Le Nem chua est un produit vietnamien fermenté à base de viande porcine. Notre étude a pour but de formuler des starters lactiques afin de standardiser le processus de fabrication du Nem chua et améliorer la qualité des produits finis. Le pH de la pâte de viande diminue progressivement tandis que la population lactique se développe au cours des 5 jours de fermentation. Parmi les 131 souches identifiées, les Lactobacillus brevis et Lb. plantarum étaient les plus fréquents. Les autres bactéries lactiques telles que Leuconostoc mesenteroides, Pediococcus pentosaceus, Lactococcus lactis sont présentes mais en plus faible pourcentage. L’utilisation de la combinaison des Lb. brevis et Pe. pentosaceus (6.106 UFC.g-1 pâte de viande, proportion de 1:1) donne des produits préférés par le jury de dégustateurs vietnamiens. Ces résultats permettent d’ouvrir de nouvelles perspectives de production et d’application au niveau industriel des starters lactiques choisis afin d’avoir les produits à la qualité bien maîtrisée et en sécurité alimentaire dans la fabrication des Nem chua du Vietnam, qui pouvant s’appliquer à d’autres fermentations carnées similaires. / Nem chua is a very popular fermented meat product in Vietnam. Our research aimed at the formulation of autochthonous starter cultures in order to standardise the production process of Nem chua and to improve the quality of final product. The paste meat pH progressively decreased while LAB increased during the fermentation. Among 131 isolates identified, the most frequent LAB revealed were Lactobacillus brevis and Lb. plantarum. The other LABs such as Leuconostoc mesenteroides, Pediococcus pentosaceus, Lactococcus lactis, … existed in lowest percentage. The results of our sensorial experiments demonstrated significant effects of Lb. brevis and Pe. pentosaceus strains, which were previously isolated from Nem chua, on the sensory quality of this traditional fermented meat product. The use of both Lb. brevis and Pe. pentosaceus strains (6.106CFU.g-1 meat paste, strain ratio of 1:1) as starters for Nem chua offered the best sensorial quality. These results suggest further studies on the practical ability of using and producing these LABs in combination as commercial starters in order to produce products of well-controlled quality and safety for Nem chua in Vietnam and probably of other similar fermented meat products.

[Truncated abstract] Antimicrobial growth promoters are added to feed to prevent lactic acidosis in ruminant animals by selectively inhibiting rumen bacteria that produce lactic acid. However, recently imposed or impending bans on the use of antimicrobial growth promoters in animal production have lead to a critical need to find practical alternatives that are safe for the animal and consumer and that obtain similar production benefits. I investigated bioactive plants of Australia for their potential to prevent lactic acidosis in ruminants. The unifying hypothesis tested was that plants would be identified that selectively inhibit lactic acid-producing bacteria and consequently protect against lactic acidosis. This hypothesis was tested in a three phase process: phase 1, plant selection and collection; phase 2, a three stage protocol for screening plants and essential oils; phase 3, in vivo experiments and chemical fractionation of the most promising plant. I developed an in vitro bioassay that simulated acidosis by adding glucose to rumen fluid in Bellco tubes and incubating for 5 h (Chapter 4). The pH and gas production were used as indicators of acidosis and fermentation activity. I used this bioassay to screen ninety-five plants (dried and ground material from 79 species) and ten essential oils and included a negative control (oaten chaff) and a positive control (virginiamycin). One plant, Eremophila glabra, produced a similar pH (5.63) to the positive control (5.43) although it inhibited gas production to a moderate extent (P < 0.05). ... Seven serrulatane diterpenes were identified to be the major secondary metabolites in E. glabra. The metabolites were screened using a broth dilution and microtitre spectrophotometry method and were selective against S. bovis at between 320 and 1077 [mu]g/ mL. The serrulatanes from E. glabra were probably responsible for the activity against acidosis that I observed in vitro, because they selectively inhibited lactateproducing bacteria. It is also possible that a synergy between serrulatanes and possibly other metabolites are responsible for the activity observed in vitro. The results from my experiments support the role that bioactive plants may have to replace the antibiotics that are added to livestock feed. Australian plants were identified containing compounds that were active against the bacterial processes responsible for ruminant acidosis. To my knowledge this is the first work undertaken to identify bioactive plants of Australia for their potential to prevent acidosis. I developed in vitro screening bioassays that targeted key indicators of acidosis. These bioassays enabled me to identify 5 plants from the 104 screened that could potentially control acidosis. One of these plants in particular, E. glabra, showed a level of activity in vitro that was comparable to antibiotic protection against acidosis. The exciting in vitro results were not demonstrated in vivo but only one dose level of E. glabra was used, which was based on the in vitro work. In contrast to the in vitro system the rumen is a continuous flow system with greater complexity and it is possible that the concentration of E. glabra that I used in vivo was not optimum. This places importance on future dose response experiments to confirm the efficacy of E. glabra in vivo.

