Investigation on the inactivation effect and mechanism of Listeria monocytogenes in fresh-cut cucumber during storage by ultrasound combined with sodium hypochlorite

Ultrasound and lactic/malic acid treatment for mitten crab decontamination: Efficacy and mechanisms against A. hydrophila

The Chinese mitten crab (Eriocheir sinensis), recognized as a high-value aquatic product, necessitates effective cleaning to ensure both safety and quality. Conventional cleaning methods frequently fail to eliminate biofilms and pathogenic bacteria, such as Aeromonas hydrophila, which pose significant health risks and contribute to spoilage. This study explores the bactericidal efficacy and underlying mechanisms of ultrasound treatment combined with a lactic acid and malic acid complex solution for decontaminating crabs and enhancing food safety. Employing a range of methodologies, including microscopic imaging, live/dead staining, RT-qPCR, and texture and microstructure analysis, the results indicate that the combined treatment significantly reduced A. hydrophila counts by 4.16 lg CFU/mL and induced substantial bacterial membrane damage, as evidenced by scanning electron microscopy (SEM). Gene expression analysis revealed a pronounced downregulation of biofilm-related genes. Notably, the treatment also preserved the texture and sensory properties of crab meat, thereby ensuring high product quality. These findings suggest that the application of ultrasound in conjunction with a lactic acid-malic acid solution represents a green and effective strategy for improving food safety and quality in the processing of aquatic products, offering a sustainable and eco-friendly alternative to traditional cleaning methods.

Comparative analysis and investigation of ultrasonication on juice yield and bioactive compounds of kinnow fruit using RSM and ANN models

Ultrasonication (US) is a promising non-thermal technique widely applied in the food sector for improving the extraction process and preserving nutrients. Kinnow fruits have yields of 40-60% juice; the rest of the parts are discarded as waste. The study explored ultrasonication (US) as a pre-treatment to improve juice expression and preserve heat-sensitive nutrients such as vitamin C. The optimization of US treatment was done by varying treatment time (30-90 min) and temperature (30-70 °C) using response surface methodology (RSM). Under optimal conditions, juice yield increased by 14.52% with 4.34% vitamin C loss. The artificial neural network (ANN) model (2-9-1 for yield and 2-10-1 for vitamin C) outperformed the RSM in terms of fitting, predictive ability and accuracy. The kinetic study further indicated that longer US treatment enhanced the total soluble solids (TSS), total phenolic content (TPC), and total color change (ΔE), whereas antioxidant activity and vitamin C content decreased. The yield followed an inverted parabola trend during the kinetic study; yield increased with a k-value of 0.0582 until 30 min and then declined until 60 min with a 0.0253 k-value. These results suggested that US technology has the potential to improve juice yield and maintain nutritional quality.

Microbial decontamination of fresh-cut celery using simultaneous ultrasound and plasma-activated water treatment

This study investigated an ultrasound (US) treatment strategy in plasma-activated water (PAW) (UP treatment) to inactivate indigenous aerobic bacteria, Escherichia coli O157:H7, and Listeria monocytogenes in fresh-cut celery. Both plasma discharge and US treatment times contributed to the inactivation of indigenous bacteria in celery. The predicted optimal UP treatment conditions included a discharge time of 61.5 min and treatment time of 338 s, resulting in the inactivation of indigenous bacteria, E. coli O157:H7, and L. monocytogenes by 2.7, 1.7, and 3.2 log CFU/g, respectively. With an increase in plasma discharge time or US treatment time, the oxidation-reduction potential and electrical conductivity values of PAW increased, while the pH decreased. UP treatment effectively inactivated bacteria non-thermally, without altering the color of celery. Furthermore, UP treatment led to an increase in cell lipid peroxidation, reactive oxygen species production, and the number of non-viable E. coli O157:H7 and L. monocytogenes cells with membrane damage. This study highlights the potential of UP treatment for bacterial decontamination of fresh-cut celery.

A novel virulent core genome multilocus sequence type CT 11424 of Listeria monocytogenes isolate causing stillbirth in Bangladesh

BACKGROUND

Listeria monocytogenes is a foodborne pathogen that can lead to severe pregnancy outcomes. This study reports the clinical and genomic characteristics of a Listeria-mediated stillbirth identified in January 2022 through the Child Health and Mortality Prevention Surveillance (CHAMPS) project in Bangladesh. The Lm-BD-CHAMPS-01 isolate was recovered from the blood and cerebrospinal fluid (CSF) of a male stillborn. Maternal history, clinical, and demographic data were collected by the CHAMPS surveillance platform. An expert panel evaluated all reports to determine the role of L. monocytogenes infection in the causal chain of stillbirth. Genomic characterization included multilocus sequence typing (MLST), core genome MLST (cgMLST), serotyping, and the presence or absence of virulence genes. Genetic divergence and phylogenetic analyses were conducted to determine the relationship with other reported isolates globally.

