Bactericidal action of binary and ternary mixtures of carvacrol, thymol, and eugenol against Listeria innocua

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.

Antimicrobial Activity of Some Essential Oils-Present Status and Future Perspectives

Extensive documentation on the antimicrobial properties of essential oils and their constituents has been carried out by several workers. Although the mechanism of action of a few essential oil components has been elucidated in many pioneering works in the past, detailed knowledge of most of the compounds and their mechanism of action is still lacking. This knowledge is particularly important for the determination of the effect of essential oils on different microorganisms, how they work in combination with other antimicrobial compounds, and their interaction with food matrix components. Also, recent studies have demonstrated that nanoparticles (NPs) functionalized with essential oils have significant antimicrobial potential against multidrug- resistant pathogens due to an increase in chemical stability and solubility, decreased rapid evaporation and minimized degradation of active essential oil components. The application of encapsulated essential oils also supports their controlled and sustained release, which enhances their bioavailability and efficacy against multidrug-resistant pathogens. In the recent years, due to increasingly negative consumer perceptions of synthetic preservatives, interest in essential oils and their application in food preservation has been amplified. Moreover, the development of resistance to different antimicrobial agents by bacteria, fungi, viruses, parasites, etc. is a great challenge to the medical field for treating the infections caused by them, and hence, there is a pressing need to look for new and novel antimicrobials. To overcome these problems, nano-encapsulation of essential oils and exploiting the synergies between essential oils, constituents of essential oils, and antibiotics along with essential oils have been recommended as an answer to this problem. However, less is known about the interactions that lead to additive, synergistic, or antagonistic effects. A contributing role of this knowledge could be the design of new and more potent antimicrobial blends, and understanding of the interplay between the components of crude essential oils. This review is written with the purpose of giving an overview of current knowledge about the antimicrobial properties of essential oils and their mechanisms of action, components of essential oils, nano-encapsulated essential oils, and synergistic combinations of essential oils so as to find research areas that can facilitate applications of essential oils to overcome the problem of multidrug-resistant micro-organisms.

Oregano Essential Oil as an Antimicrobial and Antioxidant Additive in Food Products

Food consumers and industries urged the need of natural alternatives to assure food safety and quality. As a response, the use of natural compounds from herbs and spices is an alternative to synthetic additives associated with toxic problems. This review discusses the antimicrobial and antioxidant activity of oregano essential oil (OEO) and its potential as a food additive. Oregano is a plant that has been used as a food seasoning since ancient times. The common name of oregano is given to several species: Origanum (family: Lamiaceae) and Lippia (family: Verbenaceae), amongst others. The main compounds identified in the different OEOs are carvacrol and thymol, which are responsible for the characteristic odor, antimicrobial, and antioxidant activity; however, their content may vary according to the species, harvesting season, and geographical sources. These substances as antibacterial agents make the cell membrane permeable due to its impregnation in the hydrophobic domains, this effect is higher against gram positive bacteria. In addition, the OEO has antioxidant properties effective in retarding the process of lipid peroxidation in fatty foods, and scavenging free radicals. In this perspective, the present review analyzes and discusses the state of the art about the actual and potential uses of OEO as an antimicrobial and antioxidant food additives.

Synergistic Activity of Essential Oils from Herbs and Spices Used on Meat Products against Food Borne Pathogens

Essential oils (EOs) could be utilized as natural agents to improve the safety of meat products. However, the high concentration required to achieve an antimicrobial effect in foods might be incompatible with their sensory acceptance. To avoid this problem, combinations of EOs provide an effective approach reducing the odds of sensory rejection. In our study, 13 EOs of herbs and spices commonly used in the seasoning of meat products were assessed for their antimicrobial activity against Salmonella spp., Listeria monocytogenes, Escherichia coli and Staphylococcus aureus. However, only 7 of them were selected to study their synergistic effect based on their antimicrobial activity and minimum inhibitory concentration (MIC) against foodborne pathogens. EOs of thyme and cinnamon presented the largest antibacterial activity against foodborne pathogens. Combinations of selected EOs displayed a synergic effect against foodborne pathogens and also an important decrease in their individual MIC. Thyme EO presented the lowest individual MIC, but its utilization in combination decreased the MIC of the other EOs. Utilization of cinnamon EO also improved the reduction of the individual MICs of the EOs of cumin and parsley. Our results suggest the potential use of EO mixtures to control foodborne pathogens in meat products. Although the individual MIC values of selected EOs decreased, the sensory impact on meat products needs to be assessed.

