The antimicrobial activity of hydrophobic essential oil constituents acting alone or in combined processes of food preservation

W/O/W emulsion-filled sodium alginate hydrogel beads for co-encapsulation of vitamins C and E: Insights into the fabrication, lipolysis, and digestion behavior

In this study, vitamins C and E were simultaneously encapsulated in water-in-oil-in-water (W/O/W) emulsion-filled sodium alginate (SA) hydrogel beads, as well as the effects of SA concentrations (0.5%, 1.0%, 1.5%, and 2.0%) on the structures and lipolysis the of hydrogel beads were investigated. With increasing SA concentration, the beads showed larger sizes, denser structures and better textures. The droplets tightly penetrated the gel network at high SA concentrations. Digestion behavior revealed the disintegrated intramolecular structure at low SA concentrations. The beads with 0.5% SA were fragmented, losing the initial shape during digestion in the intestinal fluid. Additionally, lipid phases were released as W/O/W and O/W emulsion droplets after digestion. However, the high SA concentration-containing beads exhibited a well-preserved morphological structure after digestion, and the release profiles of lipid phase were mainly O/W emulsion droplets. Furthermore, vitamins C and E encapsulated in the beads exhibited high bioaccessibility (vitamin C: 90.20% and vitamin E: 95.19%).

Investigating the Antimicrobial Properties of Essential Oil Constituents and Their Mode of Action

Essential oils (EOs) and plant extracts, rich in beneficial chemical compounds, have diverse applications in medicine, food, cosmetics, and agriculture. This study investigates the antibacterial activity of nine essential oil constituents (EOCs) against Escherichia coli, focusing on the effects of treatment pH and biosynthetic requirements. The impact of EOCs on bacterial inactivation in E. coli strains was examined using both nonselective and selective culture media. Computer-assisted drug design (CADD) methods were employed to identify critical binding sites and predict the main binding modes of ligands to proteins. The EOCs, including citral, α-terpinyl acetate, α-terpineol, and linalool, demonstrated significant bacterial inactivation, particularly under acidic conditions. This study revealed that EOCs have an effect on the presence of sublethal damage to both the cytoplasmic membrane and the outer membrane in Gram-negative bacteria. Adding penicillin G to the repair medium prevents the recovery of sublethal injuries in E. coli treated with α-terpinyl acetate, α-terpineol, linalool, and citral, indicating that peptidoglycan synthesis is essential for recovering from these injuries. However, penicillin G did not hinder the recovery process of most sublethally injured cells treated with the other assessed EOCs. Molecular docking studies revealed the favorable binding interactions of α-terpinyl acetate, α-terpineol, linalool, and citral with the β-lactamase enzyme Toho-1, indicating their potential as effective antibacterial agents. The findings suggest that EOCs could serve as viable alternatives to synthetic preservatives, offering new strategies for combating antibiotic-resistant bacteria.

Effects of microencapsulated essential oils and organic acids preparation on growth performance, slaughter characteristics, nutrient digestibility and intestinal microenvironment of broiler chickens

To develop effective antibiotics alternatives is getting more and more important to poultry healthy production. The study investigated the effects of a microencapsulated essential oils and organic acids preparation (EOA) on growth performance, slaughter performance, nutrient digestibility and intestinal microenvironment of broilers. A total of 624 1-day-old male Arbor Acres broilers were randomly divided into 6 groups including the control group (T1) fed with basal diet, the antibiotic group (T2) supplemented with basal diet with 45 mg/kg bacitracin methylene disalicylate (BMD), and 4 inclusion levels of EOA-treated groups (T3, T4, T5, T6 groups) chickens given basal diet with 200, 400, 600, and 800 mg EOA/kg of diet, respectively. Results showed that compared with the control, the 200 mg/kg EOA group increased average daily gain (ADG) and average body weight (ABW) during the early stage (P < 0.05). EOA addition decreased crypt depth of the ileum (P < 0.05), but villus height to crypt depth ratio was increased by EOA addition at 200 and 400 mg/kg at d 21 (P < 0.05). Compared with the control, dietary addition EOA at 200, 400 and 600 mg/kg increased the lipase activity in the duodenum at d 21 (P < 0.05). Increased lactic acid bacteria population was found in cecal digesta of the 400 mg/kg EOA group at d 21 (P < 0.05), and higher concentration of butyric acid level was observed in cecal digesta at d 21 and d 42 in the 200 mg/kg EOA group compared with the control (P < 0.05). RT-PCR analysis found that dietary EOA addition decreased the gene expression of IL-1β, COX-2 and TGF-β4 in the ileum at d 21 (P < 0.05), while only the 200 mg/kg EOA increased the gene expression of IL-10, TGF-β4, Claudin-1, ZO-1, CATH-1, CATH-3, AvBD-1, AvBD-9 and AvBD-12 in the ileum at d 42 (P < 0.05) compared with the control. In summary, adding 200 mg/kg and 400 mg/kg of the EOA to the diet could improve the growth performance and intestinal microenvironment through improving intestinal morphology, increasing digestive enzymes activity and cecal lactic acid bacteria abundance and butyric acid content, improving intestinal barrier function as well as maintaining intestinal immune homeostasis. The improving effect induced by EOA addition in the early growth stage was better than that in the later growth stage. Overall, the EOA product might be an effective antibiotic alternative for broiler industry.

