Effects of electrolysed water combined with ultrasound on inactivation kinetics and metabolite profiles of Escherichia coli biofilms on food contact surface

Predictive Modeling for Inactivation of Escherichia coli Biofilm with Combined Treatment of Thermosonication and Organic Acid on Polystyrene Surface

The present study aimed to evaluate the antibiofilm effect of combined sonication treatment with organic acids on polystyrene surfaces and to develop a predictive model for the inactivation of Escherichia coli biofilms. Polystyrene plates containing E. coli biofilms were subjected to sonication using different inactivation solutions (PBS, lactic acid, and acetic acid) at varying temperatures (20 °C, 40 °C, and 50 °C) and durations (2 and 5 min). The effects of temperature, treatment duration, and inactivation solution on E. coli biofilm removal were statistically significant (p < 0.05). The use of organic acids, along with increased treatment time and temperature, led to a significant reduction in viable cell counts (0.43-6.21 log CFU/mL) and optical density (0.13-0.72 at OD600) of E. coli biofilms (p < 0.05). The highest E. coli biofilm inactivation, with a reduction of 6.21 CFU/mL and 0.72 OD, was achieved by combining organic acid and thermosonication at 50 °C for 5 min. A significant positive correlation was observed between test methods based on viable cell count and optical density (OD) measurements. According to multiple linear regression analysis results, the R2 values of the predictive models for biofilm inactivation, based on viable cell count and OD measurements, were 0.84 and 0.80, respectively. Due to its higher accuracy, the predictive model developed using viable cell count data is recommended for applications in the food industry and processing sectors.

The influence of synergistic antibacterial saponins, sapindoside A and B, on the fatty acid composition and membrane properties of Micrococcus luteus

BACKGROUND

Saponins from Sapindus mukorossi Gaertn. are natural surfactants with excellent foaming ability, biodegradability, and safety. However, their applications in food have been rarely reported. The aim of this work was therefore to investigate the synergistic antibacterial roles of a combination of sapindoside A and B (SAB), which are major components of Sapindus saponins, in altering the properties and fatty acids (FAs) in the membrane of Micrococcus luteus, which has been identified as an opportunistic pathogen.

RESULTS

Microscopy showed that SAB destroyed the integrity of the cell membrane and internal structures and led to the leakage of the cell content. Further analysis indicated that the ratio of saturated FAs to unsaturated FAs was increased significantly, and the membrane fluidity, permeability, and integrity changed substantially. Although sapindoside A and B exerted similar synergistic effects on fatty acid composition and membrane fluidity, sapindoside A had a greater impact on membrane permeability and integrity, consistent with density functional theory.

CONCLUSION

The activity of M. luteus was inhibited more effectively by SAB than sapindoside A or B alone. It attacked cell membrane FAs, resulting in changing membrane fluidity, permeability, and integrity, eventually causing leakage of the cell contents, and ultimately cell death. This helped to provide evidence for the use of SAB as a natural antibacterial detergent additive in the food industry. © 2024 Society of Chemical Industry.

Bacillus cereus CwpFM induces colonic tissue damage and inflammatory responses through oxidative stress and the NLRP3/NF-κB pathway

Bacillus cereus (B. cereus) from cow milk poses a threat to public health, causing food poisoning and gastrointestinal disorders in humans. We identified CwpFM, an enterotoxin from B. cereus, caused oxidative stress and inflammatory responses in mouse colon and colonic epithelial cells. Colon proteomics revealed that CwpFM elevated proteins associated with inflammation and oxidative stress. Notably, CwpFM induced activation of the NLRP3/NF-κB signaling, but suppressed antioxidant NFE2L2/HO-1 expression in the intestine and epithelial cells. Consistently, CwpFM exposure led to cytotoxicity and ROS accumulation in Caco-2 cells in a dose-dependent manner. Further, NAC (ROS inhibitor) treatment abolished NLRP3/NF-κB activation due to CwpFM. Moreover, overexpression of Nfe2l2 or activation of NFE2L2 by NK-252 reduced ROS production and inhibited activation of the NLRP3/NF-κB pathway. Inhibition of NF-κB by ADPC and/or suppression of NLRP3 by MCC950 attenuated CwpFM-induced inflammatory responses in Caco-2 cells. Collectively, CwpFM induced oxidative stress and NLRP3/NF-κB activation by inhibiting the NFE2L2/HO-1 signaling and ROS accumulation, leading to the development of intestinal inflammation. Our data elucidate the role of oxidative stress and innate immunity in CwpFM enterotoxicity and contribute to developing diagnostic and therapeutic products for B. cereus-related food safety issues.

A biphasic accelerated strand exchange amplification strategy for culture-independent and rapid detection of Salmonella enterica in food samples

Salmonella enterica is a common foodborne pathogen that can cause food poisoning in humans. The organism also infects and causes disease in animals. Rapid and sensitive detection of S. enterica is essential to prevent the spread of this pathogen. Traditional technologies for the extraction and detection of this pathogen from complex food matrices are cumbersome and time-consuming. In this study, we introduced a novel strategy of biphasic assay integrated with an accelerated strand exchange amplification (ASEA) method for efficient detection of S. enterica without culture or other extraction procedures. Food samples are rapidly dried, resulting in a physical fluidic network inside the dried food matrix, which allows polymerases and primers to access the target DNA and initiate ASEA. The dried food matrix is defined as the solid phase, while amplification products are enriched in the supernatant (liquid phase) and generate fluorescence signals. The analytical performances demonstrated that this strategy was able to specifically identify S. enterica and did not show any cross-reaction with other common foodborne pathogens. For artificially spiked food samples, the strategy can detect 5.0 × 101 CFU mL-1S. enterica in milk, 1.0 × 102 CFU g-1 in duck, scallop or lettuce, and 1.0 × 103 CFU g-1 in either oyster or cucumber samples without pre-enrichment of the target pathogen. We further validated the strategy using 82 real food samples, and this strategy showed 92% sensitivity. The entire detection process can be finished, sample-to-answer, within 50 min, dramatically decreasing the detection time. Therefore, we believe that the proposed method enables rapid and sensitive detection of S. enterica and holds great promise for the food safety industry.