Role of carvacrol in cardioprotection against myocardial ischemia/reperfusion injury in rats through activation of MAPK/ERK and Akt/eNOS signaling pathways

Carvacrol (CAR) is a compound isolated from some essential oils, many studies have demonstrated its therapeutic potential on different diseases. This study aims to evaluate the protective effect of CAR against myocardial ischemia/reperfusion (I/R) injury in rats. Male adult rats underwent ligation of the left anterior descending coronary artery (LAD) in I/R models. Rats were treated with CAR after LAD. The levels of I/R- induced infarct size, cardiomyocyte apoptosis and cardiac functional impairment were examined. Levels of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) were detected by western blotting. Cardiomyocytes induced by hypoxic reperfusion (H/R) injury were tested by Hoechst 33258. Our results revealed that CAR administration significantly protected the heart function, attenuated myocardial infarct size, increased SOD and CAT levels, reduced MDA level and especially decreased cardiomyocytes apoptosis. Western blotting showed that CAR treatment up-regulated phosphorylated ERK (p-ERK), while producing no impact onp38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK). The cardioprotection of CAR was reversed by the ERK inhibitor PD-98059, demonstrating the involvement of the MAPK/ERK pathway in the anti-apoptotic mechanisms of CAR. Besides, the results in vitro also showed the protective efficiency of CAR on cardiomyocytes H/R injury. Furthermore, pretreatment with CAR markedly increased the activation of Akt/eNOS pathway in cardiomyocytes subjected to H/R, and the protective effects of CAR were abolished in the presence of the Akt inhibitor LY294002. Therefore, the cardioprotective effects of CAR may be attributed to its antioxidant and antiapoptotic activities through activations of the MAPK/ERK and Akt/eNOS signaling pathways.

Hydrosol of Thymbra capitata Is a Highly Efficient Biocide against Salmonella enterica Serovar Typhimurium Biofilms

Salmonella is recognized as one of the most significant enteric foodborne bacterial pathogens. In recent years, the resistance of pathogens to biocides and other environmental stresses, especially when they are embedded in biofilm structures, has led to the search for and development of novel antimicrobial strategies capable of displaying both high efficiency and safety. In this direction, the aims of the present work were to evaluate the antimicrobial activity of hydrosol of the Mediterranean spice Thymbra capitata against both planktonic and biofilm cells of Salmonella enterica serovar Typhimurium and to compare its action with that of benzalkonium chloride (BC), a commonly used industrial biocide. In order to achieve this, the disinfectant activity following 6-min treatments was comparatively evaluated for both disinfectants by calculating the concentrations needed to achieve the same log reductions against both types of cells. Their bactericidal effect against biofilm cells was also comparatively determined by in situ and real-time visualization of cell inactivation through the use of time-lapse confocal laser scanning microscopy (CLSM). Interestingly, results revealed that hydrosol was almost equally effective against biofilms and planktonic cells, whereas a 200-times-higher concentration of BC was needed to achieve the same effect against biofilm compared to planktonic cells. Similarly, time-lapse CLSM revealed the significant advantage of the hydrosol to easily penetrate within the biofilm structure and quickly kill the cells, despite the three-dimensional (3D) structure of Salmonella biofilm.

IMPORTANCE

The results of this paper highlight the significant antimicrobial action of a natural compound, hydrosol of Thymbra capitata, against both planktonic and biofilm cells of a common foodborne pathogen. Hydrosol has numerous advantages as a disinfectant of food-contact surfaces. It is an aqueous solution which can easily be rinsed out from surfaces, it does not have the strong smell of the essential oil (EO) and it is a byproduct of the EO distillation procedure without any industrial application until now. Consequently, hydrosol obviously could be of great value to combat biofilms and thus to improve product safety not only for the food industries but probably also for many other industries which experience biofilm-related problems.

Stress Conditions Induced by Carvacrol and Cinnamaldehyde on Acinetobacter baumannii

