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International audience; [Technical Session 7 – Food Processing Technologies]Introduction: The high demand for minimally processed food makes high pressure processing (HPP) one of the most promising non-thermal technologies for food application. While HPP efficiently inactivates vegetative bacteria, bacterial spores show strong resistance, especially at mild temperatures. To ensure spore inactivation in food matrices, the addition of other hurdle(s), such as mild heat or antimicrobial agents, is necessary.Purpose: HPP in combination with nisin was investigated as a non-thermal method for the inactivation of pathogenic and thermoresistant bacterial spores in food matrices.Methods: Six bacterial strains were studied with regard to the diversity of their origins and properties: Bacillus pumilus, Bacillus sporothermodurans, Bacillus licheniformis, Bacillus weihenstephanensis, Bacillus subtilis and Clostridium sp. (botulinum type E-like). Spores were treated in a buffer, skim milk or a liquid medium simulating cooked ham. Pressure levels ranging from 200 MPa to 600 MPa were applied for 10 min at 20°C or 50°C. Nisin was added during and/or after HPP to a final concentrations of 50 or 20 UI/mL.Results: While no significant reduction of spore cultivability was observed at any pressure at 20 °C, the addition of nisin at low concentration (ten times lower than the legal concentration) during and after HPP treatment induced a highly synergistic effect on Bacillus spp. inactivation, with spore count below the detection limit (inactivation > 6 log/mL). Moreover, spores remained sensitive to nisin up to 6h after HPP.Significance: The food industry usually pressurizes foods at room temperature, resulting in, only, inactivation of vegetative cells. The present work shows that combining HPP with nisin can lead to a synergistic Bacillus spp. spore inactivation, even after treatments at 20°C. The addition of nisin in foods before their pressurization can, therefore, be an efficient way to ensure the inactivation of bacterial spores.

The chemical composition and the biological activities of Mentha pulegium leaves extracts were evaluated. The main components of M. pulegium EO were menthone (41.7%), cis-isopulegone (31.71%) and isomenthone (15.03%). The methanol extract of M. pulegium was rich in phenols and flavonoids. The EO showed much better antioxidant activity than the methanol extract against the DPPH and ABTS radicals scavenging. The EO showed strong antibacterial and antifungal activities against 10 tested microorganisms (Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Pseudomonas aeruginosa, Aeromonas hydrophila, Listeria monocytogenes, Bacillus cereus, Aspergillus niger, Aspergillus flavus, Candida albicans) tested whereas the methanol extract almost remained inactive. The IZ diameters and minimal inhibitrice concentration values for tested microorganisms were in the range of 15–30 mm and 0.05–0.8% (v/v), respectively. Future studies should focus on to determine the usage ability of M. pulegium EO in foods as natural preservative in effective dose. Practical Applications The replacement of synthetic additives by natural active compounds fosters research on the screening of medicinal plants as sources of new antioxidants. Moreover, such compounds can be used for extension of product shelf life by inhibiting the growth of foodborne spoilage bacteria. This study focused on the evaluation of biological activities of M. pulegium EO because of its application in food industries as a reasonably safe agent. Thus, this species might be a good candidate for further investigation in developing new antioxidants, as well as preservatives in food against the well-known causal agents of foodborne diseases and food spoilage, particularly E. coli, S. typhimurium, L. monocytogenes, P. aeruginosa and S. aureus.

International audience; The secondary metabolite composition, antioxidant activities, and microbial inhibition properties of leaves of two Cistus species; C. monspeliensis and C. salvifolius were investigated using three solvent extracts (ethanol, hexane and distilled water). Ethanol extracts were most efficient at extracting phenolics, flavonoids and condensed tannins compared to hexane and distilled water for both Cistus species. A total antioxidant test (TAA) and two radical scavenging tests (DPPH and ABTS) indicated that the 70% ethanolic extract from C. salvifolius leaves had stronger antioxidant activity compared to the C. monspeliensis 70% ethanol extract, while the aqueous extract of C. monspeliensis was much stronger than the aqueous extract or the 70% ethanol extract of C. salvifolius. Overall, the polar extracts were more active in both species than the non-polar extracts. Thus aqueous ethanol extracts of the leaves of each Cistus species were tested for their ability to inhibit seven pathogenic microbial strains, including Escherichia coli ATCC 8739, Salmonella typhimurium NCTC 6017, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 29213, Enterococcus faecalis, Aspergillus niger, and Candida albicans. Leaf ethanol extracts from both species were active against each microbial species, but the C. monspeliensis leaf ethanolic extract was much more active against several microbial species than that of C. salvifolius. For example, the C. salvifolius 70% ethanol extract showed its highest antimicrobial activity against P. aeruginosa and A. niger (MIC 3.1 mg/ml and MBC 6.3 mg/ml for both), while the C. monspeliensis extract showed much higher overall activity against E. coli, P. aeruginosa and C. albicana. (MIC 6.25 mg/ml and MBC 12.5 mg/ml for all three). In conclusion, maceration with 70% ethanol was the most efficient method for extracting total polyphenols, flavonoids, and condensed tannins from the two Cistus species, and the aqueous-ethanol extracts displayed the highest antioxidant and antimicrobial activities. Hence, the aqueous-ethanolic extracts of both species may be considered as potential sources of natural antioxidants and antimicrobial agents.