Ultrasound improves the decontamination effect of thyme essential oil nanoemulsions against Escherichia coli O157: H7 on cherry tomatoes

A novel synthesized Vanillin-Based Deep Eutectic Agent (V-DEA) mitigates postharvest fungal decay and improve shelf life and quality of cherry tomatoes

Fusarium oxysporum and Botrytis cinerea are the main pathogens that cause fruit decay and reduce the postharvest shelf life of cherry tomatoes. Boosting the potency of natural products requires implementing structural modification to combat postharvest pathogens. Herein, we developed a novel Vanillin-Deep Eutectic Agent (V-DEA) from natural compounds and evaluated its effectiveness against tomato fruit rot pathogens. The results demonstrated that V-DEA suppressed mycelium growth and spore germination of F. oxysporum and B. cinerea by enhancing cell membrane permeability, increasing lipid peroxidation, and inhibiting enzyme activities. Importantly, using 8-mM V-DEA successfully prevented postharvest decay in cherry tomatoes, while 4-mM significantly extended their shelf life by reducing weight loss and shriveling, and enhancing key fruit qualities such as total soluble solids, ascorbic acid, tartaric acid, and lycopene. In conclusion, V-DEA exhibits dual properties as a potent pathogen inhibitor and antioxidant activity, thus prolonging the shelf life of cherry tomatoes.

Multimode ultrasonic-assisted decontamination of fruits and vegetables: A review

Fruits and vegetables (F&V) are a significant part of our diet consumption. Microbial and pesticide residues are the predominant safety hazards of F&V consumption. Ordinary water washing has a very limited effect on removing microorganisms and pesticide residues and requires high water usage. Ultrasound, as an environmentally friendly technology, shows excellent potential for reducing microbial contamination and pesticide residue. This paper summarizes the research on ultrasound application in F&V washing, including the removal of microbial and pesticide residues and the comprehensive effect on their physicochemical characteristics. Furthermore, multimode ultrasonic-assisted techniques like multi-frequency and sequential ultrasound, combined with novel and conventional methods, can enhance the ultrasound-based effect and be more effective and sustainable in preventing F&V from microbial contamination. Overall, this work explicitly establishes the background on the potential for ultrasound cleaning and disinfection in the food industry as a green, effective, and ultimate method of preventing foodborne illnesses.

Stress response of Salmonella Newport with various sequence types toward plasma-activated water: Viable but nonculturable state formation and outer membrane vesicle production

This study aims to investigate the response of Salmonella Newport to plasma-activated water (PAW), a novel disinfectant that attracts attention due to its broad-spectrum antimicrobial efficacy and eco-friendliness. In this work, we demonstrated that S. Newport of different sequence types (STs) could be induced into the viable but nonculturable (VBNC) state by PAW treatment. Notably, a remarkable 99.96% of S. Newport ST45 strain entered the VBNC state after a 12-min PAW treatment, which was the fastest observed among the five S. Newport STs (ST31, ST45, ST46, ST166, ST2364). Secretion of outer membrane vesicles was observed in ST45, suggesting a potential strategy against PAW treatment. Genes related to oxidative stress (sodA, katE, trxA), outer membrane proteins (ompA, ompC, ompD, ompF) and virulence (pagC, sipC, sopE2) were upregulated in the PAW-treated S. Newport, especially in ST45. A reduction of 38-65% in intracellular ATP level after PAW treatment was observed, indicating a contributor to the formation of the VBNC state. In addition, a rapid method for detecting the proportion of VBNC cells in food products based on pagC was established. This study contributes to understanding the formation mechanism of the VBNC state in S. Newport under PAW stress and offers insights for controlling microbial risks in the food industry.

Green Preparation and Antibacterial Activity Evaluation of AgNPs-Blumea balsamifera Oil Nanoemulsion

Bacterial infection is a thorny problem, and it is of great significance to developing green and efficient biological antibacterial agents that can replace antibiotics. This study aimed to rapidly prepare a new type of green antibacterial nanoemulsion containing silver nanoparticles in one step by using Blumea balsamifera oil (BBO) as an oil phase and tea saponin (TS) as a natural emulsifier and reducing agent. The optimum preparation conditions of the AgNPs@BBO-TS NE were determined, as well as its physicochemical properties and antibacterial activity in vitro being investigated. The results showed that the average particle size of the AgNPs@BBO-TS NE was 249.47 ± 6.23 nm, the PDI was 0.239 ± 0.003, and the zeta potential was -35.82 ± 4.26 mV. The produced AgNPs@BBO-TS NE showed good stability after centrifugation and 30-day storage. Moreover, the AgNPs@BBO-TS NE had an excellent antimicrobial effect on Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. These results demonstrated that the AgNPs@BBO-TS NE produced in this study can be used as an efficient and green antibacterial agent in the biomedical field.

Synergistic bactericidal effect and mechanism of ultrasound combined with Lauroyl Arginate Ethyl against Salmonella Typhimurium and its application in the preservation of onions