RESULTS

The isolate Lm-BD-CHAMPS-01 was identified as a novel cgMLST CT11424. It belonged to ST 308, Serotype 4b, Clonal Complex 1, and Phylogenetic Lineage 1. Key L. monocytogenes virulence genes facilitating the crossing of the placental barrier, including full-length inlA, LIPI-1, and LIPI-3, were detected. The isolate was closely related to clinical L. monocytogenes isolates, as determined by GrapeTree based on cgMLST. SNP-based phylogenetic analysis found Lm-BD-CHAMPS-01 to be the most distant from other CC1 isolates in the database. Possible sources of infection included the consumption of contaminated raw vegetables or exposure to pigeons.

CONCLUSIONS

This is the first genome sequence of clinical L. monocytogenes from Bangladesh, which also caused stillbirth. Rural healthcare professionals should be aware of L. monocytogenes infection risks during pregnancy. Pregnant women should be counseled on the dangers of exposure to animals or birds and consumption of potentially contaminated raw food to prevent adverse pregnancy outcomes due to L. monocytogenes infection.

Synergistic inactivation effect and mechanism of ultrasound combined with Zanthoxylum schinifolium essential oil nanoemulsions against Escherichia coli O157:H7 and its application on fresh-cut cucumber

Fresh-cut produce is often contaminated with Escherichia coli O157, posing a significant risk to public health. This study investigated the synergistic inactivation effect and underlying mechanism of ultrasound (US) combined with Zanthoxylum schinifolium essential oil nanoemulsion (ZEO-NE) against E. coli O157:H7, and explored its potential application in fresh-cut cucumbers. The results demonstrated that combined treatment of US and ZEO-NE significantly reduced the viable counts of E. coli O157:H7 compared to treatment with US or ZEO-NE alone. In particular, US (20 kHz, 345 W/cm2) + ZEO-NE (1.0 mg/mL) treatment for 12 min achieved an 8.91 log colony-forming units (CFU)/mL reduction in viable counts of E. coli O157:H7. Moreover, biofilm formation assay revealed that US+EO-NE treatment significantly reduced mobility, altered surface properties, and inhibited biofilm formation of E. coli O157:H7 cells compared to single treatments. The synergistic inactivation mechanism of US+ZEO-NE treatment against E. coli O157:H7 was revealed to involve increased cell membrane permeability, resulting in leakage of nucleic acids, proteins, and LDH, AKP, and ATP, disruption of cell membrane integrity, and alterations in membrane potential. Additionally, the US+ZEO-NE treatment induced reactive oxygen species accumulation and disrupted cell morphology, ultimately leading to E. coli O157:H7 cell death. Notably, the US+EO-NE treatment also significantly reduced the E. coli O15:H7 counts in fresh-cut cucumbers compared to single treatments, without adversely affecting the quality and sensory properties of the produce during storage at 4 °C for 12 days. Overall, these findings suggest that US+EO-NE is a promising technique for bacterial inactivation, and holds potential for improving microbial safety in fresh-cut produce.

Preservation of minimally processed carrots using the combination of ultrasound and mild heat ascorbic acid

Ultrasound (US) in combination with chemical disinfectants is an efficient and cost-effective hurdle technology for disinfecting minimally processed produce (MPP). However, the demand for non-chemical disinfection methods is increasing. In addition, chemical methods have been ineffective in simultaneously improving the physiological properties and inactivating pathogens in MPP. In this study, a novel and safe method called mild heat ascorbic acid (MHAsA; 1 % AsA at 50 °C) was combined with US to process minimally processed carrots. Physiological properties and microbial inactivation efficacy were analyzed during the storage period (0-5 days). The findings indicated that US-MHAsA induced the highest levels of antioxidant enzymes (superoxide dismutase and catalase) activities and accelerated the glutathione-ascorbate cycle, resulting in lower reactive oxygen species (ROS) and malondialdehyde content compared to US and MHAsA. The efficacy of US-MHAsA in inactivating phenylalanine lyase, the initial enzyme in the lignin synthesis process, was lower than that of US. On the other hand, its ability to inactivate cinnamyl alcohol dehydrogenase, the final enzyme in the process, was better than that of both US and MHAsA. However, there were no significant differences in lignin content among the three groups. The inactivation efficacy against enzymes (polyphenol oxidase and peroxidase) involved in browning was consistent across the three treatments. Analysis of the disinfection efficacy against Escherichia coli O157:H7 and Salmonella Typhimurium revealed that US-MHAsA achieved the lowest cross-contamination incidence (10-12 %) during washing, which was significantly lower than the incidence achieved by US (75-82 %). During the period from day 0 to day 5, two pathogens on carrots in the control group increased from 6.25 to 6.64 log CFU/g, while the lowest counts were observed in the US-MHAsA group, decreasing from 4.44 to 3.74 log CFU/g. However, the counts in the US group increased from 5.22 to 6.32 log CFU/g, and the counts at day 5 were not significantly lower than the control. These findings indicate that US-MHAsA is a novel hurdle technology that effectively reduces the risk of pathogen contamination and enhances the ability of MPP to scavenge ROS.

