Etudes des interactions entre une bactérie bioprotectrice, Lactococcus piscium CNCM I-4031, et Brochotrix thermosphacta et Listeria monocytogenes dans la crevette tropicale

Le potentiel bioprotecteur de Lactococcus piscium CNCM I-4031 vis à vis d une bactérie altérante, Brochothrix thermosphacta, a été testé sur de la crevette cuite décortiquée conservée sous atmosphère protectrice. En co-culture, L. piscium permet d inhiber la croissance de B. thermosphacta de 4 log ufc/g, tout en améliorant la qualité sensorielle du produit pendant 31 jours. L inhibition n est pas due à la production d acide lactique ni à une compétition pour les acides aminés libres. La croissance de L. piscium et B. thermosphacta a été modélisée en fonction du pH, de la température et du taux de NaCl. Les valeurs optimales de croissance sont proches mais B. thermosphacta présente une tolérance au sel plus élevée et L. piscium un caractère psychrotolérant plus marqué. L effet du niveau d inoculation par L. piscium, en combinaison avec la température et le sel, sur l interaction avec B. thermosphacta a été modélisé. Un inoculum fort en L. piscium (6-7 log ufc/g) est nécessaire pour maintenir le nombre de B. thermosphacta inférieur à 4 log ufc/g, cependant une amélioration sensorielle de la crevette est obtenue même avec un inoculum assez bas. L inhibition de Listeria monocytogenes par L. piscium a ensuite été testée sur la crevette cuite, montrant une inhibition de 4 log ufc/g. Les mécanismes d action impliqués dans cette activité ont été étudiés sur un milieu chimiquement défini (MSMA) reproduisant l inhibition. Celle-ci n est pas liée à la consommation du glucose, la production d acide lactique ou la compétition pour les acides aminés, les bases ou les vitamines. En revanche le contact cellulaire entre les deux bactéries est nécessaire pour obtenir l inhibition.The bioprotective potential of Lactococcus piscium CNCM I-4031 towards a specific spoilage organism, Brochothrix thermosphacta, was studied on tropical cooked peeled shrimp packed under modified atmosphere. In co-culture, the growth of this spoilage bacterium was inhibited by 4 log ufc/g by L. piscium and the sensory quality of the product was improved during 31 days. The inhibition could not be attributed to lactic acid or nutritional competition for amino acids. The growth modelling of L. piscium and B. thermosphacta was performed in different conditions of temperature, pH and NaCl concentrations. The optimal growth values of these two bacteria are quite similar, however L. piscium seemed to be more psychrotolerant than B. thermosphacta but twice less tolerant to salt. The effect of the inoculation level of L. piscium in combination with temperature and salt on the interaction with B. thermosphacta was modelled. A high concentration (6-7 log ufc/g) was necessary to maintain the number of B. thermosphacta lower than 4 log ufc/g. However sensory improvement of shrimp was obtained with lower inoculation level. Lastly, the interaction between L. piscium and Listeria monocytogenes was studied on cooked peeled shrimp showing a 4 log cfu/g inhibition. The mechanisms involved in this inhibition were studied on a chemically defined medium (MSMA) allowing to obtain a similar inhibition. The inhibitory activity was not linked to glucose consumption, lactic acid production or competition for amino acids, bases or vitamins. However, cellular contact is necessary to obtain the inhibition.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Influence of lactate and acetate removal on the microbiota of French fresh pork sausages

International audienceThe microbiota of fresh French pork sausages were characterised in five batches of comminuted pork meat that were equally divided into two formulations either containing the acid-based preservatives lactate and acetate, or no preservatives. Conventional microbiological analysis and high-throughput 16S rDNA amplicon sequencing methods were performed on meat batches packed under modified atmosphere (70% oxygen and 30% carbon dioxide) during chilled storage. In addition, meat pH and colour, and gas composition of the packages were monitored until the end of the shelf-life. During storage, the population of mesophilic and lactic acid bacteria increased from 4 log CFU/g to 8 log CFU/g after 15 days of chilled storage, both with and without preservatives. Despite similar changes of the physical and chemical parameters, such as pH and package gas composition, spoilage was delayed in the meat containing the preservatives, suggesting that lactate and acetate are effective against spoilage. Metagenetic analysis showed that at the end of the shelf-life, the species distribution differed between both the formulations and the batches. Lactic acid bacteria were shown to dominate both with and without preservatives; however, samples containing no preservatives were characterised by the presence of an increased population of Brochothrix spp. and Pseudomonas spp. whereas, Leuconostoc mesenteroides/pseudomesenteroides and Lactobacillus curvatus/graminis were more abundant in the meat with preservatives

Influence of temperature, pH and NaCl concentration on the maximal growth rate of Brochothrix thermosphacta and a bioprotective bacteria Lactococcus piscium CNCM I-4031

International audienceThe maximum specific growth rate (mu(max)) of Brochothrix thermosphacta, a spoilage bacteria of cooked peeled shrimp, and Lactococcus piscium CNCM I-4031, a bioprotective strain, was investigated under different conditions of temperature, NaCl concentrations and pH. The basic modelling approach used was the Gamma concept (gamma-concept) and the model developed was then adapted to shrimp. Cardinal growth parameters were quite similar for the two strains, except for NaCl. No NaCl was required for growth and the NaClmax was three-times higher for B. thermosphacta than for L. piscium (62 and 23 g l(-1) respectively). However, tolerance to NaCl was higher in seafood than in liquid broth, possibly due to presence of osmoltically active molecules. L. piscium and B. thermosphacta were psychrotolerant, with T-min = -4.8 and -3.4 degrees C, T-opt = 23.4 and 27.0 degrees C and T-max = 27.2 and 30.8 degrees C respectively. The optimal pH was neutral and growth possible till pH = 4.8 for the two strains, assuming possible applications of the bioprotective strain in lightly marinated seafood. The mu(max) of B. thermosphacta in shrimp was a little higher than in L piscium whatever the environmental conditions. Validation of the model showed that the gamma-concept was suitable for predicting mu(max) of B. therm osphacta in shrimp. Data generated in this study can be used to adapt the model to other foods with few additional experiments and the effect of different parameters may be added in the future. The model was less accurate for the bioprotective strain and the effect of NaCl must be studied in more detail directly in the matrix. (C) 2012 Elsevier Ltd. All rights reserved

