Essential oils as antimicrobials in food systems – A review

Solid lipid microparticles loaded with cinnamon oleoresin: Characterization, stability and antimicrobial activity

Cinnamon bark oleoresin (CO) is a natural flavoring that has several biological properties and can act as an antimicrobial agent. However, oleoresins are susceptible to degradation by light, oxygen and temperature. Thus, the objective of this work was the production and characterization of microparticles loaded with CO obtained by the spray chilling technique. Hardfat (PH) and palm oil (PO) were used as carriers in different proportions: 100:0; 80:20; 60:40, respectively. The active concentration was 1 and 2%. Solid lipid microparticles (SLM) were stored at 25 and 45°C having their polymorphism, retention capacity of the volatile compounds and antimicrobial capacity assessed over 28 days. CO presented cinnamaldehyde (Cn), O-methoxy cinnamaldehyde (OmCn) and coumarin (Co) as the major volatile components. The minimum inhibitory concentration (MIC) of the CO against molds, yeasts and Gram-negative bacteria was of 0.1% (v/v), for every microorganism. In the SLM characterization there was a significant size variation, with a mean diameter (d 0.5) in the range of 8-72 μm. Most of the formulations showed crystals in the polymorphic form β '. The formulation containing only PH as the carrier agent and 2% CO was able to better retain the volatile compounds. During the storage period, formulations F2 and F3, containing proportions of HP and OP of 80:20 and 60:40, respectively, and 2% CO, showed the best stabilities in relation to the concentration of Cn. The antimicrobial activity of the SLM against Candida pseudointermedia and Penicillium paneum, evaluated by the diameter of inhibition zone, increased over the 28 days of storage.

Essential Oils as Feed Additives-Future Perspectives

The inconsistency of phytogenic feed additives' (PFA) effects on the livestock industry poses a risk for their use as a replacement for antibiotic growth promoters. The livestock market is being encouraged to use natural growth promotors, but information is limited about the PFA mode of action. The aim of this paper is to present the complexity of compounds present in essential oils (EOs) and factors that influence biological effects of PFA. In this paper, we highlight various controls and optimization parameters that influence the processes for the standardization of these products. The chemical composition of EOs depends on plant genetics, growth conditions, development stage at harvest, and processes of extracting active compounds. Their biological effects are further influenced by the interaction of phytochemicals and their bioavailability in the gastrointestinal tract of animals. PFA effects on animal health and production are also complex due to various EO antibiotic, antioxidant, anti-quorum sensing, anti-inflammatory, and digestive fluids stimulating activities. Research must focus on reliable methods to identify and control the quality and effects of EOs. In this study, we focused on available microencapsulation techniques of EOs to increase the bioavailability of active compounds, as well as their application in the animal feed additive industry.

Preservative potential of Tinospora cordifolia, a novel natural ingredient for improved lipid oxidative stability and storage quality of chevon sausages

Purpose

The purpose of this study was to assess the preservative potential of Tinospora cordifolia as a novel natural preservative in muscle foods.

Design/methodology/approach

Chevon sausages were used as a model system and were prepared by incorporating different levels of T. cordifolia, namely, T1 (0.25 per cent), T2 (0.50 per cent) and T3 (0.75 per cent), and assessed for lipid oxidative stability and storage quality under refrigerated (4 ± 10°C) conditions.

Findings

Lipid oxidative stability showed a significant improvement as the products incorporated with T. cordifolia exhibited significantly (p = 0.001) lower thiobarbituric acid reacting substances (mg malonaldehyde/kg) in comparison to control. A significant improvement was also observed in the microbial stability as T. cordifolia-incorporated products showed significantly lower values for total plate count (log cfu/g, p = 0.001), psychrophilic count (log cfu/g, p = 0.003), yeast and mould count (log cfu/g, p = 0.02) and free fatty acid (percentage of oleic acid, p = 0.01). Significantly higher scores were observed for various sensory parameters of the treated products during storage.

