Nanocapsular dispersion of thymol for enhanced dispersibility and increased antimicrobial effectiveness against Escherichia coli O157:H7 and Listeria monocytogenes in model food systems

Thymol-Loaded Eudragit RS30D Cationic Nanoparticles-Based Hydrogels for Topical Application in Wounds: In Vitro and In Vivo Evaluation

Natural medicines formulated using nanotechnology-based systems are a rich source of new wound-treating therapeutics. This study aims to develop thymol-loaded cationic polymeric nanoparticles (CPNPs) to enhance the skin retention and wound healing efficacy of thymol. The developed materials exhibited entrapment efficiencies of 56.58 to 68.97%, particle sizes of 36.30 to 99.41 nm, and positively charged zeta potential. In Vitro sustained release of thymol up to 24 h was achieved. Selected thymol CPNPs (F5 and C2) were mixed with methylcellulose to form hydrogels (GF5 and GC2). An In Vivo skin-retention study revealed that GF5 and GC2 showed 3.3- and 3.6-fold higher retention than free thymol, respectively. An In Vitro scratch-wound healing assay revealed a significant acceleration in wound closure at 24 h by 58.09% (GF5) and 57.45% (GC2). The potential for free thymol hydrogel, GF5, and GC2 to combat MRSA in a murine skin model was evaluated. The bacterial counts, recovered from skin lesions and the spleen, were assessed. Although a significant reduction in the bacterial counts recovered from the skin lesions was shown by all three formulations, only GF5 and GC2 were able to reduce the bacterial dissemination to the spleen. Thus, our study suggests that Eudragit RS30D nanoparticles-based hydrogels are a potential delivery system for enhancing thymol skin retention and wound healing activity.

Metabolomics insights into the potential of encapsulated essential oils as multifunctional food additives

Growing consumer concern about foodborne disease outbreaks and health risks associated with chemical additives has propelled the usage of essential oils (EOs) as novel food additives, but are limited by instability. In this regard, a series of EOs nano/micro-capsules have been widely used to enhance their stability and improve food quality. However, classical food quality assessment methods are insufficient to fully characterize the effects of encapsulated EOs on food properties, including physical, biochemical, organoleptic, and microbial changes. Recently, the rapid development of high-throughput sequencing is accelerating the application of metabolomics in food safety and quality analysis. This review seeks to present the most recent achievements in the application of non-targeted metabolomics to identify and quantify the overall metabolite profile associated with food quality, which can guide the development of emerging food preservation technologies. The scientific findings confirm that metabolomics opens up exciting prospects for biomarker screening in food preservation and contributes to an in-depth understanding of the mechanisms of action (MoA) of EOs. Future research should focus on constructing food quality assessment criteria based on multi-omics technologies, which will drive the standardization and commercialization of EOs for food industry applications.

Novel Bionanocomposites Based on Cinnamon Nanoemulsion and TiO2-NPs for Preserving Fresh Chicken Breast Fillets

In this study, bionanocomposite coating solutions were created using polyvinyl alcohol (PVA) and chitosan (Cs), with different concentrations of cinnamon essential oil in nanoemulsion (n-CEO; 0%, 5%, 10%, and 20%) and TiO2 nanoparticles (TiO2-NPs). The bionanocomposite was characterized using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy with EDX, and mechanical and barrier property assessment. Additionally, antimicrobial and antioxidant properties and total phenols were evaluated. Generally, mechanical and barrier properties were enhanced with increasing n-CEO concentrations with a favorable distribution in film matrix. Moreover, total phenols, antioxidant, and antimicrobial activities were also enhanced a broader inhibition pattern against A. flavus, gram-positive, and gram-negative bacteria. The influence of n-CEO and TiO2-NPs blended into bionanocomposite on preservation of fresh chicken breast fillets during 21 days of refrigeration was evaluated. Added n-CEO concentration, especially 20%, and TiO2-NPs enhanced antimicrobial properties and extended preservation time up to 14 days compared to uncoated samples. Furthermore, weight loss was decreased during storage of coated samples. Thus, PVA/Cs/TiO2–NPs with n-CEO bionanocomposites may be useful as a coating for chicken breast fillets to control microbial growth and reduce weight loss during cold storage.

