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Ce travail de thèse a permis la mise au point d'un procédé d'encapsulation de bactéries probiotiques dans des matrices ne contenant que des ingrédients laitiers. L'étude à l'échelle laboratoire puis, le dimensionnement du procédé à l'échelle pilote ont permis la production de microparticules stables dans des milieux aqueux et résistantes à des conditions simulant l'estomac. La nature des protéines présentes mais également leurs proportions ont influencé la localisation des bactéries dans les microparticules : à la surface pour une matrice uniquement composée de caséine et à l'intérieur pour une matrice composée à la fois de caséines et de protéines solubles. L'interprétation de ces résultats par une étude à l'échelle moléculaire des interactions qui s'établissent entre les bactéries probiotiques et les protéines laitières a été possible grâce à l'utilisation de la microscopie à force atomique. Les protéines solubles interagissent de façon spécifique avec les bactéries alors que les caséines interagissent de façon non spécifique. De même, la présence de pili à la surface de la bactérie est favorable à la l'établissement d'interactions fortes entre LGG et les protéines solubles. Ce travail a donc permis d'expliquer des résultats obtenus à l'échelle macroscopique (taux d'encapsulation et de survie dans des conditions gastriques) grâce à des observations microscopiques et une étude à l'échelle nanoscopique des interactions entre les différents composants. Cette approche multi-échelle a élucidé certains mécanismes régissant l'encapsulation de bactéries probiotiques dans des matrices laitières / In this work thesis, an encapsulation process for probiotic bacteria using only milk proteins is developed. The laboratory scale followed by a pilot and an industrial scale development of the process allow the production of stable and resistant microparticles both in aqueous and gastric media. The nature and quantities of proteins added is found to influence the bacterial location in the microparticles. The bacteria are located mostly at the surface when only caseins are present. Oppositely, well encapsulated bacteria are observed when addition of whey proteins are performed. A molecular study of interactions established between milk proteins and bacteria is possible with the use of atomic force microscopy. Whey proteins are found to specifically interact with bacteria whereas the caseins establish non-specific links. In addition, the presence of piliated bacteria is found favorable to establish strong and long interactions between proteins and bacteria. This work permits the interpretation of results obtained at a macroscale (encapsulation rate and bacterial survival in stomach conditions) thanks to microscopic observations and nanoscopic interactions study. This multiscale approach permits the elucidation of mechanisms driving the probiotic encapsulation in milk matrices

A UHT -processed skim milk (85%)/orange juice (15%) drink was developed. Product integrity and stability were maintained by two methods. Proper homogenization of the blend before UHT processing stabilized a drink formulation containing .25% carboxymethyl cellulose and .025% carrageenan. Adjusting the pH of the blend (pH 6.3 and 6.5) resulted in a different stabilization. After 28 days at room temperature, settling of milk solids was 5.2% of volume height in the prehomogenized sample and 86.9% of volume height in the same blend that had not been homogenized prior to UHT processing. After storage, the two treatments were analyzed to verify that there was no perceived textural difference between the pH adjusted and unadjusted blends. A consumer product acceptability evaluation resulted in a split population, and more panelists liked the product than disliked it.

This research investigates the protein interactions that occur when soy protein is added to milk and subjected to renneting or heating. Milk was fortified with 20% soy protein and enzymic coagulation studied at 35°C at various pH's and CaCl2 levels. The first part deals with the interaction between milk and soy proteins during rennet-induced milk coagulation. The first goal was to determine how soy proteins affected milk coagulation. The effects of native versus heat-denatured soy proteins on rennet coagulation time and curd firmness were compared. lmmunogold labeling along with transmission electron microscopy was used to identify and localfze soy proteins in coagulated milk. Partitioning of ß-conglycinin and glycinin, the two main soy protein fractions, between cheese and whey was determined by electrophoresis. Soy proteins affected milk coagulation to the greatest extent at pH 6.6. Both heat-denatured and native soy proteins increased rennet coagulation time. Only heat-denatured soy proteins affected final curd firmness. Most of ß-conglycinin was lost in whey, whereas glycinin was retained in curd. Soy proteins existed in the curd as aggregates that were less electron dense than casein micelles. At pH 6.6, heat-denatured soy proteins were fibrous and adhered to the surfaces of casein micelle, preventing direct micelle-micelle contact. This would delay aggregation rate and decrease curd firmness by decreasing the number and strength of links between casein micelles. Native soy proteins did not bind to the casein micelles but rather were physically trapped within curd. Their effect of delaying aggregation is thought to be a function of their binding of calcium. Adding CaCl2 or lowering the pH to 6.3 or 6.0 helped restore coagulation properties. The second goal was to determine what heat-induced interaction occurs between milk and soy proteins, specifically between κ-casein and glycinin. Both κ-casein and glycinin are heat labile and form insoluble aggregates when heated. When glycinin and κ-casein were heated together, some acidic polypeptides of glycinin crosslinked with κ-casein via disulfide linkages. However, when disulfide linkage was prevented by adding ß-mercaptoethanol , non-covalent interactions between κ-casein and both acidic and basic polypeptides of glycinin occurred that prevented the heat precipitation of glycinin. This non-covalent interaction between glycinin polypeptides and κ-casein may explain why the heat-treated soy proteins became attached to the surfaces of casein micelles during rennet coagulation of milk.