Les effets anti-allergiques des bactéries lactiques sont suggérés par plusieurs études épidémiologiques, des essais cliniques et des modèles expérimentaux d’allergie. Cependant, les propriétés immunomodulatrices des bactéries lactiques sont sous-exploitées par les stratégies vaccinales développées pour combattre l’allergie et les mécanismes empruntés par ces bactéries pour moduler l’allergie restent peu caractérisés.<p>Dès lors, nous avons caractérisé les propriétés immunomodulatrices qu’exerce Lactobacillus plantarum NCIMB8826, une bactérie lactique modèle, sur la cellule dendritique étant donné le rôle déterminant de cette cellule sur la réponse allergique. Nous montrons que L. plantarum induit une forte sécrétion d’IL-12 p40, d’IL-12 p70, de TNF-a mais une faible production d’IL-10. Cette faculté à induire la sécrétion de cytokines polarisantes dépend de TLR2, de TLR9, de MyD88, de NF-kB, des MAPKs (en particulier JNK, p38 et ERK 1/2), de la composition de l’acide lipotéichoïque de L. plantarum et de CD14. Nous montrons aussi que l’ADN génomique de L. plantarum est un agoniste de TLR9 et que CD14 et CD36 facilitent la liaison de la cellule dendritique avec L. plantarum.<p>Ensuite, nous avons évalué le potentiel vaccinal d’une coadministration L. plantarum + Der p 1 dans un modèle murin d’allergie à Der p 1. Cette formulation vaccinale prévient la production d’IgE Der p 1-spécifique et atténue l’éosinophilie pulmonaire tout en stimulant une forte production d’anticorps IgG2a Der p 1-spécifiques et d’IFN-g par les cellules spléniques. Ces effets bénéfiques nous ont conduit à élaborer une bactérie lactique recombinante dérivée de L. plantarum produisant Der p 1 pour la vaccination contre l’allergie aux acariens. La forme antigénique que nous avons réussi à faire produire par L. plantarum correspond à une protéine de fusion entre la Maltose Binding Protein de E. coli et ProDer p 1 (le zymogène de Der p 1), la présence de ce partenaire de fusion étant indispensable à la production de ProDer p 1. En prophylaxie, la vaccination par cette bactérie recombinante prévient la production d’anticorps IgE-Der p 1-spécifiques et stimule la production d’anticorps IgG2a spécifiques, reproduisant les effets de la coadministration L. plantarum + Der p 1. Elle réduit de manière drastique la production d’IL-5 des cellules spléniques et des cellules ganglionnaires médiastinales et prévient l’éosinophilie pulmonaire mais n’a pas d’effet sur l’hyperréactivité bronchique. Der p 1 étant un des allergènes d’acarien les plus immunodominants, cet ensemble de données montre donc que cette bactérie recombinante constitue un vaccin prophylactique prometteur pour la prévention de l’allergie aux acariens. Des résultats préliminaires obtenus à partir de cellules dendritiques humaines et lymphocytes T autologues montrent la forte capacité de cette bactérie recombinante à induire le développement d’une réponse Th1 fortement polarisée (production d’IFN-g en l’absence de production d’IL-4 et d’IL-5), ce qui suggère que l’utilisation de cette bactérie recombinante pourrait être envisagée pour le traitement de l’allergie chez l’homme. <p> / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

Akamu is a lactic acid bacteria fermented cereal-based food that complements infant diets in most African countries. Uncontrolled fermentation increases the variability in quality and safety of akamu. This study was aimed at the controlled fermentation of akamu with selected lactic acid bacteria (LAB), investigation of the probiotic potential of the LAB and the effect of variation in production method on the product quality and sensory properties. PCR-DGGE analysis of traditional akamu samples revealed LAB community dominated by Lactobacillus fermentum, L. plantarum, L. delbrueckii subsp. bulgaricus and L. helveticus. Isolated yeasts were Candida tropicalis, C. albicans, Clavispora lusitaniae and Saccharomyces paradoxus. The isolated Lactobacillus plantarum strains (NGL5 and NGL7) fermented irradiated ground maize slurries and produced significant levels of lactic acid (>73 mmol L-1) and low pH ≤3.63 displaying inhibitory activity