Recent advances in polysaccharide-based edible coatings for preservation of fruits and vegetables: A review

Harvested fruits and vegetables are prone to decay and quality deterioration during storage. Although traditional packaging and chemical treatments are effective, they are harmful to the environment and human health. Hence, higher requirements for food preservation technology are increasingly proposed. Nontoxic, renewable, degradable, and edible packaging for fruits and vegetables has become a research hotspot in recent years. Chitosan, alginate, cellulose, pectin, starch, and other polysaccharides as coating materials have been widely used. Compared with traditional plastic packaging and chemical treatment, these coatings exhibited a better preservation effect and higher safety. In this paper, the preservation mechanism of fruits and vegetables by edible coatings treatment was described, and the research on edible coatings used in fruits and vegetables was summarized. The effects polysaccharide-based edible coatings on physicochemical quality and antimicrobial effect of fruits and vegetables were reviewed.

Protective Effects of Natural Antioxidants on Inflammatory Bowel Disease: Thymol and Its Pharmacological Properties

Inflammatory bowel disease (IBD) is a gastrointestinal disease that involves chronic mucosal or submucosal lesions that affect tissue integrity. Although IBD is not life-threatening, it sometimes causes severe complications, such as colon cancer. The exact etiology of IBD remains unclear, but several risk factors, such as pathogen infection, stress, diet, age, and genetics, have been involved in the occurrence and aggravation of IBD. Immune system malfunction with the over-production of inflammatory cytokines and associated oxidative stress are the hallmarks of IBD. Dietary intervention and medical treatment suppressing abnormal inflammation and oxidative stress are recommended as potential therapies. Thymol, a natural monoterpene phenol that is mostly found in thyme, exhibits multiple biological functions as a potential adjuvant for IBD. The purpose of this review is to summarize current findings on the protective effect of thymol on intestinal health in the context of specific animal models of IBD, describe the role of thymol in the modulation of inflammation, oxidative stress, and gut microbiota against gastrointestinal disease, and discuss the potential mechanism for its pharmacological activity.

Coacervation as a Novel Method of Microencapsulation of Essential Oils-A Review

These days, consumers are increasingly "nutritionally aware". The trend of "clean label" is gaining momentum. Synthetic additives and preservatives, as well as natural ones, bearing the E symbol are more often perceived negatively. For this reason, substances of natural origin are sought tfor replacing them. Essential oils can be such substances. However, the wider use of essential oils in the food industry is severely limited. This is because these substances are highly sensitive to light, oxygen, and temperature. This creates problems with their processing and storage. In addition, they have a strong smell and taste, which makes them unacceptable when added to the product. The solution to this situation seems to be microencapsulation through complex coacervation. To reduce the loss of essential oils and the undesirable chemical changes that may occur during their spray drying-the most commonly used method-complex coacervation seems to be an interesting alternative. This article collects information on the limitations of the use of essential oils in food and proposes a solution through complex coacervation with plant proteins and chia mucilage.

The Effect of Pimpinella Anisum and Origanum Vulgare Extracts Against Streptococcus Sanguinis, Streptococcus Mutans, and Streptococcus Salivarius

Statement of the Problem

There are global efforts for introducing a new herbal antimicrobial agent with minimal side effects. There are some reports about the antimicrobial properties of Pimpinella anisum and Oregano Vulgare.

Purpose

In this study, the antimicrobial properties of Pimpinella anisum and Oregano Vulgare have been assessed.

Material and Method

In this experimental in vitro study, the dental plaque samples were collected from children aged 3 to 5 years old who were referred to a private dental office with diagnosis of dental caries. After determination of the bacterial colonies of Streptococcus sanguinis, Streptococcus mutans and Streptococcus salivarius, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ethanolic and methanolic extracts of Pimpinella anisum and Oregano vulgare were measured by macrodilution and microdilution methods.

Results

The mean MIC and MBC of Pimpinella anisum extract and Oregano vulgare extract and their combination against Streptococcus mutans, Streptococcus sanguinis, and Streptococcus salivarius were statistically different (p< 0.001). The combination of these extracts showed the lowest MIC and MBC.

Conclusion

Hydroalcoholic extracts of the Pimpinella anisum and Oregano Vulgare were effective antibacterial agent against Streptococcus mutans, Streptococcus salivarius, and Streptococcus sanguinis so the combination of these two extracts showed the highest antibacterial properties on all the bacteria evaluated.

