Made available in DSpace on 2014-06-12T18:01:34Z (GMT). No. of bitstreams: 2 arquivo5613_1.pdf: 3162255 bytes, checksum: bdac9b39b506bae5c929d7b3b3caec94 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Faculdade de Amparo à Ciência e Tecnologia do Estado de Pernambuco / Procederam-se aos desenvolvimentos dos processos catalíticos de hidrogenação e oxidação da lactose tendo em vista a valorização do soro de queijo, fonte biomássica desse sacarídeo. Foram consideradas, via os citados processos, as possibilidades de produções contínuas de polióis e ácidos orgânicos. Soluções aquosas de lactose e soro de queijo pré-tratado e caracterizado foram processadas, recorrendo-se às atividades dos catalisadores de níquel (Ni,14,81% em massa/C) e de paládio (Pd, 0,10%-Bi, 0,68% em massa/C; Pd, 0,16% em massa/SiO2), respectivamente, para hidrogenação e oxidação. Avaliações cinético-operacionais operadas em reatores de leito de lama confirmaram a ocorrência da atividade dos catalisadores e permitiram estabelecer condições de operação em termos de temperatura e pressão, 373K - 433K, 24,0 bar na hidrogenação e 323 - 343K, 1,0 bar na oxidação. Proposições de taxas de reação para as representações dos processos conduziram a ajustes do modelo versus evoluções experimentais, a partir da otimização dos valores das constantes de velocidade de reação e de equilíbrio de adsorção. Na direção da operacionalização dos processos contínuos, utilizou-se um reator trifásico de leito gotejante. Os gases para hidrogenação e oxidação foram hidrogênio e oxigênio, respectivamente e as fases líquidas, contendo lactose (solução, soro de queijo), em presença dos catalisadores de níquel ou de paládio, dependendo da respectiva reação. As condições para a hidrogenação foram 373 433 K, 10,0 bar, 50,0 100,0 L.h-1 de H2, 2,0 L.h-1 de solução e para a oxidação foram 323 - 343 K, 8,0 bar, 25,0 50,0 L.h-1 de O2, 2,0 L.h-1 de solução, NaOH 0,5 M, pH 8 - 9. Predições realizadas através de soluções das equações de modelo, aplicadas em regime estacionário, evidenciando regimes fluidodinâmicos com dispersão axial e molhamento parcial do leito catalítico, foram validadas em comparação com os perfis axiais de concentração de reagentes e produtos presentes na fase líquida, medidos em diferentes posições ao longo do reator. Perfis de concentração calculados e observados indicaram que, na saída do reator, as condições mais apropriadas de produção foram 433 K e 10,0 bar na hidrogenação, com conversão da lactose do soro de 29,28% e rendimento em lactitol de 29,76 %; na oxidação a 343 K e 8,0 bar, conversão da lactose do soro de 50,63% e rendimento em ácido lactobiônico de 37,21%

No description available.

The purpose of this research was to relate lactose reactivity and age gelation of UHT processed concentrated milk. Skim milk was pasteurized, diafiltered batchwise to reduce lactose concentration to less than 0.05%, and UF concentrated to 3X (one-third volume reduction). Lactose and sucrose were then each added at 3% or 6% w/v to part of the concentrate. The five samples, control ( < 0.05% lactose), 3% w/v lactose, 6% w/v lactose, 3% w/v sucrose, and 6% w/v sucrose, were UHT processed at 140°C for 4 s using the indirect heating method. Samples were collected aseptically in presterilized plastic containers and stored at 4°C, 20°C, and 35°C for periodic analysis. All samples stored at 4°C and 20°C gelled after 21 weeks of storage. The viscosity changed slightly during the first 19 weeks of storage but increased suddenly (> 100 cPs) just before gelation. Samples stored at 35°C did not gel but showed sedimentation. Samples stored at 4°C or 20°C underwent little browning; but samples containing 3% and 6% lactose, stored at 35°C, browned considerably. The SOS-PAGE patterns of gelled samples showed new bands because of proteolysis whereas samples stored at 35°C showed bands due to proteolysis and protein crosslinking and a streaking pattern. Electron micrographs of gelled samples showed various casein particles connected together by hairy appendages protruding from the surface of casein particles, to form a continuous three-dimensional network. In non-gelled samples, the micelles were not joined into a continuous network and few hairy appendages protruded from their surfaces. Hairy appendages were not a result of Maillard reaction occurring during storage. Maillard reaction neither provided protection against nor promoted age gelation. Proteolysis was not the only cause for gelation. Protein modifications prevented gelation in samples stored at 35°C. Age gelation was probably a two-step process involving dissociation of proteins from the casein micelles that reformed onto the micelle surface as hairy appendages. Aggregation of the protein particles occurred through these appendages rather than through the original micelle surface.