Optimisation of Three Essential Oils against Salmonella spp. and Escherichia coli by Mixture Designa

The aim of this work is to optimise the antibacterial activity of essential oils (EOs) from Eucalyptus camaldulensis (ECEO), Mentha pulegium (MPEO) and Rosmarinus officinalis (ROEO) plants against Salmonella spp. and Escherichia coli. The qualitative antimicrobial effect was assessed using the disc diffusion method, the broth microdilution method was used to determine the minimum inhibitory concentrations (MIC). Polynomial models were created using an augmented centroid simplex mixture design to highlight the synergy of EOs. The results show a significant antibacterial effect of ECEO and MPEO against both bacterial strains, with inhibition zones (IZs) of 13 and 12 mm respectively against E. coli, and 13 and 11 mm against Salmonella spp. The latter strain showed a MIC of 0.625 % (v : v) by the ECEO, while E. coli exhibited a MIC of 0.0781 % (v : v). The binary combinations of essential oils display a synergistic effect, the proportions of the optimum EOs in the mixture giving the lowest MICm were of the order of 50.51 % ECEO and 49.49 % ROEO against Salmonella spp. and around 50 % MPEO and 50 % ECEO against E. coli. These results indicate the effectiveness of binary combinations EOs against resistant bacterial strains and suggest their importance in bacterial infections treatment.

Phenotypic and Genotypic Comparison of Antimicrobial-Resistant Variants of Escherichia coli and Salmonella Typhimurium Isolated from Evolution Assays with Antibiotics or Commercial Products Based on Essential Oils

On account of the widespread development and propagation of antimicrobial-resistant (AMR) bacteria, essential oils (EOs) have emerged as potential alternatives to antibiotics. However, as already observed for antibiotics, recent studies have raised concerns regarding the potential emergence of resistant variants (RVs) to EOs. In this study, we assessed the emergence of RVs in Escherichia coli and Salmonella enterica Typhimurium after evolution assays under extended exposure to subinhibitory doses of two commercial EOs (AEN and COLIFIT) as well as to two antibiotics (amoxicillin and colistin). Phenotypic characterization of RVs from evolution assays with commercial EOs yielded no relevant increases in the minimum inhibitory concentration (MIC) of E. coli and did not even modify MIC values in S. Typhimurium. Conversely, RVs of E. coli and S. Typhimurium isolated from evolution assays with antibiotics showed increased resistance. Genotypic analysis demonstrated that resistance to commercial EOs was associated with enhanced protection against oxidative stress and redirection of cell energy toward efflux activity, while resistance to antibiotics was primarily linked to modifications in the cell binding sites of antibiotics. These findings suggest that AEN and COLIFIT could serve as safe alternatives to antibiotics in combating the emergence and dissemination of antimicrobial resistance within the agrifood system.

Synthesis, anti-amoebic activity and molecular docking simulation of eugenol derivatives against Acanthamoeba sp

Amoebae of the genus Acanthamoeba can cause diseases such as amoebic keratitis and granulomatous amoebic encephalitis. Until now, treatment options for these diseases have not been fully effective and have several drawbacks. Therefore, research into new drugs is needed for more effective treatment of Acanthamoeba infections. Eugenol, a phenolic aromatic compound mainly derived from cloves, has a variety of pharmaceutical properties. In this study, nine eugenol derivatives (K1-K9), consisting of five new and four known compounds, were synthesized and screened for their antiamoebic properties against Acanthamoeba sp. The structure of these compounds was characterized spectroscopically by Fourier transform infrared (FTIR), Ultraviolet-Visible (UV-Vis), 1H and 13C Nuclear Magnetic Resonance (NMR) and mass spectrometer (MS). The derived molecules were screened for antiamoebic activity by determining IC50 values based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and observation of amoeba morphological changes by light and fluorescence microscopy. Most of the tested compounds possessed strong to moderate cytotoxic effects against trophozoite cells with IC50 values ranging from 0.61 to 24.83 μg/mL. Observation of amoebae morphology by light microscopy showed that the compounds caused the transformed cells to be roundish and reduced in size. Furthermore, fluorescence microscopy observation using acridine orange (AO) and propidium iodide (PI) (AO/PI) staining showed that the cells have damaged membranes by displaying a green cytoplasm with orange-stained lysosomes. Acidification of the lysosomal structure indicated disruption of the internal structure of Acanthamoeba cells when treated with eugenol derivatives. The observed biological results were also confirmed by interaction simulations based on molecular docking between eugenol derivatives and Acanthamoeba profilin. These interactions could affect the actin-binding ability of the protein, disrupting the shape and mobility of Acanthamoeba. The overall results of this study demonstrate that eugenol derivatives can be considered as potential drugs against infections caused by Acanthamoeba.