Acinetobacter baumannii has emerged as a major cause of nosocomial infections. The ability of A. baumannii to display various resistance mechanisms against antibiotics has transformed it into a successful nosocomial pathogen. The limited number of antibiotics in development and the disengagement of the pharmaceutical industry have prompted the development of innovative strategies. One of these strategies is the use of essential oils, especially aromatic compounds that are potent antibacterial molecules. Among them, the combination of carvacrol and cinnamaldehyde has already demonstrated antibacterial efficacy against A. baumannii. The aim of this study was to determine the biological effects of these two compounds in A. baumannii, describing their effect on the rRNA and gene regulation under environmental stress conditions. Results demonstrated rRNA degradation by the carvacrol/cinnamaldehyde mixture, and this effect was due to carvacrol. Degradation was conserved after encapsulation of the mixture in lipid nanocapsules. Results showed an upregulation of the genes coding for heat shock proteins, such as groES, groEL, dnaK, clpB, and the catalase katE, after exposure to carvacrol/cinnamaldehyde mixture. The catalase was upregulated after carvacrol exposure wich is related to an oxidative stress. The combination of thiourea (hydroxyl radical scavenger) and carvacrol demonstrated a potent bactericidal effect. These results underline the development of defense strategies of the bacteria by synthesis of reactive oxygen species in response to environmental stress conditions, such as carvacrol.

Antimicrobial Activity of Individual and Combined Essential Oils against Foodborne Pathogenic Bacteria

The antimicrobial activities of essential oils from Mexican oregano (Lippia berlandieri Schauer), mustard (Brassica nigra), and thyme (Thymus vulgaris) were evaluated alone and in binary combinations against Listeria monocytogenes, Staphylococcus aureus, or Salmonella Enteritidis. Chemical compositions of the essential oils were analyzed by gas chromatography-mass spectrometry. The MICs of the evaluated essential oils ranged from 0.05 to 0.50% (vol/vol). Mustard essential oil was the most effective, likely due to the presence of allyl isothiocyanate, identified as its major component. Furthermore, mustard essential oil exhibited synergistic effects when combined with either Mexican oregano or thyme essential oils (fractional inhibitory concentration indices of 0.75); an additive effect was obtained by combining thyme and Mexican oregano essential oils (fractional inhibitory concentration index = 1.00). These results suggest the potential of studied essential oil mixtures to inhibit microbial growth and preserve foods; however, their effect on sensory quality in selected foods compatible with their flavor needs to be assessed.

Antimicrobial Activity of Rhoeo discolor Phenolic Rich Extracts Determined by Flow Cytometry

Traditional medicine has led to the discovery of important active substances used in several health-related areas. Phytochemicals in Rhoeo discolor extracts have proven to have important antimicrobial activity. In the present study, our group determined the antimicrobial effects of extracts of Rhoeo discolor, a plant commonly used in Mexico for both medicinal and ornamental purposes. We evaluated the in vitro activity of phenolic rich extracts against specifically chosen microorganisms of human health importance by measuring their susceptibility via agar-disc diffusion assay and flow cytometry: Gram-positive Listeria innocua and Streptococcus mutans, Gram-negative Escherichia coli and Pseudomonas aeruginosa, and lastly a fungal pathogen Candida albicans. Ten different extracts were tested in eight different doses on all the microorganisms. Analytical data revealed a high content of phenolic compounds. Both agar-disc diffusion assay and flow cytometry results demonstrated that Pseudomonas aeruginosa was the least affected by extract exposure. However, low doses of these extracts (predominantly polar), in a range from 1 to 4 μg/mL, did produce a statistically significant bacteriostatic and bactericidal effect on the rest of the microorganisms. These results suggest the addition of certain natural extracts from Rhoeo discolor could act as antibacterial and antimycotic drugs or additives for foods and cosmetics.

Variable effects of nicotine, anabasine, and their interactions on parasitized bumble bees

Secondary metabolites in floral nectar have been shown to reduce parasite load in two common bumble bee species. Previous studies on the effects of nectar secondary metabolites on parasitized bees have focused on single compounds in isolation; however, in nature, bees are simultaneously exposed to multiple compounds. We tested for interactions between the effects of two alkaloids found in the nectar of Nicotiana spp. plants, nicotine and anabasine, on parasite load and mortality in bumble bees ( Bombus impatiens) infected with the intestinal parasite Crithidia bombi. Adult worker bees inoculated with C. bombi were fed nicotine and anabasine diet treatments in a factorial design, resulting in four nectar treatment combinations:  2 ppm nicotine, 5 ppm anabasine, 2ppm nicotine and 5 ppm anabasine together, or a control alkaloid-free solution. We conducted the experiment twice: first, with bees incubated under variable environmental conditions ('Variable'; temperatures varied from 10-35°C with ambient lighting); and second, under carefully controlled environmental conditions ('Stable'; 27°C incubator, constant darkness). In 'Variable', each alkaloid alone significantly decreased parasite loads, but this effect was not realized with the alkaloids in combination, suggesting an antagonistic interaction. Nicotine but not anabasine significantly increased mortality, and the two compounds had no interactive effects on mortality. In 'Stable', nicotine significantly increased parasite loads, the opposite of its effect in 'Variable'. While not significant, the relationship between anabasine and parasite loads was also positive. Interactive effects between the two alkaloids on parasite load were non-significant, but the pattern of antagonistic interaction was similar to that in the variable experiment. Neither alkaloid, nor their interaction, significantly affected mortality under controlled conditions. Our results do not indicate synergy between Nicotiana nectar alkaloids; however, they do suggest a complex interaction between secondary metabolites, parasites, and environmental variables, in which secondary metabolites can be either toxic or medicinal depending on context.

