Citrus fruit extracts with carvacrol and thymol eliminated 7-log acid-adapted Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes: A potential of effective natural antibacterial agents

Preparation and Efficacy of Microemulsion Carvacrol-Based Fruit and Vegetable Cleaner and Its Application on Cherry Tomatoes

Carvacrol, a natural plant compound with antibacterial, antioxidant, and various biological activities, serves as the basis for developing a micro-emulsion fruit and vegetable cleaner. The study found that carvacrol demonstrated a minimum inhibitory concentration (MIC) ranging between 0.25 and 0.5 mg/mL against four foodborne pathogenic bacteria and three spoilage fungi. The formulated cleaner, containing 67 mg/mL of carvacrol, demonstrated superior characteristics (a particle size of 228 nm, an absolute zeta potential of 21.4 mv, and a stability coefficient of 91.2%). Remarkably, the cleaner remained stable when stored at room temperature for at least 3 months. Its efficacy against pesticides ranged from 76% to 91%. The cleaning effectively inhibited microbial colonies and the decay rate of cherry tomatoes during storage at 4 °C. Furthermore, the cleaning treatment was found to minimize changes in color and hardness. Overall, this study provides evidence that a fruit and vegetable cleaner based on carvacrol enhances the safety of the food industry effectively.

Investigating the synergistic antibacterial effects of chlorogenic and p-coumaric acids on Shigella dysenteriae

Chlorogenic acid (CGA) is a well-known plant secondary metabolite exhibiting multiple physiological functions. The present study focused on screening for synergistic antibacterial combinations containing CGA. The combination of CGA and p-coumaric acid (pCA) exhibited remarkably enhanced antibacterial activity compared to that when administering the treatment only. Scanning electron microscopy revealed that a low-dose combination treatment could disrupt the Shigella dysenteriae cell membrane. A comprehensive analysis using nucleic acid and protein leakage assay, conductivity measurements, and biofilm formation inhibition experiments revealed that co-treatment increased the cell permeability and inhibited the biofilm formation substantially. Further, the polyacrylamide protein- and agarose gel-electrophoresis indicated that the proteins and DNA genome of Shigella dysenteriae severely degraded. Finally, the synergistic bactericidal effect was established for fresh-cut tomato preservation. This study demonstrates the remarkable potential of strategically selecting antibacterial agents with maximum synergistic effect and minimum dosage exhibiting excellent antibacterial activity in food preservation.

Effects of hesperidin, thymol, rosmarinic acid and their combined effect on growth performance, intestinal barrier function and cecal microbiota in broilers

This study aims to investigate the effects of hesperidin (Hes), thymol (Thy), rosmarinic acid (RA) and their combined effect on broiler growth performance, intestinal barrier function, and cecal microbiota. A total of 240 newly hatched Arbor Acres broiler chicks were randomly divided into 5 treatments with 6 replicates of 8 chickens. The birds were fed a basal diet (Con group), a basal diet supplemented with 40 mg/kg Hes (Hes group), a basal diet supplemented with 40 mg/kg Thy (Thy group), a basal diet supplemented with 20 mg/kg RA (RA group), or a basal diet supplemented with 40 mg/kg Hes + 40 mg/kg Thy + 20 mg/kg RA (HTR group) for 42 d. The results indicated that dietary Hes and HTR supplementation enhanced average daily gain, final body weight, and eviscerated yield of broilers compared with the Con group (P < 0.05). Notably, the HTR treatment showed a decrease in abdominal fat yield and ratio of feed to weight gain (P < 0.05). HTR treatment increased ileal villus height, villus height/crypt depth, and number of goblet cells, decreased the crypt depth (P < 0.05), up-regulated the mRNA expression of tight junction proteins (ZO-1, Claudin-1, Occludin) and MUC2 (P < 0.05). Hes, Thy, RA, HTR treatment decreased the concentrations of pro-inflammatory factors (IL-8, IFN-γ and TNF-α), and down-regulated the mRNA expression of TLR4/MyD88/NF-κB (P < 0.05). Importantly, the supplementation of HTR increased the relative abundance of beneficial bacteria (Parabacteroides, Lachnosiraceae NK4A136 and Turicbacter) and significantly decreased the relative abundance of opportunistic pathogenic bacteria such as Colidextribacter (P < 0.05). Additionally, the concentrations of propionate and butyrate in the cecum were elevated in the HTR group (P < 0.05). These findings indicate that the diet supplemented with HTR improved the growth performance and intestinal barrier function in broilers by modulating the cecal microbiota and its metabolites.