Lactose in milk has relatively low variation regardless of season, breed, or country. The study of lactose concentration and correlation among other milk components is limited. Furthermore, dairy farmers have limited access to the lactose data and are not familiar with it. This study was conducted to: 1) investigate the phenotypic correlation between lactose and other milk components; and 2) determine the importance of lactose for dairy herds. Monthly DHIA records from Utah (DHIA), Dairy Herd Performance Test (DHTP) records from Ibaraki, Japan, and California herd average data (CHAD) covering 27 states were used to analyze the relationships between milk lactose concentrations and parameters related to milk production. Record spans for each data sets for DHIA, DHTP and CHAD were 7 consecutive years ending August 2017, 12 consecutive years ending August 2017, and 9 consecutive years ending August 2017 respectively. Means for the DHIA records were 187.9 days in milk, 34.6 kg/d milk yield, 4.08% lactose, 3.88% fat, 3.15% protein, 8.86% SNF, 14.4 mg/dl MUN, 256,000 SCC, and 2.4 parity. A negative correlation was observed between lactose concentration and parity (r = -0.27). Positive phenotypic correlations between lactose percentage and milk yield (r = 0.28), and negative correlations with fat (r = -0.17), protein (r = -0.21) and SCC (r = -0.30) were observed. No seasonal fluctuations of milk lactose concentrations were observed. Mean for the DHTP records were 4.55% lactose, 3.95% fat, 3.29% protein, 8.74% SNF, 283 mOsm/kg osmotic pressure, 19,600 bacteria count, and 222,000 SCC. A seasonality in the lactose concentrations were observed, with the lowest concentrations of lactose observed in late summer and fall. There were no phenotypic correlations between lactose concentrations and protein, but a negative correlation with fat (r = -0.12) was observed. A significant negative correlation with SCC (r = -0.28) was also observed. Based on the CHAD records, cows with lower lactose concentrations showed a higher culling rate, which indicates that the milk lactose concentration could be a potential indicator of problems in a dairy herd. This study suggest that lactose level could be an indicator for managing dairy farms. Dairy farmers should be able to access lactose data, and these data should be provided by DHIA.

Two studies were conducted to examine the effects of lactose hydrolysis on freezing point and dipping characteristics of ice cream. The overall research objective was to determine changes in freezing point, texture and ease of dipping ice cream as a result of lactose hydrolysis. It was also the goal of this research to relate observations from the sensory dippability study with hardness and yield stress data to determine if the latter methods could be used as an alternative to human testing of dippability. In the first experiment, ice cream mixes were treated with lactase (EC 3.2.1.23) to cause 0 to 83% lactose hydrolysis. Lactose hydrolysis decreased the freezing point from -1.63oC in the control (0% hydrolysis) to -1.74oC in the 83% hydrolyzed sample (p < 0.05). Firmness decreased from 0.35 J in the control sample to 0.08 J in the 83% hydrolyzed sample. Lactose hydrolyzed samples melted at a faster rate than the control. There was a difference (p < 0.05) in ease of dipping between samples treated with lactase and the control. There were no perceived differences in sweetness and coldness. In the second study, ice cream mixes were treated with lactase (EC 3.2.1.23) from the microbial sources Kluyveromyces lactis and Aspergillus oryzae to cause 0 to 100% lactose hydrolysis. Compression measurements and yield stress as measured by the vane method were both affected by the temperature of the samples. R2 values for compression measurements as related to lactose hydrolysis were higher then those obtained for yield stress measurements. Human evaluation determined a difference (p < 0.05) between the control samples (0% hydrolyzed) and the treatment groups (80% and 100% hydrolyzed). This research demonstrated a relationship between lactose hydrolysis and ease of dipping ice cream. The results implied that the effect of lactose hydrolysis on the dipping characteristics could be evaluated successfully by three different methods: the vane method, compression measurements, and human evaluation. Changes in freezing point due to lactose hydrolysis were minimal, implying that monitoring freezing point is not enough to determine textural characteristics. / Master of Science

No description available.