In the present study, the synergistic bactericidal effect and mechanism of ultrasound (US) combined with Lauroyl Arginate Ethyl (LAE) against Salmonella Typhimurium were investigated. On this basis, the effect of US+LAE treatment on the washing of S. Typhimurium on the surface of onions and on the physical and chemical properties of onion during fresh-cutting and storage were studied. The results showed that treatment with US+LAE could significantly (P < 0.05) reduce the number of S. Typhimurium compared to US and LAE treatments alone, especially the treatment of US+LAE (230 W/cm2, 8 min, 71 μM) reduced S. Typhimurium by 8.82 log CFU/mL. Confocal laser scanning microscopy (CLSM), flow cytometry (FCM), protein and nucleic acid release and N-phenyl-l-naphthylamine (NPN) assays demonstrated that US+LAE disrupted the integrity and permeability of S. Typhimurium cell membranes. Reactive oxygen species (ROS) and malondialdehyde (MDA) assays indicated that US+LAE exacerbated oxidative stress and lipid peroxidation in cell membranes. Field emission scanning electron microscopy (FESEM) demonstrated that US+LAE treatment caused loss of cellular contents and led to cell crumpling and even lost the original cell morphology. US+LAE treatment caused a significant (P < 0.05) decrease in the number of S. Typhimurium on onions, but there was no significant (P > 0.05) effect on the color, hardness, weight and ascorbic acid content of onions. This study elucidated the synergistic antibacterial mechanism of US+LAE and verified the feasibility of bactericidal effect on the surface of onions, providing a theoretical basis for improving the safety of fresh produce in the food industry and to propose a new way to achieve the desired results.

Effect of Gamma Irradiation on Pathogenic Staphylococcus aureus in Packaged Ready-to-Eat Salads Treated with Biological Extracts

Providing pathogen-free ready-to-eat (RTE) salads is critical for all consumers, especially individuals with weakened immunity. In this study, the efficacy of γ-irradiation on Staphylococcus aureus (S. aureus) in freshly packaged salads (4.24 log CFU/g) treated with essential oil (EO) and myrtle juice during 10 days of storage and their impact on organoleptic properties were investigated. EO was extracted by hydrodistillation and the chemical composition was analyzed by gas chromatography with Flame Ionization Detector (GC/FID) and gas chromatography/mass spectrometry (GC/MS). Myrtle juice was prepared from fresh fruits. The cytotoxic effects of Thymus capitatus (T. capitatus) EO against a normal human umbilical vein endothelial cell (HUVEC) were assessed. GC/FID and GC-MS analysis of the thyme EO revealed the presence of 13 compounds, including carvacrol (79.55%) and p-cymene (7.93%) as major components. The EO was found to be noncytotoxic, with concentrations lower than 0.16 µL/mL. A reduction of more than 3 log CFU/g and a total inactivation of S. aureus were achieved with the combination of gamma irradiation at 0.5 kGy with myrtle juice at 6 µL/mL and EO at 0.08 µL/mL, respectively. The treatment of fresh RTE salads with thyme and myrtle juice was evaluated as acceptable by the sensory panel. The combined effect showed a synergistic potential on the inactivation of S. aureus.

Effects of bacterial cellulose/thyme essential oil emulsion coating on the shelf life of chilled chicken meat

BACKGROUND

Bacterial cellulose (BC) is a fiber substance produced by microbial fermentation. It is widely used in the food preservation industry because of its extremely pure texture, high crystallinity and high biocompatibility. In the present study, bacterial cellulose/thyme essential oil (BC/TEO-E) with antibacterial and fresh-keeping functions was prepared by ultrasonic treatment of modified bacterial cellulose for encapsulation of thyme essential oil, which effectively inhibited the spoilage of chilled chicken.

RESULTS

The purified BC, produced by Acetobacter xylinum ATCC 53524, was ultrasonically treated wih different times (0, 30, 60 and 90 min). Transmission electron microscopy, scanning electron microscopy, Fourier transformed infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and zeta potential were used to characterize the structure of BC after ultrasound, showing that BC, treated for 30 min, had the optimal fiber structure, crystallinity (85.8%), thermal stability (347.77 °C) and solution stability (-26.63 ± 1.96 mV). BC/TEO-E was prepared by a homogenizer for the preservation of chilled chicken. Optical microscopy indicated that the BC/TEO-E prepared by 0.5% BC had optimal dispersion and stability, and even no delamination was observed in the emulsion. Compared with other groups (control, 0.5% BC and Tween-E), the total number of colonies and coliforms in chilled chicken treated with 0.5% BC/TEO-E was the lowest during the whole storage period (12 days), indicating that it can effectively inhibit bacterial growth. In addition, total volatile base nitrogen (TVB-N), thiobarbituric acid reactive substances, pH and drip loss results showed that 0.5% BC/TEO-E could effectively inhibit the spoilage of chilled chicken compared to the other treatment groups.

CONCLUSION

All of the results acquired in the present study indicate that BC/TEO-E has a potential application in chilled chicken preservation. © 2024 Society of Chemical Industry.

Antibacterial effect of ultrasound and β-citronellol against Listeria monocytogenes and its application in carrot preservation

This study investigated the antibacterial effects of ultrasound (US), β-citronellol (CT), and a combination of the two treatments on Listeria monocytogenes. Results showed that US or CT alone did not show apparent antibacterial effect (0.02-0.76 log CFU/mL reduction). The combined treatment showed obviously inactivate effect of L. monocytogenes, the populations of L. monocytogenes decreased by 8.93 log CFU/mL after US (253 W/cm2, 20 kHz) + 0.8 mg/mL CT treatment. US + CT treatment also had a significant (P < 0.05) antibacterial effect on isolates of L. monocytogenes from three different serotypes. In this study, the damage of US + CT on cell morphology had been observed using field emission scanning electron microscopy, while the damage to cell membranes by US + CT was observed by confocal laser scanning microscopy and flow cytometry. Meanwhile, the uptake of N-phenyl-l-naphthylamine and the absorbance at 260 and 280 nm also indicated that the combined treatment disrupted the permeability and integrity of L. monocytogenes membranes. Reactive oxygen species and malondialdehyde assays showed that US + CT exacerbated cellular oxidative stress and lipid peroxidation. In addition, the US + CT treatment reduced L. monocytogenes by 3.14-4.24 log CFU/g on the surface of carrots. Total phenolic and carotenoid contents in carrots were elevated after US + CT treatment. During storage, compared to control, US + CT did not significantly (P > 0.05) change the surface color of carrots but significantly (P < 0.05) decreased both hardness and weight, and has an impact on the sensory. This study showed that US + CT is a promising cleaning method that will provide new ideas for the preservation of fresh agricultural produce.

