Synergistic effect of ohmic heating and UV-C irradiation for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in buffered peptone water and tomato juice

Control of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes inoculated in beetroot or watermelon juice by combined treatments with organic acid or lemon (Citrus limon) extract and mild heat

The study aimed to evaluate the synergistic interaction of organic acids (OAAs) or lemon extract (LE) plus mild heat (MH; 55 °C) against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes inoculated in beetroot and watermelon juices. A mixed culture cocktail of E. coli O157:H7, S. Typhimurium or L. monocytogenes was inoculated in beetroot or watermelon juice, followed by treatments with MH, citric acid + MH, malic acid + MH, tartaric acid + MH, and LE + MH. Approximately < 2.0-log reductions in the number of E. coli O157:H7, S. Typhimurium, and L. monocytogenes were observed when these bacteria were heated in juices at 55 °C for 5 min. A combination of 1.0% OAAs or 20% LE and MH (55 °C) for 5 min resulted in an additional log-reduction in the count of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 2.2-5.0, 4.5-5.0, and 1.5-5.0, respectively.

Bactericidal efficacy of plasma-activated water against Vibrio parahaemolyticus on Litopenaeus vannamei

In this study, the antimicrobial mechanism of plasma-activated water (PAW) against Vibrio parahaemolyticus and the effectiveness of PAW in artificially contaminated Litopenaeus vannamei were investigated. The results demonstrated a significant reduction (p < 0.05) in viable counts of V. parahaemolyticus with increasing plasma discharge time (5, 10, 20, and 30 min) and PAW immersion time (3, 5, 10, 20, and 30 s). Specifically, the count of V. parahaemolyticus decreased by 2.1, 2.7, 3.3, and 4.4 log CFU/mL after exposed to PAW 5, PAW 10, PAW 20, and PAW 30 for 30 s, respectively. Significant cell surface wrinkling, accompanied by notable nucleic acid and protein leakage were observed after treatment with PAW. The permeability of the inner and outer cell membranes was significantly increased (p < 0.05), along with an increase in electrical conductivity (p < 0.05). The reactive oxygen species (ROS) within V. parahaemolyticus cells were significantly increased (p < 0.05), while superoxide dismutase (SOD) activity, and the relative expression of the ompW, emrD, and luxS genes were significantly decreased (p < 0.05). A reduction number of 1.3, 1.8, 2.1, and 2.2 log CFU/g of V. parahaemolyticus in artificially contaminated L. vannamei was obtained with PAW for 5 min. The study elucidated that PAW could destroy cell membranes, leading to cell death. The findings would strengthen strategies for V. parahaemolyticus control and provide a potential application of PAW for preserving aquatic products.

Effect of Optimized UV-LED Technology on Modeling, Inactivation Kinetics and Microbiological Safety in Tomato Juice

This research analyzed, optimized and modeled the inactivation kinetics of pathogenic bacteria (PB1: Escherichia coli O157:H7 and PB2: Listeria monocytogenes) and determined the microbiological safety of tomato juice processed by UV-LED irradiation and heat treatment. UV-LED processing conditions were optimized using response surface methodology (RSM) and were 90% power intensity, 21 min and 273-275 nm (251 mJ/cm2) with R2 > 0.96. Using the optimal conditions, levels of PB1 and PB2 resulted a log reduction of 2.89 and 2.74 CFU/mL, respectively. The Weibull model was efficient for estimating the log inactivation of PB1 and PB2 (CFU/mL). The kinetic parameter δ showed that 465.2 mJ/cm2 is needed to achieve a 90% log (CFU/mL) reduction in PB1 and 511.3 mJ/cm2 for PB2. With respect to the scale parameter p > 1, there is a descending concave curve. UV-LED-treated tomato juice had an 11.4% lower Listeria monocytogenes count than heat-treated juice on day 28 (4.0 ± 0.82 °C). Therefore, UV-LED technology could be used to inactivate Escherichia coli O157:H7 and Listeria monocytogenes, preserving tomato juice for microbiological safety, but studies are required to further improve the inactivation of these pathogens and analyze other fruit and vegetable juices.