Ultrasound combined with FeSO4 facilitated the occurrence of ferroptosis in Vibrio parahaemolyticus

Ultrasound (US) as a sustainable non-thermal sterilization technology that is employed either independently alone or in combination with other processing methods to eliminate food-borne pathogens in the food industry. In the present study, the synergistic effects of US combined with FeSO4 against Vibrio parahaemolyticus were investigated. The results demonstrated that the combination of ultrasound and FeSO4 had an excellent bactericidal activity on V. parahaemolyticus. Treatment with US (100 W) and FeSO4 (8 μM) for 15 min could kill more than 99.9 % cells. Furthermore, the observed cell death was identified as classical ferroptosis, characterized by ferroptosis hallmarks including iron-dependent, ROS burst, membrane damage and lipid peroxide accumulation. Addition of ferroptosis inhibitor liproxstatin-1 alleviated the cell death induced by the combination treatment. Transcriptome analysis further revealed that the US-FeSO4 treatment significantly influenced pathways related to fatty acid metabolism, ferroptosis, biofilm formation, RNA degradation, oxidative phosphorylation and other key processes, which likely contributed to the occurrence of ferroptosis. Based on these findings, we speculated that cavitation effect of US promoted the entry of Fe2+, leading to the generation of free radicals primarily responsible for ferroptosis by US-FeSO4. Taken together, this study provides valuable insights into the biological pathway involved in ultrasound sterilization and presents an alternative strategy to eradicate microorganism in food products.

Transcriptomic and Physiological Analysis Reveals the Possible Mechanism of Inhibiting Strawberry Aroma Changes by Ultrasound after Harvest

The volatile compounds in strawberries play a significant role in the formation of strawberry aroma. However, these compounds undergo continual changes during storage, resulting in a decline in quality. In this study, a total of 67 volatile organic compounds (VOCs) were identified in strawberries through quantitative analysis. At the end of the storage period, the VOC content in the ultrasonic group was 119.02 µg/kg higher than that in the control group. The results demonstrated that the ultrasonic treatment increased the contents of terpenes and esters at the end of storage. Among these, linalool increased from 67.09 to 91.41 µg/kg, while ethyl cinnamate increased from 92.22 to 106.79 µg/kg. Additionally, the expression of the key metabolic genes closely related to these substances was significantly up-regulated. The expression of the FaNES gene, related to terpene metabolism, was up-regulated by 2.8 times in the second day, while the expression of the FaAAT gene, related to ester metabolism, was up-regulated by 1.5 times. In summary, this study provides a theoretical basis for exploring the mechanism of ultrasonic effect on strawberry flavor and quality after harvest.

Lethal puncturing of planktonic Gram-positive and Gram-negative bacteria by magnetically-rotated silica hexapods

Planktonic bacterial presence in many industrial and environmental applications and personal health-care products is generally countered using antimicrobials. However, antimicrobial chemicals present an environmental threat, while emerging resistance reduces their efficacy. Suspended bacteria have no defense against mechanical attack. Therefore, we synthesized silica hexapods on an α-Fe2O3 core that can be magnetically-rotated to inflict lethal cell-wall-damage to planktonic Gram-negative and Gram-positive bacteria. Hexapods possessed 600 nm long nano-spikes, composed of SiO2, as shown by FTIR and XPS. Fluorescence staining revealed cell wall damage caused by rotating hexapods. This damage was accompanied by DNA/protein release and bacterial death that increased with increasing rotational frequency up to 500 rpm. Lethal puncturing was more extensive on Gram-negative bacteria than on Gram-positive bacteria, which have a thicker peptidoglycan layer with a higher Young's modulus. Simulations confirmed that cell-wall-puncturing occurs at lower nano-spike penetration levels in the cell walls of Gram-negative bacteria. This approach offers a new way to kill bacteria in suspension, not based on antimicrobial chemicals.