against Salmonella enterica serovar Enteritidis NCTC 5188, Escherichia coli 1077 (NCTC 11560), Bacillus cereus NCIMB 11925, Staphylococcus aureus NCTC 3750 and Listeria monocytogenes NCTC 7973 in MRS agar and E. coli 1077 in maize slurry fermentation. Viability of both strains of L. plantarum at pH 2 after 3 h was reduced from ≥8.26±0.05 to ≤4.94±0.49 Log10 CFU mL-1 while incubation in 0.3% bile allowed growth to 5.73±0.13 and 7.93±0.12 Log10 CFU mL-1 after 6 h for NGL5 and NGL7 respectively. Auto-aggregation of the L. plantarum strains at 37oC (≥25 after 5 h) correlated with adhesion to hydrocarbons (<15, 26, 33 and 64% for Hexane, Hexadecane, Ethyl acetate and Chloroform respectively). The strains failed to exhibit gelatinase or haemolytic activity but adhered to porcine mucin (OD403 nm ≥0.63 with viability ≥6.52 Log10 CFU mL-1) and Caco-2 cells (≥5.13 Log10 CFU mL-1). The ash, mineral (Ca, K, Mg, Na, S and Zn), IDF, SDFP and TDF content of the L. plantarum fermented ground maize slurries were significantly (p≤0.05) higher than that of the traditional akamu but the peak and final viscosities (139.5 and 68.5 cP respectively) were significantly (p≤0.05) the least. The aroma, appearance, colour, flavour and texture of the resultant porridges were liked moderately by 75% of the assessors. This study demonstrated that fermentation with the L. plantarum strains would contribute towards product safety and the L. plantarum strains possessed some probiotic potential that could be beneficial to the consumers particularly in those developing countries were the main staple foods are fermented cereals.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Lactic acid bacteria (LAB) play a vital role in reducing wine acidity and also contributing to its aroma and flavour. However, they can also be responsible for many wine spoilage problems that compromise the quality and value of wine. While Oenococcus oeni contributes positive characteristics to the sensory properties of wine, certain species of the genera, Lactobacillus and Pediococcus can affect the wholesomeness of wine by producing undesirable compounds, such as biogenic amines and ethyl carbamate. Chemical preservatives like sulphur dioxide (SO2) are used to prevent the growth of spoilage micro-organisms during the winemaking process. SO2 also acts as a reducing agent and maintains the benefits of antioxidant properties of the polyphenols of wine. However, there is a worldwide demand to reduce SO2 levels due to the increasing health related risks and other factors. All these considerations have increased the interest in research to look for new preservation strategies, and LAB-produced bacteriocins seem to be a potential alternative that has been explored in the last decade. Various types of bacteriocins have been identified and characterized. However, there are few reports on bacteriocins produced by LAB of oenological origin or on bacteriocins present in the finished wine. The present study screened 155 LAB isolates from the IWBT culture collection for bacteriocin production. The isolates originated from South African red wines undergoing spontenous malolactic fermentation (MLF). Eight strains (5%) were identified to be producers, as evidenced by strong inhibition zones formed against sensitive organisms on agar plates. The producers demonstrated a broad spectrum of antimicrobial activity by inhibiting Lactobacillus spp., Leuconostoc mesenteroides, Listeria monocytogenes and Pediococcus pentosaceus strains. Some of these bacterial genera are important in winemaking since they are potential wine spoilage bacteria. Hence these strains and/or the bacteriocins they produce could possibly find application in the food fermentation industry. The physiological results, biochemical tests and sugar fermentation profiles all gave the same results for the seven isolates, which were indicative of enterococci. The identification through 16S rRNA gene sequencing revealed that the seven tested isolates were all Enterococccus faecium. RAPD-PCR fingerprinting gave the same profile for the seven strains confirming that they were all identical on genetic