Les bactériocines des bactéries lactiques : caractéristiques et intérêts pour la bioconservation des produits alimentaires

Bacteriocins from lactic acid bacteria: interest for food products biopreservation. Bacteriocins from lactic acid bacteria are low molecular weight antimicrobial peptides. They have inhibitory activity against the bacteria that are closed related to the producer strains and a narrow inhibitory spectrum. Nevertheless, most of them have activity against some food-born pathogenic bacteria as Listeria monocytogenes. The application of bacteriocins or bacteriocin producing lactic acid bacteria in food products to inhibit pathogenic or food-spoilage bacteria has then been suggested. This review focuses on the classification, structure, function, mode of action, biosynthesis and current food applications of bacteriocins from lactic acid bacteria

Les lipases sont des hydrolases atypiques : principales caractéristiques et applications

ipases are atypical hydrolases: principal characteristics and applications. Due to their kinetic and substrate specificities, triacylglycerol acyl-hydrolases or lipases are atypical enzymes. In function of their microenvironment, lipases are able to act as hydrolases in aqueous solution or as biocatalysts in organic synthesis. As hydrolases, they are responsible of the triglycerids catabolism into fatty acids and glycerol. In many organisms, this reaction plays a major role in the fat and lipid metabolism. In addition, lipases are also able to hydrolyse phospholipids and cholesterol esters. In organic solvent, lipases could catalyse reactions such as esterifications, acidolysis or alcoolysis with enantio-, regio- and chimioselectivity. Lipases form a mixed class of enzyme due to their animal, vegetal or microbial origins. All those properties led to the development of many applications in the food and chemical industries but also in the medical and therapeutic field

PAMPs, MAMPs, DAMPs and others: an update on the diversity of plant immunity elicitors

Plants possess a broad array of defenses that could be actively expressed in response of pathogenic organisms or parasites but also following beneficial saprophytic microorganisms recognition. Specifically, there are compounds derived from these organisms and called elicitors that are perceived by the plant to induce a locally or systemically expressed resistance. The understanding of the physiological and biological basis of these induced immunity mechanisms have greatly advanced over the past years but a deeper investigation of the mechanisms underlying the perception of elicitors is essential to develop novel strategies for pest control. The application of chemical and biological stimulators of plant immune defenses in conventional agriculture is expected to increase within the next years. Because of their organic origin and as they provide means for conferring plant protection in a non-transgenic manner, elicitors of plant immunity have a huge potential as biocontrol products. Through this review, we want to illustrate the diversity of compounds identified as stimulators of the plant immune system and describe the mechanisms by which they could be recognized at the plasma membrane level

Caractéristiques moléculaires de l'immunité des plantes induite par les rhizobactéries non pathogènes

Molecular characteristics of the rhizobacteria-triggered plant immunity. Recognition of certain non-pathogenic rhizobacteria by plants can trigger a systemic resistance reaction that renders the host less susceptible to subsequent infection by a virulent agent. Used in combination with other approaches, this induced systemic resistance (ISR) phenomenon is considered as a promising strategy for plant disease control both in greenhouse cultures and under field conditions. This review emphasizes the molecular aspects of this three-step process involving sequentially the perception by plant cells of elicitors produced by the inducing agents that initiates the phenomenon, signal transduction that is needed to propagate the induced state systemically through the plant and expression of defense mechanisms sensu stricto that limit or inhibit pathogen penetration into the host tissues. The current state of knowledge about rhizobacteria-stimulated ISR is discussed in parallel with the better characterized systemic acquired resistance induced by incompatible pathogens

Inhibitory activity of Lactobacillus curvatus CWBI-B28 against Listeria monocytogenes and ST2-verotoxin producing Escherichia coli O157

A bacteriocin-producing strain of Lactobacillus curvatus CWBI-B28 isolated from raw meat was shown to inhibit Listeria monocytogenes and pathogenic strains of Escherichia coli by the well diffusionassay. To confirm whether the bacteriocin was involved in E. coli O157 inhibition, growth of the pathogen was monitored in the neutralized cell-free supernatant (NCFS) pre-treated with pronase E orcatalase. Alternatively, E. coli O157 (VH21) was co-cultured with Lb. curvatus CWBI-B28 in MRS broth. The results of the well-diffusion assay suggested that the inhibition of E. coli O157 (VH21) was partially due to the bacteriocin; however, growth monitoring indicated that such inhibition is exclusively due to hydrogen peroxide. In pronase-added NCFS (i.e., absence of bacteriocin) the colony forming units (cfus) of E. coli O157 (VHA21) declined to below the detectable limit after 24 h of incubation at 37°C. However, in presence of catalase no inhibition of the pathogen was observed and the cfus increasedsteadily to reach 8 log units in 24 h. Moreover, in co-culture, a significantly accelerated inhibition of E. coli O157 (VH21) was observed in MRS broth as compared to the NCFS without added catalase and the cfus decreased to below the detectable limit in 8 h instead of 24 h, respectively

Les produits de la mer au Sénégal et le potentiel des bactéries lactiques et des bactériocines pour la conservation