Originality/value

Tinospora cordifolia successfully improved the lipid oxidative and microbial stability of the model meat product and may be commercially exploited as a novel preservative in muscle foods.

Matricaria genus as a source of antimicrobial agents: From farm to pharmacy and food applications

Matricaria is a widespread genus of flowering plants of the family Asteraceae that grow in temperate regions of Europe, Asia, America and Africa. Some of the species are also naturalized in Australia. Some species of this genus such as Chamomiles are recognized medicinal plants and cultivated in several countries for commercial purposes: to obtain its blue essence, as herbal tea, and for pharmaceutical or cosmeceutical uses. The phytochemical composition of Matricaria spp. includes volatile terpenoids (e.g., α-bisabolol, bisabolol oxide A and B, β-trans-farnesene and chamazulene), sesquiterpene lactones such as matricin, and phenolic compounds (flavonoids, coumarins and phenolic acids). Their essential oil is obtained from the fresh or dried inflorescences by steam distillation, and additionally cohobation of the remaining water. The volatile composition of the essential oil, especially the content of the valuable components α-bisabolol and chamazulene, depends on the plant part, origin and quality of the source, genetic, and environmental factors. Moreover, other parameters, such as season of harvest and methods of extraction, can affect the extraction yield of the essential oils/extracts, their composition and, therefore, their bioactivity. Due to the importance of this genus and particularly M. recutita (M. chamomilla), this review focus on its cultivation, factor affecting essential oils' composition and their role in traditional medicine, as antibacterial agents and finally as food preservatives.

Effect of low thermal pasteurization in combination with carvacrol on color, antioxidant capacity, phenolic and vitamin C contents of fruit juices

Mild thermal treatment in combination with natural antimicrobials has been described as an alternative to conventional pasteurization to ensure fruit juices safety. However, to the best of our knowledge, no study has been undertaken to evaluate what could be its effect on their color and nutritional value. This study therefore aimed at assessing how a low thermal pasteurization in combination with carvacrol could affect these parameters, with orange, pineapple, and watermelon juices as selected fruit juices. The experimental design used had levels ranging from 50 to 90°C, 0 to 60 μl/L, and 0 to 40 min for temperature, concentration of carvacrol supplemented, and treatment length, respectively. The only supplementation of fruit juices with carvacrol did not affect their color. In comparison with high thermal pasteurization (>70°C), a combined treatment at mild temperatures (50-70°C) better preserved their color, antioxidant capacity (AOC), and vitamin C content, and increased their total phenolic content (TPC). Globally, carvacrol supplementation had a positive impact on the TPC of thermally treated juices and increased the AOC of treated watermelon juice, which was the lowest of the three fruit juices. Mild heat treatment in combination with natural antimicrobials like carvacrol is therefore an alternative to limit the negative effects of conventional pasteurization on fruit juices quality.

Essential oil based nanoemulsions to improve the microbial quality of minimally processed fruits and vegetables: A review

Due to the convenience and nutritional value, minimally processed fruits and vegetables (MPFV) are one of the rapid growing sectors in the food industry. However, their microbiological safety is a cause of great concern. Essential oils (EOs), known for potent antimicrobial efficacy have been shown to reduce microbial load in MPFV, but their low water solubility, high volatility and strong organoleptic properties limit their wide use. Encapsulating EOs to nanoemulsion offers a viable remedy for such limitations. Due to the unique properties of the EOs nanoemulsion, there has been an increasing interest in their fabrication and use in food system. The present review article encompasses the overview of the prominent microflora present in MPFV, the recent developments on the fabrication and stability of EOs based nanoemulsion, their in vitro antimicrobial activity and their application in MPFV. This review also discusses the EOs based nanoemulsions antimicrobial mechanism of action and their regulatory issues related to their use. Application of EOs based nanoemulsion either as washing disinfectant or with incorporation into edible coatings have been shown to considerably improve the microbial quality and safety of MPFV. This efficacy has been further shown to increase when combined with other hurdles. However, further studies are required on the toxicity of EOs based nanoemulsion to assure its commercial exploitation.