UV-C Light: A Promising Preservation Technology for Vegetable-Based Nonsolid Food Products

A variety of bioactive substances present in fruit- and vegetable-processed products have health-promoting properties. The consumption of nutrient-rich plant-based products is essential to address undernutrition and micronutrient deficiencies. Preservation is paramount in manufacturing plant-based nonsolid foods such as juices, purees, and sauces. Thermal processing has been widely used to preserve fruit- and vegetable-based products by reducing enzymatic and microbial activities, thereby ensuring safety and prolonged shelf life. However, the nutritional value of products is compromised due to the deleterious effects of thermal treatments on essential nutrients and bioactive compounds. To prevent the loss of nutrients associated with thermal treatment, alternative technologies are being researched extensively. In studies conducted on nonsolid food, UV-C treatment has been proven to preserve quality and minimize nutrient degradation. This review compiles information on the use of UV-C technology in preserving the nutritional attributes of nonsolid foods derived from fruit and vegetables. The legislation, market potential, consumer acceptance, and limitations of UV-C are reviewed.

Simultaneous vacuum ultra violet-amalgam lamp radiation and near-infrared radiation heating for a synergistic bactericidal effect against Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in black peppercorn

This study evaluated the effect of simultaneous irradiation with vacuum ultraviolet (VUV)-amalgam lamp and near-infrared radiation (NIR) to inactivate foodborne pathogens in black peppercorn (Piper nigrum) while monitoring its piperine content and color. NIR treatment for 20 min caused an increase in black peppercorn temperature to 70 °C, and its bactericidal effect showed only 3.14 and 1.88 log reductions of Escherichia coli O157:H7 and Salmonella Typhimurium respectively. Single treatment with a VUV-amalgam lamp for 20 min achieved 2.26 and 1.55 log reductions of E. coli O157:H7 and S. Typhimurium, respectively. However, simultaneous treatment for 15 min produces a greater than 5-log reduction of both foodborne pathogens without changes of black peppercorn quality. The underlying bactericidal mechanism of the VUV-amalgam lamp is 254 nm irradiation with ozone generated by 185 nm irradiation. The ozone concentration was maintained with VUV-amalgam lamp single treatment but decreased during simultaneous treatment. In contrast, due to the drying effect of NIR irradiation, water vapor reacts with 185 nm irradiation or ozone to produce a variety of reactive oxygen species (ROS) such as hydrogen peroxide and hydroxyl radical during simultaneous treatment. The hydrogen peroxide concentration measured by Gastec increased during simultaneous treatment. We also investigated various generated types of ROS that can contribute to a synergistic bactericidal effect. We compared the bactericidal effect of sequential and simultaneous treatments with NIR and VUV-amalgam lamps to black peppercorn. Although sequential treatment showed additional inactivation efficacy, reductions of pathogens were significantly lower than with simultaneous treatment. These findings suggest that simultaneous VUV-amalgam lamp and NIR irradiation treatment via generation of ROS can increase bacterial inactivation efficacy of foodborne pathogens in black peppercorns without quality changes.

Inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on stainless steel by synergistic effects of tap water-based neutral electrolyzed water and lactic acid

Contaminated food contact surface is one of the most important transmission routes for foodborne pathogens. Stainless steel is one such food-contact surface that is widely used in food-processing environments. The present study aimed to evaluate the synergistic antimicrobial efficacy of a combination of tap water-based neutral electrolyzed water (TNEW) and lactic acid (LA) against the foodborne pathogens Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on stainless steel. The results revealed that simultaneous treatment with TNEW (ACC of 4.60 mg/L) and 0.1% LA (TNEW-LA) for 5 min resulted in 4.99-, 4.34-, and >5.4- log CFU/cm² reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes on stainless steel, respectively. Of these, 4.00-, 3.57-, and >4.76-log CFU/cm² reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively were exclusively attributed to the synergistic action of the combined treatments after factoring out the reductions due to individual treatments. Furthermore, five mechanistic investigations revealed that the key mechanisms underlying the synergistic antibacterial effect of TNEW-LA were reactive oxygen species (ROS) production, cell membrane damage resulting from membrane lipid oxidation, DNA damage, and inactivation of intracellular enzymes. Overall, our findings suggest that the TNEW-LA combination treatment could be effectively used in the sanitization of food processing environments, especially the food contact surfaces, to control major pathogens and enhance food safety.