Assessment of trans-cinnamaldehyde and eugenol assisted heat treatment against Salmonella Typhimurium in low moisture food components

Increased thermal resistance of Salmonella at low water activity (a_w) is a significant food safety concern in low-moisture foods (LMFs). We evaluated whether trans-cinnamaldehyde (CA, 1000 ppm) and eugenol (EG, 1000 ppm), which can accelerate thermal inactivation of Salmonella Typhimurium in water, can show similar effect in bacteria adapted to low a_w in different LMF components. Although CA and EG significantly accelerated thermal inactivation (55 °C) of S. Typhimurium in whey protein (WP), corn starch (CS) and peanut oil (PO) at 0.9 a_w, such effect was not observed in bacteria adapted to lower a_w (0.4). The matrix effect on bacterial thermal resistance was observed at 0.9 a_w, which was ranked as WP > PO > CS. The effect of heat treatment with CA or EG on bacterial metabolic activity was also partially dependent on the food matrix. Bacteria adapted to lower a_w had lower membrane fluidity and unsaturated to saturated fatty acids ratio, suggesting that bacteria at low a_w can change its membrane composition to increase its rigidity, thus increasing resistance against the combined treatments. This study demonstrates the effect of a_w and food components on the antimicrobials-assisted heat treatment in LMF and provides an insight into the resistance mechanism.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Food grade nanoemulsion development to control food spoilage microorganisms on bread surface

In this study, the effect of emulsifier mixture and their concentrations on the development of nanoemulsion was studied. The impact of sonication and microfluidization processing conditions on the physicochemical properties and in vitro antimicrobial activity was also evaluated. The optimal nanoemulsion formulation was then evaluated on bread surface against B. subtilis. Results showed that a hydrophilic-lipophilic balance HLB = 12 and emulsifier: oil ratio of 1:1 allowed the formation of stable nanoemulsion. Also, both microfluidization and sonication allowed the formation of nanoscale-emulsion. Sonication treatment for 10 min allowed a maintain the total flavonoid content and a slight reduction of total phenol content. Furthermore, employing sonication resulted to the lowest polydispersity index suggesting more stable nanoemulsion. Nanoscale-emulsion showed a good in vitro antimicrobial activity against L. monocytogenes and E. coli. The application of nanoemulsion on bread surface inoculated with B. subtilis showed a delay of the decay.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05660-5.

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

Combined Effect of High Hydrostatic Pressure, Sous-Vide Cooking, and Carvacrol on the Quality of Veal, Plant-Based, and Hybrid Patties during Storage

The effect of carvacrol added to patties stored at 4 °C for 14 days, previously pressurized and vacuum-cooked (HPP-SVCOOK), was investigated. Three formulations were prepared (veal, plant-based product, and hybrid product). An emulsion made with olive and linseed oils was added. The physicochemical and microbiological qualities were assessed. Microbial tests indicated negligible growth of spoilage organisms in treated patties. No significant effect of carvacrol on the microbial loads of patties was noticed. Sulfite-reducing clostridia and Enterobacteriaceae were absent in the treated patties, whereas, in the treated veal and hybrid samples, 3 and 2 units of log cfu/g reduction for lactic acid bacteria and molds and yeasts were noted, respectively. On day 7 of storage, veal patties exhibited a significant reduction (p < 0.05) in the L* (53.9−49.3), hardness (32.3−21.4 N), springiness (0.8−0.7 N), cohesiveness (0.49−0.46), and chewiness (12.2−7.1) and a hike in the a* value (5.3−9.4). No significant changes in L* (59.1−58.6), a* (8.57−8.61), hardness (11.6−10.6 N), or cohesiveness (0.27−0.26) were observed in plant-based patties over the storage times, whereas reductions in springiness (0.5−0.4), chewiness (1.9−1.3), and b* (26.6−29.1) were noted in them. In hybrid patties, the L* (53.9−52.5) and b* values (24.9−24.3) were consistent but had a significant decrease in a* value (5.9−3.5) along the days of storage under study. The texture parameters of the hybrid patties altered were similar to those of veal patties during the 14-day storage time. In all samples, pH decreased with storage time. HPP-SVCOOK was effective on rendering safe and shelf-stable, ready-to-eat patties regardless of their matrix formulation. The addition of carvacrol had limited effects on the textural qualities of the HPP-SVCOOK products. Future studies need to be undertaken to assess the treated patties’ consumer acceptability and sensory profile. The study provides the basis for the development of novel meat-based and plant-based products that are microbiologically safe, with minimum physicochemical alterations during storage.

Combined Pulsed Electric Field with Antimicrobial Caps for Extending Shelf Life of Orange Juice

The purpose of this study was to investigate the effectiveness of combined pulsed electric fields (PEF) and antimicrobial packaging treatment in maintaining the quality and stability of orange juice stored at 10 °C. Orange juice was treated by PEF and stored in glass jars with antimicrobial caps coated with 10 µL of carvacrol essential oil (AP). Microbial reductions and physiochemical properties of juice samples were determined after treatments and during storage at 10 °C. Orange juice samples subjected to the combined treatment (PEF+AP) had the lowest yeast and mold populations after 14 day-storage at 10 °C. There were no significant differences in pH, acidity, color, total soluble solid contents, total phenol compounds, and Vitamin C among all samples after treatments. Storage studies showed that PEF, AP, and PEF+AP treatments maintained the quality and stability of orange juice stored at 10 °C for 5 weeks but lost Vitamin C. This study provides valuable information to juice processors for consideration and design of nonthermal pasteurization with antimicrobial packaging of juice products.

