of evaluating the impact of all influencing factors along the pre-implantation handling chain in the material selection process.

Decontamination Of Endospores By Plasma Sources On Dried Surfaces: A Review Of Key Parameters And Inactivation Results

The efficiency of plasmas sources for the decontamination of heat-sensitive devices has been proven for more than 20 years, but commercial plasma-based sterilizers still have a narrow range of applications. This can be partially explained by difficulties to determine reliable bio-indicators and standardized microbiological test procedures required by industrial uses. In this paper, we examine the influence of environmental factors on the inactivation rate of microorganisms deposited on surfaces and treated by plasma sources. In addition, we present a literature review showing that several in-discharge and afterglow plasma sterilizers offer shorter treatment times than conventional low-temperature sterilizers to reduce the concentration of endospores on contaminated surfaces by 6-log. Finally we make a few recommendations for future plasma decontamination standards.

State of the art in nonthermal plasma processing for biomedical applications: Can it help fight viral pandemics like COVID-19?

Plasma processing finds widespread biomedical applications, such as the design of biosensors, antibiofouling surfaces, controlled drug delivery systems, and in plasma sterilizers. In the present coronavirus disease (COVID‐19) situation, the prospect of applying plasma processes like surface activation, plasma grafting, plasma‐enhanced chemical vapor deposition/plasma polymerization, surface etching, plasma immersion ion implantation, crosslinking, and plasma decontamination to provide timely solutions in the form of better antiviral alternatives, practical diagnostic tools, and reusable personal protective equipment is worth exploring. Herein, the role of nonthermal plasmas and their contributions toward healthcare are timely reviewed to engage different communities in assisting healthcare associates and clinicians, not only to combat the current COVID‐19 pandemic but also to prevent similar kinds of future outbreaks.

Susceptibility of Staphylococcus epidermidis to Argon Cold Plasma Jet by Oxygen Admixture

Cold atmospheric pressure sterilization is one of the nominated and efficient techniques to prevent the spread of diseases. Reactive species such as O and OH and other radicals play a major role in the mechanism of plasma sterilization. Therefore, in this work, oxygen was mixed with different parentage from (0.2 to 1.2%) to argon to enhance the generation of the reactive species and increase the argon atmospheric pressure plasma sterilization efficacy. The emission spectra from the jet increase the radicle line intensities by increasing the percentage admixture of O2 with the argon gas to reach a maximum power at 0.8; then, it gradually decreases with a higher O2 percentage. The OH band intensity decreases with increasing the admixture of O2. The jet with different O2 percentages was tested against Gram-positive S. epidermidis, which is the causal agent of nosocomial infections. The maximum reduction in colony-forming units (CFU) was observed at 0.2% O2. No bacterial growth was observed at the later concentration applied for 8 min and the same case was detected at 0.4% O2 applied to 16 min.

Safety and efficacy of cold atmospheric plasma for the sterilization of a Pasteurella multocida–contaminated subcutaneously implanted foreign body in rabbits

To determine whether a stainless steel implant sterilized with a novel cold atmospheric plasma sterilization (CAPS) device adversely affects local tissues in rabbits and whether CAPS was as effective as steam sterilization with an autoclave to inactivate Pasteurella multocida. 31 healthy New Zealand White rabbits. Steam-autoclaved stainless steel implants inoculated with P multocida underwent a second steam autoclave sterilization (AIA) or CAPS (AICAPS). One AIA implant and 3 AICAPS implants were randomly placed subcutaneously at 4 sites in 21 rabbits (84 implants). These rabbits were monitored daily for 5 days for evidence of systemic illness and local tissue reactions at the implantation sites and then euthanized. Samples were taken from each implant site for bacterial culture and histologic examination. Cultures of samples obtained from all sites were negative for bacterial growth. No significant difference was observed in mean skin thickness or erythema between AIA and AICAPS implant sites on any observed day. Also, individual histologic grades for the epidermis, dermis, subcutis, and muscle and total histologic grade were not significantly different between AIA and AICAPS implant sites. Cold atmospheric plasma sterilization was noninferior to steam sterilization of P multocida-contaminated stainless steel implants in the rabbits in the present study. However, studies of the efficacy of CAPS for inactivation of other important bacteria are needed.