Ultrasonically functionalized chitosan-gallic acid films inactivate Staphylococcus aureus through envelope-disruption under UVA light exposure

The significant threat of foodborne pathogens contamination has continuously promoted the development of efficient antimicrobial food packaging materials. Here, an antimicrobial film was prepared with gallic acid-grafted-chitosan (CS/GA) that obtained by a two-step ultrasound method. The resultant films exhibited good transparency, improved UV barrier performance, and enhanced mechanical strength. Specifically, with the grafting of 1.2 % GA, the UV blocking ability of CS/GA film at 400 nm was significantly increased by 19.7 % and the tensile strength was nearly two times higher than that of CS film. Moreover, the CS/GA films exhibited an inspiring photoactivated bactericidal ability under 400 nm UVA light irradiation that eradicated almost 99.9 % of Staphylococcus aureus (S. aureus) cells within 60 min. To gain more insights into the antibacterial mechanism, the treated S. aureus cells were further investigated by visualizing bacterial ultrastructure and analyzing membrane properties. The results pointed to the peptidoglycan layer as the primary action target when bacteria come into contact with CS/GA films. Afterward, the intracellular oxidative lesions, disrupted bacterial integrity, and disordered membrane functional properties collectively resulted in eventual cell death. The findings revealed the unique peptidoglycan targeting and membrane disruptive mechanisms of CS/GA films, confirming the application values in controlling foodborne pathogens.

Training in tools to develop quantitative microbial risk assessment of ready-to-eat food with a comparison between the Romanian and Spanish food supply chains

The prevention and control of bacterial contamination on ready-to-eat (RTE) fresh produce is an essential task to ensure food safety. Therefore, the development of novel and effective decontamination technologies to ensure microbiological safety of fruits and vegetables has gained considerable attention and new sanitisation methods are needed. The antimicrobial activity of essential oils (EOs) is well documented, but their application in fresh produce remains a challenge due to their hydrophobic nature. Thus, nanoemulsions efficiently contribute to support the use of EOs in foods by enhancing their dispersibility, their contact area and facilitating the introduction into bacterial cells. The combination of these factors ultimately increases their antimicrobial activity. Quantitative microbial risk assessment (QMRA) is gaining more attention as an effective tool to assess and prevent potential risks associated with food-borne pathogens. In this context, the current project aims to study the effectiveness of different washing methods based on nanoemulsified EOs, comparing them against traditional methods, using a QMRA model for Escherichia coli O157:H7 on cherry tomatoes. Different simulations within a stochastic risk assessment model were implemented using the biorisk package for R, aiming to describe microbial behaviour and biological risk along the Romanian and Spanish food supply chains of RTE fresh produce. Nanoemulsions were prepared using oregano and rosemary EOs, each from Romania and Spain. The four nanoemulsions were evaluated as decontamination treatments to control the growth of E. coli O157:H7 on artificially contaminated cherry tomatoes. The decontamination treatments showed encouraging results, comparable to commonly used chlorine solutions. Therefore, oregano and rosemary nanoemulsions are promising and could be a feasible alternative for chlorine solutions in the reduction of microbiological contaminants.

Detection of Cyclomodulin CNF-1 Toxin-Producing Strains of Escherichia coli in Pig Kidneys at a Slaughterhouse

Food is often contaminated with Escherichia coli (E. coli) bacteria strains, which have been associated with different diseases, including urinary tract infections. The consumption of meat by humans is a potential route of transmission of antimicrobial resistance, and food-producing animals have been associated as a major reservoir of resistant bacterial strains. The aim of this study was to determine the presence of the E. coli strains producing the CNF-1 toxin in pig kidneys. Pig kidneys were collected from a Mexican slaughterhouse and classified according to their coloration into reddish kidneys (RK) and yellowish kidneys (YK). A tissue sample from each kidney was processed for histological analysis, the presence of E. coli was determined by conventional PCR assay, and the CNF-1 toxin was detected by both conventional PCR and Western blotting. Herein, an inflammatory cell infiltrate was found in all collected kidneys, regardless of macroscopic differences. Surprisingly, E. coli and the CNF-1 toxin were detected in all kidney samples. We clearly demonstrate contamination by CNF-1 toxin-producing E. coli in pork kidneys from a slaughterhouse, even in those without apparent damage. This suggests that pork may serve as a reservoir for pathogens, representing an important risk to human health.

Prevalence of Escherichia coli generic and pathogenic in pork meat: systematic review and meta-analysis

This research aimed to analyze scientific information regarding the prevalence of generic and pathogenic E. coli in the production and supply chain of pork meat, considering different types of samples, places of sampling, and pathotypes using a systematic review and meta-analysis tools. The meta-analysis for the prevalence of generic and pathogenic E. coli was conducted by estimating the effects within subgroups. Data subsets were analyzed using the DerSimonian-Laird method for binary random effects. The average prevalence of generic E. coli in different types of pork meat samples was determined to be 35.6% (95% CI 19.3-51.8), with no significant differences observed between pork meat and carcasses. Conversely, the average prevalence of E. coli pathotypes in samples related to the supply chain of pork meat was found to be 4.7% (95% CI 3.7-5.7). In conclusion, these findings suggest the possibility of establishing an objective threshold for E. coli prevalence as a benchmark for comparison within the meat industry. By utilizing this data, it becomes possible to propose a standardized limit that can serve as a reference point for evaluating and improving processes in the industry.