Preparation and Enhanced Antimicrobial Activity of Thymol Immobilized on Different Silica Nanoparticles with Application in Apple Juice

In order to diminish the application limitations of essential oils (EOs) as natural antimicrobial components in the food industry, novel antimicrobial materials were designed and prepared by immobilization of thymol derivatives on silica particles with different morphologies (hollow mesoporous silica nanoparticles, MCM-41, amorphous silica). The structural characteristics of antimicrobial materials were estimated by FESEM, FT-IR, TGA, N2 adsorption-desorption, and small-angle XRD, and the results revealed that both mesoporous silica nanoparticles maintained the orderly structures and had good immobilization yield. Furthermore, the antibacterial performance tests showed that mesoporous silica nanoparticles greatly enhanced the antimicrobial activity of thymol against two representative foodborne bacteria (Escherichia coli and Staphylococcus aureus), and the application of the antimicrobial support was tested in apple juices inoculated with E. coli. The MBC of functionalized mesoporous silica supports was established to be below 0.1 mg/mL against E. coli and S. aureus, which is much lower than that of free thymol (0.3 mg/mL and 0.5 mg/mL against E. coli and S. aureus, respectively). In addition, at a range from 0.05 mg/mL to 0.2 mg/mL, immobilized hollow mesoporous silica nanoparticles (HMSNs) can inhibit the growth of E. coli in apple juice and maintain good sensory properties during 7 days of storage.

Advances in biopolymeric active films incorporated with emulsified lipophilic compounds: a review

The attention towards active films has increased due to consumer demand for high-quality foods without chemical additives. Active biopolymer-based films have shown great potential for active films by impacting food safety, acting as the carriers of various natural antioxidant and antimicrobial compounds, and decreasing environmental pollution from petrol-derived packaging materials. However, there is a wide range of challenges concerning the different characteristics of biopolymers and plasticizers, often hygroscopic/hydrophilic, compared to numerous lipophilic bioactive compounds. Therefore, recent studies have focused on applying oil-in-water emulsion-based systems to enhance the lipophilic bioactive compounds' dispersibility into the film matrix, improving their performance. It is worth emphasizing that resulting complex systems give rise to new challenges such as (i) dispersion technology of the bioactive compounds with minimum adverse effects on its bioactivities, (ii) interactions between different components of the active films, giving rise to new physicochemical properties, and (iii) the change of the diffusion properties of bioactive compounds into the active films, resulting in different release properties. These challenges are profound and critically discussed in this review, as well as the encapsulation techniques employed in preparing emulsions loaded with lipophilic bioactive compounds for the active film development. An outlook of future directions in the research, development, and application of these active films are given.

Antimicrobial Activity and Chemical Characterization of a Non-Polar Extract of Saffron Stamens in Food Matrix

The production of saffron spice generates large quantities of plant by-products: over 90% of the plant material collected is discarded, and a consideration fraction of this waste is plant stamens. This work investigated the chemical composition and the antimicrobial activities of the non-polar fraction extracted from four different saffron flower stamens. The chemical composition of ethereal extracts of the saffron stamens was qualitatively assessed by means of gas-chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) analyses. These analyses revealed ethereal extracts to possess a high polyunsaturated fatty acid content. In vitro antibacterial activity of stamen extracts showed no large differences between Gram-positive and Gram-negative bacteria in terms of minimal inhibitory concentration (MIC). In food matrix microbial analysis of the bacterial strains belonging to the main foodborne pathogen species, including Staphylococcus aureus DSM 20231, Escherichia coli DSM 30083, and Listeria monocytogenes DSM 20600, using low-fat UHT milk, revealed a statistically significant reduction in the number of cells (particularly for E. coli and S. aureus with a complete elimination of the population of the two target bacteria following incubation in diethyl ether extracts of saffron stamen (DES) at high concentrations tested, both at 37 °C and 6 °C (for 48 h and 7 days, respectively). A synergic effect was observed when the pathogens were incubated at 6 °C with DES. This work shows these by-products to be excellent sources of bioactive compounds, which could be exploited in high-added-value products, such as food, cosmetics, and drugs.

Thymol ameliorates ammonium toxicity via repressing polyamine oxidase-derived hydrogen peroxide and modulating ammonium transporters in rice root

Background

Ammonium is an indispensable nutrient for crop growth, but anoxic conditions or inappropriate fertilizer usage result in the increase in ammonium content in soil. Excessive ammonium causes phytotoxicity. Thymol is a kind of natural phenolic compound with anti-microbial properties. However, little is known about the role of thymol in modulating plant physiology. Here we find the novel role of thymol in protecting rice from ammonium toxicity.

Results

Thymol remarkably rescued rice seedlings growth from ammonium stress, which may resulted from the attenuation of reactive oxygen species (ROS) accumulation, oxidative injury, and cell death in both shoots and roots. Polyamine oxidase (PAO) metabolizes polyamines to produce ROS in plants in response to stress conditions. Thymol blocked ammonium-induced upregulation of a set of rice PAOs, which contributed to the decrease in ROS content. In rice seedlings upon ammonium stress, thymol downregulate the expression of ammonium transporters (AMT1;1 and AMT1;2); thymol upregulated the expression of calcineurin B-like interacting protein kinase 23 (CIPK23) and calcineurin B-like binding protein 1 (CBL1), two negative regulators of AMTs. This may help rice avoid ammonium overload in excessive ammonium environment. Correlation analysis indicated that PAOs, AMTs, and CBL1 were the targets of thymol in the detoxification of excessive ammonium.

