Master of Science / Food Science Institute / Jayendra K. Amamcharla / Milk protein concentrate (MPC) powders are high-protein dairy ingredients obtained from membrane filtration processes and subsequent spray drying. MPC powders have extensive applications due to their nutritional, functional, and sensory properties. However, their flow properties, rehydration behavior, and morphological characteristics are affected by various factors such as processing, storage, particle size, and composition of the powder. Literature has shown that knowledge about the powder flowability characteristics is critical in their handling, processing, and subsequent storage. For this study, FT4 powder rheometer (FT4, Freeman Technologies, UK) was used to characterize the flowability of MPC powders during storage. This study investigated the flowability and morphological characteristics of commercial MPC powders with three different protein contents (70, 80, and 90%, w/w) after storage at 25ºC and 40ºC for 12 weeks. Powder flow properties (basic flowability energy (BFE), flow rate index (FRI), permeability, etc.) and shear properties (cohesion, flow function, etc.) were evaluated. After 12 weeks of storage at 40ºC, the BFE and FRI values significantly increased (P < 0.05) as the protein content increased from 70 to 90% (w/w). Dynamic flow tests indicated that MPC powders with high protein contents displayed higher permeability. Shear tests confirmed that samples stored at 40ºC were relatively less flowable than samples stored at 25ºC. Also, the lower protein content samples showed better shear flow behavior. The results indicated that MPC powders stored at 40ºC had more cohesiveness and poor flow characteristics than MPC powders stored at 25ºC. The circle equivalent diameter, circularity, and elongation of MPC powders increased as protein content and storage temperature increased, while the convexity decreased as protein content and storage temperature increased. Overall, the MPC powders evidently showed different flow properties and morphological characteristics due to their difference in composition and storage temperature. Literature has shown various methods for determining the solubility of dairy powders, but it requires expensive instruments and skilled technicians. The front-face fluorescence spectroscopy (FFFS) coupled with chemometrics could be used as an efficient alternative, which is commonly used as fingerprints of the various food products. To evaluate FFFS as a useful tool for the non-destructive measurement of solubility in the MPC powders, commercially procured MPC powders were stored at two temperatures (25 and 40ºC) for 1, 2, 4, 8, and 12 weeks to produce powders with different rehydration properties, which subsequently influenced their fluorescence spectra. The spectra of tryptophan and Maillard products were recorded and analyzed with principal components analysis. The solubility index and the relative dissolution index (RDI) obtained from focused beam reflectance measurement was used to predict solubility and dissolution changes using fluorescence spectra of tryptophan and Maillard products. The solubility index and RDI showed that the MPC powders had decreased solubility as the storage time and temperature increased. The results suggest that FFFS has the potential to provide rapid, nondestructive, and accurate measurements of rehydration behavior in MPC powders. Overall, the results indicated that solubility and dissolution behavior of MPC powders were related to protein content and storage conditions that could be measured using FFFS.

Le lait de chamelle constitue l'une des principales ressources alimentaires pour les peuples nomades. Malgré sa richesse en différents composants et sa production non négligeable au niveau mondial, ce produit demeure relativement peu transformé à cause du manque d’études menées sur les caractéristiques et les aptitudes technologiques de ce lait.Dans la première partie de cette thèse, l’évolution de la structure au cours de la coagulation enzymatique et acide des laits de chamelle et de vache crus et chauffés (50 et 70 °C) enrichis en minéraux (calcium et phosphate) a été étudiée. Les cinétiques de coagulation enzymatique et acide des échantillons du lait ont été suivies aux moyens du test de cisaillement dynamique et de la spectroscopie de fluorescence frontale. Les résultats obtenus ont permis, d’une part, de montrer des différences significatives entre les propriétés du coagulum obtenu à partir du lait de chamelle et celui du lait de vache, et d’autre part, d’évaluer l'impact de l’ajout des minéraux (calcium et phosphate) sur les propriétés du coagulum. L’analyse des spectres de fluorescence par analyse en composantes principales (ACP) a permis de caractériser sur le plan moléculaire la structure des gels, et également de discriminer les différentes conditions de coagulation. Les résultats rhéologiques ont montré que l’enrichissement de ces deux types de lait avec le calcium améliorait la fermeté du gel et diminuait le temps de gélification, alors que des effets inverses ont été observés suite à l’ajout du phosphate. L’analyse conjointe des données spectrales et rhéologiques au moyen de l’analyse en composantes communes et poids spécifiques (ACCPS) a montré une forte relation entre la structure au niveau moléculaire et la texture au niveau macroscopique. La deuxième partie de cette thèse a porté sur l’impact du traitement thermique (55 à 75 °C à différents intervalles de temps) sur les changements moléculaires du lait de chamelle. L’application de l’ACCPS aux spectres de la vitamine A, des produits fluorescents de la réaction du Maillard (PFRM) et du NADH a montré une bonne discrimination des échantillons en fonction du couple température-temps. Les résultats obtenus montrent que, de par sa rapidité, la spectroscopie de fluorescence frontale couplée aux méthodes chimiométriques présente un potentiel intéressant pour la caractérisation du lait de chamelle dans différentes conditions. En outre, le spectre de fluorescence d’un lait pourrait être considéré comme une empreinte digitale de celui-ci permettant de l’identifier. / Camel milk is one of the main food resources for nomadic people. Despite its richness in different components and its production in the world, this product remains poorly processed because of the lack of studies conducted on the characteristics and the technological abilities of this milk. In the first part of this thesis, the evolution of the structure during the enzymatic and acid coagulation of raw and heated (50 and 70 °C) camel and cow’s milk following the addition of minerals (calcium and phosphate) was studied. The kinetics of acid and enzymatic-induced coagulation of milk were followed using shear dynamic testing rheology at the macroscopic level and front-face fluorescence spectroscopy at the molecular scale. The obtained results showed significant differences between the properties of the coagulum that depends on the milk species and the level of added minerals (calcium and phosphate). The analysis of spectral data by principal component analysis allowed to characterize the coagulum structure at the molecular level as well as the discrimination of different coagulation conditions. The rheological results showed that the enrichment of both types of milk with calcium improved the gels firmness and reduced the gelation time, while opposite trend was observed following the addition of phosphate. The joint analysis of fluorescence spectral data and rheological measurements by applying common components and specific weights analysis showed a strong relationship between the structure at the molecular scale and the texture at the macroscopic level. The second part of this thesis focused on the impact of heat treatment (55 to 75 °C at different times) on the molecular changes in camel milk. The application of common components and specific weights analysis to the vitamin A, fluorescent Maillard reaction products and NADH fluorescence spectra enabled the discrimination of milk samples according to the temperature and time. The obtained results showed that front-face fluorescence spectroscopy coupled with chemometric tools enabled the characterization of camel milk in different conditions. Additionally, the fluorescence spectrum recorded on milk could be considered as a fingerprint allowing its identification.