Résumé
2.1 About 200 million tons of whey are produced worldwide each year, and the production is constantly increasing. Whey is a by-product rich in proteins, lactose and minerals, but its composition largely varies depending on its manufacturing process. To be valorized, whey is usually processed into whey powder, protein concentrate and lactose by a spray-drying step. However, the high level of organic acids in acid wheys has an influence on the amorphous form of lactose. Consequently, its hygroscopicity is greater and affects its behavior upon drying, leading to caking tendency and poorly rehydratable powder for further purposes. Pressure- and electrically driven membrane technologies are capable of fractionating the whey components to enhance its powder quality and obtain high-value products. In this chapter a quick presentation of the main membrane technologies will be given as well as an overview of research studies dealing with these technologies, prior to the drying step of whey, for demineralization, delactozation and/or deacidification. Depending on the case, the technology and the objective of the study, about 50–95% of minerals, 50–60% of lactose and 30–80% of lactic acid could be removed from the whey, enhancing its dryability and reducing drastically the energy consumption costs up to 40%.2.2 In the dairy industry, concentration by vacuum evaporation is widely used for the production of concentrated products, such as evaporated milk, sweetened condensed milk and concentrated yoghourt. It is also implemented as an intermediate step for the manufacture of powders. The operation is carried out predominantly in falling-film evaporators that can be considered as a combination of vertical shell-and-tube heat exchangers. This book chapter provides an overview of the vacuum concentration operation; it is composed of four main parts. Section 2.2.1 describes the working principles and the design of the evaporators directed towards energy savings. Section 2.2.2 focuses on the physicochemical and structural changes induced by the evaporation process, while Section 2.2.3 deals with the flow and heat transfer phenomena involved in the operation. Lastly, Section 2.2.4 discusses the fouling and cleaning of evaporators, as fouling problems occur after several hours of production runs as for any heat exchanger, requiring appropriate cleaning procedures to recover their optimal performances.2.3 Lactose crystallization in whey or permeate is a key stage in the manufacture of whey, permeate and lactose powders. Controlling this stage at an industrial level should increase the prospects of improving the process and also the physicochemical quality of powders. Lactose crystallization occurs in highly supersaturated solutions, indicating that the phenomena of nucleation and crystal growth can take place simultaneously. At an industrial level, lactose crystallization is also performed in a medium of complex chemical composition. Some macromolecules, such as whey proteins or mineral components, influence the kinetics of lactose crystallization. The presence of other components at each change of state can modify the kinetics. For a better understanding of their influence, it is necessary to determine their specific effects on lactose solubility and the laws of the kinetics controlling the stages of mutarotation, nucleation and growth, by taking into account the process–product interactions.2.4 The mechanical process of homogenization is involved in the manufacture of fat-filled spray-dried powders to disperse fat into individual droplets and assure their physical stability. This book chapter is structured in five main parts: Section 2.4.2 presents the mechanical process of homogenization; Section 2.4.3 discusses the position of the homogenization process in the technological scheme of spray-dried powder production; Section 2.4.4 examines the possible organizations of fat within spray-dried powders; Section 2.4.5 evaluates the potentialities of homogenization in the preparation of nanostructured lipid carriers, and Section 2.4.6 describes the key role played by homogenization in the preparation of dairy products such as infant milk formula and highlights the potentialities of homogenization for innovation in the near future.2.5 This chapter will firstly discuss some strategies in the control of the spray-drying process with reference to the multistage layout of the process. In particular, the discussion will center on the control of the outlet temperature, fines return and agglomeration, and in the manipulation of the spray feed viscosity. The different forms of spray-dryer modeling (one-dimensional and computational fluid dynamics simulations) will be introduced, and the capabilities and expected outcomes from these modeling frameworks will be discussed. The development of two unique techniques to better understand the spray-drying process will be introduced: the single-droplet drying and the monodisperse spray-drying techniques. These techniques are now commercially available, and the latter can be used to produce products with high uniform homogeneity in particle sizes. The last part of this chapter touches on the use of superheated steam as a potential drying medium in spray dryers. This new approach may offer the potential to produce powder with improved wettability.2.6 The agglomeration process has been widely used by the dairy industry for many years to produce instant powders with improved rehydration properties. The chapter provides an overview of the three main processes for the agglomeration of dairy powders (agglomeration during spray drying, fluidized-bed agglomeration and steam-jet agglomeration). For each of these technologies, we present the principle associated with the technology, the characteristics of the equipment, the mechanisms involved during agglomeration and the influence of process control factors on the characteristics and usage properties of the agglomerated powders.2.7 This chapter will explain a new concept and application for the fluidized-bed drying stage in dairy powder processing. The fluidized-bed dryer has been primarily used for powder conditioning, further reducing residual moisture content (secondary drying) from the spray dryer, and agglomeration. In this chapter, the crystallization (post-drying) and modification of particle microstructure and the physical properties of powders are described. The new application is designed based on conventional equipment, with minimal modification, to reduce the capital cost for implementation. Process integration and development based on the mathematical modelling of the underlying physics are covered. A new heterogeneous particle microstructure is introduced in which the particle is partially crystalized. Analytical results for product performance and physicochemical properties, and effects on stability and shelf life have been reported and discussed. The crystalline surface layers enhance the powder physico-chemical properties and shelf life, while the amorphous core maintains the rehydration and bioavailability