Plant Secondary Metabolite-Derived Polymers: A Potential Approach to Develop Antimicrobial Films

The persistent issue of bacterial and fungal colonization of artificial implantable materials and the decreasing efficacy of conventional systemic antibiotics used to treat implant-associated infections has led to the development of a wide range of antifouling and antibacterial strategies. This article reviews one such strategy where inherently biologically active renewable resources, i.e., plant secondary metabolites (PSMs) and their naturally occurring combinations (i.e., essential oils) are used for surface functionalization and synthesis of polymer thin films. With a distinct mode of antibacterial activity, broad spectrum of action, and diversity of available chemistries, plant secondary metabolites present an attractive alternative to conventional antibiotics. However, their conversion from liquid to solid phase without a significant loss of activity is not trivial. Using selected examples, this article shows how plasma techniques provide a sufficiently flexible and chemically reactive environment to enable the synthesis of biologically-active polymer coatings from volatile renewable resources.

Fabrication and Release Behavior of Microcapsules with Double-Layered Shell Containing Clove Oil for Antibacterial Applications

In this study, double-layer polyurethane/poly(urea-formaldehyde) (PU/PUF) shell microcapsules containing clove oil with antibacterial properties were successfully synthesized via in situ and interfacial polymerization reactions in an oil-in-water emulsion. The morphology, core-shell structure, and composition of the microcapsules were investigated systematically. Additionally, the release behaviors of microcapsules synthesized under different reaction parameters were studied. It was found that the release rate of clove oil can be controlled by tuning the amount of PU reactants and the length of PUF deposition time. The release profile fitted well against the Baker-Lonsdale model, which indicates diffusion as the primary release mechanism. Experimental results based on the ASTM E2315 time kill test revealed that the fabricated microcapsules have great antibacterial activities against the marine bacteria Vibrio coralliilyticus, Escherichia coli, Exiguobacterium aestuarii, and marine biofilm-forming bacteria isolated from the on-site contaminated samples, showing their great potential as an eco-friendly solution to replace existing toxic antifouling agent.

Foliar application of ascorbic and citric acids enhanced 'Red Spur' apple fruit quality, bioactive compounds and antioxidant activity

This study aimed to assess the effect of the foliar application of ascorbic acid (AA) and citric acid (CA) on total antioxidant activity (TAA), total phenolics, total flavonoids, total anthocyanin content, antioxidant enzymes, phenylalanine ammonialyase (PAL), and polyphenol oxidase (PPO) activities in apple 'Red Spur'. The experiment was conducted on 12-years-old trees 'Red Spur' grafted on MM₁₀₆ rootstock. The trees were sprayed with AA (0, 200 and 400 mg L^-1) and/or CA (0, 200 and 400 mg L^-1) at three different times during summer. Foliar application with AA and CA significantly (p < 0.01) enhanced all measured quality attributes and decreased the activity of PPO. Fruit from trees treated with AA at 400 mg L^-1 and CA at 200 mg L^-1 showed the highest TAA and catalase (CAT) enzyme activity. Total phenolics increased in fruits when trees were sprayed with AA and CA. Contrasting, AA treatment, CA had no significant effect on guaiacol peroxidase (G-POD). A significant decrease in PPO activity was detected in fruits when treated with both AA and CA. Both treatments significantly decreased the activity of PAL at 400 mg L^-1. Considering the results, foliar application of AA and CA, either alone or in combination improved the quality and nutraceutical properties of 'Red Spur' apple.

Ethnoveterinary perspectives and promising future

In this review, we have discussed the recent potential effects of plants and their derivatives in treating diseases of veterinary importance in livestock. The therapeutic value of these natural products depends upon their bioactive metabolites that are developed and isolated from crude plants, thus produced a selective action on the body. The crises of drug resistance in most pathogenic bacteria and parasites that cause economic loss in animals necessitate developing new sources for drugs to overcome therapeutic failure. We summarized the different antibacterial and antiparasitic plants with their bioactive compounds that have widely used in animals. Finally, the environmental friendly feed additives that may be used as alternatives to an antibiotic growth promoter for broiler chickens were illustrated.

