Effect of Power Levels on Inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in Tomato Paste Using 915-Megahertz Microwave and Ohmic Heating

Inactivation of foodborne pathogens in ground pork tenderloin using 915 MHz microwave heating depending on power level

The main purpose of this research was to investigate the effect of power level of 915 MHz microwave heating on the inactivation of foodborne pathogens in ground pork and its bactericidal mechanism. It was demonstrated that the heating rate was proportional to the power level. For instance, the heating rates observed at microwave heating powers of 2, 3, 4, and 5 kW were 1.70, 2.77, 3.35, and 4.03℃/s, respectively. The bactericidal effect of microwave heating also significantly (P < 0.05) increased with increasing power level. In particular, when ground pork was subjected to microwave heating at 5 kW, the reduction level of pathogens was>2 log units higher than at 2 kW. To determine the bactericidal mechanism of microwave heating depending on power level, changes in transmembrane potential and DNA damage were determined using fluorescence. The extent of depolarization in membrane potential of pathogens significantly (P < 0.05) increased as power level increased. There was no significant difference in degree of DNA damage at different power levels. However, the percentage of DNA damage was>86% at all power levels. The transmembrane potential assay indicates that the bacteria exhibited dramatic pore formation on the membrane at 5 kW. Through transmission electron microscopy, the electroporation effect was enhanced as power level increased. Moreover, the quality of ground pork subjected to microwave heating at 2-5 kW was determined by measuring the moisture content, cooking loss, and texture profile.

Recent trends in bacterial decontamination of food products by hurdle technology: A synergistic approach using thermal and non-thermal processing techniques

Researchers are continuously discovering varied technologies for microbial control to ensure worldwide food safety from farm-to-fork. The microbial load and virulence of spoilage causing microorganisms, including bacteria, fungi, yeasts, virus, and protozoa, determines the extent of microbial contamination in a food product. Certain pathogenic microbes can cause food poisoning and foodborne diseases, and adversely affect consumers' health. To erade such food safety-related problems, various traditional and novel food processing methods have been adopted for decades. However, some decontamination techniques bring undesirable changes in food products by affecting their organoleptic and nutritional properties. Combining various thermal and non-thermal food processing methods is an effective way to impart a synergistic effect against food spoilage microorganisms and can be used as an alternative way to combat certain limitations of food processing technologies. The combination of different techniques as hurdles put the microorganisms in a hostile environment and disturbs the homeostasis of microorganisms in food temporarily or permanently. Optimization and globalization of these hurdle combinations is an emerging field in the food processing sector. This review gives an overview of recent inventions in hurdle technology for bacterial decontamination, combining different thermal and non-thermal processing techniques in various food products.

Ohmic Heating in the Food Industry: Developments in Concepts and Applications during 2013–2020

Various technologies have been evaluated as alternatives to conventional heating for pasteurization and sterilization of foods. Ohmic heating of food products, achieved by passage of an alternating current through food, has emerged as a potential technology with comparable performance and several advantages. Ohmic heating works faster and consumes less energy compared to conventional heating. Key characteristics of ohmic heating are homogeneity of heating, shorter heating time, low energy consumption, and improved product quality and food safety. Energy consumption of ohmic heating was measured as 4.6–5.3 times lower than traditional heating. Many food processes, including pasteurization, roasting, boiling, cooking, drying, sterilization, peeling, microbiological inhibition, and recovery of polyphenol and antioxidants have employed ohmic heating. Herein, we review the theoretical basis for ohmic treatment of food and the interaction of ohmic technology with food ingredients. Recent work in the last seven years on the effect of ohmic heating on food sensory properties, bioactive compound levels, microbial inactivation, and physico-chemical changes are summarized as a convenient reference for researchers and food scientists and engineers.