Dans le présent travail, l’électro-isomérisation du lactose en lactulose a été étudiée. Les variables indépendantes mises à l’étude dans ce projet sont : 1) l’effet de la concentration du lactose (5 et 10%), l’effet de la densité du champ électrique appliqué au réacteur d’électro-activation (100 et 200 mA). L’électro-isomérisation du lactose à 5% a été également comparée à celle observée dans du lactosérum ayant une concentration de lactose ≈ 5%. Les variables réponse principales (variables dépendantes) mises à l’étude étaient le taux de conversion du lactose en lactulose, le taux de formation de sous-produits de la réaction et l'efficacité du procédé exprimée en termes de résistance électrique globale du système d’électro-activation. Une surface totale de l’aire cathodique de 21,5 cm2 a été utilisée, donnant ainsi des densités de courant électrique de 4,65 et 9,30 mA/cm2, respectivement. Les analyses statistiques des données obtenues ont montré que l’effet du temps d’électro-activation sur le taux d’électro-isomérisation du lactose (rendement de formation de lactulose) ainsi que la résistance électrique du réacteur électro-activation était significatif. Le processus d’électro-activation a été réalisé pendant 60 min et des échantillons ont été prélevés chaque 10 min. Les résultats obtenus ont montré la grande efficacité de l'électro-activation, en tant qu’approche novatrice, pour transformer le lactose en lactulose. Après 60 min d’électro-activation à température ambiante (23 +/- 1 °C), 25% de rendement d’électro-isomérisation a été obtenu. En excluant le lactose, la pureté du produit final était de 96,28 +/- 0,18%. En outre, aucune formation d’epilactose n’a été observée. De façon non systématique, du galactose a été détecté dans certains échantillons (&lt; 1,5%) et seulement quelques traces de fructose ont été observées (&lt; 0,31%). La résistance électrique globale du réacteur d’électro-activation diminuait avec l’augmentation du temps d'électro-activation, indiquant une grande efficacité énergétique de cette nouvelle technologie d’isomérisation du lactose en lactulose. / In the present work, electro-isomerization of lactose into lactulose has been studied. Effects of lactose concentration (5 and 10%) and applied DC-electric field (100 and 200 mA) on the electro-isomerization of lactose into lactulose and on process efficiency were investigated. Total cathode area of 21.5 cm2 was used; giving electric current density of 4.65 mA/cm2 and 9.30 mA/cm2, respectively. Milk whey permeate (4.7 +/- 0.15% lactose) obtained by ultrafiltration was also used as feed solution in the electro-activation reactor. The effect of processing time on lactose electro-isomerization rate (lactulose formation yield), by-product (glucose, galactose, epilactose and fructose) formation, and global electric resistance of the electro-activation reactor has been investigated. The process was run during 60 min and samples were taken every 10 min. Obtained results showed the high effectiveness of the developed electro-activation technology to convert lactose into lactulose. After 60 min electro-activation at ambient temperature (23 +/- 1 °C), 25% electro-isomerisation yield was obtained. By excluding lactose, the end product purity was 96.28 +/- 0.18%, which is similar to the pharmakopoeia requirements for lactulose powder. Moreover, no epilactose was formed. Not systematically, galactose was detected in some samples (&lt; 1.5%) and only some traces of fructose were detected (&lt; 0.31%). The global electric resistance of the electro-activation reactor decreased as the electro-activation time was increased indicating the high energetic effectiveness of this new electro-isomerization technology.