level. Determining the molecular weight using SDS-PAGE showed the peptides to be below 4.6 kDa in size. PCR amplification of the enterocin P gene, sequencing and BLAST search results confirmed that all eight strains contained the enterocin P gene from Ent. faecium. The enterocin tested in this study was heat stable at 100°C (30 min), but lost 50% of its activity at 121°C (15 min). Factors such as bacteriocin production and heat resistance are among many that enable enterococci to be dominant in fermented products such as dairy foods or meat. Therefore, enterococci producing bacteriocins have potential applications in various foods and fermented products. The pH tests showed enterocin to be active over a broad pH range (2-10). Enterocin activity over a wide pH range make them potentially more suitable as natural preservatives of foods and fermented products where products are acidified or pH decreases due to natural LAB present. They also have potential applications in oenological process where pH levels are as low as 3 and 4. Proteolytic enzyme treatments with lysozyme, lipase, lyticase and catalase could not inhibit enterocin activity. This indicated that their antimicrobial activity was independent of lipid or carbohydrate moieties or hydrogen peroxide. α-Chymotrypsin and proteinase K inactivated enterocin, which indicated that the compound was proteinaceous in nature. Bacteriocin production tested in two of the isolates, #16.3 and 128.1, coincided with the exponential growth phase which occurred after 6 hours of incubation at 30°C, which was an indication of primary metabolite kinetics. The highest production of 400 AU/ml was observed after eight hours and was maintained for several hours (46 hours) in the stationery phase. The bactericidal effect of the cell free supernatants from #16.3 and 128.1 against the sensitive culture of Lactobacillus pentosus DSM 20314 was clearly demonstrated by complete inhibition of growth for most of the experimental period, while the control increased exponentially throughout the experiment. In conclusion, this study has confirmed the isolation and identification of Ent. faecium strains from wine, a genus that is rarely found in the wine environment. Although one can speculate on the origin of this bacterium in the wine e.g. human handling and contaminated water, these bacterial isolates produced enterocin P which have antimicrobial action against wine-related LAB genera and therefore have a potential role in wine spoilage control. / AFRIKAANSE OPSOMMING: Melksuurbakterieë (MSB) speel ‘n belangrike rol in die redusering van die suurgehalte van wyn en dra ook by tot die aroma en smaak daarvan. Hulle kan egter ook verantwoordelik wees vir vele wynbederfprobleme wat die gehalte en waarde van wyn negatief beïnvloed. Hoewel Oenococcus oeni positiewe karaktertrekke aan die sensoriese eienskappe van wyn verleen, kan sekere spesies van die genus, Lactobacillus en Pediococcus, die heilsaamheid van wyn beïnvloed deur ongewenste verbindings, soos biogeniese amienes en etielkarbamaat, te produseer. Chemiese preserveermiddels, soos swaweldioksied (SO₂), word gebruik om die groei van bederfmikro-organismes tydens die wynbereidingsproses te voorkom. SO₂ fungeer ook as ‘n reduseermiddel en onderhou die voordele van die antioksidant eienskappe van die poli-fenole van wyn. Daar is egter ‘n wêreldwye vraag na die redusering van SO₂-vlakke as gevolg van die toename in gesondheidsverwante risiko’s en ander faktore. Al hierdie oorwegings het belangstelling in die navorsing van nuwe preserveringstrategieë laat toeneem en MSB-geproduseerde bakteriosiene lyk na ‘n potensiële alternatief wat in die laaste dekade ondersoek word. Verskeie tipes bakteriosiene is geïdentifiseer en getipeer. Daar is egter nog weinig gerapporteer oor bakteriosiene wat deur MSB van wynkundige oorsprong geproduseer is of oor bakteriosiene wat in afgeronde wyn teenwoordig is. Die huidige studie het 155 MSB isolate van die Instituut vir Wynbiotegnologie se kultuurversameling vir bakteriosien-produsering gegradeer. Agt stamme (5%) is as produseerders geïdentifiseer, soos gestaaf is deur sterk