Chemical composition and antimicrobial activity of essential oils of Ocimum basilicum, Ocimum canum and Ocimum gratissimum in function of harvesting time

BACKGROUND: The aim of present the study was to investigate the chemical composition and the antimicrobial activity of essential oils of Ocimum basilicum, Ocimum canum and Ocimum gratissimum from Benin as affected by harvesting time. The chemical composition of hydrodistillated essential oils were analyzed by GC-FID (gas chromatography – flame ionization detector) and GC-MS (gas chromatography-mass spectrometry). Disc diffusion and broth microdilution assays were used to evaluate the antibacterial activity of essential oils against two foodborne pathogens. RESULTS: Based on the composition analysis, major components were as follows: estragol (43.0 -44.7 %) and linalool (24.6 -29.8 %) in O. basilicum oils; carvacrol (12.0 -30.8 %) and p-cymene (19.5 -26.2 %) in O. canum oils; thymol (28.3 -37.7 %) and γ-terpinene (12.5 -19.3 %) in O. gratissimum oils. The tested oils and their components exhibited notable antimicrobial activities against Listeria monocytogenes and Salmonella typhimurium. The O. canum and O. gratissimum oils collected at 7h and 19h showed significant higher activities against L. monocytogenes and S. typhimurium (MICs and MBCs 0.34 – 2.5 µL/mL) (p < 0.05), whereas O. basilicum showed lower activity (MICs and MBCs 2.0 – 8.0 µL/mL) at any daytime of harvest, the weakest being at 19h (MIC and MBC 12.0 – 32.0 µL/mL). CONCLUSION: The daytime of harvest can influence the composition of oils and their activities on bacteria

Engineering Synthetic Microbial Communities through a Selective Biofilm Cultivation Device for the Production of Fermented Beverages

Production of Cambodian rice wine involves complex microbial consortia. Indeed, previous studies focused on traditional microbial starters used for this product revealed that three microbial strains with complementary metabolic activities are required for an e ective fermentation, i.e., filamentous fungi (Rhizopus oryzae), yeast (Saccharomyces cerevisiae), and lactic acid bacteria (Lactobacillus plantarum). Modulating the ratio between these three key players led to significant di erences, not only in terms of ethanol and organic acid production, but also on the profile of volatile compounds, in comparison with natural communities. However, we observed that using an equal ratio of spores/cells of the three microbial strains during inoculation led to flavor profile and ethanol yield close to that obtained through the use of natural communities. Compartmentalization of metabolic tasks through the use of a biofilm cultivation device allows further improvement of the whole fermentation process, notably by increasing the amount of key components of the aroma profile of the fermented beverage (i.e., mainly phenylethyl alcohol, isobutyl alcohol, isoamyl alcohol, and 2-methyl-butanol) and reducing the amount of o -flavor compounds. This study is a step forward in our understanding of interkingdom microbial interactions with strong application potential in food biotechnology

First isolation of Clostrioides difficile from smoked and dried freshwater fish in Cambodia

In Cambodia, freshwater aquaculture is the most important source of food production. Fresh fish meat is considered a highly perishable food that requires the use of different manipulations and preservation techniques to inhibit the proliferation of undesirable bacteria. These bacteria are naturally present in the raw product or could be acquired during manipulation by cross-contamination. Many studies worldwide have investigated the epidemiology of Clostridioides difficile (C. difficile) in food, but to date, there are no publications about the bacterium in ready-to-eat fish or descriptions in Cambodia. The objective of this study was to assess the presence of C. difficile in one of the main food supplies of this country, smoked freshwater fish, originating from different provinces. A total of 25 samples were collected directly from local markets, yielding 4 C. difficile isolates and an overall recovery rate of 16%. Most of the isolates were toxigenic and classified as rare PCR profiles, and they were resistant to clindamycin. These findings indicate contamination during handling and/or contamination of the raw fish, followed by insufficient heat treatment to kill the spores. The presence of C. difficile in smoked and dried fish implies a potential risk of human exposure, contamination and infection

Prospects for Food Fermentation in South-East Asia, Topics From the Tropical Fermentation and Biotechnology Network at the End of the AsiFood Erasmus+Project

Fermentation has been used for centuries to produce food in South-East Asia and some foods of this region are famous in the whole world. However, in the twenty first century, issues like food safety and quality must be addressed in a world changing from local business to globalization. In Western countries, the answer to these questions has been made through hygienisation, generalization of the use of starters, specialization of agriculture and use of long-distance transportation. This may have resulted in a loss in the taste and typicity of the products, in an extensive use of antibiotics and other chemicals and eventually, in a loss in the confidence of consumers to the products. The challenges awaiting fermentation in South-East Asia are thus to improve safety and quality in a sustainable system producing tasty and typical fermented products and valorising by-products. At the end of the “AsiFood Erasmus+ project” (www.asifood.org), the goal of this paper is to present and discuss these challenges as addressed by the Tropical Fermentation Network, a group of researchers from universities, research centers and companies in Asia and Europe. This paper presents current actions and prospects on hygienic, environmental, sensorial and nutritional qualities of traditional fermented food including screening of functional bacteria and starters, food safety strategies, research for new antimicrobial compounds, development of more sustainable fermentations and valorisation of by-products. A specificity of this network is also the multidisciplinary approach dealing with microbiology, food, chemical, sensorial, and genetic analyses, biotechnology, food supply chain, consumers and ethnology