Succinylated starch emulsified Eugenol and Carvacrol nanoemulsions improved digestive stability, bio-accessibility and Salmonella typhimurium inhibition

The ultrasonically processed Eugenol (EU) and Carvacrol (CAR) nanoemulsions (NE) were successfully optimized via response surface methodology (RSM) to achieve broad spectrum antimicrobial efficacy. These NE were prepared using 2 % (w/w) purity gum ultra (i.e., succinylated starch), 10 % (v/v) oil phase, 80 % (800 W) sonication power, and 10 min of processing time as determined via RSM. The second order Polynomial method was suitable to RSM with a co-efficient of determination >0.90 and a narrow polydispersity index (PDI) ranging 0.12-0.19. NE had small droplet sizes (135.5-160 nm) and low volatility at high temperatures. The EU & CAR entrapment and heat stability (300 °C) confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Further, the volatility of EU & CAR NE was 18.18 ± 0.13 % and 12.29 ± 0.11 % respectively, being lower than that of bulk/unencapsulated EU & CAR (i.e., 23.48 ± 0.38 % and 19.11 ± 0.08 %) after 2 h at 90 °C. Interestingly, both EU & CAR NE showed sustained release behaviour till 48 h. Their digest could inhibit Salmonella typhimurium (S. typhimurium) via membrane disruption and access to cellular machinery as evident from SEM images. Furthermore, in-vivo bio-accessibility of EU & CAR in mice serum was up to 80 %. These cost-effective and short-processed EU/CAR NE have the potential as green preservatives for food industry.

Immobilization of Natural Antimicrobial Compounds on Food-Grade Supports as a New Strategy to Preserve Fruit-Derived Foods

The use of natural antimicrobials in the food industry is being proposed as an eco-friendly postharvest technology to preserve fruit-derived foods. In this context, this systematic review aims to describe and discuss the application of naturally occurring antimicrobial compounds in the processing of fruit-derived foods by the PRISMA methodology. In a first step, the use of free natural antimicrobials was investigated as an approach to identify the main families of bioactive compounds employed as food preservatives and the current limitations of this dosage form. Then, the use of immobilized antimicrobials, in an innovative dosage form, was studied by distinguishing two main applications: addition to the food matrix as preservatives or use during processing as technological aids. Having identified the different examples of the immobilization of natural antimicrobial compounds on food-grade supports, the mechanisms of immobilization were studied in detail to provide synthesis and characterization guidelines for future developments. Finally, the contribution of this new technology to decarbonization and energy efficiency of the fruit-derived processing sector and circular economy is discussed in this review.

Investigation of antioxidant and antibacterial effects of citrus fruits peels extracts using different extracting agents: Phytochemical analysis with in silico studies

The peels extracted from various citrus species are major source of phenols, flavonoids and anti-microbial agents. The purpose of this study was a detailed investigation of the phytochemical and pharmacological character of the ethanolic (80%), methanolic and acetone extracts of the peel of local variants of orange (lemon, grape fruit, mousami, fruiter, and shikri malta). The extracts were studied to find out the total phenolic contents (TPC), and total flavonoids (TF) present. The antioxidant activities were assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging effect, and the reducing power was determined through free radical scavenging activity (FRAP) assays. The sensitivity of four bacterial strains to peels extracts was examined by applying the diffusion disc on agar medium method. It was found that ethanol was the best extracting agent for TPC and TF in fruit peels under study. The highest TPC (21.33 ± 0.06 mg GAE/g) was quantified in orange peels, whereas fruiter contained the lowest TPC (20.40 ± 0.03 mg GAE/g) in ethanolic extract. The highest amount of TF (2.02 ± 0.08 mg QE/g) was quantified in lemon peels, whereas shikri malta contained lowest quantity of TF (1.04 ± 0.02 mg QE/g). The highest free radical scavenging activity (93.1%) of DPPH was exhibited by lemon peels, whereas the least activity (78.6%) was shown by mousami peels. Ethanolic extract of orange peels demonstrated more reducing power while showing an absorption of 1.98, followed by methanolic (1.11) and acetone (0.81) extracts. The inhibition effect of methanolic extract of lemon peels (inhibition zone = 18 mm) against B. subtilis was considerable and comparable to that of ciprofloxacin. Gas chromatography/mass spectrometry (GC/MS) was used to detect the compounds in ethanolic extract and up to 14 compounds were detected. These compounds were also assessed for their docking scores. Plausible binding modes with polyphenol oxidase and four best compounds were selected for molecular dynamics (MD) simulation to analyze their structural stability with receptor.