Comparative essential oil composition of aerial parts of Tanacetum dumosum Boiss. from Southern Zagros, Iran

The essential oils of leaves and flowers of Tanacetum dumosum Boiss., an endemic medicinal shrub, were extracted by using hydrodistillation method and analysed using GC and GC-MS. A total of 43 and 44 compounds were identified in the essential oils from the leaves and flowers of T. dumosum, respectively. The major chemical constituents of leaves oil were borneol (27.9%), bornyl acetate (18.4%), 1,8-cineol (17.5%), α-terpineol (5.3%), cis-chrysanthenyl acetate (3.3%), camphene (2.7%) and terpinene-4-ol (1.9%), while the main components of the flower oil were isobornyl-2-methyl butanoate (41.1%), trans-linalyl oxide acetate (11.9%), 1,8-cineole (7.7%), thymol (4.2%), linalool (3.9%), camphor (2.9%), isobornyl propanoate (2.9%), α-terpineol (2.1%) and caryophyllene oxide (2.0%). Major qualitative and quantitative variations for some main chemical compounds among different aerial parts of T. dumosum were identified. High contents of borneol, bornyl acetate, 1,8-cineol and linalool in the leaves and flowers of T. dumosum show its potential for use in the food and perfumery industry.

An update on approaches to controlling coccidia in poultry using botanical extracts

1. This paper reviews the use of botanical extracts in the control of coccidial infection in poultry. 2. Some plants and their respective volatile oils and extracts have the potential to alleviate coccidiosis and reduce its severity. 3. Most plant bioactives improve some, but not all, aspects of coccidiosis with variable effectiveness against different species of Eimeria. 4. Difficulties in comparing research findings have arisen from the use of different experimental models, different active components and infectious dose of Eimeria. 5. Current knowledge of their potential anti-coccidial effects may provide guidance for the use of botanical extracts in the control of the coccidiosis.

Antiviral efficacy and mechanisms of action of oregano essential oil and its primary component carvacrol against murine norovirus

AIMS

To investigate the antiviral efficacy of oregano oil and its primary active component, carvacrol, against the nonenveloped murine norovirus (MNV), a human norovirus surrogate.

METHODS AND RESULTS

Along with an observed loss in cell culture infectivity, the antiviral mechanisms of action were determined in side-by-side experiments including a cell-binding assay, an RNase I protection assay and transmission electron microscopy (TEM). Both antimicrobials produced statistically significant reductions (P ≤ 0·05) in virus infectivity within 15 min of exposure (c. 1·0-log10). Despite this, the MNV infectivity remained stable with increasing time exposure to oregano oil (1·07-log10 after 24 h), while carvacrol was far more effective, producing up to 3·87-log10 reductions within 1 h. Based on the RNase I protection assay, both antimicrobials appeared to act directly upon the virus capsid and subsequently the RNA. Under TEM, the capsids enlarged from ≤35 nm in diameter to up to 75 nm following treatment with oregano oil and up to 800 nm with carvacrol; with greater expansion, capsid disintegration could be observed. Virus adsorption to host cells did not appear to be affected by either antimicrobial.

CONCLUSIONS

Our results demonstrate that carvacrol is effective in inactivating MNV within 1 h of exposure by acting directly on the viral capsid and subsequently the RNA.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides novel findings on the antiviral properties of oregano oil and carvacrol against MNV and demonstrates the potential of carvacrol as a natural food and surface (fomite) sanitizer to control human norovirus.