Two experiments were conducted to examine the effects of type of milk (whole; nonfat; nonfat, 70% lactose-reduced) and type of egg (fresh, whole egg; egg substitute) on the quality of baked custards. The egg substitute was a combination of dried egg whit e solids, dried low-fat, low-cholesterol egg yolk solids, and xanthan gum. Custard formulations served as prototypes for use in studies conducted in the Department of Food Science and Technology, Virginia Tech. In those studies, the effects of processing parameters on the quality of the custards were examined. The goal of all the studies was to develop shelf-stable lactose-reduced custard mixes that have potential for use in the foodservice industry. In Experiment I, chemical, physical, and sensory characteristics of a dessert type baked custard, made with sucrose, were examined. In Experiment II, the same characteristics were examined for a cheese flavored, entree type custard made without sucrose. Results indicate that use of nonfat and nonfat, 70% lactose-reduced milk in place of whole milk decreased significantly total fat and cholesterol concentrations in both types of custard mixes. Lactose-reduced milk also decreased lactose and increased galactose concentrations. The egg substitute decreased total fat and cholesterol concentrations and increased protein concentration. In general, lactose reduction had little effect on the physical and sensory characteristics of both types of custards, but the egg substitute affected these characteristics. Custards made with the egg substitute had less intense yellow color and greater gel strength than those made with fresh, whole egg. These custards also were less bright and more uneven in color and had weaker egg flavor and aftertaste. Based on results of this study, development of a lactose-reduced custard is feasible. However, additional studies are needed to examine potential for use of the formulations in the foodservice industry. Because the mixes could be used as bases for other types of products, such as custard pies, filled pastries, and quiches, studies that focus on development of those products could help define the niche for the mixes in the foodservice industry. Because of the trend in today1s market for reduced-fat, reduced-cholesterol foods, additional studies could be done to examine the effects of various types of egg substitutes on the quality of the custards. / Master of Science

Le surplus mondial et le faible prix du lactose ont attiré l’attention de chercheurs et de l’industrie pour développer des procédés novateurs pour la production de dérivés du lactose à valeur ajoutée, tels que l’acide lactobionique (ALB), qui est un produit à haute valeur ajoutée obtenu par l’oxydation du lactose, avec d’excellentes propriétés pour des applications dans les industries alimentaire et pharmaceutique. Des recherches sur la production d’ALB via l’oxydation catalytique du lactose avec des catalyseurs à base de palladium et de palladium-bismuth, ont montré des bonnes conversions et sélectivités envers l’ALB. Cependant, le principal problème de ces catalyseurs est leur instabilité par lixiviation et désactivation par suroxydation au cours de la réaction. Les catalyseurs à base d’or ont montré une meilleure performance que les catalyseurs de bismuth-palladium pour l’oxydation de glucides. Cependant, trouver un catalyseur robuste pour l’oxydation du lactose est encore un grand défi. Dans cette dissertation, des nouveaux catalyseurs à base d’or supportés sur des matériaux mésostructurés de silicium (Au/MSM) ont été synthétisés par deux méthodes différentes, et évalués comme catalyseurs pour l’oxydation du lactose. Les catalyseurs ont été caractérisés à l’aide de la physisorption de l’azote, DRX, FTIR, TEM et XPS. Les effets des conditions d’opération, telles que la température, le pH, la charge d’or et le ratio catalyseur/lactose, sur la conversion du lactose ont été étudiés. Finalement, le procédé de déminéralisation de la solution de lactobionate de sodium à la sortie du réacteur a été étudié à l’aide de deux approches: l’électrodialyse avec des membranes bipolaires (EDMB) et la technologie d’échange d’ions. Des catalyseurs Au/MSM hautement actifs ont été synthétisés avec succès par la co-condensation d’un mélange de bis [3-(triéthoxysilyl) propyle] tétrasulfide (BTESPTS), tétra-éthyle ortho-silicate (TEOS) et le précurseur d’or (HAuCl4) en milieu acide, avec le tribloc co-polymère EO20PO70EO20 utilisé comme agent structurant. Il a été trouvé que l’augmentation du ratio molaire BTESPTS/TEOS provoque un changement dans la structure des matériaux, laquelle passe d’une structure 2D-hexagonal très ordonnée à une structure mixte de type hexagonal-vésicule et mousse cellulaire. Dans les conditions opératoires optimales (charge d’or = 0.7% en poids, T = 65ºC, catalyseur/lactose ratio = 0.2, pH = 8-9, débit d’air = 40 mL·min-1), le lactose a été complètement converti en ALB après 80-100 min de réaction, lorsqu’on a utilisé les catalyseurs synthétisés à partir des mélanges contenant une concentration molaire de BTESPTS entre 