Lactoferrin, chitosan and Melaleuca alternifolia-natural products that show promise in candidiasis treatment

The evolution of microorganisms resistant to many medicines has become a major challenge for the scientific community around the world. Motivated by the gravity of such a situation, the World Health Organization released a report in 2014 with the aim of providing updated information on this critical scenario. Among the most worrying microorganisms, species from the genus Candida have exhibited a high rate of resistance to antifungal drugs. Therefore, the objective of this review is to show that the use of natural products (extracts or isolated biomolecules), along with conventional antifungal therapy, can be a very promising strategy to overcome microbial multiresistance. Some promising alternatives are essential oils of Melaleuca alternifolia (mainly composed of terpinen-4-ol, a type of monoterpene), lactoferrin (a peptide isolated from milk) and chitosan (a copolymer from chitin). Such products have great potential to increase antifungal therapy efficacy, mitigate side effects and provide a wide range of action in antifungal therapy.

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

Despite the widespread belief that citrus fruit extracts (CFEs) are microbiologically safe due to their acidity, limited bactericidal effect results in low applicability as antibacterial agent and outbreaks occurred by acid-adapted pathogens. Here, we examined the antibacterial effects of CFEs [lime (Citrus medica), lemon (Citrus limon), calamansi (Citrus microcarpa)] combined with essential oil components (EOCs; carvacrol and thymol) against non-acid-adapted/acid-adapted Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes under 22 °C for 5 min. CFEs (<20%) alone or small amounts of EOCs (2.0 mM; 0.032%) alone could not inactivate the target bacteria effectively. However, combined treatments exhibited marked synergy: CFE + EOCs eliminated all the bacteria (>6.9 log CFU/ml). Among the CFEs tested, the highest synergism was shown by calamansi, an exotic citrus fruit previously unrecognized as an antibacterial agent. Although acid-adaptation improved bacterial survival, calamansi (<20%) + EOCs (<0.032%) completely inactivated even the most resistant pathogen (E. coli O157:H7). Validation test also showed that all tested commercial juice products also eliminated acid-adapted pathogens when used with EOCs. Physicochemical analysis of tested CFEs (pH measurement and HPLC analysis of components) revealed that low pH and flavanone (hesperidin) did not contribute to the synergistic bactericidal effects. Rather, the high citric acid content is likely to contribute to the strong synergistic effect with EOCs by damaging susceptible bacterial membranes. Sensory scores for CFEs were not altered by addition of EOCs at concentrations up to 1.5 mM. This study provides new insight into the utility of CFEs with EOCs to improve not only the microbiological safety of food products containing CFEs but also their applicability as natural antibacterial complex.

Effect of thyme and oregano essential oils on the shelf life of salmon and seaweed burgers

The effect of different essential oils on the quality and shelf life of fish and seaweed burgers during storage was evaluated. For this purpose, thyme and oregano essential oils were selected at a concentration of 0.05% (v/w). Three types of salmon and seaweed burgers were prepared: without essential oil, burgers with red thyme essential oil (0.05% (v/w)) and burgers with oregano essential oil (0.05% (v/w)), which were vacuum packaged and stored at 4 ℃ for 17 days. Physicochemical and microbiological analyses were carried out periodically throughout storage. The addition of both essential oils did not have any effect on the evolution of the pH, the moisture content or texture parameters. Only the thyme essential oil managed to slightly slow down the increase of total volatile basic nitrogen and trimethylamine nitrogen. The samples with oregano essential oil and especially those with thyme essential oil showed minor oxidation. The salmon and seaweed burgers without essential oils and those which contained oregano essential oil showed a faster increase of mesophilic counts than those which had thyme essential oil, but no noticeable improvement was observed in the shelf life of the burgers with thyme essential oil. To improve the shelf life of the fish and seaweed burgers, it would be necessary to increase the concentration of both essential oils.

