Antimicrobial activities of various essential oils against foodborne pathogenic or spoilage moulds

The use of essential oils in the food industry, as natural sanitizing agents, requires the definition of optimal conditions. The aim of the present work was to evaluate some antimicrobial activity parameters as mycelial growth inhibition, minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of six essential oils against Aspergillus niger, Aspergillus terreus,Chaetomium globosum, Penicillium chrysogenum, Penicillium pinophilum, Trichoderma harzianum and Trichoderma viride. The antimicrobial activity of essential oils was monitored by the macrodiluition technique. The mycelial growth inhibition, fungistatic and fungicidal concentrations were recorded for each strain that showed sensitivity to the essential oils. The essential oils of catnip, cinnamon, tea tree and thyme essential oils exhibited a large spectrum antimicrobial activities; those of clary sage and laurel inhibited the mycelial growth in a few fungal strains. The essential oils of cinnamon and thyme had the lowest MIC and MFC values against all the fungi assayed, followed by catnip, tea tree, clary sage and laurel. The use of these natural products rather than, the currently used antifungal chemicals, may be of interest given that: i) essential oils are of natural origin which means they are safer for human health and the environment and ii) there is less chance that the pathogenic microorganisms will develop resistance.     

In vitro activity of essential oils extracted from plants used as spices against fluconazole-resistant and fluconazole-susceptible Candida spp

In the present study, the antifungal activity of selected essential oils obtained from plants used as spices was evaluated against both fluconazole-resistant and fluconazole-susceptible Candida spp. The Candida species studied were Candida albicans, Candida dubliniensis, Candida tropicalis, Candida glabrata, and Candida krusei. For comparison purposes, they were arranged in groups as C. albicans, C. dubliniensis, and Candida non-albicans. The essential oils were obtained from Cinnamomum zeylanicum Breyn, Lippia graveolens HBK, Ocimum basilicum L., Origanum vulgare L., Rosmarinus officinalis L., Salvia officinalis L., Thymus vulgaris L., and Zingiber officinale. The susceptibility tests were based on the M27-A2 methodology. The chemical composition of the essential oils was obtained by gas chromatography-mass spectroscopy and by retention indices. The results showed that cinnamon, Mexican oregano, oregano, thyme, and ginger essential oils have different levels of antifungal activity. Oregano and ginger essential oils were found to be the most and the least efficient, respectively. The main finding was that the susceptibilities of fluconazole-resistant C. albicans, C. dubliniensis, and Candida non-albicans to Mexican oregano, oregano, thyme, and ginger essential oils were higher than those of the fluconazole-susceptible yeasts (P<0.05). In contrast, fluconazole-resistant C. albicans and Candida non-albicans were less susceptible to cinnamon essential oil than their fluconazole-susceptible counterparts (P<0.05). A relationship between the yeasts' susceptibilities and the chemical composition of the essential oils studied was apparent when these 2 parameters were compared. Finally, basil, rosemary, and sage essential oils did not show antifungal activity against Candida isolates at the tested concentrations.     

Antioxidant activity of selected Indian spices

Spices and vegetables possess antioxidant activity that can be applied for preservation of lipids and reduce lipid peroxidation in biological systems. The potential antioxidant activities of selected spices extracts (water and alcohol 1:1) were investigated on enzymatic lipid peroxidation. Water and alcoholic extract (1:1) of commonly used spices (garlic, ginger, onion, mint, cloves, cinnamon and pepper) dose-dependently inhibited oxidation of fatty acid, linoleic acid in presence of soybean lipoxygenase. Among the spices tested, cloves exhibited highest while onion showed least antioxidant activity. The relative antioxidant activities decreased in the order of cloves, cinnamon, pepper, ginger, garlic, mint and onion. Spice mix namely ginger, onion and garlic; onion and ginger; ginger and garlic showed cumulative inhibition of lipid peroxidation thus exhibiting their synergistic antioxidant activity. The antioxidant activity of spice extracts were retained even after boiling for 30 min at 100 degrees C, indicating that the spice constituents were resistant to thermal denaturation. The antioxidant activity of these dietary spices suggest that in addition to imparting flavor to the food, they possess potential health benefits by inhibiting the lipid peroxidation.     