inhibisiesones wat teen sensitiewe organismes op agarplate gevorm het. Die produseerders het ‘n breë spektrum van antimikrobiese aktiwiteit by inhiberende Lactobacillus spp., Leuconostoc mesenteroides, Listeria monocytogenes en Pediococcus pentosaceus stamme gedemonstreer. Sommige van hierdie bakteriese genera is belangrik in wynbereiding, omdat dit potensiële wynbederfbakterieë is. Hierdie isolate en/of die bakteriosiene wat dit produseer, kan dus moontlik toepassing in die voedselfermentasiebedryf vind. Die fisiologiese resultate, biochemiese toetse en suikerfermentasieprofiele het almal dieselfde resultate vir die sewe isolate, wat indikatief van enterococci was, gelewer. Die identifisering deur 16S rRNA-basispaaropeenvolging het onthul dat die sewe getoetste isolate almal Enterococccus faecium was. RAPD-PKR-vingerafdrukke het dieselfde profiel vir die sewe rasse gelewer, wat bevestig dat die rasse almal identies op genetiese vlak was. Deur die molekulêre gewig vas te stel deur middel van SDSPAGE, het dit getoon dat die peptiede kleiner as 4.6 kDa in grootte is. PKR-amplifikasie van die enterosien-P geen, die bepaling van basispaaropeenvolging en BLAST-soekresultate het bevestig dat al agt rasse die enterosien-Pgeen van Ent. faecium bevat. Die enterosien wat in hierdie studie getoets is, was hitte-stabiel teen 100°C (30 min), maar het 50% van sy aktiwiteit teen 121°C (15 min) verloor. Faktore soos bakteriosienproduksie en hittebestandheid, is van die vele faktore wat enterococci in staat stel om dominant in gefermenteerde produkte, soos suiwelprodukte of vleis te wees. Enterococci wat bakteriosiene produseer het dus potensiële toepassings in verskeie kossoorte en gefermenteerde produkte. Die pH-toetse het getoon dat enterosien-P oor ‘n breë pH spektrum (2-10) aktief was. Enterosienaktiwiteit oor ‘n wye pH spektrum maak dit potensieel meer geskik as natuurlike preserveermiddels vir kossoorte en gefermenteerde produkte waar produkte versuur word of die pH afneem as gevolg van natuurlike MSB wat teenwoordig is. Dit het ook potensiële toepassings in enologiese prosessering waar pH-vlakke so laag as 3 en 4 is. Proteolitiese ensiembehandelings met lisosiem, lipase, litikase en katalase kon nie enterosienaktiwiteit inhibeer nie. Daar is getoon dat hul antimikrobiese aktiwiteit onafhanklik was van lipiede, koolhidraatdele óf waterstofperoksied. α-Chymotripsien en proteïenase-K het enterosien onaktief gemaak, wat getoon het dat die samestelling proteïenagtig van nature is. Bakteriosienproduksie wat in twee van die stamme #16.3 en 128.1 getoets is, het ooreengestem met die eksponensiële groeifase wat na 6 ure van inkubasie teen 30°C plaasgevind het, en wat ‘n aanduiding is van primêre metabolitiese kinetika. Die hoogste produksie van 400 AU/ml is na agt ure waargeneem en is vir etlike ure (46 uur) in die stasionêre fase gehandhaaf. Die bakterie-dodende effek van die selvrye supernatant van #16.3 en 128.1 teenoor die sensitiewe kultuur van Lactobacillus pentosus DSM 20314 is duidelik gedemonstreer deur totale inhibisie van groei vir die grootste deel van die eksperimentele periode, terwyl die kontrole eksponensieel deur die hele eksperiment toegeneem het. Hierdie studie het dus die isolering en identifisering van Ent. faecium-stamme, ‘n genus wat baie selde gevind word in ‘n wynomgewing, vanuit wyn bevestig. Alhoewel daar gespekuleer kan word oor die oorsprong van hierdie bakterie in wyn bv. menslike hantering en besmette water, het hierdie rasse wel enterosien geproduseer en daarom die potensiaal om ‘n rol te speel in beheer teen verskeie bederf-MSB-genera. / TIA, NRF and THRIP