Optimization of a natural antimicrobial formulation against potential meat spoilage bacteria and food-borne pathogens: Mixture design methodology and predictive modeling

This study is about the combined antimicrobial effect of essential oils (EOs), namely Mediterranean (MN) EO, German thyme (GT) EO, Cinnamon (CN) EO, Indian (IN) EO, Asian (AN) EO, and citrus extract (CE) against spoilage bacteria (Lactobacillus sakei, Lactobacillus curvatus, Leuconostoc mesenteroides, Carnobacterium divergens, Brochothrix thermosphacta, and Pseudomonas aeruginosa) and selected pathogenic bacteria (E. coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes). Firstly, each EO and CE were screened for antibacterial activity by microdilution assay, and the most efficient antimicrobial extracts were selected based on the lowest MIC values to perform the combination assays. Afterward, a simplex-centroid mixture design was used to develop optimal antimicrobial mixtures capable of protecting meat from spoilage and pathogenic bacteria. The optimization tool allowed us to postulate models and validate them statistically as well as to create a prediction profile of the experiment. Thus, the optimal mixtures named active formulation 1 (AF1) containing MN EO/GT EO/VC EO/CE with a ratio of 1:2:2:1 and active formulation 2 (AF2) containing IN EO/AN EO/CE/VC EO with a ratio of 2:2:1:2, were developed based on the demonstration of their synergistic effect against tested bacteria. The obtained formulations at organoleptically acceptable concentrations could be applied in the preservation of meat and meat products.

Synergistic effects of benzyl isothiocyanate and resveratrol against Listeria monocytogenes and their application in chicken meat preservation

This study aimed to investigate the synergistic effects of benzyl isothiocyanate (BITC) and resveratrol (RS) on Listeria monocytogenes and their application in chicken meat preservation. BITC combined with RS (BR) significantly enhanced the antimicrobial activity and inhibited the growth of Listeria monocytogenes within 24 h compared to individual treatment, as well as suppressing bacterial swimming and swarming motility, reducing biofilm formation by 56.4%, increasing cell membrane disruption, and inducing intracellular ROS surges. Synergistic effects were associated with the inhibition of biofilm formation, cell membrane destruction, and ROS production. Biofilm removal facilitated the direct antimicrobial action of BR. RS disrupted cell membrane permeability, allowing more BITC into the cells, resulting in increased intracellular antibacterial levels, cell membrane hyperpolarization, and rapid ROS accumulation. Furthermore, BR visibly slowed the microbial growth in chicken flesh stored at 25 °C and 4 °C. Therefore, BR is expected to be a new strategy for food preservation.

Health-Promoting Properties and Potential Application in the Food Industry of Citrus medica L. and Citrus × clementina Hort. Ex Tan. Essential Oils and Their Main Constituents

Citrus is an important genus in the Rutaceae family, with high medicinal and economic value, and includes important crops such as lemons, orange, grapefruits, limes, etc. The Citrus species is rich sources of carbohydrates, vitamins, dietary fibre, and phytochemicals, mainly including limonoids, flavonoids, terpenes, and carotenoids. Citrus essential oils (EOs) consist of several biologically active compounds mainly belonging to the monoterpenes and sesquiterpenes classes. These compounds have demonstrated several health-promoting properties such as antimicrobial, antioxidant, anti-inflammatory, and anti-cancer properties. Citrus EOs are obtained mainly from peels, but also from leaves and flowers, and are widely used as flavouring ingredients in food, cosmetics, and pharmaceutical products. This review focused on the composition and biological properties of the EOs of Citrus medica L. and Citrus clementina Hort. Ex Tan and their main constituents, limonene, γ-terpinene, myrcene, linalool, and sabinene. The potential applications in the food industry have been also described. All the articles available in English or with an abstract in English were extracted from different databases such as PubMed, SciFinder, Google Scholar, Web of Science, Scopus, and Science Direct.