Comparative genomic analysis and multilocus sequence typing of Staphylococcus aureus reveals candidate genes for low-temperature tolerance

Staphylococcus aureus is one of the most frequently detected foodborne pathogens in cold chain foods. Worryingly, small colony variants (SCVs) can survive in cold environments for a long time and can revert to rapidly growing cells in suitable environments, causing serious food safety issues. This study investigated the underlying mechanism of SCV formation at low temperature (4 °C) via comparative genomics. Multilocus sequence typing (MLST) of 105 strains of S. aureus was divided into 9 sequence types. The ST352 strains exhibited the greatest tolerance to low temperature, with a mean reduction in survival rate of 10.34 % (p < 0.05). Comparative genomics revealed a total of 1941 core genes in the three S. aureus strains, and BB-1 had 468 specific genes, which were enriched mainly in translation, DNA recombination, DNA repair, metabolic pathways, two-component systems, and quorum sensing. Molecular docking analysis revealed that the binding of the RsbW protein to the SigB protein of BB-1 decreased due to base mutations in rsbW, while the binding to the RsbV protein was enhanced. In addition, the results of real-time quantitative PCR showed that the RsbV-RsbW/SigB system of BB-1 may play a role in the low-temperature survival of S. aureus and the formation of SCVs. These results suggest that genes specific to BB-1 may contribute to the mechanism of adaptation to low temperature and the formation of SCVs. This study helps elucidate the causes of SCV formation by S. aureus at low temperature at the molecular level and provides a basis for exploring the safety control of cold chain food environments.

Back propagation artificial neural network (BP-ANN) for prediction of the quality of gamma-irradiated smoked bacon

This study investigated the effect of gamma irradiation on smoked bacon quality during storage and developed a multi-quality prediction model based on gamma irradiation. Gamma irradiation reduced moisture content and improved the microbial safety of smoked bacon. It also accelerated protein and lipid oxidation and altered free amino acids and fatty acids composition. It was effective in slowing down quality deterioration and sensory quality decline during storage. The backpropagation artificial neural network (BP-ANN) model was constructed by using physical and chemical indicators, irradiation dose, and storage time as input variables, and the total number of colonies and sensory scores as output layers. The transfer functions of the input-hidden layer and hidden-output layer were ReLu and Sigmoid, respectively. There were 13 neurons in the hidden layer. Results showed that BP-ANN based on physical and chemical indicators, irradiation dose, and storage time had great potential in predicting the multiple quality of smoked bacon.

Effects of substrates and suppliers of ingredients on microbial community and metabolites of traditional non-salt Suancai

Aim: Non-salt Suancai is an acidic fermented vegetable consumed by the Chinese Yi ethnic group. Traditionally, it is produced by fermentation without salt in a cold environment. The present study aimed to investigate the metabolite and microbial characteristics, and the effects of substrates/suppliers ingredients on non-salt Suancai. Methods: A simulated fermentation system of non-salt Suancai was constructed by using different substrates/suppliers' ingredients. The coherence and differential detection of the metabolite and microbial characteristics were done through non-target metabolomic and metagenomic analysis. Results: Lactic acid was the predominant organic acid across all samples. The enumeration of the Lactic acid bacteria showed no discernible differences between study groups, but that of yeast was highest in the mustard leaf stem (Brassica juncea var. latipa). The three major biological metabolic pathways were metabolism, environmental information, and genetic information processing based on the KEGG database. The metabolite diversity varied with the substrate/supplier of ingredients based on the PLS-DA plot. Lactiplantibacillus, Leuconostoc, and Lactococcus were prevalent in all samples but differentially. The microbial diversity and richness varied significantly, with 36~291 species being identified. Among the various substrates collected from the same supplier, 29, 59, and 29 differential species were identified based on LEfSe [linear discriminant analysis (LDA) > 2, P < 0.05]. Leuconostoc citreum, Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, Lactiplantibacillus plantarum, and Leuconostoc lactis were likely to be used as the species to discriminate samples collected from different suppliers. Conclusions: This research contributed to the exploration of microbial and metabolite characteristics behind the ingredient restriction of non-salt Suancai using traditional technology.