Combined effects of oregano essential oil and salt on the growth of Escherichia coli in salad dressing

There is a broad research interest in the search for alternatives to chemical additives for use as natural food preservatives. Although many natural compounds have biological in vitro properties evidenced, in situ studies are still scarce. This study evaluated the effect of oregano essential oil (OEO) and salt (NaCl) concentrations against Escherichia coli (ATCC 8739), in salad dressing, using the response surface methodology. The experiment included a 2² central composite rotatable design (CCRD) in a total of 11 formulations of salad dressings. Oregano essential oil was characterized by gas chromatography and salad dressings by ash, lipids, proteins and moisture. OEO was composed mainly by carvacrol (65.1%) and p-cymene (12.0%). Salad dressings showed similar chemical profiles. A mathematical model for the prediction of the antibacterial activity in salad dressing was obtained. The results revealed that the interaction between OEO and salt showed effect on the bacterial count. However, the effect of salt was negative suggesting that the highest NaCl concentrations decreases the bacterial count. Therefore, within the parameters studied, the use of OEO to control E. coli in salad dressing can be considered promising and allows reduction in the levels of salt to be incorporated in food.

Antilisterial activity of Cymbopogon citratus on crabsticks

Listeria monocytogenes is a gram positive, psychrotrophic, facultative anaerobic bacterium and it is the etiological agent of listeriosis, a severe foodborne disease of major public health concern. There is a rising concern about the cross-contamination of surimi-based products with L. monocytogenes during handling and storage. Lemon grass (Cymbopogon citratus) is known to exhibit strong antimicrobial activity against bacteria due to the presence of citral. The objectives of this research were: (i) to develop a water-based extraction procedure for the antimicrobial component(s) in lemon grass and (ii) to evaluate the antimicrobial effect of a concentrated water-based extract and commercial essential oil (EO) of lemon grass against L. innocua (ATCC 33090), a surrogate strain of L. monocytogenes, in vitro and on crabsticks. Briefly, antilisterial activity of concentrated extract and commercial EO of lemon grass was tested using the agar well diffusion technique. Crabsticks were subsequently inoculated with L. innocua to a final density of ca. 4 log cfu/g and then coated with 500 μl of either concentrated extract or 0.5% commercial EO and stored at 4 °C for up to 15 days. Samples were then subjected to microbiological analysis every 5 days to enumerate counts of Listeria. Following the agar well diffusion assay, inhibition zones with mean diameters of 18.3 and 21.0 mm were obtained with the concentrated extract and commercial EO respectively. The population of L. innocua in WBE-coated (4.2 log cfu/g) and 0.5% EO-coated (2.7 log cfu/g) samples were significantly lower (P < 0.05) after 15 days than their untreated control counterpart (5.2 log cfu/g). Lemon grass extract and essential oil have the potential to control growth of L. monocytogenes in seafood surimi products with minimal adverse effect on the organoleptic characteristics of the product and thus can possibly be used as a natural food preservative.

Synergistic effect of eugenol with Colistin against clinical isolated Colistin-resistant Escherichia coli strains

Background

Bacterial infections have become more challenging to treat due to the emergence of multidrug-resistant pathogenic bacteria. Combined antibiotics prove to be a relatively effective method to control such resistant strains. This study aim to investigate synergistic activity of eugenol combined with colistin against a collection of clinical isolated Escherichia coli (E.coli) strains, and to evaluate potential interaction.

Methods

Antimicrobial susceptibility, minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FICI) of the bacteria were determined by disk diffusion assay, broth microdilution method and checkerboard assay, respectively. The mcr-1 mRNA expression was measured by Real-time PCR. To predict possible interactions between eugenol and MCR-1, molecular docking assay was taken.

Results

For total fourteen strains including eight colistin-resistant strains, eugenol was determined with MIC values of 4 to 8 μg/mL. Checkerboard dilution test suggested that eugenol exhibited synergistic activity when combined with colistin (FICI ranging from 0.375 to 0.625). Comparison analysis of Real-time PCR showed that synergy could significantly down-regulate expression of mcr-1 gene. A metal ion coordination bond with catalytic zinc atom and a hydrogen bond with crucial amino acid residue Ser284 of MCR-1 were observed after molecular docking, indicating antibacterial activity and direct molecular interactions of eugenol with MCR-1 protein.