Conclusion

Thymol facilitates rice tolerance against ammonium toxicity by decreasing PAO-derived ROS and modulating ammonium transporters. Such findings may be applicable in the modulation of nutrient acquisition during crop production.

Graphical abstract

Corn Starch/Chitosan Nanoparticles/Thymol Bio-Nanocomposite Films for Potential Food Packaging Applications

This work aims to develop corn starch/chitosan nanoparticles/thymol (CS/CNP/Thy) bio-nanocomposite films as potential food packaging materials that can enhance the shelf life of food. CS/CNP/Thy bio-nanocomposite films were prepared by the addition of different concentrations of thymol (0, 1.5, 3.0, 4.5 w/w%) using a solvent casting method. The resulting films were characterized in terms of optical, mechanical, and water vapor permeability (WVP) properties. The addition of thymol was found to reduce the tensile strength (TS), elongation at break (EAB), and Young’s modulus (YM) of the films. Generally, the increment in the concentration of thymol did not significantly affect the TS, EAB, and YM values. The addition of 1.5 w/w% thymol increased the WVP of the films but the WVP reduced with the increase in thymol concentrations. CS/CNP/Thy-3% bio-nanocomposite films demonstrated the potential to lengthen the shelf life of cherry tomatoes packed with the films, whereby the cherry tomatoes exhibited no significant changes in firmness and the lowest weight loss. In addition, no mold growth was observed on the sliced cherry tomatoes that were in direct contact with the films during 7 days of storage, proving the promising application of the films as active food packaging materials.

Antimicrobial efficacy of white mustard essential oil and carvacrol against Salmonella in refrigerated ground chicken

Essential oils in combination with other antimicrobials can be added to food products to reduce the levels of target microbes lower than the infectious dose required to cause human illness. The purpose of this study was to investigate the antimicrobial efficacy of white mustard essential oil (WMEO) and carvacrol against Salmonella in ground chicken stored at 4 and 10°C. At 4°C, 0.75% WMEO +0.1% carvacrol treatment had significantly lower (P < 0.05) Salmonella at the end of 12-day storage than the control, which contained no antimicrobials. A combination of 0.75% WMEO and 0.01% carvacrol had a bacteriostatic effect against Salmonella in ground chicken samples stored at 10°C for 7 D. The application of the antimicrobials controlled the growth of Salmonella by delaying the exponential phase at temperature abuse and reducing levels of Salmonella to less than the positive control at 4°C. The use of WMEO and carvacrol shows potential in reducing levels of Salmonella under refrigerated conditions and controlling its growth under temperature abuse conditions in raw poultry products. Further research is needed to investigate the toxicity of the compounds and the most efficient way to apply it to a food product to maximize antimicrobial activity.

Nanocomplexation between thymol and soy protein isolate and its improvements on stability and antibacterial properties of thymol

The complexation of thymol with soy protein isolate (SPI) at various mixing mass ratios, as well as some physicochemical characteristics, stability and antibacterial properties of the resultant complexes, was evaluated. The loading capacity of thymol in complexes formed at a mixing mass ratio of 2.5:12 was 10.36%, and the particles were spherical with a z-average diameter less than 110 nm. Fluorescence spectroscopy results indicated the SPI-thymol nanocomplexes were formed mainly through hydrophobic interactions. Upon nanocomplexation, the solubility, sustained release, thermal stability and antibacterial activity of thymol were greatly improved. Moreover, the encapsulation efficiency and solubility of thymol in complexes were improved with the increasing mixing mass ratio, while the stability and antibacterial activity of thymol were not significantly different among all the complexes. These findings suggest that SPI could be used as a nanocarrier for improving solubility and stability of thymol.