Experimental Studies on Physicochemical Parameters of Water Samples before and after Treatment with a Cold Atmospheric Plasma Jet and its Optical Characterization

Cold plasma-liquid interaction becomes a growing interdisciplinary area of research involving plasma physics, fluid science, and chemistry. Plasma-liquid interaction has gained more interest over the last many years due to its potential applications in different fields. Cold atmospheric plasma jet is an emerging technology for surface drinking water treatment to improve quality and surface modification that is chemical-free and eco-friendly. Cold plasma treatment of water samples results in changes in turbidity, pH, and conductivity and in the formation of reactive oxygen and nitrogen species (RONS). As a result, plasma-activated water has a different chemical composition than water and can serve as an alternative technique for microbial disinfection. CAPJ has been generated by a high voltage 5 kV and a high frequency 19.56 kHz power supply. The discharge has been characterized by an optical method. To characterize the cold atmospheric pressure argon plasma jet, discharge plume temperature, and electron rotational and vibrational temperature have been determined. Cold atmospheric argon plasma jet produced at atmospheric condition contains high energetic electrons, ions, UV radiation, reactive oxygen, and nitrogen species named as cold plasma which has a wide range of applications in the biomedical industry, as well as in water treatment. Nowadays, researches have been carried out on ozonation through plasma jet interaction with surface drinking water. In this paper, we compare the change in physical and chemical parameters of surface water used for drinking purposes. The significant change in the physical parameters such as pH, turbidity, and electrical conductivity was studied. In addition, the significant changes in the concentration and absorbance of nitrate, ferrous, and chromium ions with respect to treatment time were studied. Our results showed that plasma jet interaction with surface drinking water samples can be useful for the improvement of water quality and an indicator for which reactive species play an important role in plasma sterilization.

Resurgence of plasma sterilization: A review

Sterilization is the backbone of a health-care organization and ensures high-quality patient care. While the horizon of medical and surgical devices has undergone vast expansions, not many discoveries have been made as far as novel sterilization procedures are concerned. Steam sterilization remains the most widely used modality of sterilization of equipment to date in most health-care organizations. Its limitation lies in the fact that there are many medical and surgical devices in the market today which are heat and pressure sensitive and can be damaged by the high temperature and pressure levels of steam sterilization. Novel sterilization techniques which are helpful in the sterilization of such sensitive instruments that are being widely used today include ethylene oxide (ETO) gas sterilization and plasma sterilization. ETO sterilization requires the instruments to undergo aeration after the sterilization process, which takes a significant amount of time. Since the sterilized materials can be used only after the aeration period, stocking up of medical instruments is required which incurs extra cost and entails further investment in this regard. In the last few decades, there have also been concerns over the safety of ETO gas itself. Hence, attention has shifted to plasma sterilization which has spiked the interest of medical professionals due to both its safety and economic running costs. This article reviews the evolution of plasma sterilization along with its working principle, methods of inactivation of microorganisms, advantages, and disadvantages. A literature search using the keywords “plasma sterilization” was carried out in PubMed and Google Scholar platforms. Out of the suggestions available, the search was zeroed down to the most relevant articles and a few landmark articles, with focus on the origin of plasma sterilization as a procedure, methods of generation of gas plasma, phases of plasma sterilization, and antimicrobial properties of plasma. A review of articles comparing the efficacy of steam sterilization, ETO sterilization, and plasma sterilization was performed. Standard textbooks, as cited in the references, were referred to as required. The operation and maintenance instruction manual for low-temperature hydrogen peroxide sterilizer ACTIPLAZR model HP-3041, Hanshin Medical Co. Ltd, South Korea, 2019, was used as the primary reference when describing the working of the aforementioned model (HP-3041) of plasma sterilizer.

UV Dissociation and Calculation for O3 Gas Generated from Nonthermal Atmospheric-Pressure Biocompatible Plasma Sterilizer

UV Dissociation and Calculation for O3 Gas Generated from Nonthermal Atmospheric-Pressure Biocompatible Plasma Sterilizer

Development of a Compact Plasma Sterilization Device for Contact Lenses

Development of a Compact Plasma Sterilization Device for Contact Lenses

Monitoring the Effective Sterilization of Low-Temperature Hydrogen Peroxide Gas Plasma Sterilizers in 58 Hospitals - 22 PLADs, China, June 2015-December 2019.

What is already known on this topic?Hydrogen peroxide sterilizeation is widely used for luminal devices. However, the low penetrability of the sterilant is of major concern.What is added by this report?This report investigated the effective sterilization of low-temperature hydrogen peroxide gas plasma sterilizers and compared the applicability of different biological monitoring methods based on medical luminal devices.What are the implications for public health practice?It is recommended to use a biological process challenge device for monitoring the sterilization of luminal devices with low-temperature hydrogen peroxide gas plasma sterilizers.

