Antibacterial activity and action mechanism of microencapsulated dodecyl gallate with methyl-β-cyclodextrin

Biocontrol of Salmonella Schwarzengrund and Escherichia coli O157:H7 planktonic and biofilm cells via combined treatment of polyvalent phage and sodium hexametaphosphate on foods and food contact surfaces

Salmonella Schwarzengrund and Escherichia coli O157:H7 are ones of foodborne pathogens that can produce biofilms and cause serious food poisoning. Bacteriophages are an emerging antibacterial strategy used to prevent foodborne pathogen contamination in the food industry. In this study, the combined antibacterial effects of the polyvalent phage PS5 and sodium hexametaphosphate (SHMP) against both pathogens were investigated to evaluate their effectiveness in food applications. The combined treatment with phage PS5 (multiplicity of infection, MOI = 10) and 1.0% SHMP inhibited the growth of S. Schwarzengrund and E. coli O157:H7, and the viable counts of both decreased by more than 2.45 log CFU/mL. In KAGOME vegetable and fruit mixed juice, the combined treatment with PS5 (MOI = 100) and 1.0% SHMP also resulted in significant pathogen inactivation at 4 °C after 24 h. PS5 (1010 PFU/mL) and 1.0% SHMP showed stronger synergistic effects on biofilm formation and the removal of established biofilms on polystyrene plates. Additionally, we evaluated their combined effects on reducing the biofilms of S. Schwarzengrund and E. coli O157:H7 on glass tubes and cabbage leaves at 4 °C. These findings indicate the utility of this approach in the biocontrol of the planktonic and biofilm cells of S. Schwarzengrund and E. coli O157:H7 on foods and food contact surfaces.

Controlled release characteristics of alkyl gallates and gallic acid from β-cyclodextrin inclusion complexes of alkyl gallates

The freeze-drying approach was used to create inclusion complexes utilizing alkyl gallates and β-cyclodextrin, namely dodecyl gallate, octyl gallate, butyl gallate, and ethyl gallate, which are exemplary examples of phenolic esters. The everted-rat-gut-sac model demonstrated that the inclusion complexes released alkyl gallates, which were subsequently hydrolyzed to generate free gallic acid, as evidenced by HPLC-UV analysis. Both gallic acid and short-chain alkyl gallates were capable of permeating the small intestinal membrane. The transport rate of gallic acid (or alkyl gallates) exhibited an initial rise followed by a drop when the carbon-chain lengths varied. The inclusion complex groups exhibited a superior sustained-release effect compared to the comparable alkyl gallates groups, thus possibly leading to higher bioavailability and stronger bioactivity. Moreover, altering the length of the carbon chain will allow for the effortless achievement of regulated release of phenolic compounds and short-chain phenolic esters from such β-cyclodextrin inclusion complexes.

Antibacterial effect and mechanism of theaflavin against Listeria monocytogenes and its application on apple skins

Theaflavin 3,3'-digallate (TF3), a major polyphenolic component of black tea, exhibits antibacterial effects against many foodborne pathogens. However, the antibacterial mechanisms of TF3 against Listeria monocytogenes remain unclear. In this study, we investigated the effects of TF3 on viability, biofilm, and membrane function of L. monocytogenes by the conventional plating method, crystal violet staining, and microscopy using fluorescent dyes JC-1 and Laurdan, respectively. It was found that TF3 showed excellent antibacterial activity against L. monocytogenes with the minimum inhibitory concentration of 62.5 mg/L. The viable count determined on TSA decreased by 3 log after the treatment for 2 h with TF3 at 62.5 mg/L. The viable count determined on TSA containing 4% NaCl decreased by more than 4 log after the treatment for 30 min with TF3 at the same concentration, suggesting that TF3 gave damage on the cells, enhancing the antibacterial action of 4% NaCl, but the damage was recoverable in the absence of 4% NaCl. To explore the antibacterial mechanisms of TF3, the effects of TF3 on membrane potential and membrane fluidity were investigated. TF3 reduced both membrane potential and fluidity of L. monocytogenes at 62.5 mg/L, suggesting that TF3 damaged the structural integrity of the cell membrane. TF3 reduced biofilm mass of mature biofilm of L. monocytogenes. Moreover, THEAFLAVIN TF40, a commercially available Camellia sinensis leaf extract containing TF3, reduced viable count of L. monocytogenes by 2 log on apple skin. These results suggest the potential of theaflavins as a natural anti-Listeria disinfectant.