Unpacking the Global Rice Trade Network: Centrality, Structural Holes, and the Nexus of Food Insecurity

The challenging international landscape and exacerbated extreme weather conditions contribute to the instability of global grain trade, complicating its impact on food security. This complexity is particularly pronounced for varieties like rice, which are heavily affected by policy-driven trade restrictions. There is insufficient research on how a country's rice trade characteristics affect food security. A network analysis approach is adopted to intricately dissect the structural characteristics of rice trade. To explore causality with food insecurity, this paper chooses structural holes and centrality as representatives of trade network characteristics and regresses them on the food insecurity indicator. With cross-national data spanning over 30 years, the network analysis provides a clear portrayal of the dynamic changes in international rice trade. The overall resilience of the trade network has increased, but specific countries' vulnerability has also risen. Unlike the changing trends in features observed in grain and food trade networks, there is a notable intensification in the imbalance of power distribution in the rice trade network compared to over 30 years ago. The panel data regression results show that constraint, indicating the scarcity of structural holes or connections to stronger trading partners, significantly and positively influences a country's level of food insecurity. Based on these findings, the policy proposal for importing countries emphasizes creating strategic trade connections. By choosing appropriate trade partners that reduce constraint, food security can be enhanced, even without improvements in other conditions.

Novel NaCl reduction technologies for dry-cured meat products and their mechanisms: A comprehensive review

Sodium chloride (NaCl) confers a unique flavor and quality in meat products, however, due to growing concerns about the adverse effects of excessive NaCl consumption, how to reduce NaCl content while ensuring quality and safety has become a research hotspot in this field. This review mainly discusses the role of NaCl in dry-cured meat, as well as novel salt-reducing substances that can substitute for the effects of NaCl to achieve sodium reduction objectives. New technologies, such as vacuum curing, ultrahigh pressure curing, ultrasonic curing, pulsed electric field curing, and gamma irradiation, to facilitate the development of low-sodium products are also introduced. The majority of current salt reduction technologies function to enhance salt diffusion and decrease curing time, resulting in a decrease in NaCl content. Notably, future studies should focus on implementing multiple strategies to compensate for the deficiencies in flavor and safety caused by NaCl reduction.

Chemical Analysis and Investigation of Antimicrobial and Antibiofilm Activities of Prangos trifida (Apiaceae)

Plants of the genus Prangos are intensively investigated as potential new sources of bioactive isolated products. In this work, the chemical composition of volatile constituents (essential oils and headspace volatiles) and dichloromethane extracts, as well as antimicrobial and antibiofilm activities of essential oils and MFDEs (methanol fractions of dichloromethane extracts) of Prangos trifida from Serbia, were investigated. Volatiles of roots, leaves, stems and fruits, and fatty acids and phytosterols in dichloromethane extracts of roots and fruits were analyzed by GC-FID-MS, whereas coumarins in MFDEs by LC-MS and some isolated coumarins by 1H-NMR. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations/minimum fungicidal concentrations (MBCs/MFCs) of essential oils and MFDEs were determined against 13 microorganisms. Antibiofilm activity was assessed against four microorganisms. Additionally, congo red and ergosterol binding assays were conducted to elucidate selected mechanisms of antibiofilm action in the case of Candida albicans. Total of 52 volatile constituents, 16 fatty acids, eight phytosterols and 10 coumarins were identified. Essential oils demonstrated significant activity, surpassing that of commercial food preservatives, against six tested molds from the Aspergillus, Penicillium and Trichoderma genera, as well as against bacteria Staphylococcus aureus and Bacillus cereus. Most of the oils strongly inhibited the formation of biofilms by S. aureus, Listeria monocytogenes and Escherichia coli. MFDEs exhibited noteworthy effects against B. cereus and the tested Aspergillus species, particularly A. niger, and significantly inhibited C. albicans biofilm formation. This inhibition was linked to a marked reduction in exopolysaccharide production, while antifungal mechanisms associated with ergosterol remained unaffected.

Synergistic effect of electrolyzed water generated by sodium chloride combined with dimethyl dicarbonate for inactivation of Listeria monocytogenes on lettuce

BACKGROUND

Electrolyzed water (EW) is recognized as an effective way to control and reduce pathogens in vegetables. However, the disinfection efficacy of EW alone is limited. In this work, the bactericidal activity and biofilm removal capability of EW, generated by adding NaCl to a portable EW generator, were investigated with special reference to Listeria monocytogenes. Furthermore, the impact of EW in combination with dimethyl dicarbonate (DMDC) in reducing the microbial load and improving the overall quality of lettuce during refrigerated storage was evaluated.

RESULTS

EW with 0.3% NaCl (SEW) had the highest bactericidal activity against L. monocytogenes. The pathogen treated with SEW exhibited lower superoxide dismutase activity and more leakage of proteins and nucleic acids than in the case of EW. Furthermore, the use of SEW resulted in changes in the cell permeability and morphology of L. monocytogenes. A decrease in adhesion and collapse of the biofilm architecture were also observed, indicating that SEW was more effective for inactivating L. monocytogenes cells compared to EW. For untreated lettuce, the populations of the total plate count and inoculated L. monocytogenes decreased by 2.47 and 2.35 log CFU g-1 , respectively, after the combined SEW/DMDC treatment for 3 min. The use of SEW alone or combined with DMDC did not negatively impact the lettuce color values, titratable acid, ascorbic acid and soluble solids compared to the control group.

CONCLUSION

SEW in combination with DMDC can be used as a novel and potentially effective disinfection strategy for ensuring the safety of vegetable consumption. © 2023 Society of Chemical Industry.