Evaluation of The Performance Of Two Different Hydrogen Peroxide Gas Plasma Sterilizers in Lumenic Medical Devices

Amaç: Hidrojen peroksitin penetrasyon özelliği zayıftır. Lümenli tıbbi cihazlarda, çap ve uzunluk sınırlaması olduğundan uygunluk açısından firmaların önerileri dikkate alınmalıdır. Bu çalışmada, iki farklı Hidrojen peroksit gaz plazma (H2O2 GP) cihazının lümenli tıbbi cihazları steril etmede uzunluk ve lümen çapı açısından, etilen oksitle sterilizasyona göre bir farklarının olup olmadığının araştırılması amaçlanmıştır.
 Yöntem: Özel olarak hazırlanmış, biyolojik indikatörün her iki ucundan da gaz girişine müsaade ettiği, biyolojik validasyon kitinin içine uzunlukları ve lümen çapları birbirinden farklı polietilen lümenli cihazlar konularak polyolefin paketleme malzemesi (Tyvek 60 gr, PMS; Türkiye) içine paketlendi. Sterilizasyon koşullarının en kötü olduğu vakum çıkış noktasına yakın bir yere konularak kısa döngüde sterilizasyon işlemi yapıldı. Bu işlemler Sterrad 100S (Advanced Sterilization Products; ABD) cihazında 55 °C’de 55 dk, LK/MJG-150 (Laoken, Low Temperature and Examination Center, State Food and Drug Administration; Çin) cihazında 55°C’de 35 dk sürdü. Bu işlemler her bir uzunluk ve çap için altı kez tekrarlandı. Aynı işlemler etilen oksit sterilizatör (Steri-Vac sterilizer/aerator model 8XL;3M; ABD) için de yapıldı. Çevrim sonunda, üretici firmanın önerileri doğrultusunda tüp kırıldı ve indikatöre uygun inkübatöre yerleştirildi ve uygun sıcaklıkta inkübe edildi. İnkübasyon süresi bitiminde üreme varlığı hem görsel hem de mikrobiyolojik olarak değerlendirildi. Ayrıca her bir döngü için pozitif kontroller sterilizasyona maruz bırakılmadan kırılarak inkübatöre yerleştirildi.
 Bulgular: Bir mm lümen çaplı, 2000 mm’ye kadar uzunluktaki ve 0.55mm çaplı-800mm uzunluğundaki polietilen lümenli cihazların, her iki H2O2 GP sterilizatör ile de biyolojik indikatörlerde pozitiflik ve mikrobiyolojik olarak da üreme saptanmadı. Bununla birlikte 0.55 mm çaplı, 1000 mm uzunluğundaki polietilen lümenli cihazların sterilizasyonunda Sterrad 100 S H2O2GP (2/6) ve LK/MJG-150 H2O2 GP sterilizatörlerinde (4/6) biyolojik indikatörlerde pozitiflikler saptandı ve mikrobiyolojik olarak doğrulandı. EO ile sterilizasyon yöntemiyle ise denenen tüm lümen uzunluklarında ve çaplarında negatiflik saptandı.
 Sonuç: Biyolojik indikatör sonuçlarına göre iki farklı H2O2 GP sterilizatörünün karşılaştırıldığı çalışmamızda, her iki sterilizatör ile de yaklaşık olarak benzer sonuçlar elde edildi. Ama indikatörlerin kontrol edildikleri yükte bulunan malzemelerin steril olduklarının kanıtı olmadığı bilinmelidir. Sterilizasyon işleminin etkili olmasının, kontamine olmuş cihazların kapsamlı ve doğrulanmış bir şekilde temizlenmesi, paketleme malzemesi ve yöntemi, paketlerin sterilizatöre uygun şekilde yerleştirilmesi gibi birçok faktöre bağlı olduğu unutulmamalıdır.

Reprocessing of N95 masks: Experience from a resource-limited setting in India

ObjectivesDue to the surge in demand for N95 masks during the Covid-19 pandemic, and considering the situation in countries grappling with acute shortages of N95 masks, this study investigated the possibilities of decontamination and reuse of masks. MethodsThree N95 masks of different makes (A, B and C) were subjected to six decontamination methods: ultraviolet (UV) irradiation, isopropyl alcohol (IPA) dip, plasma sterilization (Sterrad®), ethylene oxide (ETO, 3M®), dry heat sterilization, and moist heat sterilization (autoclaving). The integrity of the N95 masks was assessed by measuring their particle filtering efficiency at particle sizes ranging 0.3–0.5 microns. ResultsAll the masks decontaminated with ETO and plasma sterilization retained over 95% particle filtering efficiency. Masks decontaminated using IPA dip and autoclaving showed a drop, and UV irradiation showed variations in particle size efficiency degradation after decontamination. ConclusionsPlasma sterilization is recommended for decontamination of N95 masks in low-resource settings. ETO is not recommended due to hazards associated with handling of ethylene oxide, although the filtering efficiency was retained. Since the UV irradiation method showed variations in results, evaluation of UV decontamination for N95 masks needs to be performed on a case-by-case basis.