Ephedra foeminea as a Novel Source of Antimicrobial and Anti-Biofilm Compounds to Fight Multidrug Resistance Phenotype

Plants are considered a wealthy resource of novel natural drugs effective in the treatment of multidrug-resistant infections. Here, a bioguided purification of Ephedra foeminea extracts was performed to identify bioactive compounds. The determination of antimicrobial properties was achieved by broth microdilution assays to evaluate minimal inhibitory concentration (MIC) values and by crystal violet staining and confocal laser scanning microscopy analyses (CLSM) to investigate the antibiofilm capacity of the isolated compounds. Assays were performed on a panel of three gram-positive and three gram-negative bacterial strains. Six compounds were isolated from E. foeminea extracts for the first time. They were identified by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) analyses as the well-known monoterpenoid phenols carvacrol and thymol and as four acylated kaempferol glycosides. Among them, the compound kaempferol-3-O-α-L-(2″,4″-di-E-p-coumaroyl)-rhamnopyranoside was found to be endowed with strong antibacterial properties and significant antibiofilm activity against S. aureus bacterial strains. Moreover, molecular docking studies on this compound suggested that the antibacterial activity of the tested ligand against S. aureus strains might be correlated to the inhibition of Sortase A and/or of tyrosyl tRNA synthase. Collectively, the results achieved open interesting perspectives to kaempferol-3-O-α-L-(2″,4″-di-E-p-coumaroyl)-rhamnopyranoside applicability in different fields, such as biomedical applications and biotechnological purposes such as food preservation and active packaging.

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.

Potential Mechanisms of Quercetin Influence the ClfB Protein During Biofilm Formation of Staphylococcus aureus

This study aimed to establish the mode of binding between Quercetin (QEN) and an essential protein called ClfB in forming biofilm in Staphylococcus aureus (S. aureus). In this study, the raw data of GSE163153 were analyzed for quality control, alignment, and gene counts, and the differential analysis detected the key differentially expressed genes (DEGs) assisting in the formation of the S. aureus biofilm. Then, the protein-protein interaction (PPI) and gene function enrichment analyses of the target genes, identified a gene called clfB to be closely related to biofilm formation. ClfB was structurally characterized, molecularly docked, and kinetically simulated to unravel the mode of binding of QEN to ClfB. Meanwhile, the growth curve and transmission electron microscopy methods examined the effect of QEN on the S. aureus growth. Results indicated that the clfB gene was increasingly expressed during biofilm formation and was involved in cell adhesion, pathogenicity, and infection. We identified 5 amino acid sites of ClfB (D272, R331, I379, K391, E490) as potential sites for binding QEN, which would indirectly influence the changes in the functional sites N234, D270, Y273, F328, inhibiting the formation of biofilm. Meanwhile, 128 μg/ml of QEN could significantly inhibit the S. aureus biofilm formation. This manuscript serves as a molecular foundation for QEN as an antibacterial drug providing a new perspective for developing antibacterial drugs.

Synergistic antibacterial activity and mechanism of action of nisin/carvacrol combination against Staphylococcus aureus and their application in the infecting pasteurized milk

Synergistic antibacterial effect is a promising way to overcome the challenge of microbial contamination in food. In this study, we detected the synergistic interactions of nisin and carvacrol. The MIC of nisin and carvacrol against S. aureus were 60 and 125 μg/mL, respectively. The FICI and FBCI were 0.28125 and 0.09375, which suggested that the nisin/carvacrol combination presented synergistic antibacterial effect against S. aureus. The antibacterial activity of nisin/carvacrol combination was much higher than their individuals and the dose of antibacterials was obviously reduced. The combination could completely kill S. aureus within 8 h, accelerate the destruction of cell membrane, and inhibit formation of biofilm. Under the intervention of nisin, more CAR could enter cell to hunt intracellular targets, leading to an increase in intracellular antibacterial level. Besides, in the storage of pasteurized milk, the combinational treatment successfully inhibited microbial reproduction at 25 °C and 4 °C. Thus, the combination of nisin and carvacrol was a potential synergistic strategy for food preservation.

Chemical profiling, in vitro antimicrobial and antioxidant activities of pomegranate, orange and banana peel-extracts against pathogenic microorganisms

Background

The use of natural preservatives became of great interest; good examples of these natural preservation agents are plant peels. The use of plant peels has dual benefits; first is their antimicrobial activity against food-borne pathogens, while the second is minimizing agro-industrial wastes.