Efficacy of commercial peroxyacetic acid on Vibrio parahaemolyticus planktonic cells and biofilms on stainless steel and Greenshell™ mussel (Perna canaliculus) surfaces

The potential of using commercial peroxyacetic acid (PAA) for Vibrio parahaemolyticus sanitization was evaluated. Commercial PAA of 0.005 % (v/v, PAA: 2.24 mg/L, hydrogen peroxide: 11.79 mg/L) resulted in a planktonic cell reduction of >7.00 log10 CFU/mL when initial V. parahaemolyticus cells averaged 7.64 log10 CFU/mL. For cells on stainless steel coupons, treatment of 0.02 % PAA (v/v, PAA: 8.96 mg/L, hydrogen peroxide: 47.16 mg/L) achieved >5.00 log10 CFU/cm2 reductions in biofilm cells for eight strains but not for the two strongest biofilm formers. PAA of 0.05 % (v/v, PAA: 22.39 mg/L, hydrogen peroxide: 117.91 mg/L) was required to inactivate >5.00 log10 CFU/cm2 biofilm cells from mussel shell surfaces. The detection of PAA residues after biofilm treatment demonstrated that higher biofilm production resulted in higher PAA residues (p < 0.05), suggesting biofilm is acting as a barrier interfering with PAA diffusing into the matrices. Based on the comparative analysis of genomes, robust biofilm formation and metabolic heterogeneity within niches might have contributed to the variations in PAA resistance of V. parahaemolyticus biofilms.

Engineering acetyl-CoA metabolism to enhance stress tolerance of yeast by regulating membrane functionality

Zygosaccharomyces rouxii has excellent fermentation performance and good tolerance to osmotic stress. Acetyl-CoA is a crucial intermediate precursor in the central carbon metabolic pathway of yeast. This study investigated the effect of engineering acetyl-CoA metabolism on the membrane functionality and stress tolerance of yeast. Firstly, exogenous supplementation of acetyl-CoA improved the biomass and the ability of unsaturated fatty acid synthesis of Z. rouxii under salt stress. Q-PCR results suggested that the gene ACSS (coding acetyl-CoA synthetase) was significantly up-expressed. Subsequently, the gene ACSS from Z. rouxii was transformed and heterologously expressed in S. cerevisiae. The recombinant cells exhibited better multiple stress (salt, acid, heat, and cold) tolerance, higher fatty acid contents, membrane integrity, and fluidity. Our findings may provide a suitable means to enhance the stress tolerance and fermentation efficiency of yeast under harsh fermentation environments.

Comparison of the efficacy of physical and chemical strategies for the inactivation of biofilm cells of foodborne pathogens

Biofilm formation is a strategy in which microorganisms generate a matrix of extracellular polymeric substances to increase survival under harsh conditions. The efficacy of sanitization processes is lowered when biofilms form, in particular on industrial devices. While various traditional and emerging technologies have been explored for the eradication of biofilms, cell resistance under a range of environmental conditions renders evaluation of the efficacy of control challenging. This review aimed to: (1) classify biofilm control measures into chemical, physical, and combination methods, (2) discuss mechanisms underlying inactivation by each method, and (3) summarize the reduction of biofilm cells after each treatment. The review is expected to be useful for future experimental studies and help to guide the establishment of biofilm control strategies in the food industry.

Antibacterial and antibiofilm performance of low-frequency ultrasound against Escherichia coli O157:H7 and its application in fresh produce

Ultrasound technology has been focused on due to its unique advantages in biofilm removal compared with traditional antibacterial methods. Herein, the anti-biofilm properties of low-frequency ultrasound (LFUS) were studied against Enterohemorrhagic Escherichia coli O157: H7 (E. coli O157:H7). After ultrasonication (20 kHz, 300 W) for 5 min, the removal rate of biofilm from polystyrene sheets reached up to 99.999 %. However, the bacterial cells could not be inactivated completely even extending the duration of ultrasonic irradiation to 30 min. Fortunately, this study indicated that LFUS could efficiently weaken the metabolic capacity and biofilm-forming ability of bacterial cells separated from biofilm. It could be associated with the removal of cell surface appendages and damage to cell membrane induced by mechanical vibration and acoustic cavitation. Besides, the genetic analysis proved that the transcription level of genes involved in curli formation was significantly down-regulated during ultrasonic irradiation, thus impeding the process of irreversible adhesion and cells aggregation. Finally, the actual application effect of LFUS was also evaluated in different fresh produces model. The results of this study would provide a theoretical basis for the further application of ultrasound in the food preservation.

Drying kinetics and quality dynamics of ultrasound-assisted dried selenium-enriched germinated black rice

Black rice is a functional food due to its higher protein, fiber, iron, antioxidant compounds, and other health benefits than traditional rice. The ultrasonic (US) pretreatments (10, 20, and 50 min) followed by hot-air drying (50, 60, and 70 °C) were applied to study the drying kinetics, mathematical modeling, thermodynamics, microstructure, bioactive profile, volatile compounds and to lock the nutritional composition of selenium-enriched germinated black rice (SeGBR). Ultrasonic-treated samples exhibited a 20.5% reduced drying time than control ones. The Hii model accurately describes the drying kinetics of SeGBR with the highest R2 (>0.997 to 1.00) among the fifteen studied models. The activation energy values in US-SeGBR varied from 3.97 to 13.90 kJ/mol, while the specific energy consumption ranged from 6.45 to 12.32 kWh/kg, which was lower than untreated. The obtained thermodynamic attributes of dried black rice revealed that the process was endothermic and non-spontaneous. Gallic acid, kaempferol, and cyanidin 3-glucoside were present in high concentrations in phenolics, flavonoids, and anthocyanins, respectively. The HS-SPME-GC-MS investigation detected and quantified 55 volatile compounds. The US-treated SeGBR had more volatile compounds, which may stimulate the release of more flavorful substances. The scanning electronic micrograph shows that the US-treated samples absorbed high water through several micro-cavities. Selenium concentration was significantly higher in US-treated samples at 50 °C than in control samples. In conclusion, ultrasound-assisted hot-air drying accelerated drying and improved SeGBR quality, which is crucial for the food industry and global promotion of this healthiest rice variety.