Effects of PEF on Cell and Transcriptomic of Escherichia coli

Pulsed electric field (PEF) is an up-to-date non-thermal processing technology with a wide range of applications in the food industry. The inactivation effect of PEF on Escherichia coli was different under different conditions. The E. coli inactivated number was 1.13 ± 0.01 lg CFU/mL when PEF was treated for 60 min and treated with 0.24 kV/cm. The treatment times were found to be positively correlated with the inactivation effect of PEF, and the number of E. coli was reduced by 3.09 ± 0.01 lg CFU/mL after 100 min of treatment. The inactivation assays showed that E. coli was inactivated at electrical intensity (0.24 kV/cm) within 100 min, providing an effective inactivating outcome for Gram-negative bacteria. The purpose of this work was to investigate the cellular level (morphological destruction, intracellular macromolecule damage, intracellular enzyme inactivation) as well as the molecular level via transcriptome analysis. Field Emission Scanning Electron Microscopy (TFESEM) and Transmission Electron Microscope (TEM) results demonstrated that cell permeability was disrupted after PEF treatment. Entocytes, including proteins and DNA, were markedly reduced after PEF treatment. In addition, the activities of Pyruvate Kinase (PK), Succinate Dehydrogenase (SDH), and Adenosine Triphosphatase (ATPase) were inhibited remarkably for PEF-treated samples. Transcriptome sequencing results showed that differentially expressed genes (DEGs) related to the biosynthesis of the cell membrane, DNA replication and repair, energy metabolism, and mobility were significantly affected. In conclusion, membrane damage, energy metabolism disruption, and other pathways are important mechanisms of PEF's inhibitory effect on E. coli.

Effect of Pretreatments on the Chemical, Bioactive and Physicochemical Properties of Cinnamomum camphora Seed Kernel Extracts

Cinnamomum camphora seed kernels (CCSKs) are rich in phytochemicals, especially plant extracts. Phytochemicals play a vital role in therapy due to their strong antioxidant and anti-inflammatory activities. Extracts from CCSK can be obtained through multiple steps, including pretreatment, extraction and purification, and the purpose of pretreatment is to separate the oil from other substances in CCSKs. However, C. camphora seed kernel extracts (CKEs) were usually considered as by-products and discarded, and their potential bioactive values were underestimated. Additionally, little has been known about the effect of pretreatment on CKE. This study aimed to investigate the effects of pretreatment methods (including the solvent extraction method, cold pressing method, aqueous extraction method and sub-critical fluid extraction method) on the extraction yields, phytochemical profiles, volatile compounds and antioxidant capacities of different CKE samples. The results showed that the CKE samples were rich in phenolic compounds (15.28-20.29%) and alkaloids (24.44-27.41%). The extraction yield, bioactive substances content and in vitro antioxidant capacity of CKE pretreated by the sub-critical fluid extraction method (CKE-SCFE) were better than CKEs obtained by other methods. CKE pretreated by the solvent extraction method (CKE-SE) showed the best lipid emulsion protective capacity. Moreover, the volatile substances composition of the CKE samples was greatly influenced by the pretreatment method. The results provided a fundamental basis for evaluating the quality and nutritional value of CKE and increasing the economic value of by-products derived from CCSK.

Antimicrobial polysaccharide hydrogels embedded with methyl-β-cyclodextrin/thyme oil inclusion complexes for exceptional mechanical performance and chilled chicken breast preservation

While hydrogels have potential for food packaging, limited research on hydrogels with excellent mechanical performance and antibacterial activity for preserving chicken breasts. Herein, we created antibacterial hydrogels by embedding methyl-β-cyclodextrin/thyme oil inclusion complexes (MCD/TO-ICs) into a polyvinyl alcohol matrix containing dendrobium polysaccharides and guar gum in varying ratios using freeze-thaw cycling method. The resulting hydrogels exhibited a more compact structure than those without MCD/TO-ICs, enhancing thermal stability and increasing glass transition temperature due to additional intermolecular interactions between polymer chains that inhibited chain movement. XRD analysis showed no significant changes in crystalline phase, enabling formation of a 3D network through abundant hydrogen bonding. Moreover, the hydrogel demonstrated exceptional durability, with a toughness of 350 ± 25 kJ/m3 and adequate tearing resistance of 340 ± 30 J/m2, capable of lifting 3 kg weight, 1200 times greater than the hydrogel itself. Additionally, the hydrogels displayed excellent antimicrobial activity and antioxidant properties. Importantly, the hydrogels effectively maintained TVB-N levels and microbial counts within acceptable ranges, preserving sensory properties and extending the shelf life of chilled chicken breasts by four days. This study highlights the potential of MCD/TO-IC-incorporated polysaccharide hydrogels as safe and effective active packaging solutions for preserving chilled chicken in food industry.

