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Aouadhi C.,Pasteur Institute of Tunisia IPT | Aouadhi C.,University of Nantes | Aouadhi C.,French National Center for Scientific Research | Aouadhi C.,National Institute of Agronomy | And 8 more authors.
Food Microbiology | Year: 2012

Bacillus sporothermodurans produces highly resistant endospores that can survive ultra-high-temperature treatment in milk. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk sterility. In this work, the rate of spore germination of B.sporothermodurans LTIS27 was measured in distilled water after high-pressure treatments with varying pressure (50-600MPa), treatment temperature (20-50°C), pressure-holding time (5-30min) and post-pressurization incubation time (30-120min) at 37°C or 4°C. The results showed that pressure-induced germination was maximal (62%) after a treatment at 200MPa and 20°C and increased with pressure-holding time and post-pressurization incubation time. Treatment temperature had no significant effect on germination. A central composite experimental design with three factors (pressure, pressure-holding time, and post-pressurization incubation time) using response surface methodology was used to optimize the germination rate in distilled water and in skim milk. No factor interaction was observed. Germination was induced at lower pressure and was faster in milk than in distilled water, but complete germination was not reached. The optimum germination obtained with experimental data was 5.0logcfu/mL in distilled water and 5.2logcfu/mL in milk from 5.7logcfu/mL of spores initially present in the suspension. This study shows the potential of using high hydrostatic pressure to induce the germination of B.sporothermodurans spores in milk before a heat treatment. © 2011 Elsevier Ltd. Source


Mezni F.,National Institute for Researches on Rural Engineering | Aouadhi C.,Pasteur Institute of Tunisia IPT | Khouja M.L.,National Institute for Researches on Rural Engineering | Khaldi A.,National Institute for Researches on Rural Engineering | Maaroufi A.,Pasteur Institute of Tunisia IPT
Natural Product Research | Year: 2014

Pistacia lentiscus L. is known in some Tunisian forest area by its fixed oil used in traditional medicine as an antiseptic product. This investigation is the first to study the antimicrobial activity of P.lentiscus edible oil and its phenolic extract. Oil was extracted from fruits harvested from six provenances located in Tunisia. The antimicrobial activity was tested using disc diffusion assay and the broth dilution method. Kbouch and Sidi Zid oils were most efficient (p < 0.003) against, respectively, Staphylococcus aureus and Aspergillus niger with an inhibition zone of 9.33 mm. The phenolic extract had the largest spectrum of sensitive microorganisms. The minimum inhibitory concentration and minimum bactericidal concentration results showed that all strains were inhibited by both oil and extract. © 2014 © 2014 Taylor & Francis. Source


Aouadhi C.,Pasteur Institute of Tunisia IPT | Aouadhi C.,University of Nantes | Aouadhi C.,French National Center for Scientific Research | Aouadhi C.,National Institute of Agronomy | And 8 more authors.
LWT - Food Science and Technology | Year: 2013

Bacillus sporothermodurans is a milk spoilage bacterium producing resistant endospores that survive ultra-high temperature treatment. The inactivation of B. sporothermodurans LTIS27 spores by combined hydrostatic pressure and heat treatments was studied. A central composite experimental design was used to evaluate the effect of pressure (300-500 MPa), temperature (30-50 °C), and pressure-holding time (10-30 min) on the inactivation of spores in distilled water and skim milk. The inactivation observed was shown to fit well with the values predicted by the quadratic equation, since R adj 2 were 0.970 and 0.977 in distilled water and milk, respectively. By analyzing the response surface plots, the inactivation was shown to be higher in distilled water than in milk under all the conditions tested. This was probably due to a protective effect of milk against inactivation by pressure. The optimum process parameter values for a 5-log cycle reduction of spores were calculated as 477 MPa/48 °C for 26 min and 495 MPa/49 °C for 30 min in water and in milk, respectively. This study shows the efficiency of hydrostatic pressure in combination with moderate temperature to inactivate B. sporothermodurans spores. Such treatments could be applied by the dairy industry to ensure the commercial sterility of UHT milk. © 2012 Elsevier Ltd. Source


Rebaya A.,University of Carthage | Belghith S.I.,Preparatory Institute for Engineering Studies of El Manar | Hammrouni S.,Pasteur Institute of Tunisia IPT | Maaroufi A.,Pasteur Institute of Tunisia IPT | And 3 more authors.
International Journal of Pharmaceutical and Clinical Research | Year: 2016

The objective of this study was to evaluate antimicrobial and antifungal activities of crude extracts from leaves and flower of Halimium halimifolium, and compared with those of Cistus salviifolius and Cistus monspeliensis. The tested plants (leaves and flowers) were extracted with ethanol, the activities were screened against three Gram-positive (Listeria monocytogenes, Bacillus subtilis and staphylococcus aureus), three Gram-negative bacteria (Salmonella enteric, Pseudomonas aeruginosa and Escherichia coli), and two pathogenic fungi (Candida albicans and Aspergillus niger). The efficacy of these extracts was tested against those microorganisms through a disc-diffusion method employing 15 µL of each sample per paper discs (6 mm in diameter). Comparable results were carried out using Gentamicin and Amphotericin as standard antibiotics. Ethanol extracts of different parts of plant exhibited good activity against all microorganisms tested. The inhibition zone measured ranged from 10 to 26 mm against all the bacteria and 8 to 20 mm against fungal strains. The minimum inhibitory and bactericidal concentrations (MIC and MBC) values against Staphylococcus aureus ranged from 1.562 to 12.5 mg. mL-1 and 3.125 to 25 mg. mL-1 respectively. The Cistus salviifolius leaves had the most potent bactericidal activity. On the other hand, Candida albicans and Aspergillus Niger were the least susceptible microorganisms to all Cistus extracts. In the present work, the antimicrobial potential of ethanol extracts of leaves and flower of Halimium halimifolium, Cistus salviifolius and Cistus monspeliensis is demonstrated. The high levels of antibacterial activities of have been detected, indicating that this plant may serve as an excellent source of natural antibacterial for disease prevention. © 2016, International Journal of Pharmaceutical and Clinical Research. All rights reserved. Source


Aouadhi C.,Pasteur Institute of Tunisia IPT | Aouadhi C.,University of Nantes | Aouadhi C.,French National Center for Scientific Research | Aouadhi C.,National Institute of Agronomy Tunis INAT | And 4 more authors.
Food Microbiology | Year: 2013

Spores of Bacillus sporothermodurans are known to be contaminant of dairy products and to be extremely heat-resistant. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk stability. In this study, the nutrient-induced germination of B.sporothermodurans LTIS27 spores was studied. Testing the effect of 23 nutrient elements to trigger an important germination rate of B.sporothermodurans spores, only d-glucose, l-alanine, and inosine were considered as strong independent germinants. Both inosine and l-alanine play major roles as co-germinants with several other amino acids. A central composite experimental design with three factors (l-alanine, d-glucose, and temperature) using response surface methodology was used to optimize the nutrient-induced germination. The optimal rate of nutrient-induced germination (100%) of B.sporothermodurans spores was obtained after incubation of spore for 60min at 35°C in presence of 9 and 60mM of d-glucose and l-alanine, respectively. The results in this study can help to predict the effect of environmental factors and nutrients on spore germination, which will be beneficial for screening of B.sporothermodurans in milk after induction their germination. Moreover, the chosen method of optimization of the nutrient-induced germination was efficient in finding the optimum values of three factors. © 2013 Elsevier Ltd. Source

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