Conclusions

Our results demonstrated that eugenol exhibited synergistic effect with colistin and enhanced its antimicrobial activity. This might further contribute to the antibacterial actions against colistin-resistant E.coli strains.

Graphical abstract

Synergistic effect of eugenol with colistin against colistin-resistant Escherichia coli isolates.

Comparison of Cinnamon Essential Oils from Leaf and Bark with Respect to Antimicrobial Activity and Sensory Acceptability in Strawberry Shake

Cinnamon leaf and bark essential oils have long been used as natural preservatives and flavoring agents in foods. This study determined antimicrobial effects of leaf and bark of cinnamon essential oils (CEOs) against 2 foodborne pathogens, Salmonella Typhimurium (S.T.) and Listeria monocytogenes (L.m.), at 2 initial bacterial levels (4- and 9-log CFU/mL) in strawberry shakes. The antimicrobial study of CEOs at 0.1% and 0.5% in strawberry shakes against S.T. and L.M. showed a significant difference (P < 0.05) in log reductions of both bacterial growth at low (4-log CFU/mL) and high (9-log CFU/mL) initial bacterial levels. Addition of 0.5% CEOs into strawberry shakes at 4 °C completely inhibited both bacteria after a period of 8 d storage. Shelf-life study showed that acidity and total solid content were not affected during storage. The strawberry shakes containing bark CEO had higher ratings of sensory acceptability compared to leaf CEO, with or without the addition of 1% masking agent. In conclusion, this study demonstrated that CEO derived from bark was better than that from leaf in terms of their antimicrobial activity and sensory aspect.

PRACTICAL APPLICATION

This study demonstrates that essential oils derived from cinnamon bark and leaf have the potential to be used as natural antimicrobial ingredient in milk beverages with respect to sensory aspect. This finding promotes the acceptance of natural antimicrobials among consumers, while providing enhanced safer products to the food industry application.

Antimicrobial Carvacrol-Containing Polypropylene Films: Composition, Structure and Function

Significant research has been directed toward the incorporation of bioactive plant extracts or essential oils (EOs) into polymers to endow the latter with antimicrobial functionality. EOs offer a unique combination of having broad antimicrobial activity from a natural source, generally recognized as safe (GRAS) recognition in the US, and a volatile nature. However, their volatility also presents a major challenge in their incorporation into polymers by conventional high-temperature-processing techniques. Herein, antimicrobial polypropylene (PP) cast films were produced by incorporating carvacrol (a model EO) or carvacrol, loaded into halloysite nanotubes (HNTs), via melt compounding. We studied the composition-structure-property relationships in these systems, focusing on the effect of carvacrol on the composition of the films, the PP crystalline phase and its morphology and the films’ mechanical and antimicrobial properties. For the first time, molecular dynamics simulations were applied to reveal the complex interactions between the components of these carvacrol-containing systems. We show that strong molecular interactions between PP and carvacrol minimize the loss of this highly-volatile EO during high-temperature polymer processing, enabling semi-industrial scale production. The resulting films exhibit outstanding antimicrobial properties against model microorganisms (Escherichia coli and Alternaria alternata). The PP/(HNTs-carvacrol) nanocomposite films, containing the carvacrol-loaded HNTs, display a higher level of crystalline order, superior mechanical properties and prolonged release of carvacrol, in comparison to PP/carvacrol blends. These properties are ascribed to the role of HNTs in these nanocomposites and their effect on the PP matrix and retained carvacrol content.