Inactivation of Salmonella using ultrasound in combination with Litsea cubeba essential oil nanoemulsion and its bactericidal application on cherry tomatoes

The presence of Salmonella in nature poses a significant and unacceptable threat to the human public health domain. In this study, the antibacterial effect and mechanism of ultrasound (US) combined with Litsea cubeba essential oil nanoemulsion (LEON) on Salmonella. LEON + US treatment has a significant bactericidal effect on Salmonella. Reactive oxygen species (ROS), malondialdehyde (MDA) detection, N-phenyl-l-naphthylamine (NPN) uptake and nucleic acid release assays showed that LEON + US exacerbated cell membrane lipid peroxidation and increased the permeability of the cell membrane. The results of field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) showed that LEON + US treatment was able to alter cell morphology. It can be observed by flow cytometry (FCM) that LEON + US treatment can cause cell apoptosis. In addition, bacterial counts of cherry tomatoes treated with LEON (0.08 μL/mL) + US (345 W/cm²) for 9 min were reduced by 6.50 ± 0.20 log CFU/mL. This study demonstrates that LEON + US treatment can be an effective way to improve the safety of fruits and vegetables in the food industry.

Ultrasound applications in drying of fruits from a sustainable development goals perspective

This review focuses on the many contributions of ultrasound technologies for fruit drying toward the United Nations Sustainable Development Goals (SDG). Along this review, several aspects attained from the application of ultrasound technologies are correlated with the SDGs. The main ultrasonic technologies applied for fruit drying, such as ultrasonic bath, probe ultrasound, air-borne ultrasound air-drying, and ultrasound-assisted contact air-drying, are presented. An in-depth discussion on ultrasound contributions, its advantages, disadvantages, and limitations are made. The effects of ultrasound on water diffusivity in several fruits are presented by correlating this effect with drying time and cost of energy. Ultrasound-assisted fruit drying, like other food processing technologies, directly impacts Zero Hunger, but ultrasound technologies contribute to much more than delivering long shelf-life food. This technology can be used to produce healthy foods and provide well-being, which will be discussed by correlating the effects of ultrasound-assisted air-drying with the concentration of nutritional compounds. Ultrasound-assisted fruit drying reduces wastewater toxicity and energy consumption and improves productivity, potentially improving workplaces and salaries. A walk through the technology is presented from Zero Hunger to No Poverty.

Synergistic antibacterial and anti-biofilm mechanisms of ultrasound combined with citral nanoemulsion against Staphylococcus aureus 29213

This study investigated the antibacterial and antibiofilm mechanism of ultrasound (US) combined with citral nanoemulsion (CLNE) against Staphylococcus aureus and mature biofilm. Combined treatments resulted in greater reductions in bacterial numbers compared to ultrasound or CLNE treatments alone. Confocal laser scanning microscopy (CLSM), flow cytometry (FCM), protein nucleic acid leakage, and N-phenyl-l-naphthylamine (NPN) uptake analysis showed that the combined treatment disrupted cell membrane integrity and permeability. Reactive oxygen species (ROS) and malondialdehyde (MDA) assays indicated that US+CLNE exacerbated cellular oxidative stress and membrane lipid peroxidation. Field emission scanning electron microscopy (FESEM) revealed that the synergistic processing of ultrasound and CLNE resulted in cell rupture and collapse. In addition, US+CLNE showed a more pronounced removal effect than both alone in the biofilm on the stainless steel sheet. US+CLNE reduced biomass, the number of viable cells in the biofilm, cell viability and EPS polysaccharide contents. The results of CLSM also showed that US+CLNE disrupted the structure of the biofilm. This research elucidates the synergistic antibacterial and anti-biofilm mechanism of ultrasound combined citral nanoemulsion, which provides a safe and efficient sterilization method for the food industry.

Effect of Ultrasound Combinated with Sodium Hypochlorite Treatment on Microbial Inhibition and Quality of Fresh-Cut Cucumber

The influence of ultrasound combined with sodium hypochlorite (US-NaClO) treatment on microorganisms and quality of fresh-cut cucumber during storage were investigated. Ultrasound (400 W, 40 kHz, US: 5, 10 and 15 min) and sodium hypochlorite (NaClO: 50, 75, 100 ppm) were used to treat fresh-cut cucumber in a single or combined treatment and stored at 4 °C for 8 days and analyzed for texture, color and flavor. The results showed that US-NaClO treatment had a synergistic effect on the inhibition of microorganisms during storage. It could significantly reduce (p < 0.05) the number of microorganisms by 1.73 to 2.17 log CFU/g. In addition, US-NaClO treatment reduced the accumulation of malondialdehyde (MDA) during storage (4.42 nmol/g) and water mobility, and maintained the integrity of the cell membrane, delayed the increase of weight loss (3.21%), reduced water loss, thus slowing down the decline of firmness (9.20%) of fresh-cut cucumber during storage. The degradation of chlorophyll (6.41%) was reduced to maintain the color of freshly cut cucumbers. At the same time, US-NaClO could maintain the content of aldehydes, the main aromatic substance of cucumber, and reduced the content of alcohols and ketones during storage. Combined with the electronic nose results, it could maintain the cucumber flavor at the end of the storage period and reduce the odor produced by microorganisms. Overall, US-NaClO was helpful to inhibit the growth of microorganisms during storage, improve the quality of fresh-cut cucumber.