Results

The evaluation of the antimicrobial potential of both methanolic and ethanolic extracts of three fruit peels (orange, pomegranate, and banana), against 4 Gram-positive (G⁺), 3 Gram-negative bacteria (G⁻), and 2 fungal strains revealed that both pomegranate peel extracts exhibited significantly higher inhibitory effect on all tested G⁺ bacteria. Methanolic extract of pomegranate peel gave higher activity than the ethanolic one against G⁺ and G⁻ bacteria except for S. typhimurium. Against A. flavus and A. niger, both pomegranate and orange extracts showed activity ranging between 65 and 100% more than the positive control. The ethanolic extracts of all tested peels showed a considerable capacity of antioxidant compounds compared to the methanolic extracts. The highest antioxidant capacity was found for ethanolic and methanolic extracts of pomegranate, 66.870 and 56.262 mg/ml, respectively. Generally, the concentration of total phenolic compounds was higher than that of total flavonoids followed by tannins. The highest readings of all tested constituents were reported for pomegranate extracts followed by orange and then banana. The total phenolic content, total flavonoids, and tannins were proportional to antioxidant values. GC-MS of pomegranate peel extracts identified 23 compounds in the methanolic extract versus 31 compounds in the ethanolic one. These components were identified based on their retention times and mass spectral fragmentation pattern. 5-hydroxymethylfufural (HMF) represented the major component in both methanolic and ethanolic extracts with peak area percentage of 65.78% and 48.43%, respectively.

Conclusions

The results showed negative effect of methanolic and ethanolic extracts of pomegranate on G⁺ and G⁻ bacteria and two fungal pathogenic strains. The phytochemical analysis regarded these results to the high content of phenols, flavonoids, and tannins. GC-MS chromatogram identified many compounds known to be effective as antioxidants and antibacterial and antifungal agents. These indications show that pomegranate peel may be a superior natural food-preserver, but further studies about the suitable formulation, dosage, and possible side-effects are still needed.

Natural Plant-Derived Chemical Compounds as Listeria monocytogenes Inhibitors In Vitro and in Food Model Systems

Listeria monocytogenes is a foodborne pathogen, sporadically present in various food product groups. An illness caused by the pathogen, named listeriosis, has high fatality rates. Even though L. monocytogenes is resistant to many environmental factors, e.g., low temperatures, low pH and high salinity, it is susceptible to various natural plant-derived antimicrobials (NPDA), including thymol, carvacrol, eugenol, trans-cinnamaldehyde, carvone S, linalool, citral, (E)-2-hexenal and many others. This review focuses on identifying NPDAs active against L. monocytogenes and their mechanisms of action against the pathogen, as well as on studies that showed antimicrobial action of the compounds against the pathogen in food model systems. Synergistic action of NDPA with other factors, biofilm inhibition and alternative delivery systems (encapsulation and active films) of the compounds tested against L. monocytogenes are also summarized briefly.

Genetic Variants and Phenotypic Characteristics of Salmonella Typhimurium-Resistant Mutants after Exposure to Carvacrol

The emergence of antimicrobial resistance has raised questions about the safety of essential oils and their individual constituents as food preservatives and as disinfection agents. Further research is required to understand how and under what conditions stable genotypic resistance might occur in food pathogens. Evolution experiments on Salmonella Typhimurium cyclically exposed to sublethal and lethal doses of carvacrol permitted the isolation of SeSCar and SeLCar strains, respectively. Both evolved strains showed a significant increase in carvacrol resistance, assessed by minimum inhibitory and bactericidal concentrations, the study of growth kinetics in the presence of carvacrol, and the evaluation of survival under lethal conditions. Moreover, antibiotic susceptibility tests revealed a development of SeLCar resistance to a wide range of antibiotics. Whole genome sequencing allowed the identification of single nucleotide variations in transcriptional regulators of oxidative stress-response: yfhP in SeSCar and soxR in SeLCar, which could be responsible for the increased resistance by improving the response to carvacrol and preventing its accumulation inside the cell. This study demonstrates the emergence of S. Typhimurium-resistant mutants against carvacrol, which might pose a risk to food safety and should therefore be considered in the design of food preservation strategies, or of cleaning and disinfection treatments.