Odnos porabnikov do akcijskih nakupov kot oblike pospeševanja prodaje

Optimization of Carnobacterium divergens V41 growth and bacteriocin activity in a culture medium deprived of animal protein, needs for food bioprotection, was performed by using a statistical approach. In a screening experiment, 12 factors (pH, temperature, carbohydrates, NaCl, yeast extract, soy peptone, sodium acetate, ammonium citrate, magnesium sulfate, manganese sulfate, ascorbic acid and thiamine) were tested for their influence on the maximal growth and bacteriocin activity using a two-level incomplete factorial design with 192 experiments performed in microtiter plate wells. Based on results, a basic medium was developed and three variables (pH, temperature and carbohydrates concentration) were selected for a scale-up study in bioreactor. A 23 complete factorial design was performed, allowing the estimation of linear effects of factors and all the first order interactions. The best conditions for the cell production were obtained with a temperature of 15°C and a carbohydrates concentration of 20 g/l whatever the pH (in the range 6.5–8), and the best conditions for bacteriocin activity were obtained at 15°C and pH 6.5 whatever the carbohydrates concentration (in the range 2–20 g/l). The predicted final count of C. divergens V41 and the bacteriocin activity under the optimized conditions (15°C, pH 6.5, 20 g/l carbohydrates) were 2.4 × 1010 CFU/ml and 819200 AU/ml respectively. C. divergens V41 cells cultivated in the optimized conditions were able to grow in cold-smoked salmon and totally inhibited the growth of Listeria monocytogenes (< 50 CFU g−1) during 5 weeks of vacuum storage at 4 and 8°C

La biopréservation: une stratégie d’avenir pour la conservation des aliments

N° d'article 201511121820La demande grandissante des consommateurs pour des produits alimentaires à teneur réduite en conservateurs pousse les industriels de l’agroalimentaire à rechercher des méthodes de conservation alternatives. Dans ce contexte, la bioprotection s’impose comme un procédé à fort potentiel. Cette technique consiste à inoculer sur les aliments des cultures de bactéries protectrices. Celles-ci, par l’intermédiaire de plusieurs mécanismes, vont inhiber la croissance de bactéries pathogènes et d’altération telles que Listeria monocytogenes et Salmonella. Cependant, cette technique n’a pas d’effet sur les spores bactériennes. Ainsi, l’objet central du projet de recherche ANR BlacHP vise à inactiver ces formes résistantes, notamment en combinant la biopréservation avec un procédé de traitement par hautes pressions hydrostatiques

Protective effect of a non-bacteriocinogenic Lactococcus piscium strain against Listeria monocytogenes in sterilised tropical cooked peeled shrimp

The protective activity of a non-bacteriocinogenic Lactococcus piscium CNCM I-4031 strain against Listeria monocytogenes was investigated in tropical cooked peeled shrimp stored at 8°C in modified atmosphere packaging (50% N2–50% CO2). When inoculated alone (L. piscium 107 CFU g-1 and L. monocytogenes 104 CFU g-1), protective culture and target strain grew very well on shrimp reaching a maximum cell number of 109 CFU g-1 after 7 and 14 days, respectively. In the presence of L. piscium, growth of L. monocytogenes was totally prevented after 3 days of storage. The count was 3.4 log CFU g-1 lower than in the control after 10 days and until the end of storage (31 days). Using the Seafood Spoilage and Safety Predictor Software (http://sssp.dtuaqua.dk), it was shown that pH decrease from 6.58 to 5.94 and lactic acid concentration of 89.65 mM measured in the co-inoculated batch did not fully explain the inhibition observed

Adaptation to Cold and Proteomic Responses of the Psychrotrophic Biopreservative Lactococcus piscium Strain CNCM I-4031

International audienceThere is considerable interest in the use of psychrotrophic bacteria for food biopreservation and in the understanding of cold adaptation mechanisms. The psychrotrophic biopreservative Lactococcus piscium strain CNCM I-4031 was studied for its growth behavior and proteomic responses after cold shock and during cold acclimation. Growth kinetics highlighted the absence of growth latency after cold shock, suggesting a very high promptness in cold adaptation, a behavior that has never been described before for lactic acid bacteria (LAB). A comparative proteomic analysis was applied with two-dimensional gel electrophoresis (2-DE), and upregulated proteins were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Both cold shock and cold acclimation triggered the upregulation of proteins involved in general and oxidative stress responses and fatty acid and energetic metabolism. However, 2-DE profiles and upregulated proteins were different under both conditions, suggesting a sequence of steps in cold adaptation. In addition, the major 7-kDa Csp protein was identified in the L. piscium CNCM I-4031 genome but was not cold regulated. The implication of the identified cold shock proteins and cold acclimation proteins in efficient cold adaptation, the possible regulation of a histidyl phosphocarrier protein, and the roles of a constitutive major 7-kDa Csp are discussed