6-10%. Ces catalyseurs ont été caractérisés par une structure de type « wormhole-like », favorable pour l’accessibilité des réactifs aux nanoparticules d’or (AuNPs) d’environ 8 nm intercalées dans les murs de la silice. AuNPs d’environ 5-6 nm ont été aussi chargées avec succès sur les matériaux mésoporeux SBA-15 et SBA-15-CeO2, par l’adsorption du complexe [Au(en)2]3+ (en=éthylènediamine) en milieu alcalin. Ces catalyseurs ont conservé la structure hexagonale 2D très ordonnée typique de la SBA-15, et ils ont présenté une grande activité pour l’oxydation du lactose. Après 60 min de réaction, les catalyseurs Au/SBA-15-CeO2 (ratio molaire Ce/Si = 0.2) ont présenté l’activité catalytique la plus élevée (100% conversion du lactose) et 100% de sélectivité envers l’ALB, lorsqu’ils ont été utilisés dans les conditions optimales décrites ci-dessus. Ces résultats suggèrent que l’oxyde de cérium joue un rôle dans l’augmentation de l’activité catalytique, où la coordination et les états d’agglomération des atomes du Ce pourraient avoir un effet important. En général, les résultats des analyses XPS sur les états d’oxydation de l’or à la surface des Au/MSM, ont montré la coexistence d’espèces d’or métalliques et oxydées, avec une abondance relative suivant l’ordre Au0 &gt; &gt; &gt; Au+1 &gt; Au+3. Dans le cas des catalyseurs Au/SBA-15-CeO2, la présence des deux états d’oxydation Ce3+ et Ce4+ a été aussi observée. Les expériences de recyclage des catalyseurs ont montré que l’activité des échantillons Au/SBA-15 et Au/SBA-15-CeO2 a été significativement réduite (40-65%) après des cycles de réaction d’oxydation consécutifs, lorsque le lavage avec de l’eau a été utilisé comme procédé de régénération. Par contre, les catalyseurs ont conservé leur activité catalytique, en utilisant la calcination comme méthode de régénération, ce qui indique qu’une des causes de désactivation des catalyseurs Au/MSM pourrait être due à une forte adsorption d’espèces organiques sur la surface des catalyseurs. De plus des quantités significatives d’or ont été trouvées dans la solution après des cycles de réaction consécutifs, ce qui démontre la désactivation est aussi due à la lixiviation de la phase active dans la solution de réaction. Les données expérimentales ont révélé que tant l’EDMB que la technologie d’échange d’ions pourraient être utilisées pour produire l’ALB à partir de son sel de sodium. Cependant, en tenant compte du fait que l’EDMB a été utilisée pour la première fois pour cette application, ce procédé a donc besoin d’une amélioration pour des applications industrielles. En effet, une déminéralisation de 50% a été atteinte après l’application d’une différence de potentiel de 5.0-5.5 V pendant 100-180 min aux bornes d’une cellule d’électrodialyse à trois compartiments, tandis que la solution de lactobionate de sodium a été complètement dépourvue de sodium après 10-30 min, lorsqu’on a utilisé une résine échangeuse de cations commerciale fortement acide (AmberliteTM FPC23 H). / The worldwide surplus and low cost of lactose have drawn the attention of researchers and industry to develop innovative processes for the production of value-added lactose derivatives, such as lactobionic acid (LBA), which is a high value-added product obtained from lactose oxidation, with excellent properties for applications in the food and pharmaceutical industries. Investigations on LBA production by means of catalytic oxidation of lactose over palladium and bismuth-palladium supported catalysts have shown good conversion rates and selectivities towards LBA, but the main problem of these catalysts is their instability by leaching and deactivation by over-oxidation during the reaction. Supported gold catalysts have shown to outperform palladium and bismuth-palladium catalysts for the oxidation of carbohydrates. However, there is still a big challenge in finding a robust catalyst for the lactose oxidation. In this dissertation, new gold catalysts supported on mesoporous silica materials (Au/MSM) have been synthesized by two different methods, and evaluated as catalysts in the oxidation of lactose. The catalytic materials were characterized by nitrogen physisorption, XRD, FTIR, TEM and XPS. The effects of the operating conditions such as temperature, pH, gold loading and catalyst/lactose ratio on the lactose conversion were investigated. Finally, the demineralization process of the sodium lactobionate solution obtained at the reactor outlet has been studied using two approaches: bipolar membrane electrodialysis (BMED) and ion-exchange technology. Highly active Au/MSM were successfully formulated by the co-condensation of a mixture of bis [3-(triethoxysilyl) propyl] tetrasulfide (BTESPTS), tetraethyl orthosilicate (TEOS) and the gold precursor (HAuCl4) in acidic media, using the triblock co-polymer EO20PO70EO20 as template. It was found that by increasing the BTESPTS/TEOS molar ratio, the structure of the synthesized materials changed from a highly ordered 2D hexagonal structure to a mixed hexagonal-vesicle and cellular foam structure. Under the optimal operating