Determination of the effect of plant essential oils obtained by supercritical fluid extraction on the growth and viability of Listeria monocytogenes in broth and food systems using flow cytometry

The antimicrobial properties of oregano, rosemary and laurel extracts obtained by supercritical fluid extraction were investigated by examining their influence on the growth and viability of Listeria monocytogenes in laboratory medium and broccoli juice at 30 and 8 °C. Important decreases in the L. monocytogenes population were shown in presence of all the extracts obtained from rosemary and one oregano extract. The counts were reduced below the level of detection after 4 h of exposure at 30 °C in laboratory medium. A bactericidal effect was observed also when L. monocytogenes was exposed to rosemary at 30 °C and 8 °C in broccoli juice. Significant reductions in growth rate and an increase in lag phase of L. monocytogenes were observed in presence of some of the laurel and oregano extracts at both temperatures.Flow cytometry was used as a rapid method to determine the antibacterial effect of supercritical extracts and the physiological state of L. monocytogenes. Bacterial viability performed by dual staining of L. monocytogenes with SYTO 9 and propidium iodide revealed three different cell populations, specifically, living, dead and compromised cells. Live cell percentage decreased with the time of exposure, whereas the percentage of compromised cells remained constant and the dead cells increased in the same period.     

Essential oil composition of the turpentine tree (Pistacia terebinthus L.) fruits growing wild in Turkey

Constituents of essential oils from fruit samples of the turpentine tree (Pistacia terebinthus L.) collected from fifteen different localities of Turkey on August 2001 were identified by GC–MS. Twenty-eight compounds representing 92.3–100.0% of turpentine fruit oils were identified. The oil yields varied between 0.06% and 0.16%. The highest yield of oil was obtained from fruits of Antalya origin (Akba?-Serik) (0.16%). α-Pinene (51.3%), limonene (39.0%), p-cymen-8-ol (40.0%) and caryophyllene oxide (51.0%) were found as major components for different localities in Turkey. The predominant constituents in most samples were α-pinene (9.5–51.3%), limonene (tr-39.0%) and caryophyllene oxide (tr-51.5). Except for one collection (Manavgat-Antalya), which contained spathulenol (20.7%) and p-cymen-8-ol (40.0%), all the other samples yielded oils rich in α-pinene and limonene. β-Caryophyllene oxide is the most abundant compound in Hisarönü (?zmir), Alanya (Antalya) and Yaylada? (Hatay) oils. Results confirm the effect of locality on the oil content and composition.     

Essential oil composition and biological/pharmacological properties of Salmea scandens (L.) DC

Salmea scandens (L.) DC is an indigenous edible plant whose stem bark is traditionally used as food by people of Oaxaca, México. Proximate analysis of the edible stem bark revealed abundant amounts of fiber (43.67%) and protein (9.27%). GC and GC-MS analyses demonstrated that the essential oil from leaves contained high levels of germacrene D (47.1%) and elemol (15.3%), whereas that of the stem bark contained the alkylamides N-Isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamide isomers (39.7%). Levels of these compounds in the essential oil from both organs were in similar concentrations in all seasons except winter. The HPLC purified N-Isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamide isomers produced a non-competitive inhibition on porcine pancreatic lipase. The enzymatic assays with these compounds revealed a modification on V_max (0.0431–0.0533 mM min⁻¹) whereas the K_m value (0.880–0.881 mM) was not significantly changed. Essential oil from the stem bark showed a high anti-microbial activity against some phytopathogenic microorganisms. The MIC's in μg mL⁻¹ for Pseudomonas syringae pathovars were tabaci 56.1, tomato 91.2 and phaseolitica 196.4, for Clavibacter michiganensis 35.8 and Erwinia carotovora 48.1. The fungi Fusarium oxysporum and Phytophthora infestans had MIC's in μg mL⁻¹ of 3.3 and 2.4 respectively. Same essential oil was highly effective against larvae from Aedes aegypti (LC₅₀ = 0.3 μg mL⁻¹) and Anopheles albimanis (LC₅₀ = 2.5 μg mL⁻¹).     