Sonoprocessing: mechanisms and recent applications of power ultrasound in food

There is a growing interest in using green technologies in the food industry. As a green processing technique, ultrasound has a great potential to be applied in many food applications. In this review, the basic mechanism of ultrasound processing technology has been discussed. Then, ultrasound technology was reviewed from the application of assisted food processing methods, such as assisted gelation, assisted freezing and thawing, assisted crystallization, and other assisted applications. Moreover, ultrasound was reviewed from the aspect of structure and property modification technology, such as modification of polysaccharides and fats. Furthermore, ultrasound was reviewed to facilitate beneficial food reactions, such as glycosylation, enzymatic cross-linking, protein hydrolyzation, fermentation, and marination. After that, ultrasound applications in the food safety sector were reviewed from the aspect of the inactivation of microbes, degradation of pesticides, and toxins, as well inactivation of some enzymes. Finally, the applications of ultrasound technology in food waste disposal and environmental protection were reviewed. Thus, some sonoprocessing technologies can be recommended for the use in the food industry on a large scale. However, there is still a need for funding research and development projects to develop more efficient ultrasound devices.

Synergistic bactericidal effect of ultrasound combined with citral nanoemulsion on Salmonella and its application in the preservation of purple kale

In this study, a novel citral nanoemulsion (CLNE) was prepared by ultrasonic emulsification. The synergistic antibacterial mechanism of ultrasound combined with CLNE against Salmonella Typhimurium and the effect on the physicochemical properties of purple kale were investigated. The results showed that the combined treatment showed obviously inactivate effect of S. Typhimurium. Treatment with 0.3 mg/mL CLNE combined with US (20 kHz, 253 W/cm²) for 8 min reduced S. Typhimurium populations in phosphate-buffered saline (PBS) by 9.05 log CFU/mL. Confocal laser scanning microscopy (CLSM), flow cytometry (FCM), protein and nucleic acid release assays showed that the US combination CLNE disrupt the integrity of S. Typhimurium membranes. Reactive oxygen species (ROS) and malondialdehyde (MDA) detection indicated that US+CLNE exacerbated oxidative stress and lipid peroxidation in cell membranes. The morphological changes of cells after different treatments by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) illustrated that the synergistic effect of US+CLNE treatment changed the morphology and internal microstructure of the bacteriophage cells. Application of US+CLNE on purple kale leaves for 6 min significantly (P < 0.05) reduced the number of S. Typhimurium, but no changes in the physicochemical properties of the leaves were detected. This study elucidates the synergistic antibacterial mechanism of ultrasound combined with CLNE and provides a theoretical basis for its application in food sterilization.

Essential oils and their active components applied as: free, encapsulated and in hurdle technology to fight microbial contaminations. A review

Microbial contaminations are responsible for many chronic, healthcare, persistent microbial infections and illnesses in the food sector, therefore their control is an important public health challenge. Over the past few years, essential oils (EOs) have emerged as interesting alternatives to synthetic antimicrobials as they are biodegradable, extracted from natural sources and potent antimicrobials. Through their multiple mechanisms of actions and target sites, no microbial resistance has been developed against them till present. Although extensive documentation has been reported on the antimicrobial activity of EOs, comparisons between the use of whole EOs or their active components alone for an antimicrobial treatment are less abundant. It is also essential to have a good knowledge about EOs to be used as alternatives to the conventional antimicrobial products such as chemical disinfectants. Moreover, it is important to focus not only on planktonic vegetative microorganisms, but to study also the effect on more resistant forms like spores and biofilms. The present article reviews the current knowledge on the mechanisms of antimicrobial activities of EOs and their active components on microorganisms in different forms. Additionally, in this review, the ultimate advantages of encapsulating EOs or combining them with other hurdles for enhanced antimicrobial treatments are discussed.

Effective control of antibiotic resistance using a sonication-based combinational treatment and its application to fresh food

Antibiotics have been widely used to treat several infectious diseases. However, the overuse of antibiotics has promoted the emergence and spread of antibiotic resistant bacteria (ARB) in various fields, including the food industry. In this study, the antimicrobial efficacies of two conventional sterilization methods, mild heat, and sonication, were evaluated and optimized to develop a new strategy against ARB. Simultaneous mild heat and sonication (HS) treatment led to a significant reduction in viable cell counts, achieving a 5.58-log reduction in 4 min. However, no remarkable decrease in viable cell counts was observed in individually treated groups. Interestingly, the release of antibiotic resistance genes (ARGs) increased in a time-dependent manner in the heat-treated and HS-treated groups. The inactivation levels of ARGs increased as the HS treatment time increased from 2 to 8 min, and most ARGs were degraded after 8 min. In contrast, no significant inactivation of ARGs was observed in the heat-treated and sonication-treated groups after 8 min. These results reveal the synergistic effect of the combination treatment in controlling not only ARB but also ARGs. Finally, on applying this newly developed combination treatment to fresh food (cherry tomato and carrot juice), 3.97- and 4.28-log microbial inactivation was achieved, respectively. In addition, combination treatment did not affect food quality during storage for 5 days. Moreover, HS treatment effectively inactivated ARGs in fresh food systems.

Quantitative proteomic analysis provides insight into the survival mechanism of Salmonella typhimurium under high-intensity ultrasound treatment

The survival mechanism of Salmonella treated with high-intensity ultrasound (HIU) should be explored to further enhance the bactericidal efficacy of HIU. In this study, culturable Salmonella was reduced by applying HIU. Electron microscope imaging revealed that HIU caused the disintegration of cell structure and leakage of intracellular substances. For the Salmonella after the HIU treatment, key enzymes of the tricarboxylic acid [TCA] cycle were significantly downregulated, which led to a reduced ATP content (45.25%–75.00%), although ATPase activity was augmented by 33.82%–60.64% in the Salmonella. Accordingly, surviving Salmonella could have tolerated the stress of HIU by upregulating their environmental sensing (two-component system), chemotaxis (bacterial chemotaxis), substance uptake (ABC transporter), and ATP production (oxidative phosphorylation). Therefore, synergistically blocking the ATP production, signal transduction, or substance intake of Salmonella offer promising potential strategies to improve the bactericidal effect of HIU in industrial food processing.