Evaluating the Antimicrobial Efficacy of White Mustard Essential Oil Alone and in Combination with Thymol and Carvacrol against Salmonella

It is estimated that nontyphoidal Salmonella causes approximately 1 million illnesses and 378 deaths per year in the United States. Reduction of Salmonella-related foodborne infections can be achieved through application of food antimicrobials. Essential oils in combination with other antimicrobials can be added to food products to reduce the levels of the organism below the infectious dose for healthy individuals. The purpose of this study was to investigate the antimicrobial efficacy of white mustard essential oil (WMEO) against serovars of Salmonella and its potential to be used with carvacrol or thymol to control Salmonella. Results showed that WMEO at the highest concentration of 0.84% (v/v) compared with the positive control had approximately a 6- to 7-log reduction for all serovars. It was found that no difference in susceptibility existed among the serovars tested (P > 0.05). In addition, the MICs were determined to be 0.5, 0.02, and 0.02% for WMEO, carvacrol, and thymol, respectively, against Salmonella Typhimurium. The fractional inhibitory concentration index was calculated. A score of 1 indicated an additive effect occurred when WMEO was combined with thymol or carvacrol. Combining WMEO with carvacrol or thymol indicated that the concentration of individual essential oils needed to inhibit Salmonella can be reduced using these combinations and warrants further study to determine potential use in controlling Salmonella in commercial food products.

Use of free and encapsulated nerolidol to inhibit the survival of Lactobacillus fermentum in fresh orange juice

Lactobacillus fermentum is commonly responsible for fruit juice fermentation and spoilage. The aim of this study was to investigate the potential use of nerolidol to control the spoilage of fresh orange juice by L. fermentum. Nerolidol was incorporated into hydroxypropyl-β-cyclodextrin inclusion complex, conventional liposome, and drug-in-cyclodextrin-in liposome systems. The systems were lyophilized and characterized with respect to their nerolidol content, size, and morphology. The effects of the acidity and cold storage of orange juice on the survival of L. fermentum were evaluated. Subsequently, the antibacterial activity of nerolidol in refrigerated orange juice was assessed at pH 3.3. Nerolidol showed a faster antibacterial activity at 4 000 μM (5 days) compared to 2 000 μM (8 days). Under the same conditions, the inclusion complex completely killed bacteria within 6 days of incubation at 4 000 μM, suggesting its potential application in fruit juices. Nerolidol-loaded liposomes did not exhibit an antibacterial activity and altered the appearance of juice.

Production of thymol nanoemulsions stabilized using Quillaja Saponin as a biosurfactant: Antioxidant activity enhancement

Thymol oil-in-water nanoemulsions as a potential natural alternative for synthetic antioxidant agents were developed. The nanoemulsions were formulated using Quillaja Saponin bio-surfactant and green solvents including high oleic sunflower oil (HOSO), tricaprylin (TC), and cinnamaldehyde (CA). The 4% thymol nanoemulsions containing TC and HOSO remained stable during long-term storage (at least 30 d). The antioxidant activity (AA) of free thymol and thymol nanoemulsions was compared with butylated hydroxytoluene (BHT) and ascorbic acid. The results obtained from DPPH, FRAP, and CUPRAC antioxidant assays showed a substantial improvement (p < 0.05) of the AA of free thymol through emulsification. The outcomes from the AA of the nanoemulsions in raw chicken breast meat measured by the TBARS assay revealed a significant improvement (p < 0.05) of the AA when thymol was encapsulated. These nanoemulsions may be applicable in the food industry as well as in cosmetic and health care products.

A systematic review on nanoencapsulation of food bioactive ingredients and nutraceuticals by various nanocarriers

Today, there is an ever-growing interest on natural food ingredients both by consumers and producers in the food industry. In fact, people are looking for those products in the market which are free from artificial and synthetic additives and can promote their health. These food bioactive ingredients should be formulated in such a way that protects them against harsh process and environmental conditions and safely could be delivered to the target organs and cells. Nanoencapsulation is a perfect strategy for this situation and there have been many studies in recent years for nanoencapsulation of food components and nutraceuticals by different technologies. In this review paper, our main goal is firstly to have an overview of nanoencapsulation techniques applicable to food ingredients in a systematic classification, i.e., lipid-based nanocarriers, nature-inspired nanocarriers, special-equipment-based nanocarriers, biopolymer nanocarriers, and other miscellaneous nanocarriers. Then, application of these cutting-edge nanocarriers for different nutraceuticals including phenolic compounds and antioxidants, natural food colorants, antimicrobial agents and essential oils, vitamins, minerals, flavors, fish oils and essential fatty acids will be discussed along with presenting some examples in each field.