Antifungal activity of essential oils evaluated by two different application techniques against rye bread spoilage fungi

AIMS: To study how antifungal activity of natural essential oils depends on the assay method used. METHODS AND RESULTS: Oils of bay, cinnamon leaf, clove, lemongrass, mustard, orange, sage, thyme and two rosemary oils were tested by two methods: (1) a rye bread-based agar medium was supplemented with 100 and 250 microl l-1 essential oil and (2) real rye bread was exposed to 136 and 272 microl l-1 volatile oil in air. Rye bread spoilage fungi were used for testing. Method 1 proved thyme oil to be the overall best growth inhibitor, followed by clove and cinnamon. On the contrary, orange, sage and rosemary oils had very limited effects. Mustard and lemongrass were the most effective oils by the volatile method, and orange, sage and one rosemary showed some effects. Oil compositions were analysed by gas chromatography-mass spectrography. CONCLUSIONS: Antifungal effects of the essential oils depended on the application method. Larger phenolic compounds such as thymol and eugenol (thyme, cinnamon and clove) had best effect applied directly to medium, whereas smaller compounds such as allyl isothiocyanate and citral (mustard and lemongrass) were most efficient when added as volatiles. SIGNIFICANCE AND IMPACT OF THE STUDY: This study proves that the method used for screening essential oils as potential antimicrobials should correspond with the application sought.     

Respective effects of sodium and chloride ions on filament formation and growth and ethanol production in Zymomonas mobilis fermentations

AIMS: To evaluate the antimicrobial effect of nine essential oils (EO) on P. phosphoreum and determine the effect of oregano oil on the shelf-life of modified atmosphere-packed (MAP) cod fillets. METHODS AND RESULTS: The antimicrobial effect of EO was studied in a liquid medium and in product storage trials. Oils of oregano and cinnamon had strongest antimicrobial activity, followed by lemongrass, thyme, clove, bay, marjoram, sage and basil oils. Oregano oil (0.05%, v/w) reduced growth of P. phosphoreum in naturally contaminated MAP cod fillets and extended shelf-life from 11-12 d to 21-26 d at 2 degrees C. CONCLUSIONS: Oregano oil reduced the growth of P. phosphoreum and extended the shelf-life of MAP cod fillets. SIGNIFICANCE AND IMPACT OF THE STUDY: Mild and natural preservation using EO can extend the shelf-life of MAP seafood through inhibiting the specific spoilage organism P. phosphoreum.     

Antifungal activity of volatile compounds generated by essential oils against fungi commonly causing deterioration of bakery products

AIMS: To investigate the volatile fractions of 16 essential oils for activity against the more common fungi causing spoilage of bakery products, Eurotium amstelodami, E. herbariorum, E. repens, E. rubrum, Aspergillus flavus, A. niger and Penicillium corylophilum. METHODS AND RESULTS: The study applied 50 microl of pure essential oils in a sterilized filter paper, were carried out at pH 6 and at different water activity levels (0.80-0.90). First, a wheat flour based agar medium was used, where cinnamon leaf, clove, bay, lemongrass and thyme essential oils where found to totally inhibit all microorganisms tested. These five essential oils were then tested in sponge cake analogues, but the antifungal activity detected was much more limited. CONCLUSION: Five essential oils showed potential antifungal capacity against all species tested, over a wide range of water availability. Their activity, however, seems to be substrate-dependent. More research is needed to make them work in real bakery products, as in the preliminary study limited effectiveness was found. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential of the cinnamon leaf, clove, bay, lemongrass and thyme essential oils against species belonging to Eurotium, Aspergillus and Penicillium genus has been demonstrated.     

Insulin potentiating factor and chromium content of selected foods and spices.