The effects of tangerine peel (Citri reticulatae pericarpium) essential oils as glazing layer on freshness preservation of bream (Megalobrama amblycephala) during superchilling storage

This work was aim to the application of tangerine peel essential oils (TPEOs) as glazing layer on fish preservation. In this paper, essential oils were respectively extracted from the peel of ponkan, bitter orange and sweet orange. Their compositions were analyzed using GC–MS method. Fresh sample of bream was immersed into different TPEO for the formation of glazing layers on the surface and stored at −1 ±0.2 °C for 25-days storage. A thorough study of freshness evaluation was carried out and statistics analysis was performed to analyze the effect of TPEO. The result showed that the glazing layers of TPEO can effectively slow down the degradation process of fish samples and the resulting variations in electrical, moisture, chemical, microbial, sensory and textural characteristics. Additionally, statistical analysis showed that there are significant (most of p is less than 0.05) difference between control and treated sample, but insignificant (most of p is more than 0.05) differences among the samples with glazing layer of different TPEOs.The work indicated TPEOs had remarkable effect in the storage of aquatic products.     

Chemical composition,insecticidal activity and persistence of three Asteraceae essential oils and their nanoemulsions against Callosobruchus maculatus (F.)

Essential oils from three local plants Ageratum conyzoides, Achillea fragrantissima and Tagetes minuta were obtained by hydrodistillation and analyzed using gas chromatography (GC) and GC/mass spectrometry (MS). Nanoemulsions from the obtained oils were prepared using the High Pressure Homogenization (HPH) technique. The plant oils showed considerable ovicidal, adulticidal and residual activities against the cowpea beetle, Callosobruchus maculatus, where A. conyzoides oil was the most toxic. Following a 24-h fumigation and a 48-h post exposure period, eggs were less susceptible to the oils than adults, where LC_50's ranged from 71.6 to 161.9 μl/l air and 19.2–77.8 μl/l air against eggs and adults, respectively. When mortality was counted 96 h after treatment, susceptibility of all stages was increased. When prepared as nanoemulsions and tested as fumigants, toxicity of oils was increased dramatically, where LC₅₀ values 96 h after treatment ranged from 16.1 to 40.5 μl/l air and 4.5–24.3 μl/l air against eggs and adults, respectively. In a contact toxicity bioassay, adults were susceptible to the oil-treated filter papers, where LC_50's 96 h after treatment ranged between (37.1–110.8 μl/cm²). When mixed with kaolin powder and tested as contact adulticides, activity of oils increased compared with their application alone. The plant oils showed a weak to moderate residual adulticidal activity, where A. conyzoides oil was the most effective. The study shows the potential of new ways of using the tested plant oils as natural grain protectants after the required toxicological assessments.     

Biological activities and secondary compound composition from Crithmum maritimum aerial parts

This study aimed to assess the biological activities and secondary compound composition from Algerian Crithmum maritimum and, therefore, to better characterize local medicinal plants. The aerial parts were investigated regarding their mineral, antioxidant and essential oil content, and composition. The C. maritimum aerial parts contained high levels of potassium, calcium, manganese, and iron. The phenolic fraction was composed by at least 10 identified hydroxycinnamic acids that exhibited scavenging activity against DPPH and ABTS⁺. Moreover, the C. maritimum essential oil had a strong antimicrobial activity. The essential oil was composed by a least 10 molecules comprising monoterpene hydrocarbons and oxygenated monoterpenes.     

Antimicrobial effects of modified chitosan based coating containing nanoemulsion of essential oils,modified atmosphere packaging and gamma irradiation against Escherichia coli O157:H7 and Salmonella Typhimurium on green beans