Essential Oil Nanoemulsions and their Antimicrobial and Food Applications

The consumer awareness for secure insignificantly handled food has constrained the food dealers either to decrease the measure of chemically synthetic antimicrobial substances or to replace them with natural ones. Essential oils (EO) extracted from edible, therapeutic and herbal plants have been well recognized as natural antimicrobial additives. As characteristic then viable antimicrobials, EO have been progressively observed towards control of foodborne microbes and progression of nourishment wellbeing. It is ordinarily hard to achieve high antimicrobial vulnerability when mixing with EO in nourishment based items because of low dissolvability of water and interactive binding. Subsequently, the delivery system of nanoemulsion-based EO is emerging as aviable solution to control the growth of foodborne pathogens. Lipophilic compounds are distributed uniformly in the aqueous phase with the help of nanoemulsion technique. Therefore, the nanoemulsion formulation is generally comprised of mainly three constituents i.e. oil phase, aqueous and a surfactant. Nanoemulsions droplet average diameters should below 100 nm. According to previous studies, the clove, cinnamon and thyme oil nanoemulsions which were formulated with non ionic surfactants (Spans and Tweens) were having droplet size less than 100nm. The current review emphases on essential oil based nanoemulsions which are prepared with different ingredients which hence, enhance the antimicrobial action in food items.

Evaluation of the efficacy of multiple physical, biological and natural antimicrobial interventions for control of pathogenic Escherichia coli on beef

Antimicrobial effects of multiple physical, biological and natural interventions on pathogenic Escherichia coli in raw beef were assessed. A cocktail of E. coli strains was inoculated onto gamma-irradiated beef and enumerated immediately after each intervention and during storage at 4 °C for 7 days. Of the physical interventions, silver-containing antimicrobial packaging and ozone gas treatment did not show significant antimicrobial effects, however cold plasma treatment reduced E. coli levels by 0.9 and 1.82 log₁₀ CFU/cm² after 2 and 5 min treatments, respectively. A phage cocktail reduced E. coli counts by 0.63 and 1.16 log₁₀ CFU/g after 24 h storage at 4 and 12 °C, respectively. Of the natural interventions, vinegar and lactic acid (5%) washes for 5 min caused reductions of ∼1 log₁₀ CFU/g immediately after treatment, whereas lactoferrin and nisin treatments, separately or in combination, had insignificant antimicrobial effects. Nanoemulsions containing carvacrol or thyme essential oils caused immediate E. coli reductions of 1.41 and 1.36 log₁₀ CFU/g, respectively, plus a progressive reduction in viable numbers during storage at 4 °C. Our findings suggest that cold plasma, bacteriophages, vinegar, lactic acid, or carvacrol and thyme essential oil nanoemulsions could potentially be of use to the beef industry for controlling pathogenic E. coli contamination.

Antibacterial activity of acidified sodium benzoate against Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in tryptic soy broth and on cherry tomatoes

Concerns about undesirable by-products from chlorine sanitation of fresh produce and the limited efficacy with the presence of organic matter, have led to studies on alternative washing solutions. The aim of this study was to evaluate the antibacterial activities of acidified sodium benzoate (NaB) solutions against Escherichia coli O157:H7, Salmonella enterica and Listeria monocytogenes in growth medium and on cherry tomatoes. Experimentally, the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs, >3 Log reduction) of NaB against E. coli O157:H7 ATCC 43895, S. Enteritidis, and L. monocytogenes Scott A were determined at pH 7.0-4.0 using micro-broth dilution method and agar plating method, respectively. The reduction of the three bacteria in tryptic soy broth (TSB) by 500 and 1000 ppm NaB at pH 2.0, 2.5 and 3.0 for 30 min at 21 °C was compared. Residual bacterial cocktails inoculated on cherry tomatoes were determined after soaking in 3000 ppm NaB solution adjusted to pH 2.0 for 3 min at 21 °C. Results showed that the MBC of NaB reduced from >10,000 ppm at pH 7.0 to 1000 ppm at pH 4.0 and was identical for the three bacteria. The log reduction of bacteria in TSB indicated that 1000 ppm NaB at pH 2.0 was the most effective in killing the three pathogens. The respective reduction of E. coli O157:H7 and S. enterica cocktails inoculated on cherry tomatoes immersed in 3000 ppm NaB (pH 2.0) at 21 °C for 3 min was 4.99 ± 0.57 and 4.08 ± 0.65 log CFU/g, which was significantly higher (p < 0.05) than the treatments of 200 ppm free chlorine at pH 6.5. Conversely, the reduction of L. monocytogenes on tomatoes by 3000 ppm NaB (4.88 ± 0.73 log CFU/g) was similar (p > 0.05) to 200 ppm chlorine. Furthermore, the reduction of bacterial cocktails on tomatoes by 3000 ppm NaB at pH 2.0 was not affected after adding 1% tomato puree, and bacteria were not detected in NaB washing solutions with and without 1% tomato puree and on following un-inoculated tomatoes. This study showed that acidified NaB solution may be used as an alternative post-harvest wash of produce.