This thesis examines the signaling pathways involved in the regulation of milk protein synthesis in the lactating mammary gland and their control. The protein synthetic machinery can be regulated during the transcription, translation and degradation stages of mRNA processing. Translation control in eukaryotes involves changes in the activity or other functional properties of the translation factors. These include proteins involved in initiation, peptide-chain elongation and termination of mRNA processing. Changes in the nutritional, physiological and hormonal status of the body are sensed by receptors that signal to a central protein, known as mammalian target of rapamycin (mTOR). The mTOR signaling pathway then activates or inhibits the activity of translation factors and kinases involved in the initiation and elongation stage of translation. A major objective of this thesis was to elucidate which genes and pathways are involved in the regulation of milk protein synthesis in the mammary gland and the mechanism(s) that regulate their action. The results presented here show that changes in milk protein production occurring during lactation in response to external stimuli are potentially regulated at the level of translation or subsequent processing rather than by transcriptional regulation (mRNA abundance). The results also show that in response to growth hormone (GH) treatment, which increased the yield of milk protein, the phosphorylation status of the ribosomal protein S6 (S6) is increased as well as the protein abundance of eukaryotic elongation factor 2 (eEF2) and eukaryotic initiation factor 4E (eIF4E). These results suggest an important relationship between milk protein yield and changes in the initiation and elongation stages of translation. Another major finding was the elucidation that mTOR is involved in the signaling pathways activated by GH and that this effect involves signaling through the PI-3 kinase pathway. In these experiments, increased protein synthesis was potentially achieved with the use of GH. Thus, this study suggests the mTOR signaling pathway is a key mediator of the GH effects in protein synthesis stimulation. Finally, the requirement for a functional mTOR signaling (TOS) motif in the eukaryotic initiation factor 4E binding protein (4E-BP1) was identified. This finding could help the identification of other proteins that may be controlled by mTOR and consequently are regulators of mRNA translation. In summary, this thesis unveils key signaling pathways involved in the regulation of milk protein synthesis and provides further insight into the control of the mTOR signaling pathway. These findings open new frontiers for the manipulation of milk composition.

Typescript (photocopy) By using a regression equation relating the difference between dye binding and Kjeldahl values with the total protein concentration of the milk, the accuracy of estimates of casein in milk from individual cows was improved.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2010. / Härtill 4 uppsatser.

Typescript (photocopy) / xv, 210 leaves, [2] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / By using a regression equation relating the difference between dye binding and Kjeldahl values with the total protein concentration of the milk, the accuracy of estimates of casein in milk from individual cows was improved. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Physiology, 1981

This thesis was developed to study the influence of polymorphic variants of the milk protein locus betacasein (BCN) on the production and technological quality of the milk. The genotypes of -casein (CSN2 gene) were determined by the PCR-RFLP analysis. The determination of genotypes AA, AB and BB was made in 731 dairy cows. The results of genotype frequencies showed that genotype BB represented roughly five times more frequently than the heterozygotes AB and thirty times more frequently than AA homozygotes in the population under study. The effect of the BCN genotypes on the production and composition of milk was analyzed in 418 samples. No statistically significant effect of genotypes or alleles was found in this section. Subsequent analysis of the influence of genotypes and allele on the coagulation and the determination of titratable ability of the milk was performed on 119 samples. The results did not confirm a statistically significant effect on milk coagulation. The yogurt test showed genotypic effects. This could mean that genotype AA is associated with higher milk acidity and AB genotype with lower. However, the results could be affected by lower frequency of the population and an uneven frequency of genotypes in the population surveyed.