Carvacrol Selective Pressure Allows the Occurrence of Genetic Resistant Variants of Listeria monocytogenes EGD-e

Essential oils and their constituents, such as carvacrol, are potential food preservatives because of their great antimicrobial properties. However, the long-term effects of these compounds are unknown and raise the question of whether resistance to these antimicrobials could emerge. This work aims to evaluate the occurrence of genetic resistant variants (RVs) in Listeria monocytogenes EGD-e by exposure to carvacrol. Two protocols were performed for the RVs selection: (a) by continuous exposure to sublethal doses, where LmSCar was isolated, and (b) by reiterative exposure to short lethal treatments of carvacrol, where LmLCar was isolated. Both RVs showed an increase in carvacrol resistance. Moreover, LmLCar revealed an increased cross-resistance to heat treatments at acid conditions and to ampicillin. Whole-genome sequencing identified two single nucleotide variations in LmSCar and three non-silent mutations in LmLCar. Among them, those located in the genes encoding the transcriptional regulators RsbT (in LmSCar) and ManR (in LmLCar) could contribute to their increased carvacrol resistance. These results provide information regarding the mode of action of this antimicrobial and support the importance of knowing how RVs appear. Further studies are required to determine the emergence of RVs in food matrices and their impact on food safety.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce

ABSTRACT

Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.

HIGHLIGHTS

Natural products and their semi-synthetic derivatives against antimicrobial-resistant human pathogenic bacteria and fungi

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COVID-19 pandemic has traumatized the entire world. During this outbreak, an upsurge in MDR-associated pathogenic microbial organisms has been recorded.

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The increasing human microbial diseases pose a severe danger to global human safety.

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The infectious microbes have developed multiple tolerance strategies to overcome the negative drug impacts.

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Several naturally occurring chemicals produced from bacteria, plants, animals, marine species, and other sources with antimicrobial characteristics have been reviewed.

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These compounds show promise in minimizing the globally increasing microbial diseases.

Human infectious diseases caused by various microbial pathogens, in general, impact a large population of individuals every year. These microbial diseases that spread quickly remain to be a big issue in various health-related domains and to withstand the negative drug impacts, the antimicrobial-resistant pathogenic microbial organisms (pathogenic bacteria and pathogenic fungi) have developed a variety of resistance processes against many antimicrobial drug classes. During the COVID-19 outbreak, there seems to be an upsurge in drug and multidrug resistant-associated pathogenic microbial species. The preponderance of existing antimicrobials isn’t completely effective, which limits their application in clinical settings. Several naturally occurring chemicals produced from bacteria, plants, animals, marine species, and other sources are now being studied for antimicrobial characteristics. These natural antimicrobial compounds extracted from different sources have been demonstrated to be effective against a variety of diseases, although plants remain the most abundant source. These compounds have shown promise in reducing the microbial diseases linked to the development of drug tolerance and resistance. This paper offers a detailed review of some of the most vital and promising natural compounds and their derivatives against various human infectious microbial organisms. The inhibitory action of different natural antimicrobial compounds, and their possible mechanism of antimicrobial action against a range of pathogenic fungal and bacterial organisms, is provided. The review will be useful in refining current antimicrobial (antifungal and antibacterial) medicines as well as establishing new treatment strategies to tackle the rising number of human bacterial and fungal-associated infections.

Multifunctional filter membrane for face mask using bacterial cellulose for highly efficient particulate matter removal

Abstract

Particulate matter (PM) pollution and SARS-CoV-2 (COVID-19) have brought severe threats to public health. High level of PM serves as a carrier of COVID-19 which is a global pandemic. This study fabricated filter membrane for face mask using bacterial cellulose and fingerroot extract (BC-FT) via immersion technique. The surface area, pore volume and pore size of BC were analyzed by Brunauer-Emmett-Teller. The physiochemical properties of the membrane were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffractometer. The crystallinity decreased from 63.7% in pure BC to 52.4% in BC-FT filter membrane. Young's modulus increased from 1277.02 MPa in pure BC to 2251.17 MPa in BC-FT filter membrane. The filter membrane showed excellent PM 0.1 removal efficiency of 99.83% and antimicrobial activity against Staphylococcus aureus and Escherichia coli. The fabricated membrane is excellent to prevent inhalation of PM2.5 and COVID-19 respiratory droplet.

Graphic abstract

Supplementary information

The online version contains supplementary material available at 10.1007/s10570-022-04641-3.

Current Trends in the Utilization of Essential Oils for Polysaccharide- and Protein-Derived Food Packaging Materials

Essential oils (EOs) have received attention in the food industry for developing biopolymer-derived food packaging materials. EOs are an excellent choice to replace petroleum-derived additives in food packaging materials due to their abundance in nature, eco-friendliness, and superior antimicrobial and antioxidant attributes. Thus far, EOs have been used in cellulose-, starch-, chitosan-, and protein-based food packaging materials. Biopolymer-based materials have lower antioxidant and antibacterial properties in comparison with their counterparts, and are not suitable for food packaging applications. Various synthetic-based compounds are being used to improve the antimicrobial and antioxidant properties of biopolymers. However, natural essential oils are sustainable and non-harmful alternatives to synthetic antimicrobial and antioxidant agents for use in biopolymer-derived food packaging materials. The incorporation of EOs into the polymeric matrix affects their physicochemical properties, particularly improving their antimicrobial and antioxidant properties. EOs in the food packaging materials increase the shelf life of the packaged food, inhibit the growth of microorganisms, and provide protection against oxidation. Essential oils also influence other properties, such as tensile, barrier, and optical properties of the biopolymers. This review article gives a detailed overview of the use of EOs in biopolymer-derived food packaging materials. The innovative ways of incorporating of EOs into food packaging materials are also highlighted, and future perspectives are discussed.

