Microwave-assisted Sterilization Research Articles

An Experimental Analysis of Five Household Equipment-Based Methods for Decontamination and Reuse of Surgical Masks.

The current coronavirus pandemic has increased worldwide consumption of individual protective devices. Single-use surgical masks are one of the most used devices to prevent the transmission of the COVID-19 virus. Nevertheless, the improper management of such protective equipment threatens our environment with a new form of plastic pollution. With the intention of contributing to a responsible policy of recycling, in the present work, five decontamination methods for used surgical masks that can be easily replicated with common household equipment are described. The decontamination procedures were hot water at 40 °C and 80 °C; autoclave; microwave at 750 W; and ultraviolet germicidal irradiation. After each decontamination procedure, the bacterial load reduction of Staphylococcus aureus ATCC 6538 was recorded to verify the effectiveness of these methods and, moreover, bacterial filtration efficiency and breathability tests were performed to evaluate mask performances. The best results were obtained with the immersion in 80 °C water and the microwave-assisted sterilization. Both methods achieved a high degree of mask decontamination without altering the filtration efficiency and breathability, in accordance with the quality standard. The proposed decontamination methods represent a useful approach to reduce the environmental impact of this new waste material. Moreover, these procedures can be easily reproduced with common household equipment to increase the recycling efforts.

Designing thinner wall ethylene-vinyl alcohol copolymer and polypropylene-based semi-rigid trays for microwave-assisted thermal sterilization and pasteurization processes

Abstract The goal of this research was to design a thinner wall tray for microwave-assisted thermal processing technologies. Three-layer (PP//EVOH//PP) sheets of different EVOH- and PP-layer thicknesses were coextruded. The sheets were then thermoformed into 8-oz trays with dimensions of 150 × 100 × 50 mm (L × W×D). Trays were filled with model foods and subjected to conventional and microwave-assisted pasteurization and sterilization processes. Barrier and mechanical properties were assessed before and after processing. Oxygen ingress, weight loss, and color kinetics were measured over a storage period of 3–6 months at 7, 23, and 37 °C. The newly-designed trays showed comparable or better performance in terms of O2 ingress and weight loss, with a 24 % reduction in wall thickness. Therefore, thinner EVOH and PP-based trays hold promise for use in microwave-assisted sterilization and pasteurization processes. This will result in a reduced carbon footprint and provide more economical alternatives to other forms of packaging that are currently available.

Effect of changes in microwave frequency on heating patterns of foods in a microwave assisted thermal sterilization system

This research studied the influence of frequency variation on heating patterns within prepackaged foods in a 915MHz single-mode microwave assisted sterilization (MATS) system consisting of four microwave heating cavities. The frequencies of the four generators powering the MATS system at Washington State University were measured at different power levels over one year. The effect of frequency shifts in the generators on heating patterns within a model food (whey protein gel, WPG) was studied through computer simulation. The simulated heating patterns were experimentally validated using a chemical marker. Our measurement results showed that a 0.5kW increase in the microwave power caused the operating frequencies of the generators to increase by 0.25–0.75MHz. The simulation results suggested that the heating pattern of WPG processed by the MATS system was not affected by the varying frequencies of generators within the operating frequency bandwidth (900–920MHz). In addition, the simulation results revealed that using deionized water as the circulation medium in the MATS system resulted in a 23–37% increase in the temperature of WPG as compared with that when using normal tap water, but did not alter the heating pattern.

Using mobile metallic temperature sensors in continuous microwave assisted sterilization (MATS) systems

The goal of this study was to evaluate suitability of using mobile metallic temperature sensors in continuous microwave assisted sterilization (MATS) systems. A computer simulation model using the finite difference time domain method was developed to study the influence of microwave field on the accuracy of mobile metallic temperature sensors, ELLAB, in a MATS system in which food packages with embedded sensors traveled on a conveyor belt. Simulation results indicated that the metallic temperature sensors did not change the overall heating patterns within food samples. But when a metallic temperature sensor was placed in parallel to the electric field component within microwave cavities the field intensity had intense singularity at the sensor tip and caused localized overheating. The electric field singularity adjacent to the tip of the metallic temperature sensor can be avoided by placing the sensor perpendicular to the electric field component. The simulated heating patterns and temperature profiles were verified with experimental results. It was evident from both simulated and experimental results that the metallic temperature sensor could be used to capture temperature profile in a MATS system when placed in a suitable orientation.