Proteinaceous microspheres as a delivery system for carvacrol and thymol in antibacterial applications

There is an urgent need for new materials with antimicrobial activity. Phenolic essential oil (EO) compounds with Generally Recognized As Safe (GRAS) status are attractive candidates, but they need suitable delivery systems to overcome specific drawbacks. Core-shell microspheres (MSs) of Bovine Serum Albumin (BSA) or Human Serum Albumin (HSA) encapsulating such active compounds in the oil phase are a delivery system that is novel in combination with phenolic EO compounds. Moreover, the EO compounds can also be assembled in an oil shell around a protein core by choosing an appropriate oil phase. A facile sonochemical fabrication method, which can be easily scaled-up, is developed with full characterization of the resulting EO-containing MSs by optical and electron microscopy. Bacterial growth experiments with E. coli including TEM of treated cells confirm antibacterial activity. In the case of carvacrol, the corresponding MSs are found to be both more bioactive and more stable than the free biocide.

Aerated Steam Sanitization of Whole Fresh Cantaloupes Reduces and Controls Rind-Associated Listeria but Enhances Fruit Susceptibility to Secondary Colonization

Recent bacterial illnesses and outbreaks associated with the consumption of fresh and fresh-cut fruit and vegetables emphasize the need to supply produce that is microbiologically safe while retaining its quality and nutrient value. We assessed the capacity of aerated steam to reduce initial levels and control the posttreatment proliferation of a 4-strain mixture of Listeria innocua, a surrogate for L. monocytogenes, and microflora native to the rind of whole cantaloupes. Studies were conducted at the pilot-scale level by passing deliberately contaminated melons through a prototype stainless-steel, continuous-feed heating device. Exposure for 240 s to aerated steam heated to 85 °C achieved a mean reduction in surface-inoculated L. innocua of 3.9 ± 0.6 log₁₀ CFU/cm² (n = 3) and decreased background microorganisms (yeast, moulds, and coliforms) to undetectable levels. No significant outgrowth of surviving L. innocua or yeast and moulds was observed on heat-treated melons during their storage at 4, 7, and 10 °C for 14 days. Treated fruit continued to respire. Although rind quality was altered, edible fleshy portions remained largely unaffected. Cantaloupe inoculated with L. innocua subsequent to its exposure to aerated steam provided a suitable environment for surrogate growth (mean 3.3 log₁₀ increase in rind density over 10 days at 7 °C), whereas its proliferation was restricted on nonheated cantaloupe (mean 0.7 log₁₀ increase). Steam sanitization provides an effective means for the control of pathogen and spoilage organisms, but the proliferation of surrogate organisms on heated cantaloupes raises concern regarding the impact of postprocessing contamination on consumer health risk.

PRACTICAL APPLICATION

Water vapor (steam) at a high temperature can be used to sanitize the surface of fresh, whole cantaloupe melons in a continuous-feed manner. Both Listeria bacteria and spoilage organisms are markedly reduced from initial levels and survivor outgrowth severely restricted during subsequent refrigerated storage. This approach to microorganism control is likely most applicable in situations where rinds and flesh are to be separated immediately via further processing.

Thymol and carvacrol induce autolysis, stress, growth inhibition and reduce the biofilm formation by Streptococcus mutans

Organic compounds from plants are an attractive alternative to conventional antimicrobial agents. Therefore, two compounds namely M-1 and M-2 were purified from Origanum vulgare L. and were identified as carvacrol and thymol, respectively. Antimicrobial and antibiofilm activities of these compounds along with chlorhexidine digluconate using various assays was determined against dental caries causing bacteria Streptococcus mutans. The IC₅₀ values of carvacrol (M-1) and thymol (M-2) against S. mutans were 65 and 54 µg/ml, respectively. Live and dead staining and the MTT assays reveal that a concentration of 100 µg/ml of these compounds reduced the viability and the metabolic activity of S. mutans by more than 50%. Biofilm formation on the surface of polystyrene plates was significantly reduced by M-1 and M-2 at 100 µg/ml as observed under scanning electron microscope and by colorimetric assay. These results were in agreement with RT-PCR studies. Wherein exposure to 25 µg/ml of M-1 and M-2 showed a 2.2 and 2.4-fold increase in Autolysin gene (AtlE) expression level, respectively. While an increase of 1.3 and 1.4 fold was observed in the super oxide dismutase gene (sodA) activity with the same concentrations of M-1 and M-2, respectively. An increase in the ymcA gene and a decrease in the gtfB gene expression levels was observed following the treatment with M-1 and M-2. These results strongly suggest that carvacrol and thymol isolated from O. vulgare L. exhibit good bactericidal and antibiofilm activity against S. mutans and can be used as a green alternative to control dental caries.