Dual-wavelength light radiation for synergistic water disinfection

Development of the narrow-band mercury-free light sources, such as light emitting diodes (LEDs) and excilamps, has stimulated research on inactivation of pathogenic microorganisms by dual-wavelength light radiation. To date, dual-wavelength light radiation has emerged as an advanced tool for enhancing microbial inactivation in water in view of potential synergistic effect. This is the first review that aims at elucidating its mechanisms under dual-wavelength light exposure and surveying a body of related literature in terms of yes-or-no synergy. We have proposed three key inactivation mechanisms, which function in the estimated spectrum ranges I (190-254 nm), II (250-320 nm) and III (300-405 nm) and provide a synergistic effect when combined. These mechanisms involve proteins damage and DNA repair suppression (I), direct and indirect DNA damage (II) and generation of reactive oxygen species (ROS) by endogenous photosensitizers (III), such as porphyrins and flavins. A synergy under dual-wavelength light irradiation simultaneously or sequentially occurs if coupling two wavelengths of different ranges (I + II, I + III, II + III) in order to trigger different inactivation mechanisms. Recent advances of dual-wavelength light strategy in photodynamic therapy could be applied for water disinfection. They bring opportunities for applying the sources of near-UV and visible radiation and making the disinfection processes more energy- and cost-effective. From this standpoint, the synergistically efficient dual-wavelength combinations II + III and the combinations within the extended to 700 nm range III (near-UV + VIS) appear to be promising for developing novel advanced oxidation processes for disinfection of real turbid waters.

The application of photodynamic inactivation to microorganisms in food

Nowadays, food safety issues have drawn increased attention due to the continual occurrence of infectious diseases caused by foodborne pathogens, which is an important factor causing food safety hazard. Meanwhile, the emergence of an increasing number of antibiotic-resistant pathogens is a worrisome phenomenon. Therefore, it is imperative to find new technologies with low-cost to inactivate pathogenic microorganisms and prevent cross-contamination. Compared with traditional preservatives, photodynamic inactivation (PDI) has emerged as a novel and promising strategy to eliminate foodborne pathogens with advantages such as non-toxic and low microbial resistance, which also meets the demand of current consumers for green treatment. Over the past few years, reports of using this technology for food safety have increased rapidly. This review summarizes recent progresses in the development of photodynamic inactivation of foodborne microorganisms. The mechanisms, factors influencing PDI and the application of different photosensitizers (PSs) in different food substrates are reviewed.

Effect of 405-nm light-emitting diode on environmental tolerance of Cronobacter sakazakii in powdered infant formula