Geometric accuracy of an acrylonitrile butadiene styrene canine tibia model fabricated using fused deposition modelling and the effects of hydrogen peroxide gas plasma sterilisation

BackgroundThree-dimensional (3D) printing techniques have been used to produce anatomical models and surgical guiding instruments in orthopaedic surgery. The geometric accuracy of the 3D printed replica may affect surgical planning. This study assessed the geometric accuracy of an acrylonitrile butadiene styrene (ABS) canine tibia model printed using fused deposition modelling (FDM) and evaluated its morphological change after hydrogen peroxide (H2O2) gas plasma sterilisation. The tibias of six canine cadavers underwent computed tomography for 3D reconstruction. Tibia models were fabricated from ABS on a 3D printer through FDM. Reverse-engineering technology was used to compare morphological errors (root mean square; RMS) between the 3D-FDM models and virtual models segmented from original tibia images (3D-CT) and between the models sterilised with H2O2 gas plasma (3D-GAS) and 3D-FDM models on tibia surface and in cross-sections at: 5, 15, 25, 50, 75, 85, and 95% of the tibia length.ResultsThe RMS mean ± standard deviation and average positive and negative deviation values for all specimens in EFDM-CT (3D-FDM vs. 3D-CT) were significantly higher than those in EGAS-FDM (3D-GAS vs. 3D-FDM; P < 0.0001). Mean RMS values for EFDM-CT at 5% bone length (proximal tibia) were significantly higher than those at the other six cross-sections (P < 0.0001). Mean RMS differences for EGAS-FDM at all seven cross-sections were nonsignificant.ConclusionsThe tibia models fabricated on an FDM printer had high geometric accuracy with a low RMS value. The surface deviation in EFDM-CT indicated that larger errors occurred during manufacturing than during sterilisation. Therefore, the model may be used for surgical rehearsal and further clinically relevant applications in bone surgery.Graphical abstract

Inactivation of Infectious Bacteria Using Nonthermal Biocompatible Plasma Cabinet Sterilizer.

Nonthermal, biocompatible plasma (NBP) is a promising unique state of matter that is effective against a wide range of pathogenic microorganisms. This study focused on a sterilization method for bacteria that used the dielectric barrier discharge (DBD) biocompatible plasma cabinet sterilizer as an ozone generator. Reactive oxygen species play a key role in inactivation when air or other oxygen-containing gases are used. Compared with the untreated control, Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Salmonella typhimurium (sepsis) were inhibited by approximately 99%, or were nondetectable following plasma treatment. Two kinds of plasma sterilizers containing six- or three-chamber cabinets were evaluated. There was no noticeable difference between the two configurations in the inactivation of microorganisms. Both cabinet configurations were shown to be able to reduce microbes dramatically, i.e., to the nondetectable range. Therefore, our data indicate that the biocompatible plasma cabinet sterilizer may prove to be an appropriate alternative sterilization procedure.

Innovative solutions for prehistoric paintings - atmospheric pressure plasma and phosphate consolidant for the preservation of the Magura Cave (Bulgaria)

The present study tackles the problem of a sustainable and efficient conservation of cave art, by using innovative materials and techniques for the different steps of the restoration process - Biodeactivation, Biocolonization prevention and Consolidation. The Magura cave in northwest Bulgaria is the case study. It contains an impressive display of prehistoric paintings made of guano as far back as 5’500 years ago. In the last forty years the cave suffered progressive microbial colonization. The detrimental effects are biofilm formation, physical penetration into the stone and chemical reaction with the stone/paintings by pigments. Therefore, as a first step, we investigated biodeactivation by non-thermal plasma sterilization. The oxidative atmosphere obtained introducing Ar/O2 (0.2 and 0.1) in the plasma device, was carried out on lab samples inoculated with the targeted for Magura Cave microorganisms. The main advantage of the non-contact treatment with atmospheric pressure plasma (APP) is the lack of any mechanical and chemical modification of the underlying stone/guano layers. As for sterilization of wounds on human skin the plasma treatment on wet surfaces produces mainly hydrogen peroxide and nitrates which lead to a localized reduction of the pH. The obtained biodeactivation is assured without heat (< 40 °C), toxic and environmentally harmful liquid. In a second step, we tested two possible alternatives for consolidation of the cave. A commercial ethyl silicate (ES) product was compared with an innovative phosphate treatment, based on application of a hydro-alcoholic solution of a phosphate salt (diammonium hydrogen phosphate, DAP). The consolidation efficiency and compatibility of the ES and DAP consolidants were investigated on samples representative for the Magura Cave substrate, i.e. stone alone and stone covered with guano to resemble the prehistoric drawings. In addition, a combination of plasma activation of the stone surface and consolidation was tested, to investigate whether the two treatments may have a synergistic effect, thus making the combined treatment more efficient than consolidation alone.