Chemical composition, antioxidant, antimicrobial and cytotoxic activities of Tagetes minuta and Ocimum basilicum essential oils

Chemical composition, antioxidant, antimicrobial and cytotoxic activities of Tagetes minuta (TM) essential oil (TMO) and Ocimum basilicum (OB) essential oil (OBO) were examined. The main components for TMO were dihydrotagetone (33.9%), E-ocimene (19.9%), tagetone (16.1%), cis-β-ocimene (7.9%), Z-ocimene (5.3%), limonene (3.1%) and epoxyocimene (2.03%). The main components for OBO were methylchavicol (46.9%), geranial (19.1%), neral (15.15%), geraniol (3.0%), nerol (3.0%), caryophyllene (2.4%). Inhibitory concentrations (IC₅₀) for reactive oxygen species (ROS) and reactive nitrogen species (RNS) scavenging were 12–17 and 200–250 μg/mL of TMO and OBO, respectively. Minimal inhibitory concentration (MIC) against Salmonella typhi,Escherichia coli,Staphylococcus aureus,Bacillus subtilis,Aspergillus niger, and Candida albicans were 150 ± 8, 165 ± 9, 67 ± 8, 75 ± 7, 135 ± 15, and 115 ± 8 μg/mL of TMO, respectively. MIC for S. typhi,E. coli,S. aureus,B. subtilis,A. niger, and C. albicans were 145 ± 8, 160 ± 7, 45 ± 4, 40 ± 3, 80 ± 9, and 95 ± 7 μg/mL of OBO, respectively. IC₅₀ for nasopharyngeal cancer cell line (KB) and liver hepatocellular carcinoma cell line (HepG2) were 75 ± 5 and 70 ± 4 μg/mL of TMO, respectively. IC₅₀ for KB and HepG2 were 45 ± 4 and 40 ± 3 μg/mL of OBO, respectively. Thus, they could be used as an effective source of natural antioxidant and antibacterial additive to protect foods from oxidative damages and foodborne pathogens. Furthermore, they could be promising candidate for antitumor drug design.

Plant-derived compounds as natural antimicrobials to control paper mill biofilms

Biofilms can cause severe problems in industrial paper mills, particularly of economic and technological types (clogging of filters, sheet breaks or holes in the paper, machine breakdowns, etc.). We present here some promising results on the use of essential oil compounds to control these biofilms. Biofilms were grown on stainless-steel coupons with a microbial white water consortium sampled from an industrial paper mill. Five essential oil compounds were screened initially in the laboratory in terms of their antimicrobial activity against planktonic cells and biofilms. The three most active compounds were selected and then tested in different combinations. The combination finally selected was tested at the pilot scale to confirm its efficiency under realistic conditions. All the compounds tested were as active against biofilms as they were against planktonic cells. The most active compounds were thymol, carvacrol, and eugenol, and the most efficient combination was thymol–carvacrol. At a pilot scale, with six injections a day, 10 mM carvacrol alone prevented biocontamination for at least 10 days, and a 1 mM thymol–carvacrol combination enabled a 67 % reduction in biofilm dry matter after 11 days. The use of green antimicrobials could constitute a very promising alternative or supplement to the treatments currently applied to limit biofilm formation in the environment of paper mill machines.

Carvacrol alleviates cerebral edema by modulating AQP4 expression after intracerebral hemorrhage in mice

Carvacrol is a natural compound extracted from many plants of the family Lamiaceae. Previous studies have demonstrated that carvacrol has potential neuroprotective effects in central nervous system diseases such as Alzheimer's disease and cerebral ischemia. In this study, we investigated the preclinical effect of carvacrol on cerebral edema after intracerebral hemorrhage (ICH) using a bacterial collagenase-induced ICH mouse model. Mice were randomly divided into sham (n=43), vehicle-treated (n=51), and carvacrol-treated groups (n=101). In carvacrol-treated group, carvacrol was administrated to mice at 0h, 1h, or 3h after ICH induction. Carvacrol was injected intraperitoneally with single doses of 10, 25, 50, or 100mg/kg. Neurologic dysfunctions, brain water content, aquaporins (AQPs) mRNAs level and AQP4 protein expression in the perihematomal area were evaluated post ICH. Our results showed that carvacrol administration improved neurological deficits after day 3 following ICH (p<0.05). Carvacrol reduced cerebral edema and Evans Blue leakage at day 3 (p<0.05). We also found that carvacrol treatment decreased AQP4 mRNA in a dose-dependent manner at 24h. Furthermore, AQP4 protein expression in the perihematomal area was reduced by carvacrol significantly at day 3 after ICH (p<0.05). Our findings suggest that carvacrol may exert its protective effect on ICH injury by ameliorating AQP4-mediated cerebral edema.