Studies on the Inhibition Mechanism of Linalyl Alcohol against the Spoilage Microorganism Brochothrix thermosphacta

The aim of this study was to investigate the bacterial inhibitory ability and mechanism of action of linalyl alcohol against B. thermosphacta. Linalyl alcohol causes the leakage of intracellular material by disrupting the cell wall and exposing the hydrophobic phospholipid bilayer, which binds to bacterial membrane proteins and alters their structure. In addition, linalyl alcohol causes cell membrane damage by affecting fatty acids and proteins in the cell membrane. By inhibiting the synthesis of macromolecular proteins, the normal physiological functions of the bacteria are altered. Linalyl alcohol binds to DNA in both grooved and embedded modes, affecting the normal functioning of B. thermosphacta, as demonstrated through a DNA interaction analysis.

Enhanced Antibacterial Efficiency and Anti-Hygroscopicity of Gum Arabic-ε-Polylysine Electrostatic Complexes: Effects of Thermal Induction

The aim of this investigation was to scrutinize the effects of a thermal treatment on the electrostatic complex formed between gum arabic (GA) and ε-polylysine (ε-PL), with the goal of improving the antibacterial properties and reducing the hygroscopicity of ε-PL. The heated complex with a ratio of 1:4 exhibited an encapsulation efficiency of 93.3%. Additionally, it had an average particle size of 350.3 nm, a polydispersity index of 0.255, and a zeta potential of 18.9 mV. The formation of the electrostatic complex between GA and ε-PL was confirmed through multispectral analysis, which demonstrated the participation of hydrogen bonding and hydrophobic and electrostatic interactions, as well as the enhanced effect of heat treatment on these forces within the complex. The complex displayed a core-shell structure, with a regular distribution and a shape that was approximately spherical, as observed in the transmission electron microscopy images. Additionally, the heated GA-ε-PL electrostatic composite exhibited favorable antibacterial effects on Salmonella enterica and Listeria monocytogenes, with reduced minimum inhibitory concentrations (15.6 μg/mL and 62.5 μg/mL, respectively) and minimum bactericidal concentrations (31.3 μg/mL and 156.3 μg/mL, respectively) compared to free ε-PL or the unheated electrostatic composite. Moreover, the moisture absorption of ε-PL reduced from 92.6% to 15.0% in just 48 h after being incorporated with GA and subsequently subjected to heat. This research showed a way to improve the antibacterial efficiency and antihygroscopicity of ε-PL, reducing its application limitations as an antimicrobial substance to some extent.

Anthocyanins from Malus spp. inhibit the activity of Gymnosporangium yamadae by downregulating the expression of WSC, RLM1, and PMA1

Malus plants are frequently devastated by the apple rust caused by Gymnosporangium yamadae Miyabe. When rust occurs, most Malus spp. and cultivars produce yellow spots, which are more severe, whereas a few cultivars accumulate anthocyanins around rust spots, forming red spots that inhibit the expansion of the affected area and might confer rust resistance. Inoculation experiments showed that Malus spp. with red spots had a significantly lower rust severity. Compared with M. micromalus, M. 'Profusion', with red spots, accumulated more anthocyanins. Anthocyanins exhibited concentration-dependent antifungal activity against G. yamadae by inhibiting teliospores germination. Morphological observations and the leakage of teliospores intracellular contents evidenced that anthocyanins destroyed cell integrity. Transcriptome data of anthocyanins-treated teliospores showed that differentially expressed genes were enriched in cell wall and membrane metabolism-related pathways. Obvious cell atrophy in periodical cells and aeciospores was observed at the rust spots of M. 'Profusion'. Moreover, WSC, RLM1, and PMA1 in the cell wall and membrane metabolic pathways were progressively downregulated with increasing anthocyanins content, both in the in vitro treatment and in Malus spp. Our results suggest that anthocyanins play an anti-rust role by downregulating the expression of WSC, RLM1, and PMA1 to destroy the cell integrity of G. yamadae.