Subcellular mechanism of microbial inactivation during water disinfection by cold atmospheric-pressure plasma

Although the identification of effective reactive oxygen species (ROS) generated by plasma has been extensively studied, yet the subcellular mechanism of microbial inactivation has never been clearly elucidated in plasma disinfection processes. In this study, subcellular mechanism of yeast cell inactivation during plasma-liquid interaction was revealed in terms of comprehensive factors including cell morphology, membrane permeability, lipid peroxidation, membrane potential, intracellular redox homeostasis (intracellular ROS and H2O2, and antioxidant system (SOD, CAT and GSH)), intracellular ionic equilibrium (intracellular H+ and K+) and energy metabolism (mitochondrial membrane potential, intracellular Ca2+ and ATP level). The ROS analysis show that ·OH, 1O2, ·O2−and H2O2 were generated in this plasma-liquid interaction system and ·O2−served as the precursor of 1O2. Additionally, the solution pH was reduced. Plasma can effectively inactivate yeast cells mainly via apoptosis by damaging cell membrane, intracellular redox and ion homeostasis and energy metabolism as well as causing DNA fragmentation. ROS scavengers (l-His, d-Man and SOD) and pH buffer (phosphate buffer solution, PBS) were employed to investigate the role of five antimicrobial factors (·OH, 1O2, ·O2−, H2O2 and low pH) in plasma sterilization. Results show that they have different influences on the aforementioned cell physiological activities. The ·OH and 1O2 contributed most to the yeast inactivation. The ·OH mainly attacked cell membrane and increased cell membrane permeability. The disturb of cell energy metabolism was mainly attributed to 1O2. The damage of cell membrane as well as extracellular low pH could break the intracellular ionic equilibrium and further reduce cell membrane potential. The remarkable increase of intracellular H2O2 was mainly due to the influx of extracellular H2O2 via destroyed cell membrane, which played a little role in yeast inactivation during 10-min plasma treatment. These findings provide comprehensive insights into the antimicrobial mechanism of plasma, which can promote the development of plasma as an alternative water disinfection strategy.

Design of a Switching Flyback Transformer as High Voltage and Frequency Power Supply for Raw Milk Cold Plasma Sterilization

Plasma is one of the four fundamentals states of matter other than solid, liquid and gas. In terms of temperature, plasma can be classified into Hot Plasma occurs in thermal equilibrium, Thermal Plasma occurs in non-thermal equilibrium, Cold Plasma occurs in non-thermal equilibrium Cold plasma is an ultra-fast method of sterilization that operates under ambient temperatures (ideal for thermolabile products) at a low running cost and is environment-friendly. Therefore, technology is needed to solve the problem through the innovation of a milk sterilization machine with the principle of non-thermal plasma sterilization by utilizing plasma technology to reduce microbial contamination. The output frequency and voltage are determined through software simulation using voltmeter, oscilloscope, and counter timer. After 220VAC supplies a voltage step down and rectifier circuit to produce a 12VDC output voltage to supply the Switching circuit voltage and the Flyback Transformer driver. Rated voltage and frequency reach 20kV 15kHz.The positive wire from the Flyback Transformer is connected to the acrylic box filled with water (positive electrode) and the ground wire is connected to another acrylic sheet (ground electrode. The milk medium to be sterilized can be placed on the positive electrode or between the ground and positive electrodes. Non-thermal plasma has an effective ability to decontaminate bacteria. This is because plasma is composed of a mixture of ionized particles, reactive radical molecules, and also ultraviolet Schematic circuit design has been successfully simulated. Acrylic sterilization media designs can be used to generate plasma. The mechanism of bacterial sterilization in milk is by the activity of inhibiting bacterial biofilms which can lead to bacterial DNA damage through reactive species in the non-thermal plasma used. Milk quality testing is carried out based on comparison of supporting literature with milk quality requirements according to SNI 3950: 2014.