Thesis (PhD (Microbiology))--Stellenbosch University, 2008. / One of the key selection criteria for potential probiotics is the ability to adhere and colonise the host gastrointestinal tract (GIT). Probiotics compete for receptor sites at the host intestinal surface, preventing the colonisation of pathogens, thereby protecting the host from infection. In addition, several important intestinal functions are mediated by the binding of probiotics to host tissue. However, the molecular mechanisms and genotypic characterization of adhesive elements have not received as much attention as other aspects of probiotic research. The present study aims to contribute to this area of research. The first part of the study focused on monitoring the expression of mucus adhesion genes mub, mapA, adhesion-like factor EF-Tu and bacteriocin gene plaA of Lactobacillus plantarum 423, as well as mub, surface layer protein (slp) and EF-Tu of Lactobacillus acidophilus ATCC 4356 when grown in the presence of mucin, bile, pancreatin and at low pH. Real time PCR was used. mub, mapA and EF-Tu of strain 423 were up-regulated in the presence of mucus and expression increased under increasing concentrations of mucus. Expression of mapA was up-regulated under normal gut conditions (0.3%, w/v, bile; 0.3%, w/v, pancreatin; pH 6.5) and at higher levels of bile (1.0%, w/v) and pancreatin (1.0%, w/v). Expression of mub was downregulated in the presence of bile and pancreatin at pH 6.5, whilst the expression of EFTu and plaA remained unchanged. At pH 4.0, the expression of mub and mapA remained unchanged, whilst EF-Tu and plaA were up-regulated. Expression of mapA was down-regulated in the presence of 0.1% (w/v) cysteine, suggesting that the gene is regulated by a mechanism of transcription attenuation that involves cysteine. In the case of L. acidophilus ATCC 4356, none of the genes were up-regulated under increasing concentrations of mucin, whilst only slp and EF-Tu were up-regulated under normal and stressful gut conditions in vitro. In the second part of the study, male Wistar rats were used to evaluate which section of the gastrointestinal tract are colonised by L. plantarum 423 and Enterococcus mundtii ST4SA and determine the effect of adhesion. Fluorescent in situ hybridization (FISH) incorporating strain specific oilgonucleotide probes indicated strong fluorescent signals for L. plantarum 423 along the intestinal lining of the ileum and the cecum. L. plantarum 423 did not colonise the colon as indicated by real timePCR. Fluorescent signals were recorded for E. mundtii ST4SA across the epithelial barrier of cecum and colonic tissue, suggesting that translocation took place. Real time PCR revealed highest cell numbers of strain ST4SA in the cecum and the colon. Haemotoxylin eosin staining of rat tissue revealed no change in morphology or any toxic effects induced upon adhesion of the strains. 16S rDNA PCR and denaturing gradient gel electrophoresis (DGGE) revealed a decrease in enterobacterial species whilst the lactic acid bacterial content remained unchanged. Strains 423 and ST4SA agglutinated yeast cells in vitro, indicating the possible presence of mannose receptors. It is well known that these receptors play a crucial role in the elimination of type 1 fimbriated strains of E. coli. It is thus safe to speculate that mannose receptors may have played a role in diminishing the enterobacterial content in the gut. The third part of the study encompassed characterization of cell surface proteins of L. plantarum 423 and their role in adhesion to Caco-2 cell lines. The strain lacks the typical surface layer protein whilst a multifunctional “intracellular” protein, elongation factor Tu (EF-Tu) and glycolytic enzymes glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and triosephosphate isomerase (TPI) were detected. Removal of surface proteins reduced adherence of strain 423 to Caco-2 cell lines by 40%, suggesting that these proteins play a role in adhesion. The ability of strain 423 to competitively adhere, exclude and displace Clostridium sporogenes LMG 13570 and Enterococcus faecalis LMG 13566 from Caco-2 cell lines, was studied. Adhesion of C. sporogenes LMG 13570 and E. faecalis LMG 13566 was inhibited by 70% and 90%, respectively. Strain 423 excluded C. sporogenes LMG 13570 from Caco-2 cells by 73% and displaced the pathogen by 80%. E. faecalis LMG 13566 was excluded by 60% and displaced from Caco-2 cells by 90%. Despite removal of the surface proteins, L. plantarum 423 was still capable of competitively adhering to Caco-2 cells and reduced adherence of C. sporogenes LMG 13570 by 50% and E. faecalis LMG 13566 by 70%.

