Structure function changes of casein micelles were studied as a function of concentration using a non invasive concentration method, osmotic stressing. A combination of serum analysis, light scattering and rheological measurements were used to characterize the physico-chemical properties of casein micelles. In heated and unheated milk, rheological studies indicated that casein micelles behave as hard spheres of similar volume fractions, if the viscosity changes in the serum phase and the particle particle interactions are taken into account. The differences in the distribution of the heat induced complexes between colloidal and soluble phase affected the colloidal properties of casein micelles. Above 70 g L-1 protein, the protein particles were no longer free diffusing. Re-dilution of the suspensions showed no irreversible aggregation. The data suggested that in the range of concentration studied casein micelles behave as hard spheres. Age gelation was also investigated on heated and unheated concentrated milk. In unheated concentrated milk proteolysis played an important role in imparting an increase in viscosity by causing aggregation of the casein micelles. On the other hand, in heated milk, there was a significant effect of the whey protein aggregates, which increased their interaction with the casein micelles over time. This effect, together with proteolysis caused age gelation in heated concentrated milk. The method of concentration used in this research, osmotic stressing, was then compared to ultrafiltration. It was demostrated that these two methods are not equivalent, as shear and mixing during ultrafiltration cause rearrangements to the casein micells. The differences were clearly demonstrated by adding soluble caseins to the milk before or after concentration. This project brings a better understanding on the effects of concentration on the structure-function of casein micelles and the interactions occurring in milk proteins during concentration.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21811号 / 農博第2324号 / 新制||農||1066(附属図書館) / 学位論文||H31||N5183(農学部図書室) / 京都大学大学院農学研究科農学専攻 / (主査)教授 松村 康生, 教授 白岩 立彦, 教授 丸山 伸之 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23248号 / 農博第2455号 / 新制||農||1084(附属図書館) / 学位論文||R3||N5338(農学部図書室) / 京都大学大学院農学研究科農学専攻 / (主査)教授 松村 康生, 教授 丸山 伸之, 教授 谷 史人 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Les micelles de caséines, composées de caséines, minéraux et eau, sont en équilibres dynamiques, elles échangent en permanence de leur matière avec leur environnement. Les micelles de caséines possèdent d’intéressantes fonctionnalités pour la fabrication de produits laitiers, telles que leur capacité à stabiliser des émulsions et à former des gels sous l’action de la présure. Des changements environnementaux, variations de pH, additions de sels ou d’agents chélatants, affectent les équilibres des micelles et induisent des modifications de leurs compositions et propriétés colloïdales. Ces changements modifient également leurs propriétés fonctionnelles, bien que cet aspect soit peu décri. Le but de ce projet était de comprendre les relations liant l’environnement, l’équilibre minéral, les propriétés colloïdales et fonctionnelles des micelles de caséines. L’impact de cinq facteurs (pH, Na3Cit, NaCl, CaCl2, MgCl2) modifiant les micelles fut étudié en focalisant sur leurs propriétés émulsifL’acidification et l’addition de Na3Cit ont causé les modifications minérales les plus importantes en solubilisant le phosphate de calcium micellaire. Le premier conduisit au « gonflement » des micelles alors que l’agent chélatant causa leur dissociation en petits agrégats. L’ajout de NaCl n’eut aucun impact sur le contenu minéral des micelles mais provoqua aussi la libération d’agrégats, révélée par cryo microscopie électronique et diffusion de rayons-X aux petits angles. Le rôle du phosphate de calcium sur les fonctionnalités fut confirmé et l’étude révéla l’importance de contrôler la libé / Caseins micelles, composed of caseins, minerals and water, are under dynamic equilibria, they constantly exchange materials with their surrounding environments. In addition, casein micelles possess valuable functionalities in regards to the formation of dairy products, such as the ability to stabilize emulsions or to form rennet gels. Environmental changes, such as variations in pH, additions of salts or chelating agents, affect the casein micelles equilibria and lead to modifications in their compositional and colloidal properties. Such changes also modify their functional properties, although this aspect is poorly described in the literature. This project aimed to understand the relationships that link the environmental modifications, the mineral balance, the colloidal and functional properties of the casein micelles. The impact of five modifying factors (pH, Na3Cit, NaCl, CaCl2, MgCl2) of the casein micelles were studied and the focus was placed on emulsion and rennet coagulation fuThe former only induce the swelling of casein micelles while the latter led to their disruption into smaller aggregates. NaCl had no impact on the micellar mineral content but also caused the release of small aggregates, as revealed by electronic microscopy and small angle X-ray scattering analyses. The decisive role of micellar calcium phosphate on the functionalities was confirmed and this study highlighted the importance of monitoring the release of small aggregates, as they strongly affected emulsions stability and gels firmness. CaCl2 and MgCl2 additions slightly increased the mineral c