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Cell damage and substances leakage were observed in ultrasound treated Salmonella.

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Ultrasonic treatments caused 1017 differentially expressed proteins in Salmonella.

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Ultrasound inhibited tricarboxylic acid cycle and reduced adenosine triphosphate content in Salmonella.

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Salmonella tolerated ultrasound by upregulating two-component system, ABC transport, and bacterial chemotaxis.

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These altered pathways could be potential targets to enhance the lethality of ultrasound.

Eugenol nanoemulsion inactivates Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7 on cantaloupes without affecting rind color

Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7 are the major foodborne pathogens that have been implicated in outbreaks related to consumption of contaminated cantaloupes. Current chlorine-based decontamination strategies are not completely effective for inactivating the aforementioned pathogens on cantaloupes, especially in the presence of organic matter. This study investigated the efficacy of eugenol nanoemulsion (EGNE) wash treatments in inactivating L. monocytogenes, Salmonella spp., and E. coli O157:H7 on the surface of cantaloupes. In addition, the efficacy of EGNE in inhibiting the growth of the three pathogens on cantaloupes during refrigerated and room temperature storage of 5 days was investigated. Moreover, the effect of EGNE wash treatment on cantaloupe color was assessed using a Miniscan® XE Plus. The EGNE was prepared with either Tween 80 (TW) or a combination of Gum arabic and Lecithin (GA) as emulsifiers. The cantaloupe rind was washed with EGNE (0.3, 0.6, and 1.25%), in presence or absence of 5% organic load, for 1, 5, or 10 min at 25°C. Enumeration of surviving pathogens on cantaloupe was performed by serial dilution and plating on Oxford, XLD or SMA agar followed by incubation at 37°C for 24–48 h. EGNE-GA and EGNE-TW wash significantly reduced all three pathogens by at least 3.5 log CFU/cm2 as early as 5 min after treatment. EGNE-GA at 1.25% inactivated L. monocytogenes, E. coli O157:H7 and S. Enteritidis on cantaloupes to below the detectable limit within 5 and 10 min of treatment, respectively (~4 log CFU/cm2, P &lt; 0.05). EGNE treatments significantly reduced the survival of L. monocytogenes, S. Enteritidis, and E. coli O157:H7 on cantaloupe by at least 6 log CFU/cm2 at day 5 of storage at 25 and 4°C (P &lt; 0.05). Presence of organic matter did not modulate the antimicrobial efficacy of nanoemulsion treatments (P &gt; 0.05). EGNE treatments did not affect the rind color of cantaloupes (P &gt; 0.05). In conclusion, eugenol nanoemulsions could potentially be used as a natural sanitizer to inactivate foodborne pathogens on cantaloupes. Further investigations in an industry setting are warranted.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce

ABSTRACT

Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.

HIGHLIGHTS

Application of sonodynamic technology and sonosensitizers in food sterilization: a review of developments, trends and challenges

Food safety and food waste have always been hot topics of discussion in recent years. However, the infection of human pathogenic bacteria and the waste of food resources caused by microbial-contaminated food remains common. Although traditional sterilization technology has been very mature, it causes changes in food flavor and excessive energy consumption to a certain extent. Moreover, the widespread bacterial resistance has also sounded a warning for researchers and finding a new alternative to antibiotics is urgently needed. The application of sonodynamic sterilization technology in medical treatment has aroused the interest of researchers. It provides ideas for new food sterilization technology. As a new non-thermal sterilization technology, sonodynamic sterilization technology has strong penetration, safety, less residue and by-products, and will less change the quality of the food itself. Therefore, sonodynamic sterilization technology has great potential applied in food sterilization technology. This review describes the concept of sonodynamic sterilization technology, the sterilization mechanism of sonodynamic sterilization and the inactivation mechanism of various pathogens, the classification and application of sonosensitizers, and the ultrasonic technology in sonodynamic sterilization in the application over the recent years. It provides a scientific reference for the application of sonodynamic sterilization technology in the field of food sterilization.

Antimicrobial effects of thymol-loaded phytoglycogen/zein nanocomplexes against foodborne pathogens on fresh produce

In this study, thymol-loaded hydrophobically modified phytoglycogen/zein nanocomplexes with a particle size around 100 nm were developed for improving microbial safety of fresh produce. The antimicrobial activities, including the determination of minimum inhibitory and bactericidal concentration, growth kinetic curves, and inhibition zone of the nanocomplexes against foodborne pathogens (Listeria monocytogenes, Salmonella enteritidis, and Escherichia coli) were evaluated. The results showed that the antimicrobial activities of the nanocomplexes were significantly stronger than that of free thymol control (without encapsulation), and the antimicrobial efficacy remained unchanged after storage at 4 °C for 60 days. The morphological results from atomic force microscope revealed that small micellar blebs were formed at the surface of bacteria after treatment with nanocomplexes and the gradual disappearance of the cell boundary indicated the occurrence of cytolysis. The potential applications of this nanocomplex as disinfectant agent in wash water were evaluated on different types of fresh produce (lettuce, cantaloupe, and strawberries). Notably, the nanocomplexes also demonstrated efficacy in biofilm removal. Findings from this study clearly demonstrated that the thymol-loaded nanocomplexes hold promising potential for the disinfection of fresh produce to improve their microbial safety and quality.