Variation in the Antibacterial and Antioxidant Activities of Essential Oils of Five New Eucalyptus urophylla S.T. Blake Clones in Thailand

Eucalyptus oils are widely used for a variety of purposes. This study investigates the terpenoid compositions and antibacterial and antioxidant activities of eucalypt leaf oils extracted from four E. urophylla clones and one E. urophylla × E. camaldulensis hybrid clone grown in Thailand. According to GC/MS analysis, the E. urophylla oils were mainly composed of 1,8-cineole, α-terpinyl acetate, β-caryophyllene, and spathulenol, while 1,8-cineole, α-terpinyl acetate, p-cymene, and γ-terpinene were mostly identified in the hybrid oil. All eucalypt oils exhibited a significant bacteriostatic effect against Gram-positive bacteria, Streptococcus pyogenes, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus. Only the hybrid oil had an effect on all Gram-negative bacteria tested, including Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, and Enterobacter aerogenes. These oils have antibacterial properties that vary according to their terpenoid content. Only the hybrid oil had a potent antioxidant effect, with an IC₅₀ value of 4.21 ± 0.35 mg/mL for free radical (DPPH) scavenging. This oil's antioxidant effect may be a result of the phenolic terpenoids, thymol and carvacrol. As a result, these oils may be a novel source of antibacterial and antioxidant agents. Additionally, the antibacterial and antioxidant capabilities of the E. urophylla × E. camaldulensis hybrid essential oil are reported for the first time.

Recent advances in valorization of citrus fruits processing waste: a way forward towards environmental sustainability

Citrus fruits are well known for their medicinal and therapeutic potential due to the presence of immense bioactive components. With the enormous consumption of citrus juice, citrus processing industries are focused on the production of juice but at the same time, a large amount of waste is produced mainly in the form of peel, seeds, pomace, and wastewater. This waste left after processing leads to environmental pollution and health-related hazards. However, it could be exploited for the recovery of essential oils, pectin, nutraceuticals, macro and micronutrients, ethanol, and biofuel generation. In view of the importance and health benefits of bioactive compounds found in citrus waste, the present review summarizes the recent work done on the citrus fruit waste valorization for recovery of value-added compounds leading to zero wastage. Therefore, instead of calling it waste, these could be a good resource of significant valuable components, in this way encouraging the zero-waste theory.

Modified cyclodextrin type and dehydration methods exert a significant effect on the antimicrobial activity of encapsulated carvacrol and thymol

BACKGROUND

The antimicrobial activity of essential oils and their constituents has led to increasing interest in using them as natural preservative agents. However, their high sensitivity to light and oxygen, their volatility and their low aqueous solubility are all obstacles to their application in the food, cosmetic or pharmaceutical industries. Encapsulation in cyclodextrins (CDs) is a solution for the application of such essential oils.

RESULTS

The complexation of carvacrol and thymol with hydroxypropyl (HP)-α-, HP-β- and HP-γ-CD, the behavior of the solid complexes prepared by freeze-drying and spray-drying methods and the antibacterial activity of solid complexes were studied. K_c values of HP-α- and HP-γ-CD complexes with carvacrol (118.4 and 365.7 L mol^-1 ) and thymol (112.5 and 239.7 L mol ^-1 ) were far lower than those observed for HP-β-CD complexes with carvacrol (2268.2 L mol ^-1 ) and thymol (881.6 L mol ^-1 ). The lower stability of HP-α- and HP-γ-CD complexes increased the release of compounds, thereby affecting the antimicrobial activity of carvacrol and thymol to a lesser extent than complexation with HP-β-CD, normally used in the encapsulation of carvacrol and thymol. HP-β-CD encapsulation of carvacrol and thymol markedly reduced their antimicrobial activity. The freeze-drying method barely affected the antimicrobial activity of carvacrol and thymol after encapsulation, while spray drying could be considered for the production of solid complexes in combination with the appropriate CD.

CONCLUSIONS

It was thus demonstrated that HP-α- and HP-γ-CD are very suitable alternatives for the encapsulation of carvacrol and thymol with the purpose of preserving their bacteriostatic and bactericidal activities. © 2020 Society of Chemical Industry.

Assessment of butylparaben (4-hydroxybenzoic acid butyl ester)-assisted heat treatment against Escherichia coli O157:H7 and Salmonella enterica serotype Typhimurium in meat and bone meal

Heat-resistant foodborne pathogens have been a concern in low-moisture foods and ingredients (LMFs). Due to low thermal conductivity of low moisture materials, thermal treatment is not efficient and may cause nutritional loss. This study investigated the enhancement of thermal treatment of meat and bone meal (MBM) at low water activity (a_w ) by inclusion of butylparaben (BP) as a model antimicrobial compound. Stationary phase Escherichia coli O157:H7 (Shiga toxin-negative) or Salmonella enterica serotype Typhimurium was inoculated into MBM containing 0-2000 ppm BP and incubated at 55 or 60°C for up to 5 hr. A biphasic inactivation pattern was observed for both pathogens, indicating existence of potentially thermal resistant subpopulations. Addition of 1000 ppm BP to MBM (a_w  = 0.4) significantly lowered the D-value at 55°C for E. coli O157:H7 (2.6 ± 0.5 hr) compared to thermal treatment alone (5.1 ± 0.6 h) during the treatment after the first 1 hr (p < 0.05), indicating that addition of BP accelerated the inactivation of thermal-resistant subpopulation of E. coli O157:H7 in MBM. Interestingly, similar enhancement in thermal inactivation upon addition of BP was not observed in either the sensitive or resistant subpopulation of S. Typhimurium at a_w of 0.4 or 0.7, which is likely caused by the higher thermal resistance developed by S. Typhimurium within a low a_w environment (a_w  < 0.85). These results suggest that addition of certain antimicrobial compounds can improve the thermal processing efficiency in LMFs, while their efficiency against different pathogens may vary. PRACTICAL APPLICATION: Addition of appropriate food-grade compounds may help to improve thermal treatment efficiency in low moisture foods with varied efficiency against different pathogens. This approach has the potential to reduce the required heat treatment intensity while minimizing food safety risk.