Non-thermal treatments of strawberry pulp: The relationship between quality attributes and microstructure

The relationship between quality attributes and microstructure in strawberry pulp after pasteurization (PS), ultrasound (US), electron beam irradiation (EB), and high pressure (HP) treatments was investigated. The results showed that US treatment decreased the viscosity to the lowest by 80.15% and increased the a* value, cloudy stability, and contents of titratable acid, total soluble solid, organic acids, total phenols, total flavonoids, and total anthocyanins (TAC), as well as its antioxidant capacity, due to the decrease in particle size, the destruction of microstructure, and the release of intracellular compounds. US and EB treatments could maintain the volatile compounds. The greatest deterioration in TAC and volatile compound content was found in the pulp treated with PS and HP treatments. HP treatment was beneficial to the enhancement of apparent viscosity, organic acids, and soluble sugar. These results provided insights into the enhancement of quality attributes in strawberry pulp due to the microstructure change.

Generation, mechanisms, kinetics, and effects of gaseous chlorine dioxide in food preservation

Food preservation is a critical issue in ensuring food safety and quality. Growing concern around industrial pollution of food and demand for environmentally sustainable food has led to increased interest in developing effective and eco-friendly preservation techniques. Gaseous ClO2 has gained attention for its strong oxidizing properties, high efficacy in microorganism inactivation, and potential for preserving the attributes and nutritional quality of fresh food while avoiding the formation of toxic byproducts or unacceptable levels of residues. However, the widespread use of gaseous ClO2 in the food industry is limited by several challenges. These include large-scale generation, high cost and environmental considerations, a lack of understanding of its mechanism of action, and the need for mathematical models to predict inactivation kinetics. This review aims to provide an overview of the up-to-date research and application of gaseous ClO2 . It covers preparation methods, preservation mechanisms, and kinetic models that predict the sterilizing efficacy of gaseous ClO2 under different conditions. The impacts of gaseous ClO2 on the quality attributes of fresh produce and low-moisture foods, such as seeds, sprouts, and spices, are also summarized. Overall, gaseous ClO2 is a promising preservation approach, and future studies are needed to address the challenges in large-scale generation and environmental considerations and to develop standardized protocols and databases for safe and effective use in the food industry.

Screening, characterization, and determination of suspected additives bimatoprost and latanoprost in cosmetics using NMR and LC-MS methods

Recently, many new types of cosmetic illegal additives have been screened in the market. Most of the new additives were new drugs or analogues with very similar structures to other prohibited additives, which were difficult to be identified by liquid chromatography-mass spectrometry (LC-MS) only. Therefore, a new strategy is proposed, which is chromatographic separation combined with nuclear magnetic resonance spectroscopy (NMR) structural identification. The suspected samples were screened by ultra-high-performance liquid chromatography tandem high-resolution mass spectrometry (UPLC-Q-TOF-MS), followed by purification and extraction through silica-gel column chromatography and preparative high-performance liquid chromatography (HPLC). Finally, the extracts were identified unambiguously by NMR as bimatoprost and latanoprost, which were identified to be new cosmetic illegal additives in eyelash serums in China. Meanwhile, bimatoprost and latanoprost were quantified by high-performance liquid chromatography tandem triple quadrupole mass spectrum (HPLC-QQQ-MS/MS). The quantitative method demonstrated good linearity in the range of approximately 0.25-50 ng/mL (R² > 0.9992), with limit of detection (LOD) and limit of quantification (LOQ) values of 0.01 and 0.03 mg/kg, respectively. The accuracy, precision, and reproducibility were confirmed to be acceptable.

Transcriptome analysis reveals the molecular mechanism of cinnamaldehyde against Bacillus cereus spores in ready-to-eat beef

The purpose of this study was to investigate the antibacterial effect and mechanism of cinnamaldehyde on Bacillus cereus spores in ready-to-eat beef. The colour difference and texture of the ready-to-eat beef supplemented with cinnamaldehyde did not differ greatly from the colour and texture of the blank beef. However, cinnamaldehyde has an effective antibacterial effect on the total number of bacterial colonies and B. cereus spores in ready-to-eat beef. Transmission electron microscopy (TEM) analysis revealed that the cell membrane of B. cereus was disrupted by cinnamaldehyde, leading to leakage of intracellular components. Transcriptome sequencing (RNA-seq) indicated that the B. cereus spore resistance regulation system (sigB, sigW, rsbW, rsbV, yfkM and yflT) and phosphoenolpyruvate phosphotransferase system (PTS) (ptsH, ptsI and ptsG) respond positively to cinnamaldehyde in an adverse environment. Intracellular disorders due to damage to the cell membrane involve some transporters (copA, opuBA and opuD) and some oxidative stress systems (ywrO, scdA and katE) in the regulation of the body. However, downregulation of K⁺ transport channels (kdpD and kdpB), osmotic pressure regulation (opuE) and some oxidative stress (norR and srrA)-related genes may accelerate spore apoptosis. In addition, cinnamaldehyde also effectively inhibits the spore germination-related genes (smc, mreB and gerE). This study provides new insights into the molecular mechanism of the antibacterial effect of cinnamaldehyde on B. cereus spores in ready-to-eat beef.