A Focused Insight into Thyme: Biological, Chemical, and Therapeutic Properties of an Indigenous Mediterranean Herb

A perennial wild shrub from the Lamiaceae family and native to the Mediterranean region, thyme is considered an important wild edible plant studied for centuries for its unique importance in the food, pharmaceutical, and cosmetic industry. Thyme is loaded with phytonutrients, minerals and vitamins. It is pungent in taste, yet rich in moisture, proteins, crude fiber, minerals and vitamins. Its chemical composition may vary with geographical location but is mainly composed of flavonoids and antioxidants. Previous studies have illustrated the therapeutic effects of thyme and its essential oils, especially thymol and carvacrol, against various diseases. This is attributed to its multi-pharmacological properties that include, but are not limited to, antioxidant, anti-inflammatory, and antineoplastic actions. Moreover, thyme has long been known for its antiviral, antibacterial, antifungal, and antiseptic activities, in addition to remarkable disruption of microbial biofilms. In the COVID-19 era, some thyme constituents were investigated for their potential in viral binding. As such, thyme presents a wide range of functional possibilities in food, drugs, and other fields and prominent interest as a nutraceutical. The aims of the current review are to present botanical and nutritive values of this herb, elaborate its major constituents, and review available literature on its dietetic and biological activities.

Reduction of Bacterial Enteric Pathogens and Hygiene Indicator Bacteria on Tomato Skin Surfaces by a Polymeric Nanoparticle-Loaded Plant-Derived Antimicrobial

This study determined Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium survival on tomato skins as a function of sanitization treatment, under three differing contamination and sanitization scenarios. Sanitizing treatments consisted of the plant-derived antimicrobial (PDA) geraniol (0.5 wt.%) emulsified in the polymeric surfactant Pluronic F-127 (GNP), 0.5 wt.% unencapsulated geraniol (UG), 200 mg/L hypochlorous acid at pH 7.0 (HOCl), and a sterile distilled water wash (CON). Experimental contamination and sanitization scenarios tested were: (1) pathogen inoculation preceded by treatment; (2) the pathogen was inoculated onto samples twice with a sanitizing treatment applied in between inoculations; and (3) pathogen inoculation followed by sanitizing treatment. Reductions in counts of surviving pathogens were dependent on the sanitizing treatment, the storage period, or the interaction of these independent/main effects. GNP treatment yielded the greatest reductions in pathogen counts on tomato skins; pathogen survivor counts following GNP treatment were consistently statistically lower than those achieved by HOCl or UG treatments (p < 0.05). GNP treatment provided greatest pathogen reduction under differing conditions of pre- and/or post-harvest cross-contamination, and reduced hygiene-indicating microbes the most of all treatments on non-inoculated samples. Encapsulated geraniol can reduce the risk of pathogen transmission on tomato fruit, reducing food safety hazard risks for tomato consumers.

Essential Oil Nanoemulsion as Eco-Friendly and Safe Preservative: Bioefficacy Against Microbial Food Deterioration and Toxin Secretion, Mode of Action, and Future Opportunities

Microbes are the biggest shareholder for the quantitative and qualitative deterioration of food commodities at different stages of production, transportation, and storage, along with the secretion of toxic secondary metabolites. Indiscriminate application of synthetic preservatives may develop resistance in microbial strains and associated complications in human health with broad-spectrum environmental non-sustainability. The application of essential oils (EOs) as a natural antimicrobial and their efficacy for the preservation of foods has been of present interest and growing consumer demand in the current generation. However, the loss in bioactivity of EOs from fluctuating environmental conditions is a major limitation during their practical application, which could be overcome by encapsulating them in a suitable biodegradable and biocompatible polymer matrix with enhancement to their efficacy and stability. Among different nanoencapsulated systems, nanoemulsions effectively contribute to the practical applications of EOs by expanding their dispersibility and foster their controlled delivery in food systems. In line with the above background, this review aims to present the practical application of nanoemulsions (a) by addressing their direct and indirect (EO nanoemulsion coating leading to active packaging) consistent support in a real food system, (b) biochemical actions related to antimicrobial mechanisms, (c) effectiveness of nanoemulsion as bio-nanosensor with large scale practical applicability, (d) critical evaluation of toxicity, safety, and regulatory issues, and (e) market demand of nanoemulsion in pharmaceuticals and nutraceuticals along with the current challenges and future opportunities.

The combination of ultrasound and chlorogenic acid to inactivate Staphylococcus aureus under planktonic, biofilm, and food systems

This study aimed to investigate the mechanism of different treatments, namely, ultrasound (US), chlorogenic acid (CA), and ultrasound combined with chlorogenic acid (US plus CA) on the inactivation of Staphylococcus aureus planktonic and biofilm cells. Results showed that the combined treatment of US and CA exhibited remarkable synergistic antibacterial and antibiofilm effects. Scanning electron microscopy images indicated that the combined treatment of US and CA caused the most serious damage to the cell morphology. Confocal laser scanning microscopy images revealed that the combined treatment led to sharp increase and severe damage to the permeability of the cell membrane, causing the release of ATP and nucleic acids and decreasing the exopolysaccharide contents in S. aureus biofilm. Finally, the combined treatment of US plus 1% CA for 60 min inactivated S. aureus cells by 1.13 lg CFU/g on mutton. Thus, the combined treatment of US and CA had synergistic effect against S. aureus under planktonic, biofilm, and food systems.