Disposal of the large volume of sputum positive for Mycobacterium tuberculosis by using microwave sterilisation technology as an alternative to traditional autoclaving in a tertiary respiratory care hospital in Delhi, India

Background

Everyday, tuberculosis hospitals collect enormous amount of sputum containing viable Mycobacterium tuberculosis bacilli, the disposal of which is a challenging task. Chemical (5% phenol) and physical (autoclaving) disinfection methods involve cost, space and cause further environmental degradation. Over the years, use of microwave for sterilisation of biomedical waste has become widespread. However, its efficacy to sterilise large volume of M. tuberculosis positive sputum has never been investigated.

Aim

To evaluate the effectiveness of microwave in sterilising large volumes of M. tuberculosis positive sputum samples.

Methods

226 sputum samples positive for M. tuberculosis were checked by Ziehl-Neelsen staining and liquid culture (MGIT ™) both before and after microwaving. χ² test was performed, and p-value <0.05 was considered significant.

Findings

Before microwaving, samples containing acid fast bacilli (AFB) and live M. tuberculosis bacilli were 93.8% and 95% (≈94.7%) respectively; which came down to 14.2% (32) and <1% (≈0.9%) in post microwave. In the 32 post-microwave AFB positive samples, bacilli appeared apoptotic, decreased in size, fragmented, loosely arranged and were easily missed as stain artefacts. Their beaded appearance was not appreciable. Background pus cells were of smaller size, did not take up methylene blue stain properly, and multilobed nuclear material was missing.

Conclusion

The study shows efficacy of microwave as an alternative sterilisation method for large volume sputum samples containing M. tuberculosis bacilli. Microwave can become an effective sterilisation method, especially for isolated tuberculosis care centres in countries which struggle for disposal of sputum, the biomedical waste.

Mathematical modeling of ohmic heating for inactivation of acid-adapted foodborne pathogens in tomato juice

The objective of the present study was to predict the inactivation trends of acid-adapted foodborne pathogens in tomato juice by ohmic heating through a numerical analysis method. The mathematical model based on finite element method (FEM) was used to simulate the multiphysics phenomena including electric heating, heat transfer, fluid dynamics, and pathogen inactivation. A cold spot was observed in the corner part of the ohmic heating chamber, where some pathogens survived even though all pathogens were inactivated elsewhere. Challenges of this study were how to reflect the increased resistance of pathogen by acid-adaptation. After simulation, we verified that inactivation level of acid-adapted foodborne pathogens by 25 Vrms/cm ohmic heating (1 kHz), predicted with the developed mathematical model, had no significant differences with experimental results (p > 0.05). Therefore, the mathematical approaches described in the present study will help juice processors determine the processing conditions necessary to ensure microbial safety at the cold point of a rectangular type batch ohmic heater.

Lactobacillus plantarum 5BG Survives During Refrigerated Storage Bio-Preserving Packaged Spanish-Style Table Olives (cv. Bella di Cerignola)

This paper proposes bio-preservation as a tool to assure quality and safety of Spanish-style table olives cv. Bella di Cerignola. Lactobacillus plantarum 5BG was inoculated in ready to sell olives packaged in an industrial plant by using a half-volume brine (4% NaCl; 2% sucrose). The samples were stored at 4°C. The survival of the inoculated strain, the microbiological quality, the sensory scores and the survival of a strain of Listeria monocytogenes inoculated in brines were evaluated. The persistence of the Lb. plantarum bio-preserving culture was confirmed on olives (≥6.5 Log CFU/g) and in brine (≥7 Log CFU/ml). Bio-preserved olives (SET1) showed a better sensory profile than chemically acidified control olives (SET2) and the texture was the real discriminative parameter among samples. Bio-preserved olives recorded better scores during storage because of their ability to retain good hardness, crunchiness, and fibrousness without cracks. The inoculation of Lb. plantarum positively acted on the safety of olives, as the D-value of L. monocytogenes was reduced from 40 (SET2) to 5 days (SET1). In conclusion, Lb. plantarum 5BG and the physico-chemical conditions achieved in the settled procedure are suitable for the industrial packaging of Bella di Cerignola table olives, improving the process by halving brining volumes and avoiding chemical stabilizers, and significantly reducing the salt concentration. The final product is also safely preserved for almost 5 months as suggested by the reduction of the survival rate of L. monocytogenes.