Research progress on quality deterioration mechanism and control technology of frozen muscle foods

Freezing can prolong the shelf life of muscle foods and is widely used in their preservation. However, inevitable quality deterioration can occur during freezing, frozen storage, and thawing. This review explores the eating quality deterioration characteristics (color, water holding capacity, tenderness, and flavor) and mechanisms (irregular ice crystals, oxidation, and hydrolysis of lipids and proteins) of frozen muscle foods. It also summarizes and classifies the novel physical-field-assisted-freezing technologies (high-pressure, ultrasound, and electromagnetic) and bioactive antifreeze (ice nucleation proteins, antifreeze proteins, natural deep eutectic solvents, carbohydrate, polyphenol, phosphate, and protein hydrolysates), regulating the dynamic process from water to ice. Moreover, some novel thermal and nonthermal thawing technologies to resolve the loss of water and nutrients caused by traditional thawing methods were also reviewed. We concluded that the physical damage caused by ice crystals was the primary reason for the deterioration in eating quality, and these novel techniques promoted the eating quality of frozen muscle foods under proper conditions, including appropriate parameters (power, time, and intermittent mode mentioned in ultrasound-assisted techniques; pressure involved in high-pressure-assisted techniques; and field strength involved in electromagnetic-assisted techniques) and the amounts of bioactive antifreeze. To obtain better quality frozen muscle foods, more efficient technologies and substances must be developed. The synergy of novel freezing/thawing technology may be more effective than individual applications. This knowledge may help improve the eating quality of frozen muscle foods.

Dual-Species Biofilms Formed by Escherichia coli and Salmonella Enhance Chlorine Tolerance

Outbreaks of Escherichia coli and Salmonella in food might be associated with the cross-contamination of biofilms on food-contact surfaces. The knowledge of the sanitization of mono-species biofilm on the food-contact surface is well established, while mixed-species biofilm occurs more naturally, which could profoundly affect the efficacy of sanitizer.

Sigma factor RpoS positively affects the spoilage activity of Shewanella baltica and negatively regulates its adhesion effect

Shewanella baltica is the dominant bacterium that causes spoilage of seafood. RpoS is an alternative sigma factor regulating stress adaptation in many bacteria. However, the detailed regulatory mechanism of RpoS in S. baltica remains unclear. This study aims to investigate the regulatory function of RpoS on spoilage activity and adhesion ability in S. baltica. Results revealed that RpoS had no effect on the growth of S. baltica, but positively regulated the spoilage potential of S. baltica accompanied by a slower decline of total volatile basic nitrogen, lightness, and the sensory score of fish fillets inoculated with rpoS mutant. RpoS negatively regulated the adhesion ability, which was manifested in that the bacterial number of rpoS mutant adhered to stainless steel coupon was higher than that of the S. baltica in the early stage, and the biofilm formed on glass slide by rpoS mutant was thicker and tighter compared with S. baltica. Transcriptomic analysis showed that a total of 397 differentially expressed genes were regulated by RpoS. These genes were mainly enrichment in flagellar assembly, fatty acid metabolism/degradation, and RNA degradation pathways, which were associated with motility, biofilm formation and cold adaptation. This study demonstrated that RpoS is a primary regulator involved in flagellar assembly mediated biofilm formation and cold adaptation-related spoilage activity of S. baltica. Our research will provide significant insights into the control of microbiological spoilage in seafood.

The Role of ptsH in Stress Adaptation and Virulence in Cronobacter sakazakii BAA-894

Cronobacter sakazakii, an emerging foodborne pathogen that was isolated primarily from powdered infant formula, poses an important issue in food safety due to its high stress tolerance and pathogenicity. The Hpr (encoded by ptsH gene) has been shown to regulate carbon metabolism as well as stress response and virulence. However, the functional properties of ptsH in C. sakzakii have not been investigated. In this study, we clarified the role of ptsH in the C. sakzakii stress response and virulence, and explored its possible regulatory mechanism by RNA-seq. Compared with wild-type, the ΔptsH mutant showed a slower growth rate in the log phase but no difference in the stationary phase. Moreover, the resistance to heat stress (65 °C, 55 °C), simulated gastric fluid (pH = 2.5), biofilm formation and adhesion to HT-29 cells of ΔptsH mutant were significantly decreased, whereas the oxidative resistance (1, 5, 10 mM H₂O₂), osmotic resistance (10%, 15%, 20% NaCl), and superoxide dismutase activity were enhanced. Finally, RNA-seq analysis revealed the sulfur metabolism pathway is significantly upregulated in the ΔptsH mutant, but the bacterial secretion system pathway is dramatically downregulated. The qRT-PCR assay further demonstrated that the ΔptsH mutant has elevated levels of genes that are related to oxidative and osmotic stress (sodA, rpoS, cpxA/R, osmY). This study provides a great understanding of the role of ptsH in diverse stress responses and virulence in C. sakazakii, and it contributes to our understanding of the genetic determinant of stress resistance and pathogenicity of this important foodborne pathogen.