An unidentified factor that potentiates the action of insulin in glucose metabolism was investigated in selected foods and spices. Chromium content of these foods and spices was also determined. Foods and spices were extracted with 0.1N NH4OH (1:20, w/v) and the supernatants assayed for insulin potentiation activity in the rat epididymal fat cell assay. Among the selected foods, tuna fish, peanut butter, and vanilla ice cream had some insulin potentiating activity. Among the spices, apple pie spice, cinnamon, cloves, bay leaves, and turmeric potentiated insulin activity more than three-fold. Chromium concentration of foods ranged from 1 to 145 ng/g, and spices ranged from 4 to 1818 ng/g. Insulin potentiating activity of foods and spices did not correlate with total chromium. Spices are generally used for flavor and taste in food preparations, but cinnamon, cloves, bay leaves, and turmeric may have an additional role in glucose metabolism.     

Antimicrobial properties of plant essential oils and essences against five important food-borne pathogens

The antimicrobial properties of 21 plant essential oils and two essences were investigated against five important food-borne pathogens, Campylobacter jejuni, Salmonella enteritidis, Escherichia coli, Staphylococcus aureus and Listeria monocytogenes. The oils of bay, cinnamon, clove and thyme were the most inhibitory, each having a bacteriostatic concentration of 0·075% or less against all five pathogens. In general, Gram-positive bacteria were more sensitive to inhibition by plant essential oils than the Gram-negative bacteria. Campylobacter jejuni was the most resistant of the bacteria investigated to plant essential oils, with only the oils of bay and thyme having a bacteriocidal concentration of less than 1%. At 35 °C, L. monocytogenes was extremely sensitive to the oil of nutmeg. A concentration of less than 0·01% was bacteriostatic and 0·05% was bacteriocidal, but when the temperature was reduced to 4 °C, the bacteriostatic concentration was increased to 0·5% and the bacteriocidal concentration to greater than 1%.     

Temperature-dependent fumigant activity of essential oils against twospotted spider mite (Acari: Tetranychidae)

Fumigant activity of 34 commercial essential oils was assessed on female adults and eggs of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) at three temperatures (5, 15, and 25 degrees C). Common thyme, cinnamon, and lemongrass oils were equally effective on twospotted spider mite adults showing 85.8-100% mortality at 5 and 10 microl/liter air at 25 degrees C. At a lower temperature of 15 degrees C, lemongrass and peppermint resulted in > or =90% mortality of adults at 10 microl/liter air. Only lemongrass was relatively active at 5 microl/liter air, at 15 degrees C. At 5 degrees C, lemongrass and peppermint caused significantly higher adult mortality than controls but only at 10 microl/liter air. Common thyme oil showed the highest ovicidal activity at 5 microl/liter air at 25 degrees C. Among the main components of common thyme and lemongrass oils, citral was lethal to twospotted spider mite adults at all tested temperatures. Carvacrol, thymol, and citral caused the same inhibitory effects on the hatch of twospotted spider mite eggs at 25 degrees C. However, citral was more active than other compounds to twospotted spider mite eggs at 15 degrees C. Therefore, we conclude that citral has the best potential for development as a fumigant against twospotted spider mite on agricultural products harvested late in the growing season.     

Inhibitory effects of spices on growth and toxin production of toxigenic fungi.

The inhibitory effects of 29 commercial powdered spices on the growth and toxin production of three species of toxigenic Aspergillus were observed by introducing these materials into culture media for mycotoxin production. Of the 29 samples tested, cloves, star anise seeds, and allspice completely inhibited the fungal growth, whereas most of the others inhibited only the toxin production. Eugenol extracted from cloves and thymol from thyme caused complete inhibition of the growth of both Aspergillus flavus and Aspergillus versicolor at 0.4 mg/ml or less. At a concentration of 2 mg/ml, anethol extracted from star anise seeds inhibited the growth of all the strains.     

Inhibitory effects of spices on growth and toxin production of toxigenic fungi

The inhibitory effects of 29 commercial powdered spices on the growth and toxin production of three species of toxigenic Aspergillus were observed by introducing these materials into culture media for mycotoxin production. Of the 29 samples tested, cloves, star anise seeds, and allspice completely inhibited the fungal growth, whereas most of the others inhibited only the toxin production. Eugenol extracted from cloves and thymol from thyme caused complete inhibition of the growth of both Aspergillus flavus and Aspergillus versicolor at 0.4 mg/ml or less. At a concentration of 2 mg/ml, anethol extracted from star anise seeds inhibited the growth of all the strains.     