Nanodispersed eugenol has improved antimicrobial activity against Escherichia coli O157:H7 and Listeria monocytogenes in bovine milk

There has been great interest in intervention strategies based on plant essential oils to control pathogens such as Escherichia coli O157:H7 and Listeria monocytogenes (Lm). However, the poor solubility of essential oils in water makes it difficult to disperse evenly in food matrices, impacting food quality and antimicrobial efficacy. In the present study, eugenol was dispersed in nanocapsules prepared with conjugates of whey protein isolate (WPI) and maltodextrin (MD, of various chain lengths). When eugenol was encapsulated in the conjugate made with MD40 at a WPI:MD mass ratio of 1:2, the nanodispersion was transparent and was characterized for antimicrobial efficacy against E. coli O157:H7 strains ATCC 43889 and 43894, and Lm strains Scott A and 101 in tryptic soy broth (TSB) and milk with different fat levels (whole, 2% reduced fat, and skim) at 35 or 32 °C, with comparison to the same levels of free eugenol. In TSB, antimicrobial efficacy of nanodispersed eugenol against E. coli O157:H7 and Lm was not improved, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values being 0.25 g/L higher than those of free eugenol. Free eugenol performed better in TSB because there was no interfering compound and the MIC and MBC were below the solubility of eugenol. In milk, nanodispersed eugenol was consistently observed to be more effective than free eugenol, with MIC and MBC values above the solubility limit of eugenol. The nanodispersed eugenol was speculated to be evenly distributed in food matrices at concentrations above the solubility limit and supplied the antimicrobial locally when the binding caused eugenol level below the inhibition requirement. Nanodispersed eugenol thus provides a novel approach for incorporation in foods to improve antimicrobial efficacy without changing turbidity.

Carvacrol, a food-additive, provides neuroprotection on focal cerebral ischemia/reperfusion injury in mice

Carvacrol (CAR), a naturally occurring monoterpenic phenol and food additive, has been shown to have antimicrobials, antitumor, and antidepressant-like activities. A previous study demonstrated that CAR has the ability to protect liver against ischemia/reperfusion injury in rats. In this study, we investigated the protective effects of CAR on cerebral ischemia/reperfusion injury in a middle cerebral artery occlusion mouse model. We found that CAR (50 mg/kg) significantly reduced infarct volume and improved neurological deficits after 75 min of ischemia and 24 h of reperfusion. This neuroprotection was in a dose-dependent manner. Post-treatment with CAR still provided protection on infarct volume when it was administered intraperitoneally at 2 h after reperfusion; however, intracerebroventricular post-treatment reduced infarct volume even when the mice were treated with CAR at 6 h after reperfusion. These findings indicated that CAR has an extended therapeutic window, but delivery strategies may affect the protective effects of CAR. Further, we found that CAR significantly decreased the level of cleaved caspase-3, a marker of apoptosis, suggesting the anti-apoptotic activity of CAR. Finally, our data indicated that CAR treatment increased the level of phosphorylated Akt and the neuroprotection of CAR was reversed by a PI3K inhibitor LY-294002, demonstrating the involvement of the PI3K/Akt pathway in the anti-apoptotic mechanisms of CAR. Due to its safety and wide use in the food industry, CAR is a promising agent to be translated into clinical trials.

Essential oils in food preservation: mode of action, synergies, and interactions with food matrix components

Essential oils are aromatic and volatile liquids extracted from plants. The chemicals in essential oils are secondary metabolites, which play an important role in plant defense as they often possess antimicrobial properties. The interest in essential oils and their application in food preservation has been amplified in recent years by an increasingly negative consumer perception of synthetic preservatives. Furthermore, food-borne diseases are a growing public health problem worldwide, calling for more effective preservation strategies. The antibacterial properties of essential oils and their constituents have been documented extensively. Pioneering work has also elucidated the mode of action of a few essential oil constituents, but detailed knowledge about most of the compounds' mode of action is still lacking. This knowledge is particularly important to predict their effect on different microorganisms, how they interact with food matrix components, and how they work in combination with other antimicrobial compounds. The main obstacle for using essential oil constituents as food preservatives is that they are most often not potent enough as single components, and they cause negative organoleptic effects when added in sufficient amounts to provide an antimicrobial effect. Exploiting synergies between several compounds has been suggested as a solution to this problem. However, little is known about which interactions lead to synergistic, additive, or antagonistic effects. Such knowledge could contribute to design of new and more potent antimicrobial blends, and to understand the interplay between the constituents of crude essential oils. The purpose of this review is to provide an overview of current knowledge about the antibacterial properties and antibacterial mode of action of essential oils and their constituents, and to identify research avenues that can facilitate implementation of essential oils as natural preservatives in foods.