The antibacterial activity of modified chitosan-based coatings containing nanoemulsion of essential oils (EOs), gamma irradiation, modified atmosphere packaging (MAP), alone or in combinations, against Escherichia coli O157:H7 and Salmonella Typhimurium was evaluated on inoculated green bean samples. Firstly, four different nanoemulsions, made of carvacrol, mandarin, bergamot and lemon Eos, respectively, were compared in terms of minimum inhibitory concentration (MIC) against the two bacteria evaluated in vitro using the micro-broth dilution method. Carvacrol nanoemulsion resulted to be the most effective antibacterial agent and was therefore selected to be incorporated into modified chitosan (MC) to form a bioactive coating. Secondly, the radiosensitivity of E. coli and S. Typhimurium to gamma irradiation was evaluated on inoculated green beans after coating deposition and MAP. Results showed that, without MAP, MC-based coating containing carvacrol nanoemulsion significantly increased the radiosensitization of E. coli and S. Typhimurium by 1.32-fold and 1.30-fold, respectively. Remarkably, the use of bioactive coating under MAP caused a synergistic effect with an increase in radiosensitivity by 1.80-fold and 1.89-fold for E. coli and S. Typhimurium, respectively. Thirdly, the antibacterial effects of the antimicrobial coating, gamma irradiation, MAP alone and their combinations were evaluated against these two bacteria during a 13-days storage of green beans at 4 °C. Bioactive coating deposition or gamma irradiation treatment resulted effective in controlling the growth of the two bacteria during the entire shelf-life. Moreover, it was also found that the combined treatment of antimicrobial coating, gamma irradiation and MAP caused the reduction of microbial population to undetectable levels during the whole storage period for E. coli and from day 7 to the end of storage for S. Typhimurium. The obtained results can be interested to food companies aiming to ensure the food safety with a prolonged shelf life.     

Plant essential oils as food preservatives to control moulds,mycotoxin contamination and oxidative deterioration of agri-food commodities – Potentials and challenges

Stored food items are frequently contaminated by fungal infestations, mycotoxins secreted by toxigenic fungi, and free radical generation due to oxidative stress. In order to ensure the safety of food items, there is a need for control measures which are effective by antimicrobial, mycotoxin inhibitory as well as antioxidative action. Some synthetic chemicals used as preservatives have been reported to cause harmful effects to consumers and the environment. Different plant essential oils (EOs), naturally occurring plant-based volatile components, have often been reported to possess strong antimicrobial and antioxidant potential. Some EO formulations are currently used as food preservatives and are kept in the category “GRAS” in view of their favourable safety profile. Being volatile in nature, such EOs may be used as plant-based fumigants for stored food commodities. Hence, EOs may play a significant role in overcoming storage losses and in enhancing food shelf- life. This review presents an overview on EOs reported to have prominent efficacy against storage fungi, mycotoxins, and as antioxidants. In addition, safety concerns and future prospects as plant-based preservatives are also discussed.     

Influence of emulsifier type on the antifungal activity of cinnamon leaf,lemon and bergamot oil nanoemulsions against Aspergillus niger

Only exiguous data are currently available on the antifungal properties of essential oil (EO) nanoemulsions against spore-forming microorganisms. The aim of this work is to develop physically stable nanoemulsion-based delivery systems for different EOs (cinnamon leaf, lemon, and bergamot), to exploit their antifungal properties against Aspergillus niger. The inhibition of mycelial radial growth and spore germination were used as indicators of antifungal activity of the nanoemulsions, which were prepared at 3 wt% EO, using non-ionic Tween 80 (T80) or anionic whey protein isolate (WPI) (1 wt%) as emulsifiers, and sunflower oil (1 wt%) as ripening inhibitor. The nanoemulsions were physically stable over seven days of accelerated aging at 35 °C.The minimal inhibitory concentration of free cinnamon leaf and of both citrus EOs were 0.35 and 5.50 μg/g, respectively. The encapsulation of cinnamon leaf EO in nanoemulsions significantly enhanced the inhibiting effect against A. niger mycelial growth and spore germination, with respect to the free EO. In contrast, for citrus EOs, the encapsulation in nanoemulsions generally decreased the antifungal activity, likely because of the nanoemulsion acting as a hydrophobic sink for the main constituents of citrus EOs. The emulsifier played a fundamental role in the resulting antifungal activity, with WPI-based nanoemulsions being more effective in inhibiting the mycelial growth and the spore germination of A. niger than T80-based ones. The antifungal action was correlated to the morphological alterations observed in A. niger, such as the loss of cytoplasm in fungal hyphae and hyphal tip. The results of this study show the importance of nanoemulsions design in the development of efficient and stable natural antifungal agents for food applications.