Lipids, pH, and Their Interaction Affect the Inhibitory Effects of Carvacrol against Salmonella Typhimurium PT4 and Escherichia coli O157:H7

Although carvacrol (CAR) is considered an alternative antimicrobial for use in food, few is known about the influence of food-related parameters on its inhibitory effects against pathogens. This study assessed the influence of different amounts of proteins, using beef extract (BE) as a protein-rich source, lipids (LIP), using sunflower oil as a LIP-rich source, and pH values or their interaction on the inhibitory effects of CAR against Salmonella Typhimurium PT4 (ST) and Escherichia coli O157:H7 (EC). The specific maximum growth rate (μmax) and lag phase duration (λ) of the test pathogens when exposed to CAR in media with different amounts of BE (4, 6, and 8 g/100 mL), LIP (3.75, 5, and 6.25 mL/100 mL), and pH values (5, 5.5, and 6) were determined. The viable counts of the tested pathogens in media that promoted the highest and lowest μmax in the presence of CAR were monitored during 24 h. The lowest μmax of ST and EC exposed to 2.4 μL/mL (-1.29 and -0.82 log CFU/mL/h, respectively) or 4.8 μL/mL CAR (-1.44 and -2.17 log CFU/mL/h, respectively) were observed in media with the highest LIP amount (6.25 mL/100 mL) and pH value (pH 6). For both SE and EC, the longest λ (> 2 h) was verified in media where these pathogens showed the lowest μmax. These data indicate that the concomitant increase in LIP amounts and pH values affected positively the CAR inhibitory effects against the target pathogens. CAR (2.4 or 4.8 μL/mL) failed to inhibit the increase in ST and EC counts in media where the highest μmax values were previously observed. On the contrary, CAR inhibited the increase of ST counts (final counts 5 log CFU/mL) and decreased the EC counts (final counts 3.5 log CFU/mL) in media where the lowest μmax values were observed. These results show that the inhibitory effects of CAR on ST and EC in food matrices could be affected as a function of the interaction of LIP amounts and pH values.

Synchronous application of antibiotics and essential oils: dual mechanisms of action as a potential solution to antibiotic resistance

Antibiotic resistance has increased dramatically in recent years, yet the antibiotic pipeline has stalled. New therapies are therefore needed to continue treating antibiotic resistant infections. One potential strategy currently being explored is the use of non-antibiotic compounds to potentiate the activity of currently employed antibiotics. Many natural products including Essential Oils (EOs) possess broad spectrum antibacterial activity and so have been investigated for this purpose. This article aims to review recent literature concerning the antibacterial activity of EOs and their interactions with antibiotics, with consideration of dual mechanisms of action of EOs and antibiotics as a potential solution to antibiotic resistance. Synergistic interactions between EOs and their components with antibiotics have been reported, including several instances of antibiotic resensitization in resistant isolates, in support of this strategy to control antibiotic resistance. However, a lack of consistency in methods and interpretation criteria makes drawing conclusions of efficacy of studied combinations difficult. Synergistic effects are often not explored beyond preliminary identification of antibacterial interactions and mechanism of action is rarely defined, despite many hypotheses and recommendations for future study. Much work is needed to fully understand EO-antibiotic associations before they can be further developed into novel antibacterial formulations.

Effect of thyme essential oil and Lactococcus lactis CBM21 on the microbiota composition and quality of minimally processed lamb's lettuce

The main aim of this work was to evaluate, at pilot scale in an industrial environment, the effects of the biocontrol agent Lactococcus lactis CBM21 and thyme essential oil compared to chlorine, used in the washing step of fresh-cut lamb's lettuce, on the microbiota and its changes in relation to the time of storage. The modification of the microbial population was studied through pyrosequencing in addition to the traditional plate counts. In addition, the volatile molecule and sensory profiles were evaluated during the storage. The results showed no significant differences in terms of total aerobic mesophilic cell loads in relation to the washing solution adopted. However, the pyrosequencing data permitted to identify the genera and species able to dominate the spoilage associations over storage in relation to the treatment applied. Also, the analyses of the volatile molecule profiles of the samples during storage allowed the identification of specific molecules as markers of the spoilage for each different treatment. The sensory analyses after 3 and 5 days of storage showed the preference of the panelists for samples washed with the combination thyme EO and the biocontrol agent. These samples were preferred for attributes such as flavor, acceptability and overall quality. These results highlighted the effect of the innovative washing solutions on the quality of lettuce through the shift of microbiota towards genera and species with lower potential in decreasing the sensory properties of the product.