Chemical composition, extraction sources and action mechanisms of essential oils: Natural preservative and limitations of use in meat products

The antimicrobial activity of essential oils (EO) is associated with the presence of secondary metabolites synthesized by plants. Its mechanism of action involves the interaction of its hydrophobic components with the lipids present in the cell membrane of microorganism, resulting in metabolic damages and cell death. Spoilage and pathogenic microorganisms are contaminants in meat and meat products with considerable impacts on food quality and safety. Research shows the potential of applying essential oils in the preservation of meat food systems as compounds of low toxicity, extracted from a natural source, and as an alternative to consumer demand for healthy foods with a more natural appeal. In addition, there is a great diversity of plants from which essential oils can be extracted, whose antimicrobial activity in vitro and in meat and meat products has been proven.

Liquid and Vapor Phase of Four Conifer-Derived Essential Oils: Comparison of Chemical Compositions and Antimicrobial and Antioxidant Properties

In this study, the chemical composition of the vapor and liquid phase of Pinus cembra L., Pinus mugo Turra, Picea abies L., and Abies Alba M. needles essential oils (EOs) was investigated by Headspace-Gas Chromatography/Mass Spectrometry (HS-GC/MS). In the examined EOs, a total of twenty-eight components were identified, most of which belong to the monoterpenes family. α-Pinene (16.6-44.0%), β-pinene (7.5-44.7%), limonene (9.5-32.5%), and γ-terpinene (0.3-19.7%) were the most abundant components of the liquid phase. Such major compounds were also detected in the vapor phase of all EOs, and α-pinene reached higher relative percentages than in the liquid phase. Then, both the liquid and vapor phases were evaluated in terms of antibacterial activity against three Gram-negative bacteria (Escherichia coli, Pseudomonas fluorescens, and Acinetobacter bohemicus) and two Gram-positive bacteria (Kocuria marina and Bacillus cereus) using a microwell dilution assay, disc diffusion assay, and vapor phase test. The lowest Minimum Inhibitory Concentration (MIC) (13.28 mg/mL) and Minimal Bactericidal Concentration (MBC) (26.56 mg/mL) values, which correspond to the highest antibacterial activities, were reported for P. abies EO against A. bohemicus and for A. alba EO against A. bohemicus and B. cereus. The vapor phase of all the tested EOs was more active than liquid phase, showing the inhibition halos from 41.00 ± 10.15 mm to 80.00 ± 0.00 mm for three bacterial strains (A. bohemicus, K. marina, and B. cereus). Furthermore, antioxidant activities were also investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis (3- ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assays, and a concentration-dependent antioxidant capacity for all EOs was found. P. mugo EO showed the best antioxidant activity than the other Pinaceae EOs. The four Pinaceae EOs could be further investigated for their promising antibacterial and antioxidant properties, and, in particular, α-pinene seems to have interesting possibilities for use as a novel natural antibacterial agent.

An Overview of the Potential Therapeutic Applications of Essential Oils

The emergence of antimicrobial resistance (AMR) has urged researchers to explore therapeutic alternatives, one of which includes the use of natural plant products such as essential oils (EO). In fact, EO obtained from clove, oregano, thymus, cinnamon bark, rosemary, eucalyptus, and lavender have been shown to present significant inhibitory effects on bacteria, fungi, and viruses; many studies have been done to measure EO efficacy against microorganisms. The strategy of combinatory effects via conventional and non-conventional methods revealed that the combined effects of EO-EO or EO-antibiotic exhibit enhanced efficacy. This paper aims to review the antimicrobial effects of EO, modes of EO action (membrane disruption, efflux inhibition, increase membrane permeability, and decrease in intracellular ATP), and their compounds' potential as effective agents against bacteria, fungi, and viruses. It is hoped that the integration of EO applications in this work can be used to consider EO for future clinical applications.

Chitosan nanoemulsions of cold-pressed orange essential oil to preserve fruit juices