Lactobionic acid enhances the synergistic effect of nisin and thymol against Listeria monocytogenes Scott A in tryptic soy broth and milk

Listeria monocytogenes is a Gram-positive opportunistic human pathogen and it remains a significant cause of foodborne illnesses. A variety of natural and synthetic compounds have been studied to inhibit the growth of L. monocytogenes in foods. Antimicrobial combinations with synergistic antilisterial properties can reduce the dose of each antimicrobial, which can be further enhanced by chelating compounds. Therefore, the objective of this study was to determine antilisterial properties of binary or ternary combinations of lactobionic acid (LBA), nisin, and thymol in tryptic soy broth (TSB), 2% reduced-fat milk, and whole milk. The results showed that the minimum inhibitory concentration (MIC) of nisin, thymol and LBA was 125IU/mL, 0.25mg/mL, and 10mg/mL, respectively. The ternary combination was the most effective in reducing MICs of antimicrobials, with the MIC of nisin, thymol, and LBA being 31.25IU/mL, 0.0625mg/mL, and 1.25mg/mL, respectively. In TSB with 0.6% yeast extract, L. monocytogenes grew in individual or binary antimicrobial treatments of 31.25IU/mL nisin, 0.0625mg/mL thymol, and 1.25mg/mL LBA within 24h at 32°C, while it was completely inhibited by the ternary combination. In 2% reduced-fat milk at 21°C, the ternary combination of nisin, thymol, and LBA at respective concentrations of 250IU/mL, 2mg/mL, and 10mg/mL completely inhibited the bacterium to below the detection limit in 72h while >2log (CFU/mL) bacteria was still detected in all the binary combinations after 120h. In whole milk, the combination of 500IU/mL nisin, 2mg/mL thymol, and 10mg/mL LBA reduced bacteria to around 2log (CFU/mL) in 4h at 21°C, and no bacterial recovery was observed after 5 d. This study suggested the potential of the ternary combination of nisin, thymol and LBA for food preservation.

Enhanced antimicrobial activity of essential oil components immobilized on silica particles

The antimicrobial activity of essential oils components (EOCs) is well-known. However, their high volatility and powerful aroma limit their application in the formulation of a wide range of food products. In this context, the antimicrobial activity of carvacrol, eugenol, thymol and vanillin grafted onto the surface of three silica supports with different morphologies, textural properties and chemical reactivities (fumed silica, amorphous silica and MCM-41) was evaluated herein. Materials characterization revealed a good immobilization yield and all the devices showed a micro-scale particle size. Sensory evaluation revealed that sensory perception of EOCs decreases after covalent immobilization. Moreover, immobilization greatly enhanced the antimicrobial activity of the essential oil components against Listeria innocua and Escherichia coli compared to free components. The incorporation of EOCs immobilized on silica particles into pasteurized milk inoculated with L. innocua demonstrated their effectiveness not only for in vitro conditions, but also in a real food system.

Thymol kills bacteria, reduces biofilm formation, and protects mice against a fatal infection of Actinobacillus pleuropneumoniae strain L20

Actinobacillus pleuropneumoniae is the causative agent of the highly contagious and deadly respiratory infection porcine pleuropneumonia, resulting in serious losses to the pig industry worldwide. Alternative to antibiotics are urgently needed due to the serious increase in antimicrobial resistance. Thymol is a monoterpene phenol and efficiently kills a variety of bacteria. This study found that thymol has strong bactericidal effects on the A. pleuropneumoniae 5b serotype strain, an epidemic strain in China. Sterilization occurred rapidly, and the minimum inhibitory concentration (MIC) is 31.25μg/mL; the A. pleuropneumoniae density was reduced 1000 times within 10min following treatment with 1 MIC. Transmission electron microscopy (TEM) analysis revealed that thymol could rapidly disrupt the cell walls and cell membranes of A. pleuropneumoniae, causing leakage of cell contents and cell death. In addition, treatment with thymol at 0.5 MIC significantly reduced the biofilm formation of A. pleuropneumoniae. Quantitative RT-PCR results indicated that thymol treatment significantly increased the expression of the virulence genes purC, tbpB1 and clpP and down-regulated ApxI, ApxII and Apa1 expression in A. pleuropneumoniae. Therapeutic analysis of a murine model showed that thymol (20mg/kg) protected mice from a lethal dose of A. pleuropneumoniae, attenuated lung pathological lesions. This study is the first to report the use of thymol to treat A. pleuropneumoniae infection, establishing a foundation for the development of new antimicrobials.