Thesis (DSc)--Stellenbosch University, 1961. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming

La souche Carnobacterium maltaromaticum LMA 28, isolée d’un fromage à pâte molle, possède des propriétés physiologiques non conventionnelles pour une bactérie lactique. Sa croissance en TSB-YE et en lait traduisent son exigence nutritionnelle en facteurs de croissance facilement assimilables et sa faible vitesse de production d’acide lactique à partir de glucose, lactose, fructose et saccharose. Le galactose n’est pas métabolisé et lors de l’hydrolyse du lactose n’est pas excrété dans le milieu de culture. Les caillés lactiques sont obtenus après des durées d’incubation non compatibles avec les cadences industrielles. De plus, ils présentent une texture très friable. La numération et l’identification de cette souche, en vue de suivre son comportement dans une matrice fromagère, ont été optimisées par la mise au point du milieu de culture sélectif CM, à l’aide de plan d’expériences, et par la technique de PCR. Le comportement de C. maltaromaticum LMA 28 a été comparé à ceux de deux souches lactiques d’intérêt technologique Lc. lactis DSM 20481 et S. thermophilus INRA 302, dans une large gamme de températures (3 à 37 °C) et de pH (5,2- 8,0). Des essais en co-culture, associant cette souche avec Lc. lactis DSM 20481 ou avec S. thermophilus INRA 302, ont montré que la production d’acide lactique était due à la croissance de la souche lactique traditionnelle. Cependant C. maltaromaticum LMA 28, souche lente, n’est pas inhibée par cette acidification. L’aptitude fromagère de C. maltaromaticum LMA 28 a été testée lors de deux fabrications de fromages à pâte molle. Inoculée à différents niveaux de population, elle a été mise en évidence à tous les stades de la fabrication. Présente à une concentration très faible dans le lait de fabrication, elle devient une flore lactique dominante après l’affinage et le stockage en réfrigération. Cette aptitude technologique est en relation avec son caractère psychrotrophe et sa faculté à se développer activement à des pH alcalins. Son « alimentarité », testée par la production d’amines biogènes, a montré des niveaux nuls ou très faibles en tyramine et en histamine, comme avec S. thermophilus INRA 302 et avec Lc. lactis DSM 20481. L’optimisation de sa production de flaveurs maltées a été abordée sur milieu TSB-YE et sur lait, supplémentés avec de la leucine, de l’isoleucine ou de la valine. La production de 3-méthylbutanal est la plus importante. Les analyses sensorielles des fromages contenant des niveaux de population importants (108-109 ufc.g-1) de C. maltaromaticum LMA 28 n’ont pas permis de mettre en évidence cet arôme. Présente dans de nombreux fromages français AOC ou non AOC, cette espèce opportuniste, de statut GRAS, pourrait être considérée comme un auxiliaire de fabrication intéressant, car elle permet un ralentissement du vieillissement des fromages, en évitant notamment l’apparition de flaveurs désagréables. Cette flore lactique psychrotrophe pourrait être retenue comme flore bactérienne d’affinage / The C. maltaromaticum LMA 28 bacteria strain, isolated from soft cheese, was observed to possess non conventional lactic bacteria physiological properties. Its growth in TSB YE medium and milk was found to be characterised by the requirements for easily assimilated growth nutrients and a low kinetic rate of lactic acid production from glucose, lactose, fructose and sucrose. In addition, it was found to not metabolise galactose or not excrete it during the hydrolysis of lactose. In the process of milk fermentation, it not only took an unusually long duration but produced products of fragile texture. In order to eventually determine the behaviour of this strain in the process of cheese-making, a selective culture medium CM was developed using an experimental design and PCR techniques for its isolation and identification. The behaviour of C. maltaromaticum LMA 28 was compared with that of two strains of lactic bacteria of technological interest namely Lc. lactis DSM 20481 and S. thermophilus INRA 302, within a wide temperature range (3 to 37°C) and of pH (5.2 – 8.0). Tests carried out in co-culture associating this strain with Lc. lactis DSM 20481 or with S. thermophilus INRA 302 showed that the lactic acid production was due mainly to the growth of the traditional