Fish preservation in Senegal: potential use of lactic acid bacteria and their antibacterial metabolites. In Senegal, fish are first as staple animal protein foods for populations. Socioeconomic constraints hamper the development of industrial preservations. Traditional fish production has some inherent food safety concerns considering the high susceptibility of seafood to bacterial spoilage. Some strategies of seafood products preservation using lactic acid bacteria producing bacteriocin are not very expensive and do not consume energy very much. They can be adapted in the preservation of fish in Senegal particularly in the fermentation in which the catches, generally handled for many hours at ambient temperature, are only added salt (NaCl) and sun dried. Lactic acid bacteria producing bacteriocins could be used as starters (with addition of carbohydrates) during the preparation of fish for rendering them more resistant to the growth of spoilage and pathogenic bacteria by in situ production of organic acids and bacteriocins. A second alternative of application of these bacteria is to use bactericidal solutions obtained from their cultures as additional barrier to sodium chloride to prevent growth of the flora during fish storage for maturation. These new strategies of preparation combined with drying can be used to enhance microbiological and dietetic qualities of local seafood commodities

Munkoyo : des racines comme sources potentielles en enzymes amylolytiques et une boisson fermentée traditionnelle (synthèse bibliographique)

Munkoyo: roots as potential sources of amylolytic enzymes and a traditional fermented beverage. A review. Munkoyo is a fermented cereal-based beverage. The special feature of this beverage is the use of munkoyo roots as the source of amylolytic enzymes for manufacturing the beverage. This review summarizes the scientific knowledge on munkoyo. The following points are discussed: botanical description; distribution areas; propagation; chemical composition of roots; amylolytic enzymes in the roots and their properties; production process of the beverage; biochemical processes involved in the production of the beverage; and nutritional values and toxicity of the beverage. In order to highlight the value of munkoyo roots and to orientate research towards the optimization and/or industrialization of the production process, discussions are focused on a comparison of munkoyo with other fermented beverages and sources of amylolytic enzymes

Influence of electrical properties on the evaluation of the surface hydrophobicity of Bacillus subtilis

The surface hydrophobicity of nine Bacillus subtilis strains in different states (spores, vegetative cells, and dead cells) was assessed by water contact angle measurements, hydrophobic interaction chromatography (HIC) and bacterial adhesion to hydrocarbon (BATH). Electrokinetic properties of B, subtilis strains were characterized by zeta potential measurements and found to differ appreciably according to the strain, Correlations between HIC data, BATH data and zeta potential showed that HIC and RATH are influenced by electrostatic interactions. Water contact angle measurements thus provide a better estimate of cell surface hydrophobicity. The water contact angle of B. subtilis varied according to the strain and the state, the spores tending to be more hydrophobic than vegetative cells. (C) 2001 Elsevier Science B.V. All rights reserved

Etude socio-économique et technologique de la production du poisson fermenté et séché (Guedj) au Sénégal

Cette étude aborde les aspects socio-économiques et technologiques relatifs à l’un des maillons très important de la pêche maritime qui est la transformation du poisson en guedj ou poisson fermenté et séché. En effet, une enquête diagnostique menée à travers trois zones de production au Sénégal (Dakar, Thiès et Fatick), combinée aux données de la bibliographie et des entretiens avec les acteurs, ont permis de faire ressortir un certain nombre d’enjeux. L’étude a montré que cette activité assurée à 80% par des femmes, génère beaucoup d’emplois et de revenus, que le prix de vente fluctue entre 1000 et 3500 frs CFA.kg-1 et par conséquent qu’une grande productrice peut gagner en moyenne jusqu’à 400000 frs CFA par mois. Cependant, malgré son importance économique, elle est confrontée à d’énormes difficultés liées à la manutention, au manque d’infrastructures et de stockage adéquates et aux techniques de transformation rudimentaires utilisées. Par ailleurs, l’analyse physicochimique et microbiologique réalisée sur des échantillons prélevés dans les sites de production et de vente laisse apparaître la nécessité d’appliquer rigoureusement les bonnes pratiques de fabrication et d’hygiène afin d’améliorer la qualité sanitaire du guedj, qui fait de plus en plus l’objet de demande du marché extérieur.Mots clés : Guedj, poisson fermenté, méthode traditionnelle, étude de filière, qualité, Sénégal

Preliminary characterization of residual biomass from Hibiscus sabdariffa Calyces

Hibiscus sabdariffa calyces are mainly used for different agro-food and beverages applications. The residual biomass generated contains various useful substances that were extracted and characterized. It contained 23% (w/w) soluble pectic material, a food additive, extracted with hot acidified water (80°C, pH = 1.5) and precipitated with ethanol. The molecular weight (28.5 and 109.7 kDa), the degree of methylation (70.6 and 44.3%) and the degree of acetylation (19.0 and 4.9%) were determined for two Senegalese cultivars (koor and vimto, respectively). The effect of the extraction method on these parameters was highlighted. The residual lignocellulosic material (LCM) was chemically degraded to monosaccharides and the amount of glucose and xylose (39% of dry LCM) determined to estimate its potential as feedstock for biofuels production. However, an enzymatic degradation test revealed a recalcitrant LCM, as only 50 to 55% of its polymeric glucose content was degraded to monosaccharides without pretreatment. Xylo-oligosaccharides (XOS) are functional foods with a real market potential as prebiotics, characterized by their degree of polymerization (DP). The production of XOS synthetized by the enzymatic degradation of LCM was monitored. The results of analyses performed showed that XOS produced had mainly DP3 and DP4 values.Key words: Pectin, lignocellulosic material, enzymatic degradation, xylo-oligosaccharides