Integration of transcriptomic and proteomic approaches unveils the molecular mechanism of membrane disintegration in Escherichia coli O157:H7 with ultrasonic treatment

Ultrasonic disinfection in wastewater treatment has been studied for years at the phenotypic level, while the understanding of the molecular inactivation mechanism is still not clear. Here, the responses of Escherichia coli O157:H7 to ultrasound treatment were investigated using RNA sequencing (RNA-Seq) and tandem mass tags (TMT) based quantitative proteomics methods. The analyses revealed that 770 genes and 201 proteins were significantly changed upon ultrasound treatment. Moreover, the integrated transcriptomic and proteomic analyses uncovered a set of 59 genes or proteins were differentially expressed in ultrasound-treated cells, providing an overview of the cellular responses to ultrasonic field. According to the bioinformatic analyses, genes and proteins that may be involved in lipid asymmetry preservation and outer membrane homeostasis maintenance (including phospholipid metabolism, lipopolysaccharide biosynthesis and transport, and fatty acid metabolism) were specifically up-regulated. Therefore, we proposed that the metabolism disorder of cellular membrane lipids (lipopolysaccharide, phospholipid, and fatty acid included) was one of the main challenges for the bacteria upon ultrasonic stress. In this study, we initially proposed a novel mechanism regarding the ultrasound-induced membrane disintegration from a multi-omics perspective, which may present an important step toward deciphering the molecular inactivation mechanism of ultrasonic field and provide a theoretical foundation for the application of ultrasound technology for the control of waterborne pathogens.

Natural antimicrobial-loaded nanoemulsions for the control of food spoilage/pathogenic microorganisms

Both consumers and producers of food products are looking for natural ingredients and efficient formulation strategies to improve the shelf life of final products. Natural antimicrobial ingredients such as essential oils can be applied as alternatives to synthetic preservatives, but their main challenge is low stability, adverse effects on sensory properties, low solubility, high needed doses, etc. Formulation of these bioactive compounds into nanoemulsions can be an efficient strategy to improve their properties and practical applications in food products. In this review, after an overview on nanoemulsion formulation, ingredients and fabrication methods, different types of natural antimicrobial agents have been discussed briefly. In addition, properties and action mechanisms of antimicrobial-loaded nanoemulsions, along with their application in preservation and shelf life improvement of different food products have been explained. Finally, safety and regulatory issues of antimicrobial delivery via nanoemulsions have been examined. As a conclusion antimicrobial-loaded nanoemulsions can be promising candidates and alternatives for common synthetic preservatives in real food systems.

Inhibitory effects and mechanisms of vanillin on gray mold and black rot of cherry tomatoes

Vanillin is a natural antimicrobial agent; however, there are few reports on its antifungal effect on postharvest pathogenic fungi. This study aimed to investigate the in vivo and in vitro antifungal activities of vanillin against gray mold (caused by B. cinerea) and black rot (caused by A. alternata) of cherry tomato fruit and to explain its possible mechanism of action. Vanillin strongly inhibits Botrytis cinerea and Alternaria alternata mycelial growth, spore germination, and germ tube elongation in a concentration-dependent manner (P<0.05). In vivo experiments showed that 4000 mg L^-1 vanillin treatment inhibited cherry tomato gray mold and black rot occurrence. Besides, intercellular electrolytes, soluble proteins, and soluble sugars leakage indicated that 50 or 100 mg L^-1 vanillin treatment increased Botrytis cinerea and Alternaria alternata membrane permeability. The increase of malondialdehyde and hydrogen peroxide contents confirmed that 50 or 100 mg L^-1 vanillin treatment damages the pathogen membranes. Importantly, vanillin treatment inhibited the pathogenicity-related enzyme activities of the two pathogens to reduce their infection ability, among them PL enzyme activity in A. alternata was most inhibited, reducing by 94.7 % at 6 h treated with 100 mg L^-1 vanillin. The hyphae morphology of the two pathogens changed, the mycelia were severely damaged, and the hyphae surface was deformed, shrunk, or even broken after 100 mg L^-1 vanillin treatment. In summary, vanillin had a substantial inhibitory effect on postharvest gray mold and black rot in cherry tomato fruit. Therefore, vanillin can be an effective alternative to prevent and control cherry tomato postharvest diseases.

Antibacterial mechanism of ultrasound against Escherichia coli: Alterations in membrane microstructures and properties

This study was aimed at providing new insights on the response of bacterial cell membranes to ultrasound exposure. Escherichia coli (E. coli) O157:H7 cells were exposed to different ultrasound treatments (power intensities of 64, 191, 372, and 573 W/cm², frequency of 20 kHz, pulsed mode of 2 sec: 2 sec) and the dynamic changes in cell viability within 27 min were assessed. With an increase in ultrasonic intensity and prolonged duration, a 0.76-3.52 log CFU/mL reduction in E. coli populations was attained. The alterations in the sensitivity of ultrasound-treated cells to antimicrobial compounds were evaluated by exposure to thyme essential oil nanoemulsion (TEON). The treatment reduced the E. coli population by 2.16-7.10 log CFU/mL, indicating the effects of ultrasonic field on facilitating the antibacterial efficacy of TEON. Ultrasonic-treated E. coli cells also displayed remarkable morphological and ultrastructural damages with destroyed membrane integrity and misshaped cell structures, which was observed by electron microscopy analysis. Significant increase in outer and inner membrane permeability, along with the cytoplasmic leakage and membrane depolarization were assessed utilizing spectrophotometry. For the first time, significant reduction in the membrane fluidity in response to ultrasound exposure were investigated. Additional efforts in exploring the effect of ultrasonic field on some bacterial membrane compositions were performed with infrared spectroscopy. In this study, multiple lines of evidence effectively served to elucidate the alterations on cellular membrane structure and property during exposure to sonication that could extend our understanding of the antimicrobial molecular mechanisms of ultrasound.