Cronobacter sakazakii is an opportunistic pathogen that can survive extreme desiccation, heat, acid, and osmotic stress. This can increase the risk of infection, resulting in severe diseases, mainly in neonates. The inactivation effect of 405 ± 5-nm light-emitting diode (LED) illumination on C. sakazakii with different initial concentrations and C. sakazakii strains isolated from powdered infant formula (PIF) and baby rice cereal (BRC) were firstly evaluated. Then, the effect of 405 ± 5-nm LED on the tolerance of diverse environmental conditions of C. sakazakii in PIF was investigated. Conditions involving desiccation [PIF, Water activity (a_w): 0.2-0.5], heat (45, 50, and 55 °C), acid (simulated gastric fluid: SGF, pH 4.75 ± 0.25), and bile salt (0.2%, bile salt solution) were used to study the effects of 405-nm LED on C. sakazakii resistance. The transcription levels of ten tolerance-associated genes and changes in bacterial cell membrane were examined to understand the response of C. sakazakii to LED illumination. The results showed that 405-nm LED effectively inactivated C. sakazakii ATCC 29544 with initial concentration from 8 to 1 log CFU/g in PIF and strains isolated from PIF and BRC. Moreover, 405-nm LED could decrease the tolerance of C. sakazakii in PIF to desiccation, heat treatment at 50 and 55 °C, SGF, and bile salt to different degrees, but the resistance to the heat treatment at 45 °C was not influenced by LED illumination. In addition, the transcription levels of the ten tolerance-associated genes measured in the LED-illuminated C. sakazakii cells were significantly downregulated compared with those in unilluminated controls. The damage on cell membrane was confirmed for LED-treated cells by LIVE/DEAD® assay. These results indicate that 405-nm LED illumination may be effective at reducing the environmental resistance of C. sakazakii in PIF. Furthermore, this study suggests the potential for applying 405-nm LED technology in the prevention and control of pathogens in food processing, production, and storage environments.

Inactivation effects and mechanisms of plasma-activated water combined with sodium laureth sulfate (SLES) against Saccharomyces cerevisiae

The present study aimed to elucidate the antifungal effect and underlying mechanism of plasma-activated water (PAW) combined with sodium laureth sulfate (SLES) against Saccharomyces cerevisiae. S. cerevisiae, initially at 6.95 log₁₀ colony-forming unit (CFU)/mL, decreased to an undetectable level following the synergistic treatment of PAW and SLES (0.50 mg/mL) for 20 min. After PAW treatment combined with SLES (2.5 mg/mL) for 30 min, the S. cerevisiae cells on polyethylene films also reduced to an undetectable level from the initial load of 5.84 log₁₀ CFU/cm². PAW + SLES treatment caused severe disruption of membrane integrity and increased lipid oxidation within the cell membrane and the intracellular reactive oxygen species levels in S. cerevisiae cells. Besides, the disruption of the mitochondrial membrane potential (∆ψm) was also observed in S. cerevisiae cells after treatment of PAW and SLES at 0.01 mg/mL for 5 min. These data suggest that the combined treatment of PAW and SLES causes oxidation injury to cell membranes and abnormal ∆ψm in S. cerevisiae, which may be eventually responsible for cell death. This study demonstrates the potential application of PAW combined with SLES as an alternative disinfection method. Key Points • PAW + SLES exhibited synergistic antifungal activity against S. cerevisiae. • PAW + SLES resulted in severe disruption of membrane integrity and permeability. • PAW + SLES induced accumulation of reactive oxygen species in S. cerevisiae cells.

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.

Inactivation of Escherichia coli, Salmonella enterica serovar Typhimurium, and Bacillus cereus in roasted grain powder by radio frequency heating

AIMS

The objective of this study was to evaluate the antimicrobial effects of radio frequency (RF) heating and the combination treatment of RF heating with ultraviolet (UV) radiation against foodborne pathogens in roasted grain powder (RGP).

METHODS AND RESULTS

Foodborne pathogens inoculated on RGP were subjected to RF heating or RF-UV combination treatments. After 120 s of RF heating, 4·68, 3·89 and 4·54 log reductions were observed for Escherichia coli, Salmonella Typhimurium and Bacillus cereus vegetative cells respectively. The combined RF-UV treatment showed synergistic effects of over 1 log unit compared to the sum of individual treatment for E. coli and S. Typhimurium, but not for B. cereus vegetative cells because of their high UV resistance. Germinated B. cereus cells were not significantly inactivated by RF heating (<1 log CFU per gram), and increased heat resistance compared to the vegetative cells was verified with mild heat treatment. The colour of RGP was not significantly affected by the RF or RF-UV treatments.

CONCLUSIONS

Applying RF heating to grain-based food products has advantages for the inactivation of E. coli and S. Typhimurium in RGP.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of the present study could be used as a basis for determining the treatment conditions for inactivating E. coli and other foodborne pathogens such as S. Typhimurium and B. cereus in RGP.