Physico-chemical and antimicrobial properties of essential oil extracted from lemongrass and patchouli using the supercritical carbon dioxide

The essential oil of lemongrass (Cymbopogon citratus) and patchouli (Pogostemon cablin Benth) cultivated in the Philippines was obtained by supercritical carbon dioxide (SC-CO2) extraction. The raw materials of air-dried Lemongrass leaves and stems (100 grams) and Patchouli leaves (50 grams), was extracted in the range of temperatures of 35oC 50oC and pressures of 90 110 atm, at a constant flow rate of CO2 of 0.5m3/hr. The static extraction time was conducted for 40 minutes before the dynamic extraction to enhance the extraction yield. The oil yield from supercritical carbon dioxide extraction was potentially higher by 1.09% to 4.45% compared to that from steam distillation process. The physico-chemical properties of extract at constant temperature and highest pressure were determined. The pH of lemongrass and patchouli extract was revealed acidic with refractive index of 1.4827 and 1.5012, respectively. Moreover, lemongrass extract show a high specific gravity of 0.963 while patchouli is at 0.968. The acid and ester value of lemongrass is at 18.03 and 4.53 and patchouli is 18.32 and 5.71. Evaporation by exposure to outside room temperature was about 2 to 3.8 times faster than at room temperature. A wide range of chemical components from the extracts were identified through gas chromatography and mass spectrometry (GC/MS). The predominant components for lemongrass extract were citral (neral and geranial), myrcene, geraniol and linalool. In the case of patchouli extract, patchouli alcohol (patchoulol), bulnesene, guaiene, patchoulene and caryophellene have been found. The antimicrobial properties of both extracts were also investigated with microbiological tests against pathogenic strains of Gram-positive (Staphylococcus aureus, Bacillus subtilis), Gram-negative (Escherichia Coli, Pseudomonas aeruginosa) and fungi (Aspergillus niger, Saccharomyces cerevisiae, Candida albicans). The oils showed positively the different activities against these micro- ii - organisms with the various concentrations of 1000mg/ml, 100mg/ml, 10 mg/ml and 1 mg/ml. Key word: Supercritical Carbon Dioxide extraction, Lemongrass (Cymbopogon citratus), Patchouli (Pogostemon cablin), physico-chemical properties, antimicrobial activity

Antimicrobial activities of commercial essential oils and their components against food-borne pathogens and food spoilage bacteria.

This study was undertaken to determine the in vitro antimicrobial activities of 15 commercial essential oils and their main components in order to pre-select candidates for potential application in highly perishable food preservation. The antibacterial effects against food-borne pathogenic bacteria (Listeria monocytogenes, Salmonella Typhimurium, and enterohemorrhagic Escherichia coli O157:H7) and food spoilage bacteria (Brochothrix thermosphacta and Pseudomonas fluorescens) were tested using paper disk diffusion method, followed by determination of minimum inhibitory (MIC) and bactericidal (MBC) concentrations. Most of the tested essential oils exhibited antimicrobial activity against all tested bacteria, except galangal oil. The essential oils of cinnamon, oregano, and thyme showed strong antimicrobial activities with MIC >/= 0.125 muL/mL and MBC >/= 0.25 muL/mL. Among tested bacteria, P. fluorescens was the most resistant to selected essential oils with MICs and MBCs of 1 muL/mL. The results suggest that the activity of the essential oils of cinnamon, oregano, thyme, and clove can be attributed to the existence mostly of cinnamaldehyde, carvacrol, thymol, and eugenol, which appear to possess similar activities against all the tested bacteria. These materials could be served as an important natural alternative to prevent bacterial growth in food products

The impact of oregano (Origanum heracleoticum) essential oil and carvacrol on virulence gene transcription by Escherichia coli O157:H7

The aim of the current study was to determine, via reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis, the effect of oregano essential oil (Origanum heracleoticum) and carvacrol, its major component, on the expression of virulence-associated genes in enterohaemorrhagic Escherichia coli (EHEC) O157:H7 ATCC strain 35150. Both oregano oil and carvacrol demonstrated their efficacy firstly, by inhibiting the transcription of the ler gene involved in up regulation of the LEE2, LEE3 and LEE4 promoters and of attaching and effacing lesions and secondly by decreasing both Shiga toxin and fliC genes expression. In addition, a decrease in luxS gene transcription involved in quorum sensing was observed. These results were dose dependent and showed a specific effect of O. heracleoticum and carvacrol in downregulating the expression of virulence genes in EHEC O157:H7. These findings suggest that oregano oil and carvacrol have the potential to mitigate the adverse health effects caused by virulence gene expression in EHEC O157