A high-throughput integrated biofilm-on-a-chip platform for the investigation of combinatory physicochemical responses to chemical and fluid shear stress

Physicochemical conditions play a key role in the development of biofilm removal strategies. This study presents an integrated, double-layer, high-throughput microfluidic chip for real-time screening of the combined effect of antibiotic concentration and fluid shear stress (FSS) on biofilms. Biofilms of Escherichia coli LF82 and Pseudomonas aeruginosa were tested against gentamicin and streptomycin to examine the time dependent effects of concentration and FSS on the integrity of the biofilm. A MatLab image analysis method was developed to measure the bacterial surface coverage and total fluorescent intensity of the biofilms before and after each treatment. The chip consists of two layers. The top layer contains the concentration gradient generator (CGG) capable of diluting the input drug linearly into four concentrations. The bottom layer contains four expanding FSS chambers imposing three different FSSs on cultured biofilms. As a result, 12 combinatorial states of concentration and FSS can be investigated on the biofilm simultaneously. Our proof-of-concept study revealed that the reduction of E. coli biofilms was directly dependent upon both antibacterial dose and shear intensity, whereas the P. aeruginosa biofilms were not impacted as significantly. This confirmed that the effectiveness of biofilm removal is dependent on bacterial species and the environment. Our experimental system could be used to investigate the physicochemical responses of other biofilms or to assess the effectiveness of biofilm removal methods.

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.

Integrated metabolomics of "big six" Escherichia coli on pea sprouts to organic acid treatments

Naturally occurring organic acids (OAs) have demonstrated satisfactory effects in inhibiting common pathogens on fresh produce; however, their effectiveness on "big six" Escherichia coli serotypes, comprised of E. coli O26:H11, O45:H2, O103:H11, O111, O121:H19 and O145, remained unaddressed. Regarding this, using nuclear magnetic resonance (NMR) spectroscopy and ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS), the sanitising efficacy and the underlying antimicrobial mechanisms of 10-min treatments with 0.2 mol/L ascorbic acid (AA), citric acid (CA) and malic acid (MA) against the "big six" strains on pea sprouts were thoroughly investigated in this study. Despite the varying antimicrobial efficacy (AA: 0.12-0.99, CA: 0.36-1.72, MA: 0.75-3.28 log CFU/g reductions), the three OAs induced consistent metabolic changes in the E. coli strains, particularly in the metabolism of membrane lipids, nucleotide derivatives and amino acids. Comparing all strains, the most OA-resistant strain, O26 (0.36-1.12 log CFU/g reductions), had the largest total amino acids accumulated to resist osmotic stress; its ulteriorly suppressed cell activity further strengthened its endurance. In contrast, the lowest OA-resistance of O121 (0.99-3.28 log CFU/g reductions) might be explained by the depletion of putrescine, an oxidative stress regulator. Overall, the study sheds light on the effectiveness of a dual-platform metabolomics investigation in elucidating the metabolic responses of "big six" E. coli to OAs. The manifested antimicrobial effects of OAs, especially MA, together with the underlying metabolic perturbations detected in the "big six" strains, provided scientific basis for applying OA treatments to future fresh produce sanitisation.

Effect of chlorine sanitizer on metabolic responses of Escherichia coli biofilms "big six" during cross-contamination from abiotic surface to sponge cake

The effect of chlorine on Escherichia coli biofilm O157:H7 are well established; however, the effect on biofilm adhesion to food as well as the six emerging E. coli serotypes ("big six") have not been fully understood. Chlorine sanitization with 1-min 100 mg/L was applied against seven pathogenic E. coli (O111, O121:H19, O45:H2, O26:H11, O103:H11, O145, and O157:H7) biofilms on high-density polyethylene (HDPE) and stainless steel (SS) coupons, respectively. Using sponge cake as a food model, the adhesion behavior was evaluated by comparison of bacteria transfer rate before and after treatment. Besides, the metabolic profiles of biofilms were analyzed by nuclear magnetic resonance (NMR) spectrometer. A significant decrease in transfer rate (79% decline on SS and 33% decline on HDPE) was recorded as well as the distinctive pattern between SS and HDPE coupons was also noticed, with a low population (6-7 log CFU/coupon) attached and low survivals (0-3 log CFU/coupon) upon chlorine on SS, while high population (7-8 log CFU/coupon) attached and high survivals (5-7 log CFU/coupon) on HDPE. Moreover, O121:H19 and O26:H11 demonstrated the highest resistance to chlorine with the least metabolic status and pathways affected. O103:H11, O145, and O111 followed similar metabolic patterns on both surfaces. Distinct metabolic patterns were found in O45:H2 and O157:H7, where the former had more affected metabolic status and pathways on SS but less on HDPE, whereas the latter showed an opposite trend. Overall, a potential contamination source of STEC infection in flour products was demonstrated and metabolic changes induced by chlorine were revealed by NMR-based metabolomics, which provides insights to avoid "big six" biofilms contamination in food.