Antibacterial activity and stability of microencapsulated lemon grass essential oil in feeds for broiler chickens

SUMMARY The antibacterial effect of microencapsulated lemon grass (Cymbopogon citratus) essential oil on strains of Escherichia coli (ATCC8739), Staphylococcus aureus (ATCC 6538) and Salmonella enterica subsp. enterica (ATCC 6017), and the stability of this oil in feeds for broiler chickens were evaluated. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined by the macrodilution method, using the microencapsulated lemon grass essential oil at concentrations of 160 μL mL−1, 80 μL mL−1, 40 μL mL−1, 20 μL mL−1, and 10 μL mL−1. The oil concentration of 80 μL mL−1 presented the best results against the three bacteria evaluated. Samples of 200 g of feed mixed with 120 μL g−1 of the microencapsulated lemon grass essential oil was stored to evaluate the oil stability. Feed without microencapsulated lemon grass essential oil was prepared as control. The oil remained active for seven days, with significant reduction of S. aureus (3.08 CFU), E. coli (3.01 CFU), and S. enterica (3.10 CFU). The microencapsulated lemon grass essential oil at concentration of 80 μL mL−1 had antibacterial effect against the E. coli, S. enterica and S. aureus, and maintained stability of the feed for seven days, even with presence of organic matter, which is source of nutrients for pathogens.

Antibacterial activities of a cinnamon essential oil with cetylpyridinium chloride emulsion against Escherichia coli O157:H7 and Salmonella Typhimurium in basil leaves

This study examined the antibacterial activities of two different cinnamon essential oil emulsions against Escherichia coli O157:H7 and Salmonella Typhimurium on basil leaves. Cinnamon oil (0.25%) treatments containing CPC (0.05%) exhibited greater effects on the pathogenic bacteria than cinnamon oil treatment without this emulsifier (p < 0.05). Treatment with cinnamon bark and leaf oil emulsions (CBE and CLE, respectively) reduced the populations of E. coli O157:H7 by 4.10 and 5.10 log CFU/g, and S. Typhimurium by 2.71 and 2.82 log CFU/g, respectively. Scanning electron micrographs showed morphological changes in the two pathogenic bacteria following emulsion treatment. In addition, there was no difference in the color or ascorbic acid content of the basil leaves by the emulsion treatment. These results suggest that CBE or CLE treatment can be an effective way to ensure the microbial safety of minimally processed vegetables and a good alternative to chlorination treatment in the fresh produce industry.

Citrus essential oils: Extraction, authentication and application in food preservation

Citrus EOs is an economic, eco-friendly and natural alternatives to chemical preservatives and other synthetic antioxidants, such as sodium nitrites, nitrates or benzoates, commonly utilized in food preservation. Citrus based EOs is obtained mainly from the peels of citrus fruits which are largely discarded as wastes and cause environmental problems. The extraction of citrus oils from the waste peels not only saves environment but can be used in various applications including food preservation. The present article presents elaborated viewpoints on the nature and chemical composition of different EOs present in main citrus varieties widely grown across the globe; extraction, characterization and authentication techniques/methods of the citrus EOs; and reviews the recent advances in the application of citrus EOs for the preservation of fruits, vegetables, meat, fish and processed food stuffs. The probable reaction mechanism of the EOs based thin films formation with biodegradable polymers is presented. Other formulation, viz., EOs microencapsulation incorporating biodegradable polymers, nanoemulsion coatings, spray applications and antibacterial action mechanism of the active compounds present in the EOs have been elaborated. Extensive research is required on overcoming the challenges regarding allergies and obtaining safer dosage limits. Shift towards greener technologies indicate optimistic future towards safer utilization of citrus based EOs in food preservation.