Essential oils against multidrug resistant gram-negative bacteria

Multi-drug resistant uropathogens are responsible for urinary tract infections. The antibacterial activity of seven essential oils, oregano, thyme, clove, arborvitae, cassia, lemongrass, tea tree) was investigated by agar diffusion method, followed by determination of minimum inhibitory (MIC) and bactericidal (MBC) concentrations against five multidrug resistant isolates namely Pseudomonas aeruginosa, Escherichia coli, Enterobacter cloaceae, Morganella morganii, Proteus mirabilis. Oregano, thyme, cassia had antibacterial activity with inhibition zones ranging 25–39 mm; clove, arborvitae, tea tree and lemongrass 12–15 mm. The essential oils showed antibacterial activities with MICs ranged from 0.005% (w/v) to 0.5% (w/v). Thyme had the same MIC and MBC on all strains. The effects of the vapors of the essential oils were also tested by placing the oils on the underside of the Petri dish lid. Thyme, oregano and cassia essential oils strongly inhibited the growth of the clinical strains of bacteria tested in vapor phase. This study demonstrates the potential of investigated essential oils as natural alternatives for further application in hospital therapies in order to retard or inhibit the bacterial growth. For the first time antibacterial effects of essential oils (clove, arborvitae, tea tree, lemongrass, and cassia) were evaluated against Enterobacter cloaceae and Morganella morganii clinical isolates.     

Novel strategies of essential oils,chitosan, and nano- chitosan for inhibition of multi-drug resistant: E. coli O157:H7 and Listeria monocytogenes

Despite the wide range of available antibiotics, food borne bacteria demonstrate a huge spectrum of resistance. The current study aims to use natural components such as essential oils (EOs), chitosan, and nano-chitosan that have very influential antibacterial properties with novel technologies like chitosan solution/film loaded with EOs against multi-drug resistant bacteria. Two strains of Escherichia coli O157:H7 and three strains of Listeria monocytogenes were used to estimate antibiotics resistance. Ten EOs and their mixture, chitosan, nano-chitosan, chitosan plus EO solutions, and biodegradable chitosan film enriched with EOs were tested as antibacterial agents against pathogenic bacterial strains. Results showed that E. coli O157:H7 51,659 and L. monocytogenes 19,116 relatively exhibited considerable resistance to more than one single antibiotic. Turmeric, cumin, pepper black, and marjoram did not show any inhibition zone against L. monocytogenes; Whereas, clove, thyme, cinnamon, and garlic EOs exhibited high antibacterial activity against L. monocytogenes with minimum inhibitory concentration (MIC) of 250–400 μl 100^?1 ml and against E. coli O157:H7 with an MIC of 350–500 μl 100^?1 ml, respectively. Among combinations, clove, and thyme EOs showed the highest antibacterial activity against E. coli O157:H7 with MIC of 170 μl 100^?1 ml, and the combination of cinnamon and clove EOs showed the strongest antibacterial activity against L. monocytogenes with an MIC of 120 μl 100^?1 ml. Both chitosan and nano-chitosan showed a promising potential as an antibacterial agent against pathogenic bacteria as their MICs were relatively lower against L. monocytogenes than for E. coli O157:H7. Chitosan combined with each of cinnamon, clove, and thyme oil have a more effective antibacterial activity against L. monocytogenes and E. coli O157:H7 than the mixture of oils alone. Furthermore, the use of either chitosan solution or biodegradable chitosan film loaded with a combination of clove and thyme EOs had the strongest antibacterial activity against L. monocytogenes and E. coli O157:H7. However, chitosan film without EOs did not exhibit an inhibition zone against the tested bacterial strains.     