Sweet orange essential oil is obtained from the peels of Citrus sinensis (CSEO) by cold pressing, and used as a valuable product by the food industry. Nanoencapsulation is known as a valid strategy to improve chemical stability, organoleptic properties, and delivery of EO-based products. In the present study we encapsulated CSEO using chitosan nanoemulsions (cn) as nanocarrier, and evaluated its antimicrobial activity in combination with mild heat, as well as its sensorial acceptability in orange and apple juices. CSEO composition was analyzed by GC-MS, and 19 components were identified, with limonene as the predominant constituent (95.1%). cn-CSEO was prepared under low shear conditions and characterized according to droplet size (<60 nm) and polydispersity index (<0.260 nm). Nanoemulsions were stable for at least 3 months at 4 ± 2 °C. cn-CSEO were compared with suspensions of CSEO (s-CSEO) (0.2 μL of CSEO/mL) in terms of antibacterial activity in combination with mild heat (52 °C) against Escherichia coli O157:H7 Sakai. cn-CSEO displayed a greater bactericidal activity than s-CSEO at pH 7.0 and pH 4.0. The validation in fruit juices showed an improved bactericidal effect of cn-CSEO in comparison with s-CSEO when combined with mild heat in apple juice, but not in orange juice. In both juices, the combination of CSEO and mild heat exerted synergistic lethal effects, reducing the treatment time to cause the inactivation of up to 5 Log₁₀ cycles of E. coli O157:H7 Sakai cells. Finally, the sensory characteristics of both juices were acceptable either when using s-CSEO or CSEO nanoemulsified with chitosan. Therefore, as a promising carrier for lipophilic substances, the encapsulation of EOs with chitosan nanoemulsions might represent an advantageous alternative when combined with mild heat to preserve fruit juices.

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

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

GC-MS Analysis, Antioxidant and Antimicrobial Activities of Achillea Odorata Subsp. Pectinata and Ruta Montana Essential Oils and Their Potential Use as Food Preservatives

In order to discover new natural resources with biological properties, the chemical composition, the antioxidant and antimicrobial activities, and the potential use as food preservative of essential oils of Moroccan Achillea odorata subsp. pectinata (AO_pEO) and Ruta montana (RMEO) were studied. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the presence of 21 and 25 compounds in AO_pEO and RMEO, respectively. The results showed that the major compounds of AO_pEO are camphor (45.01%), bornyl acetate (15.07%), borneol (11.33%), β-eudesmol (4.74%), camphene (3.58%), and 1.8-cineole (eucalyptol) (2.96%), whereas 2-undecanone (63.97%), camphor (3.82%) and cyclopropanecarboxylic acid (3.66%) were the main components of RMEO. The antioxidant activities were evaluated by diphenylpicrylhydraziyl radical (DPPH) and reducing power assays. The antimicrobial activities of essential oils were tested against bacterial strains and food contaminant yeast using agar disc diffusion and microdilution methods. A significant antimicrobial activity of AO_pEO was observed against Bacillus subtilis, Proteus mirabilis and Candida albicans, compared to RMEO. The efficacy of AO_pEO was also evaluated in model food systems (cabbage and barley) artificially inoculated during storage. The results found that the adding of a minimal inhibitory concentration (MIC) and 4× MIC were potent in decreasing the Proteus mirabilis growth in food model systems. Our findings suggested that AO_pEO may be potentially used as an alternative food preservative.

Airborne exposure of Rhizobium leguminosarum strain E20-8 to volatile monoterpenes: Effects on cells challenged by cadmium

Volatile organic compounds (VOCs) are produced by plants, fungi, bacteria and animals. These compounds are metabolites originated mainly in catabolic reactions and can be involved in biological processes. In this study, the airborne effects of five monoterpenes (α-pinene, limonene, eucalyptol, linalool, and menthol) on the growth and oxidative status of the rhizobial strain Rhizobium leguminosarum E20-8 were studied, testing the hypothesis that these VOCs could influence Rhizobium growth and tolerance to cadmium. The tested monoterpenes were reported to have diverse effects, such as antibacterial activity (linalool, limonene, α-pinene, eucalyptol), modulation of antioxidant response or antioxidant properties (α-pinene and menthol). Our results showed that non-stressed cells of Rhizobium E20-8 have different responses (growth, cell damage and biochemistry) to monoterpenes, with α-pinene and eucalyptol increasing colonies growth. In stressed cells the majority of monoterpenes failed to minimize the detrimental effects of Cd and increased damage, decreased growth and altered cell biochemistry were observed. However, limonene (1 and 100 mM) and eucalyptol (100 nM) were able to increase the growth of Cd-stressed cells. Our study evidences the influence at-a-distance that organisms able to produce monoterpenes may have on the growth and tolerance of bacterial cells challenged by different environmental conditions.

Combination of mild heat and plant essential oil constituents to inactivate resistant variants of Escherichia coli in buffer and in coconut water

The growing demand for minimally processed foods with clean labels has stimulated research into mild processing methods and natural antimicrobials to replace intensive heating and conventional preservatives, respectively. However, we have previously demonstrated that repetitive exposure of some bacteria to mild heat or subinhibitory concentrations of essential oil constituents (EOCs) may induce the emergence of mutants with increased resistance to these treatments. Since the combination of mild heat with some EOCs has a synergistic effect on microbial inactivation, we evaluated the potential of such combinations against our resistant E. coli mutants. While citral, carvacrol and t-cinnamaldehyde synergistically increased heat inactivation (53.0 °C, 10 min) of the wild-type MG1655 suspended in buffer, only the combination with carvacrol (200 μl/l) was able to mitigate the increased resistance of all the mutants. Moreover, the combination of heat and carvacrol acted synergistically inactivating heat-resistant variants of E. coli O157:H7 (ATCC 43888). This combined treatment could synergistically achieve more than 5 log₁₀ reductions of the most resistant mutants in coconut water, although the temperature had to be raised to 57.0 °C. Therefore, the combination of mild heat with carvacrol appears to hold promise for mild processing, and it is expected to counteract the development of heat resistance.