Antibacterial Effect and Possible Mechanism of Salicylic Acid Microcapsules against Escherichia coli and Staphylococcus aureus

Microcapsules serve as a feasible formulation to load phenolic substances such as salicylic acid, a natural and safe antimicrobial agent. However, the antibacterial efficacy of salicylic acid microcapsules (SAMs) remains to be elucidated. Here, salicylic acid/β-cyclodextrin inclusion microcapsules were subjected to systematic antibacterial assays and preliminary antibacterial mechanism tests using Escherichia coli and Staphylococcus aureus as target organisms. It was found that the core-shell rhomboid-shaped SAMs had a smooth surface. SAMs exhibited a minimum inhibitory concentration (MIC) and a minimum bactericidal concentration (MBC) of 4 mg/mL against both bacteria. In the growth inhibition assay, 1/4 × MIC, 1/2 × MIC, and 1 × MIC of SAMs effectively retarded bacterial growth, and this effect was more prominent with the rise in the level of SAMs. Practically, SAMs possessed a rapid bactericidal effect at the 1 × MIC level with a reduction of more than 99.9% bacterial population within 10 min. A pronounced sterilization activity against E. coli and S. aureus was also observed when SAMs were embedded into hand sanitizers as antimicrobial agents. Moreover, exposure of both bacteria to SAMs resulted in the leakage of intracellular alkaline phosphatases and macromolecular substances (nucleic acids and proteins), which indicated the disruption of bacterial cell walls and cell membranes. In conclusion, SAMs were able to inactivate E. coli and S. aureus both in vitro and in situ, highlighting the promising utilization of this formulation for antimicrobial purposes in the area of food safety and public health.

Antibacterial Activity and Mechanism of Polygonum orientale L. Essential Oil against Pectobacterium carotovorum subsp. carotovorum

Infected by Pectobacterium carotovorum subsp. carotovorum (Pcc), the quality of Chinese cabbage could severely decline. Using chemical bactericides to control Pcc could cause food safety problems. Thus, we investigated the optimum extraction conditions, antibacterial activity, chemical compounds and antibacterial mechanism of Polygonum orientale L. essential oil (POEO) against Pcc in order to search a new way to control Pcc. The optimum extraction conditions of POEO (soaking time 2.6 h, extraction time 7.7 h and ratio of liquid to solid 10.3 mL/g) were optimized by response surface methodology. The minimum inhibitory concentration (MIC) of POEO against Pcc was 0.625 mg/mL. The control efficiency of protective activity of POEO against Pcc was 74.67~92.67%, and its curative activity was 76.00~93.00%. Then, 29 compounds were obtained by GC-MS; the prime compounds of POEO were phytol, phytone, n-pentacosane, 1-octen-3-ol and β-ionone. It was verified that, compared with control samples, POEO destroyed cell morphology. It increased surface potential, increased hydrophobicity, damaged cell walls, destroyed the integrity and permeability of cell membrane, reduced membrane potential (MP), and changed membrane protein conformation. It inhibited the activities of pyruvate kinase (PK), succinate dehydrogenase (SDH) and adenosine triphosphatase (ATPase). Briefly, the results of this study demonstrate that POEO showed effective inhibitory activity against Pcc, thus POEO could have potential application in controlling Pcc.

Isolation, Identification and Antibacterial Mechanism of the Main Antibacterial Component from Pickled and Dried Mustard (Brassica juncea Coss. var. foliosa Bailey)

Our previous study showed that the ethyl acetate fraction (EAF) from an ethanolic extract of pickled and dried mustard (Brassica juncea Coss. var. foliosa Bailey) had significant antibacterial activity. Here, the EAF was further separated into seven sub-fractions by silica gel column chromatography. The antibacterial activities of the EAF and its sub-fractions against Staphylococcus aureus and Pseudomonas fluorescens were assessed using the agar diffusion method and double dilution method. Among the seven sub-fractions, the third sub-fraction (Fr 3) possessed the strongest antibacterial activity. The main component in Fr 3 was identified by GC-MS, UV-vis, FT-IR, HPLC, ¹H NMR and ¹³C NMR techniques, and was found to be succinic acid. The content of succinic acid in Fr 3 was determined as 88.68% (w/w) by HPLC. Finally, the antibacterial mechanism of succinic acid against the tested strains was explored by determining the intracellular component leakage, measuring the cell particle size and observing the cell morphology. The results showed that succinic acid could damage the cell membrane structure and intracellular structure to increase the leakage of cell components and reduce the cell particle size. Our results suggest that succinic acid could be used in food industry to control bacterial contamination by S. aureus and P. fluorescens.

In Vitro Antibacterial Mechanism of High-Voltage Electrostatic Field against Acinetobacter johnsonii

This study aimed to investigate the antibacterial properties and mechanisms of a high-voltage static electric field (HVEF) in Acinetobacter johnsonii, which were assessed from the perspective of biochemical properties and stress-related genes. The time/voltage-kill assays and growth curves showed that an HVEF decreased the number of bacteria and OD600 values. In addition, HVEF treatment caused the leakage of cell contents (nucleic acids and proteins), increased the electrical conductivity and amounts of reactive oxygen substances (ROS) (16.88 fold), and decreased the activity of Na+ K+-ATPase in A. johnsonii. Moreover, the changes in the expression levels of genes involved in oxidative stress and DNA damage in the treated A. johnsonii cells suggested that HVEF treatment could induce oxidative stress and DNA sub-damage. This study will provide useful information for the development and application of an HVEF in food safety.