Insulin potentiating factor and chromium content of selected foods and spices

An unidentified factor that potentiates the action of insulin in glucose metabolism was investigated in selected foods and spices. Chromium content of these foods and spices was also determined. Foods and spices were extracted with 0.1N NH₄OH (1∶20, w/v) and the supernatants assayed for insulin potentiation activity in the rat epididymal fat cell assay (see ref.6). Among the selected foods, tuna fish, peanut butter, and vanilla ice cream had some insulin potentiating activity. Among the spices, apple pie spice, cinnamon, cloves, bay leaves, and turmeric potentiated insulin activity more than three-fold. Chromium concentration of foods ranged from 1 to 145 ng/g, and spices ranged from 4 to 1818 ng/g. Insulin potentiating activity of foods and spices did not correlate with total chromium. Spices are generally used for flavor and taste in food preparations, but cinnamon, cloves, bay leaves, and turmeric may have an additional role in glucose metabolism.     

Sensitivity assessment of thyme and lavender essential oils against clinical strains of Escherichia coli for their resistance

Strong antiseptic activity of plant essential oils and extracts has been known for a long time. The antibacterial activity of thyme and lavender essential oils were tested against 30 clinical bacterial strains of Escherichia coli from patients with different clinical conditions. The agar diffusion method was used for microbial growth inhibition at various concentrations of the oils from Thymus vulgaris and Lavandula angustifolia. Susceptibility testing to antibiotics and chemotherapeutics was carried out using disc-diffusion method. The results of experiments showed that the both oils, from T. vulgaris and L. angustifolia were active against all of the clinical strains, but thyme oil demonstrated the highest activity. Thyme and lavender essential oils were active against multi drug resistant clinical strains of Escherichia coli genera. The results of experiments justify a study related to activity other essential oils against different genus of bacteria.     

Antimicrobial activity of Pelargonium essential oils added to a quiche filling as a model food system

Eight essential oils obtained by steam distillation from the scented leaves of Pelargonium species and cultivars were added at 250, 500 and 1000 ppm to a quiche filling, inoculated with either Saccharomyces ludwigii or Zygosaccharomyces bailii (at 10⁸ cfu g⁻¹), Salmonella enteriditis or Listeria innocua (at 10⁹ cfu g⁻¹). The quiche fillings were then kept at 25 °C for 24 h and the residual number of micro-organisms determined using the pour plate technique. There was an effective antimicrobial activity by the Pelargonium essential oils at 250 ppm, comparable with that of commercial thyme oil, an excellent antimicrobial agent, against Saccharomyces ludwigii and Zygosaccharomyces bailii , and a lesser inhibition compared with commercial thyme against Salm. enteriditis. There was a greater diversity of activity against L. innocua, which was in some cases more effective than commercial thyme oil. At 500 ppm, there was a greatly increased inhibition of microbial growth using the Pelargonium essential oils, which was comparable with that of commercial thyme, clove, geranium and coriander oils. As there is no evidence for the toxicity of any of these novel Pelargonium oils, and their odour does not make the delicately flavoured quiche filling unpalatable, there is a strong potential for their use in food processing.     

Impact of essential oils on growth rate, zearalenone and deoxynivalenol production by Fusarium graminearum under different temperature and water activity conditions in maize grain

AIMS: The effect of five essential oils (oregano, cinnamon, lemongrass, clove and palmarose) on growth rate, zearalenone (ZEA) and deoxynivalenol (DON) production by Fusarium graminearum strains was assessed. METHODS AND RESULTS: The influence of the essential oils was tested on irradiated maize at two concentrations (500 and 1000 mg kg-1), at different water activity (aw) (0.95 and 0.995) and temperature (20 and 30 degrees C) levels. At 0.995 aw all essential oils tested had an inhibitory effect on growth rate of F. graminearum at both temperatures studied. At this aw level, DON production in general was inhibited by all essential oils at 30 degrees C and, although palmarose and clove were the only essential oils with statistically significant inhibitory effect on ZEA production, an inhibitory trend was observed when cinnamon and oregano oils were added to maize grain. CONCLUSIONS: Antifungal and antimycotoxigenic activity of the essential oils assayed was shown to depend on environmental conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: It is apparent that essential oils should be considered as alternative preharvest natural fungicides. Further investigation on natural maize grain might be useful to study the effectiveness of these essential oils in the presence of natural mycoflora of maize grain.     