A Flagella Hook Coding Gene flgE Positively Affects Biofilm Formation and Cereulide Production in Emetic Bacillus cereus

Bacillus cereus, an important foodborne pathogen, poses a risk to food safety and quality. Robust biofilm formation ability is one of the key properties that is responsible for the food contamination and food poisoning caused by B. cereus, especially the emetic strains. To investigate the mechanism of biofilm formation in emetic B. cereus strains, we screened for the mutants that fail to form biofilms by using random mutagenesis toward B. cereus 892-1, an emetic strain with strong biofilm formation ability. When knocking out flgE, a flagellar hook encoding gene, the mutant showed disappearance of flagellar structure and swimming ability. Further analysis revealed that both pellicle and ring presented defects in the null mutant compared with the wild-type and complementary strains. Compared with the flagellar paralytic strains ΔmotA and ΔmotB, the inhibition of biofilm formation by ΔflgE is not only caused by the inhibition of motility. Interestingly, ΔflgE also decreased the synthesis of cereulide. To our knowledge, this is the first report showing that a flagellar component can both affect the biofilm formation and cereulide production in emetic B. cereus, which can be used as the target to control the biohazard of emetic B. cereus.

Effects of electrolysed water and levulinic acid combination on microbial safety and polysaccharide nanostructure of organic strawberry

This study aimed to better understand the effects of acidic electrolysed water (AEW, 4 mg/L) and levulinic acid (LA, food grade, 2%) combination on organic strawberry over 7 days. This combined method reduced the population of strawberry's natural microbiota by 1-2 log CFU/g and kept the level of inoculated Escherichia coli O157:H7 and Salmonella below the detection limit (2 log CFU/g) during the whole storage period. Meanwhile, AEW + LA did not affect the physicochemical qualities of strawberries significantly, maintaining most texture and biochemical attributes at an acceptable level (e.g., firmness, colour, soluble solids content and organic acid content). Atomic force microscopy further revealed that the treatment containing LA preserved the sodium carbonate soluble pectin (SSP) nanostructure best by maintaining their length and height, and slowed the breakdown of SSP chains by promoting acid-induced bonding and soluble pectin precipitation. These results demonstrated that low concentration AEW and LA combination is a promising sanitising approach for organic strawberry preservation.

Formation and Transfer of Multi-Species Biofilms Containing E. coli O103:H2 on Food Contact Surfaces to Beef

Interactions of Shiga toxin–producing E. coli (STEC; O103:H2) with lactic acid bacteria (LAB) or spoilage bacteria (SP) multispecies biofilms on polyurethane (TPU) and stainless-steel (SS) were assessed at 10 and 25°C under wet and dry conditions after 6, 30, and 60 days of storage. One LAB T1: Carnobacterium piscicola + Lactobacillus bulgaricus, and two SP T2: Comamonas koreensis + Raoultella terrigena; T3: Pseudomonas aeruginosa + C. koreensis were assessed for their ability to form multispecies biofilms with O103:H2. O103:H2 single-species biofilms served as a control positive (T4). Coupons were stored dry (20–50% relative humidity; RH) or moist (60–90% RH) for up to 60 days, at which point O103:H2 transfer to beef and survival was evaluated. At 25°C, T3 decreased beef contamination with O103:H2 by 2.54 log₁₀ CFU/g (P < 0.001). Overall, at 25°C contamination of beef with O103:H2 decreased (P < 0.001) from 3.17 log₁₀ CFU/g on Day 6 to 0.62 log₁₀ CFU/g on Day 60. With 60 days dry biofilms on TPU, an antagonistic interaction was observed among O103:H2 and multispecies biofilm T1 and T3. E. coli O103:H2 was not recovered from T1 and T3 after 60 days but it was recovered (33%) from T2 and T4 dry biofilms. At 10°C, contamination of beef with O103:H2 decreased (P < 0.001) from 1.38 log₁₀ CFU/g after 6 days to 0.47 log₁₀ CFU/g after 60 days. At 10°C, recovery of O103:H2 from 60 days dry biofilms could only be detected after enrichment and was always higher for T2 than T4 biofilms. Regardless of temperature, the transfer of O103:H2 to beef from the biofilm on TPU was greater (P < 0.001) than SS. Moist biofilms also resulted in greater (P < 0.001) cell transfer to beef than dry biofilms at 10 and 25°C. Development of SP or LAB multispecies biofilms with O103:H2 can either increase or diminish the likelihood of beef contamination. Environmental conditions such as humidity, contact surface type, as well as biofilm aging all can influence the risk of beef being contaminated by STEC within multi-species biofilms attached to food contact surfaces.

Ultrasound assisted aqueous two-phase extraction of polysaccharides from Cornus officinalis fruit: Modeling, optimization, purification, and characterization

Ultrasound assisted aqueous two-phase extraction of polysaccharides from Cornus officinalis fruit was modeled by response surface methodology (RSM) and artificial neural network (ANN), and optimized using genetic algorithm coupled with ANN (GA-ANN). Statistical analysis showed that the models obtained by RSM and ANN could accurately predict the Cornus officinalis polysaccharides (COPs) yield. However, ANN prediction was more accurate than RSM. The optimum extraction parameters to achieve the highest COPs yield (7.85 ± 0.09)% was obtained at the ultrasound power of 350 W, extraction temperature of 51 ℃, liquid-to-solid ratio of 17 mL/g, and extraction time of 38 min. Subsequently, the crude COPs were further purified via DEAE-52 and Sephadex G-100 chromatography to obtain a homogenous fraction (COPs-4-SG, 33.64 kDa) that contained galacturonic acid, arabinose, mannose, glucose, and galactose in a molar ratio of 34.82:14.19:6.75:13.48:12.26. The structure of COPs-4-SG was also characterized with UV-vis, fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy (SEM), Congo-red test, and circular dichroism (CD). The findings provide a feasible way for the extraction, purification, and optimization of polysaccharides from plant resources.