lactic strain. In the process, the C. maltaromaticum LMA 28 slow strain was observed not to be inhibited by acidification. The cheese-making potential of C. maltaromaticum LMA 28 was evaluated in the process of two soft cheese manufactures. Inoculated at various levels of population, it was observed to be present at all manufacturing stages. Generally present at very weak concentrations in the starting milk, it becomes a dominant lactic flora following ripening and refrigeration storage. This technological aptitude is in relation with its psychrotrophic character and its ability to actively develop in alkaline medium. Its “alimentarity”, tested by its ability to produce biogenic amines, showed zero or very low levels in tyramine and histamine, as in the case of S. thermophilus INRA 302 and Lc. lactis DSM 20481. The optimization of its malted flavour production capacity was carried out on a TSB-YE medium and on milk supplemented with leucine, isoleucine or valine. In this process the production of 3-méthylbutanal was observed to be the most abundant product while cheese containing high levels (108-109 ufc.g-1) of C. maltaromaticum LMA 28 did not exhibit this flavour. This notwithstanding, the presence of this species of GRAS status in many French AOC and non AOC cheeses could be considered as an interesting auxiliary in cheese manufacturing process since it tends to slow down the aging process and thereby retard the development of unpleasant flavours. In this respect this strain of psychotrophic lactic bacteria could be retained as a flora for cheese ripening process

De nombreuses pathologies découlent de déséquilibres du microbiote intestinal. Ainsi, des stratégies visent à les prévenir en restaurant cet écosystème par l'apport de probiotiques, de prébiotiques et de synbiotiques. Des résultats prometteurs nécessitant d'être validés rationnellement, nous nous sommes proposés d'établir un premier crible de sélection de bactéries lactiques et de glucooligosaccharides (GOS) pour des activités anti-inflammatoires et anti-prolifératives in vitro. Les probiotiques ont inhibé des pathogènes tout en se révélant résistants aux conditions du tube digestif, tandis que deux GOS ont conduit à leur croissance sélective. De plus, les probiotiques ont réduit la réponse inflammatoire de cellules intestinales et la prolifération de cellules cancéreuses en association avec un GOS. Nous avons donc retenu des produits potentiellement actifs contre les maladies inflammatoires chroniques de l'intestin et du cancer colorectal, par un crible devant être validé in vivo. / Some pathologies are induced by intestinal microbiota disorders. Thus, some strategies aim torestore this ecosystem through probiotics, prebiotics and synbiotics. Promising results need tobe rationally validated, so we aimed to establish the screening first step of lactic acid bacteriaand glucooligosaccharides (GOS) against anti-inflammatory and anti-proliferative activity invitro. Probiotics inhibited pathogens and were resistant to digestive tract conditions whileGOS promoted specifically their growth. Moreover, probiotics reduced inflammatoryresponse of intestinal cells and proliferation of cancer cells when combined with GOS. Thus,we selected compounds potentially efficient against inflammatory bowel diseases andcolorectal cancer, through a screen that need to be validated in vivo

The objective of this research project was to evaluate the mechanical, morphological, and permeability properties of electrospun blends of polydioxanone and poly(lactic acid) for application as vascular grafts. Mechanical analysis was performed by uniaxial tensile testing to examine the peak load, peak stress, elastic modulus, and strain at break of the fibrous materials. The morphological characteristics of the polymer blends were analyzed using phase contrast microscopy, scanning electron microscopy, and image analysis software. Scanning electron microscopy and image analysis software were used to assess fiber diameter and pore size of electrospun scaffolds. Scaffold permeability measurements were also used to calculate fiber diameter and pore size, and the values were compared to those obtained using image analysis. The material property results acquired from the research suggest that the electrospun polymer blends have potential for use in vascular graft applications.