Chemical diversity in leaf and stem essential oils of Origanum vulgare L. and their effects on microbicidal activities

Essential oils (EOs) from the stems and leaves of Origanum vulgare L. grown in Saudi Arabia and Jordan were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC-flame ionization detector (FID) techniques on two different columns (polar and nonpolar). A detailed phytochemical analysis led to the identification of 153 constituents of these essential oils. Both Saudi and Jordanian plants are classified by chemotypes rich in cymyl-compounds. However, the Saudi Origanum contains carvacrol as the major component and is, thus, characterized as a carvacrol chemotype, while the Jordanian Origanum contains thymol as the major component, and, thus, it is classified as a thymol chemotype. In addition, the antimicrobial activities of the studied EOs and their major components, including carvacrol and thymol, were evaluated against various Gram-positive and Gram-negative microorganisms. All the tested compounds exhibited significant antimicrobial activity against all the tested bacteria. Among them, thymol demonstrated superior activity against all the tested organisms, followed by carvacrol. Moreover, results on oil composition and oil yield of O. vulgare L. from different parts of the world is compared in detail with the present outcomes.

Heat-Assisted Pulsed Electric Field Treatment for the Inactivation of Saccharomyces cerevisiae: Effects of the Presence of Citral

Pulsed electric field (PEF) treatment is a non-thermal technology that has shown good potential for microbial inactivation. However, in many cases, it cannot be sufficient to avoid microbial proliferation, and the combination with other stabilizing technologies is needed. In the framework of the hurdle concept, several researches have been focused on the use of PEF in combination with heat and/or antimicrobials to increase its efficacy. This study investigated the inactivation effect of PEF on a strain of Saccharomyces cerevisiae (isolated from spoiled beverages) in a model system (growth medium). The efficacy of PEF treatment was evaluated in relation to different variables, such as electric field strength (25 and 50 kV/cm), treatment time (from 1 to 5 s), initial inoculum level (4 or 6 log cfu/ml), preheating at 50°C, medium pH (4 or 6), and addition of citral at sublethal concentration (i.e., half of minimum inhibiting concentration). The data from plate counting, modeled with the Weibull equation, showed that one of the main factors affecting yeast inactivation was the preheating of the suspension at 50°C. Indeed, higher cell load reductions were obtained with heat-assisted PEF, especially in the presence of citral. The effect of initial cell load was negligible, while pH affected yeast inactivation only without preheating, with higher death kinetics at pH 6. Flow cytometry (FCM) analysis confirmed higher mortality under these conditions. However, the occurrence of injured cells, especially in samples treated at pH 4, was observed. The ability of these cells to recover from the damages induced by treatments was affected by both citral and preheating. The synergic effects of PEF, preheating, and citral were likely due to the increase of membrane permeability (especially at pH 6), as the primary target of electroporation, which favored the solubilization of citral in the cell membrane, enhancing the efficacy of the whole process. The multi-analytical approach (traditional plate counting and FCM) allowed defining parameters to increase PEF efficacy against S. cerevisiae. Moreover, FCM, able to discriminate different physiological states of the yeast population, was helpful to better clarify the action mechanism and the potential recovery of cells after treatment.

Antimicrobial and antioxidant activities of hydrocarbon and oxygenated monoterpenes against some foodborne pathogens through in vitro and in silico studies

The present work describes the antimicrobial action of 25 monoterpenes (six hydrocarbons, five ketones, two aldehydes, six alcohols and six acetate analogues) against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus and antifungal activity against Aspergillus flavus. The antibacterial activity was evaluated by broth microdilution technique as a minimum inhibitory concentration (MIC) and the antifungal activity was performed by mycelia radial growth technique as the effective concentration causing 50% inhibition of the mycelial growth (EC₅₀). The results showed that thymol and α-terpineol were the most potent against E. coli (MIC = 45 and 55 mg/L, respectively) and S. aureus (MIC = 135 and 225 mg/L, respectively). The results also showed that thymol displayed the maximum antifungal action against A. flavus with EC₅₀ 20 mg/L. Furthermore, the antioxidant activity was determined using N,N-dimethyl-1,4-phenylenediamine (DMPD) and the results showed that geraniol were the most potent compound (IC₅₀ = 19 mg/L). Molecular docking studies indicated that the compounds displayed different binding interactions with the amino acid residues at the catalytic sites of N5-carboxyaminoimidazole synthetase and oxysterol binding protein Osh4 enzymes. Non-covalent interactions including van der Waals, hydrogen bonding as well as hydrophobic were observed between the compounds and the enzymes. A significant relationship was found between the docking score and the biological activity of the tested monoterpenes compared to the ceftriaxone and carbendazim as standard bactericide and fungicide, respectively. In silico ADMET properties were also performed and displayed potential for the development of promising antimicrobial agents. For these reasons, these compounds may be considered as potential ecofriendly alternatives in food preservation to delay or prevent the microbial infection and prolong the shelf life of food products.

Influence of Antimicrobial Agents on the Thermal Sensitivity of Foodborne Pathogens: A Review

HIGHLIGHTS

Consumers are demanding more natural and organic foods and ingredients. Many additives alone are insufficient to inactivate pathogens or prevent growth. Mild heat combined with antimicrobial agents synergistically inactivate pathogens. Here we review studies using thermally assisted antimicrobial inactivation. Many opportunities exist for the application of this hurdle technology in foods.