Combined Application of Bacteriophages and Carvacrol in the Control of Pseudomonas syringae pv. actinidiae Planktonic and Biofilm Forms

Pseudomonas syringae pv. actinidiae (Psa) is the causative agent of the bacterial canker of kiwifruit (Actinidia spp.). Phage therapy has been suggested as a viable alternative approach to controlling this disease, but its efficacy is limited by the emergence of phage-resistant mutants. Carvacrol is an essential oil that may be useful for the control of Psa. Combination therapies can be used to overcome resistance development. Here, the combination of phages (single phage suspensions of phages PN05 and PN09, and a cocktail of both phages) and carvacrol was investigated in controlling Psa planktonic and biofilm forms in vitro. The phage therapy alone (with phages PN05 and PN09), and the carvacrol alone (minimum inhibitory concentration 2.0 mg/mL), inhibited Psa growth, but the combined effect of both therapies was more effective. The phages alone effectively inhibited Psa growth for 24 h, but Psa regrowth was observed after this time. The carvacrol (2.0 mg/mL) alone prevented the biofilm formation for 48 h, but did not destroy the pre-formed biofilms. The combined treatment, phages and carvacrol (2.0 mg/mL), showed a higher efficacy, preventing Psa regrowth for more than 40 h. In conclusion, the combined treatment with phages and carvacrol may be a promising, environment-friendly and cost-effective approach to controlling Psa in the kiwifruit industry.

Recent Advances in the Application of Antibacterial Complexes Using Essential Oils

Although antibacterial spectrum of essential oils (EOs) has been analyzed along with consumers’ needs on natural biocides, singular treatments generally require high concentration of EOs and long-term exposures to eliminate target bacteria. To overcome these limitations, antibacterial complex has been developed and this review analyzed previous reports regarding the combined antibacterial effects of EOs. Since unexpectable combined effects (synergism or antagonism) can be derived from the treatment of antibacterial complex, synergistic and antagonistic combinations have been identified to improve the treatment efficiency and to avoid the overestimation of bactericidal efficacy, respectively. Although antibacterial mechanism of EOs is not yet clearly revealed, mode of action regarding synergistic effects especially for the elimination of pathogens by using low quantity of EOs with short-term exposure was reported. Whereas comprehensive analysis on previous literatures for EO-based disinfectant products implies that the composition of constituents in antibacterial complexes is variable and thus analyzing the impact of constituting substances (e.g., surfactant, emulsifier) on antibacterial effects is further needed. This review provides practical information regarding advances in the EO-based combined treatment technologies and highlights the importance of following researches on the interaction of constituents in antibacterial complex to clarify the mechanisms of antibacterial synergism and/or antagonism.

Preparation and antimicrobial activity of thyme essential oil microcapsules prepared with gum arabic

Thyme essential oils (TEO) exhibit antimicrobial activities against a wide range of pathogenic microorganisms. Microcapsulation technology can be used to improve the stability, water solubility and antibacterial performance of TEO. In this paper, TEO was selected as the core material, and β-cyclodextrin (β-CD) was the wall material for microcapsulation; gum arabic (GA) was used as an emulsifier to prepare microcapsules by coprecipitation. The effects of gum arabic on the encapsulation rate, particle size and release rate of microcapsules were investigated. The optimal condition was found to be TEO : GA by 1 : 3 (w/w) ratio. In this condition, the embedding rate, release rate, and average size of the microcapsules were 87.61%, 53.00%, and 8.20 μm, respectively. Scanning electron microscopy (SEM) revealed that, under the action of gum arabic, the surface of microcapsules was more complete, and the size apparently decreased. Fourier-transform infrared spectroscopy (FTIR) indicated that there was no significant chemical interaction between gum arabic and β-CD. Gum arabic acted only as an emulsifier and remained in the mixed solution. For microcapsules with gum arabic as an emulsifier, the cumulative release rate of essential oils were slower at the initial time compared to microcapsules without added gum arabic. Antimicrobial activity assay exhibited TEO, which showed an inhibitory effect against Botryodiplodia theobromae Pat., and the inhibitory effect was especially strong against Colletotrichum gloeosporioides Penz. Finally, the obtained microcapsules showed the same antibacterial effect.

The gum arabic was, for the first time, used as an emulsifier for microcapsulation of essential oil.