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Nowadays, fat-filled spray-dried dairy powders have acquired an economic importance. Increasing the fat content leads to further quality implications such as off-flavors, and poor rehydration and flowing properties. However, the control of the drying operation and of the powder properties is still rather empirical in this case and few studies have focused on the whole issue up to now. This review aims at giving an overview of research work on fat-filled powders. The so-called "free fat" is often related to fat-filled powders, but the review also highlights the relevance of "surface fat" to powder physical properties. Quantitative and qualitative analytical techniques, mainly referring to free fat, are described here. This review focuses on the specific and combined influence of composition constituents (fat, protein, lactose and mineral elements) and process steps (such as heat treatments, homogenization, drying and storage) on physical properties of fat-filled powders (oxidation, wettability, dispersibility, solubility and flowing properties). free fat / surface fat / spray drying / fat-filled dairy powders / functional properties* Corresponding author (通讯作者): Pierre.Schuck@rennes.inra.fr 188 M.-L. Vignolles et al.peu nombreuses. Cette revue se propose de dresser un état des connaissances sur les poudres laitières enrichies en matière grasse. La matière grasse dite " libre " est souvent associée à ce type de poudres, mais cette revue insiste également sur la notion de " matière grasse de surface " qui semble un paramètre parfois plus pertinent dans l'influence de leurs propriétés physiques. Les techniques analytiques quantitatives et qualitatives de la matière grasse dans les poudres laitières, principalement de la matière grasse libre, sont décrites. Cette revue prend en compte les constituants entrant dans la composition des produits (matière grasse, protéines, lactose et minéraux), les étapes de fabrication (principalement traitements thermiques, homogénéisation, séchage et stockage) et les propriétés physiques des poudres (oxydation, mouillabilité, dispersibilité, solubilité et écoulement), ainsi que les interactions entre ces différents paramètres. matière grasse libre / matière grasse de surface / séchage par atomisation / poudre laitière enrichie en matière grasse / propriété fonctionnelle

Changes in fat properties were studied before, during, and after the drying process (including during storage) to determine the consequences on powder physical properties. Several methods were combined to characterize changes in fat structure and thermal properties as well as the physical properties of powders. Emulsion droplet size and droplet aggregation depended on the homogenizing pressures and were also affected by spray atomization. Aggregation was usually greater after spray atomization, resulting in greater viscosities. These processes did not have the same consequences on the stability of fat in the powders. The quantification of free fat is a pertinent indicator of fat instability in the powders. Confocal laser scanning microscopy permitted the characterization of the structure of fat in situ in the powders. Powders from unhomogenized emulsions showed greater free fat content. Surface fat was always overrepresented, regardless of the composition and process parameters. Differential scanning calorimetry melting experiments showed that fat was partially crystallized in situ in the powders stored at 20 degrees C, and that it was unstable on a molecular scale. Thermal profiles were also related to the supramolecular structure of fat in the powder particle matrix. Powder physical properties depended on both composition and process conditions. The free fat content seemed to have a greater influence than surface fat on powder physical properties, except for wettability. This study clearly showed that an understanding of fat behavior is essential for controlling and improving the physical properties of fat-filled dairy powders and their overall quality.

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-Despite the increasing economic impact of fat-filled dairy powders, their manufacture is still empirical. The aim of the study was to understand the mechanisms responsible for fat supramolecular structure in such a dry matrix. For the purpose, emulsions were obtained under controlled manufacturing conditions. Then, they were dried under different inlet air temperatures, leading to different drying kinetics. Fat droplet size was determined in both emulsions and powders. Free fat and surface fat were assessed to characterize fat in the resulting powders. Confocal laser scanning microscopy was used to characterize fat supramolecular structure in situ in the powder particles. Results showed that fat supramolecular structure in fat-filled dairy powders was connected with drying air temperatures, not necessarily with drying kinetics. Inlet air temperature and consequently temperature of the drying droplet had the most significant influence. Such a study considering drying air temperatures and kinetics is essential in elucidating the mechanisms of free fat formation and the presence of fat at the surface of powder particles. Mechanisms underlying fat supramolecular structure in fat-filled dairy powders are proposed: They can be used as a tool to adjust spray-drying air temperatures and kinetics.spray drying / free fat / surface composition / microstructure / mechanism Article published by EDP SciencesRésumé -Structure supramoléculaire de la matière grasse dans les poudres enrichies : un outil de décision pour ajuster les températures de séchage. Malgré l'intérêt économique croissant pour les poudres laitières enrichies en matière grasse, leur fabrication reste empirique à ce jour. L'objectif de cette étude est de comprendre les mécanismes sous-jacents à la structuration supramoléculaire de la matière grasse dans ce type de poudre. Pour cela, des émulsions ont été fabriquées dans des conditions maîtrisées. Elles ont ensuite été séchées avec différentes températures d'air d'entrée, donnant lieu à différentes cinétiques de séchage. La taille des gouttelettes de matière grasse a été mesurée dans les émulsions et les poudres réhydratées. La matière grasse libre et la matière grasse de surface ont été mesurées pour caractériser la matière grasse dans les poudres. La microscopie confocale à balayage laser a été utilisée pour caractériser la structure supramoléculaire de la matière grasse in situ dans les grains de poudre. Les résultats montrent que la structure supramoléculaire de la matière grasse dans les poudres enrichies est corrélée aux températures d'air de séchage, mais pas systématiquement aux cinétiques de séchage. La température d'air d'entrée et par là, la température de la gouttelette de produit en train de sécher, ont l'influence la plus significative. Une telle étude des températures d'air et des cinétiques de séchage est essentielle dans la compréhension des mécanismes de formation de la matière grasse libre et la présence de matière grasse en surface des grains de poudres. Les mécanismes de formatio...