Antimicrobial activity of plant essential oils against bacterial and fungal species involved in food poisoning and/or food decay

The currative properties of aromatic and medicinal plants have been recognized since ancient times and, more recently, the antimicrobial activity of plant essential oils has been used in several applications, including food preservation. The purpose of this study was to create directly comparable, quantitative data on the antimicrobial activity of some plant essential oils prepared in the National Institute of Research-Development for Chemistry and Petrochemistry, Bucharest to be used for the further development of food packaging technology, based on their antibacterial and antifungal activity. The essential oils extracted from thyme (Thymus vulgaris L.), basil (Ocimum basilicum L.), coriander (Coriandrum sativum L.), rosemary (Rosmarinus officinalis L.), sage (Salvia officinalis L.), fennel (Foeniculum vulgare L.), spearmint (Mentha spicata L.) and carraway (Carum carvi L.) were investigated for their antimicrobial activity against eleven different bacterial and three fungal strains belonging to species reported to be involved in food poisoning and/or food decay: S. aureus ATCC 25923, S. aureus ATCC 6538, S. aureus ATCC 25913, E. coli ATCC 25922, E. coli ATCC 35218, Salmonella enterica serovar Enteritidis Cantacuzino Institute Culture Collection (CICC) 10878, Listeria monocytogenes ATCC 19112, Bacillus cereus CIP 5127, Bacillus cereus ATCC 11778, Candida albicans ATCC 10231, Aspergillus niger ATCC 16404, Penicillium spp. CICC 251 and two E. coli and Salmonella enterica serovar Enteritidis clinical isolates. The majority of the tested essential oils exibited considerable inhibitory capacity against all the organisms tested, as supported by growth inhibition zone diameters, MICs and MBC's. Thyme, coriander and basil oils proved the best antibacterial activity, while thyme and spearmint oils better inhibited the fungal species.     

Effects of selected plant essential oils on the growth and development of mouse preimplantation embryos in vivo

Plant essential oils (EOs) have been reported to have health benefit properties and their preventive and therapeutic use in animals is expected to increase in the future. We evaluated the influence of five essential oils obtained from plant species which are known to have positive antimicrobial, antioxidative and anti-inflammatory effects--sage EO from Salvia officinalis L. (Lamiaceae), oregano EO from Origanum vulgare L. (Lamiaceae), thyme EO from Thymus vulgaris L. (Lamiaceae), clove EO from Syzygium aromaticum L. (Myrtaceae) and cinnamon EO from Cinnamomum zeylanicum Blume (Lauraceae) on the growth and development of mouse preimplantation embryos in vivo. Essential oils were added to commercial diet at concentrations of 0.25% for sage EO, thyme EO, clove EO, cinnamon EO and 0.1% for oregano EO, and fed to ICR female mice for 2 weeks ad libitum. Females were then mated with males of the same strain. Embryos obtained on Day 4 of pregnancy at the blastocyst stage were stained by morphological triple staining (Hoechst, PI, Calcein-AM) and evaluated using fluorescent microscopy. The effects of essential oils were estimated by the viability of embryos, number of nuclei and distribution of embryos according to nucleus number. Cinnamon EO significantly decreased the number of nuclei and the distribution of embryos according to nucleus number was significantly altered. Sage EO negatively influenced the distribution of embryos according to nucleus number. Clove and oregano EOs induced a significantly increased rate of cell death. Only thyme EO had no detectable effects on embryo development. In conclusion, none of the essential oils had any positive effect on embryo development, but some of them reduced the number of cells and increased the incidence of cell death.     

Effect of some spices as preservatives for storage of lentil (Lens esculenta L.) seeds

The high antimycotic activity of four kinds of spices,viz. Chinese cassia, cinnamon, clove and thyme, were tested as preservatives for agricultural commodities. Clove, thyme and a mixture of the four kinds of spice completely inhibited aflatoxin production on lentil seeds during eight weeks of incubation. Chinese cassia and cinnamon partially inhibited the aflatoxin production.