conditions (gold loading = 0.7%wt, T = 65ºC, catalyst/lactose ratio = 0.2, pH = 8-9, air flow = 40 mL·min-1), the lactose was completely converted into LBA after 80-100 min reaction, when using the catalysts synthesized from mixtures containing 6-10% molar concentration of BTESPTS. These catalytic materials were characterized by the predominance of a wormhole-like structure, favorable for the reagent accessibility to the gold nanoparticles (AuNPs) of about 8 nm intercalated in the silica walls. AuNPs of about 5-6 nm were also successfully loaded of mesoporous SBA-15 and SBA-15-CeO2 materials, by the wet adsorption of the gold cationic complex [Au(en)2]3+ (en=ethylenediamine) in alkaline media. These catalysts retained the well-ordered 2D hexagonal structure typical of SBA-15, and showed high activity to lactose oxidation. After 60 min of reaction, the Au/SBA-15-CeO2 catalysts (Ce/Si = 0.2) showed the highest catalytic activity (100% lactose conversion) and 100% selectivity towards LBA, when used at the optimal operating reaction conditions described above. These results suggest that ceria plays a role in the enhancement of the catalytic activity, where the coordination and agglomeration states of Ce atoms could have an important effect. In general, the XPS study on the oxidation states of gold on the Au/MSM surfaces revealed the coexistence of metallic and oxidized Au species, whose relative abundance followed the order Au0 &gt; &gt; &gt; Au+1 &gt; Au+3. In the case of Au/SBA-15-CeO2 catalysts, the presence of both Ce3+ and Ce4+ oxidation states was also observed. Catalysts’ recycling experiments showed that the activity of Au/SBA-15 and Au/SBA-15-CeO2 was significantly reduced (40-65%) after consecutive oxidation reaction cycles, when washing with water was used as regeneration process. On the contrary, these catalytic samples conserved their catalytic activity when calcination was used as regeneration method, indicating that one of the causes of deactivation of Au/MSM might be the strong adsorption of organic species on the catalyst surface. Moreover, significant amounts of Au were found in the solution after consecutive reaction cycles, demonstrating that the leaching of the active phase into the reaction solution is another important cause of the catalyst’ deactivation. Experimental data showed that both BMED and ion exchange technology might be used for producing LBA from its sodium salt. However, taking into account that it is the first time that BMED is used for this application, this process still needs further improvement for industrial applications, since a demineralization rate of 50% was achieved after applying a voltage difference of 5.0-5.5 V during 100-180 min to a three-compartment electrodialysis stack, while a complete sodium removal was achieved after 10-30 min when using a commercial strong cation exchange resin (AmberliteTM FPC23 H).

L'amélioration de la digestion de lactose est une allégation "santé" liée aux ferments viviants du yaourt : Streptococcus thermophilus (S. thermophilus) et Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) validée par l'EFSA en 2010. La physiologie de S. thermophilus et de L. bulgaricus est connue dans le lait et particulièrement le yaourt, alors qu'elle n'a été que peu étudiée dans le tractus digestif (TD). Mon travail de thèse est basé sur l'hypothèse de travail suivante : l'utilisation de modèles animaux gnotobiotiques permet de mieux connaître la physiologie des bactéries lactiques et de proposer des mécanismes d'action de leurs effets "santé". La stratégie a donc été d'obtenir des animaux mono-associés avec chacune des deux bactéries du yaourt ou les deux en même temps. Les principaux résultats obtenus sont : 1/ S. thermophilus colonise le TD en s'adaptant progressivement à l'environnement colique et y induit une glycolyse massive et une production de lactate. La glycolyse est la signature majeure de S. thermophilus dans le TD et le lactate pourrait être est la molécule "signal" qui induit une réponse chez l'hôte par une augmentation des transporteurs de mono-carboxylates (SLC16A1 et SLC5A8) et d'une protéine impliquée dans l'arrêt du cycle cellulaire p27kip1. 2/ L'apport de lactose stimule la colonisation du TD, la glycolyse ainsi que la production de L-lactate par S. thermophilus in vivo. 3/ Contrairement à ce qui est observé pour S. thermophilus, L. bulgaricus ne s'implante pas en absence de lactose. Quand les deux bactéries sont en co-culture, S. thermophilus est toujours avantagé numériquement par rapport à L. bulgaricus aussi bien in vitro qu' in vivo. Au niveau nutritionnel, tous nos résultats sont cohérents avec les allégations "santé" du yaourt avec un effet prébiotique du lactose. L'étude d'animaux gnotobiotiques a permis de proposer des nouvelles voies de régulation du métabolisme des sucres de bactéries lactiques et de nouvelles voies moléculaires (via le lactate) par lesquelles des bactéries lactiques et de nouvelles voies moléculaires (via le lactate) par lesquelles des bactéries lactiques pourraient influencer la physiologie de l'hôte. / *