Immobilization of lipase on β-cyclodextrin grafted and aminopropyl-functionalized chitosan/Fe3O4 magnetic nanocomposites: An innovative approach to fruity flavor esters esterification

The lipase from Bacillus licheniformis NCU CS-5 was immobilized onto β-cyclodextrin (CD) grafted and aminopropyl-functionalized chitosan-coated Fe₃O₄ magnetic nanocomposites (Fe₃O₄-CTS-APTES-GA-β-CD). Fourier transform infrared spectroscopy, thermogravimetry analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy showed that not only the functionalized magnetic nanoparticles were synthesized but also the immobilized lipase was successfully produced. The immobilized lipase exhibited higher optimal pH value (10.5) and temperature (60℃) than the free lipase. The pH and thermal stabilities of the immobilized lipase were improved significantly compared to the free lipase. The immobilized lipase remained more than 80% of the relative activity at temperature of 60 ℃ and pH 12.0. The immobilized lipase also remained over 80% of its relative activity after 28 days of storage and 15 cycles of application. The application of the immobilized lipase in esterification of isoamyl acetate and pentyl valerate showed that maximum esterification efficiency was achieved in n-hexane having 68.0% and 89.2% respectively. Therefore, these results indicated that the Fe₃O₄-CTS-APTES-GA-β-CD nanoparticles are novel carriers for immobilizing enzyme, and the immobilized lipase can be used as an innovative green approach to the synthesis of fruity flavor esters in food industry.

Covalent modification by phenolic extract improves the structural properties and antioxidant activities of the protein isolate from Cinnamomum camphora seed kernel

In this study, protein isolate (PI) and purified phenolic extract (PPE) were prepared from Cinnamomum camphora seed kernel (CCSK). The effects of covalent modification of PI by PPE at different concentrations (1, 2, 3, 4 and 5%, w/w) were investigated with respect to structural properties and antioxidant activities of protein. Fifteen bioactive compounds in PPE were tentatively identified by UPLC-ESI-MSⁿ. With the increase of PPE concentration, the turbidity, covalent binding rate, phenolic content and color intensity of the PI-PPE complexes were gradually increased. Fourier transform infrared spectroscopy and circular dichroism spectroscopy analysis showed that the secondary and tertiary structures of the complexes were changed and became greater order than PI. Furthermore, the complexes exhibited stronger thermal stability and antioxidant activities than those of PI. These results suggested that the protein-phenolic covalent complexes obtained from CCSK may have great potential to be used in food formulations as functional ingredients.

Development of bactericidal spinel ferrite nanoparticles with effective biocompatibility for potential wound healing applications

The current study was devised to explore the antibacterial activity and underlying mechanism of spinel ferrite nanoparticles (NPs) along with their biocompatibility and wound healing potentials. In this regard, nickel ferrite and zinc/nickel ferrite NPs were synthesized via a modified co-precipitation method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy Energy-dispersive X-ray spectroscopy (EDX). The biocompatibility of the synthesized NPs with human dermal fibroblast (HDF) and red blood cells (RBCs) was assessed. The biocompatible concentrations of the NPs were used to investigate the antimicrobial activity against various pathogenic Gram-negative and Gram-positive bacteria. The mode of bactericidal action was also explored. In vitro scratch assay was performed to evaluate the wound healing potential of NPs. The SEM-EDX analysis showed that the average particles size of nickel ferrite and zinc/nickel ferrite were 49 and 46 nm, respectively, with appropriate elemental composition and homogenous distribution. The XRD pattern showed all the characteristic diffraction peaks of spinel ferrite NPs, which confirmed the synthesis of the pure phase cubic spinel structure. The biocompatible concentration of nickel ferrite and zinc/nickel ferrite NPs was found to be 250 and 125 μg ml-1, respectively. Both the NPs showed inhibition against all the selected strains in the concentration range of 50 to 1000 μg ml-1. Studies on the underlying antimicrobial mechanism revealed damage to the cell membrane, protein leakage, and intracellular reactive oxygen species production. The in vitro scratch assay confirmed the migration and proliferation of fibroblast with artificial wound shrinkage. This study shows that nickel ferrite and zinc/nickel ferrite NPs could be a strong candidate for antibacterial and wound healing nano-drugs.