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The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal ...dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art.
Graphical abstract
Micellar casein (MC) powder must be completely dispersed and dissolved in water to fully exhibit their functional properties. However, the rehydration properties of these powders decline strongly ...during storage, leading to loss of solubility and longer rehydration time. In this work, controlled ageing was applied to a MC powder in order to better understand the mechanisms responsible for the deterioration of rehydration properties in the course of storage. The objective was to investigate evolutions of powder surface structure and composition as well as the link between these changes and the decline in rehydration properties, which were evaluated through characteristic times of different steps constituting the full rehydration process. Lipid migration (towards the particle surface) and increase of interactions between surface micellar particles during storage were proven to be responsible for major changes in different rehydration stages. First, the delay in water penetration into particles was quantified; then, the increase of particle fragmentation time was determined and finally, an extended total rehydration time was evidenced. Analysis of the characteristic times of different rehydration stages shows unambiguously that the main step increasing the total rehydration time of aged powder is not lipid migration but the crosslink formation during storage, which can thus be considered as the rate-limiting stage for rehydration of aged powder.
•Increase in the migration of surface lipids, surface crust resistance and rehydration characteristic times were demonstrated.•A strong correlation was demonstrated between migration of lipids to the surface and increase of wetting time.•It was clearly established that wetting step was not the main reason for extended total rehydration time upon ageing.•Delayed casein micelles release is considered as the rate-limiting stage for rehydration of aged powder.
•Higher total solids were reached with a Centritherm evaporator for skim milk and WPC80.•After the 2-hour concentration, no noticeable thermal damage on protein was observed.•Resulting powders ...retained satisfactory rehydration properties.
A new thin film concentration device based on a spinning cone evaporator has been specifically designed to process viscous products at low evaporation temperatures. Its effectiveness was evaluated for the concentration of skim milk and a whey protein concentrate with 80% (w/w) protein on a dry-matter basis (WPC80). The concentrates were dried and the powders were compared to standard products obtained with conventional technology.
WPC80 at 259.1gkg−1 total solids (TS) and preconcentrated skim milk at 404.9gkg−1TS were concentrated up to 425.4 and 570.5gkg−1TS, respectively. No noticeable protein denaturation was evidenced on either concentrate. Particle size and bulk density were higher in the WPC80 powder than a standard product. Although the skim milk concentrate was highly viscous, drying was possible by applying a higher pressure at the inlet of the dryer. The resulting powder had physical properties (density, particle size, solubility) comparable to those of a standard product.
Vacuum concentration and drying are valuable techniques for the removal of water and the resulting stabilization of most dairy and feed ingredients. In this study, we present methodology to calculate ...and compare the energy consumption for the production of dairy and feed powders at different processing stages of the dehydration process. The results show that the energy costs to produce 1 kg of dairy and feed powders were 6,120 and 20,232 kJ · kg ⁻¹ powder for pregelatinized starch and soy protein concentrate, respectively. For dairy products, the values were 9,072 and 15,120 kJ · kg ⁻¹ for fat-filled and demineralized whey powders, respectively. According to the type of product (biochemical composition, ratio of bound and free water) and process (demineralization, vacuum evaporation, lactose crystallization, roller and spray drying), the energy consumption for the production of powders could be calculated. These findings could be valuable for studies focusing on improvement of energy efficiency for dairy and feed processes.
The effect of caseinomacropeptide (CMP) concentration on the kinetics of denaturation of β-lactoglobulin (β-Lg) and on the size and structure of the heat-induced aggregates was investigated over a ...wide range of pH (3.0–6.7) and temperature (65–95 °C). Irrespective of pH and heating temperature, CMP increased the rate of β-Lg denaturation. When β-Lg and CMP were negatively charged (i.e., at pH 6.7), increasing CMP concentration hindered aggregate formation; the aggregates had a smaller hydrodynamic diameter and the protein solution turbidity decreased. However, when β-Lg and CMP were oppositely charged (i.e., at pH 4.0), CMP promoted aggregate formation and large particles (>5 μm) were formed on heating. Nevertheless, the covalent aggregates constituting these large particles were of smaller size than those formed on heating β-Lg in the absence of CMP. At pH 4.0, CMP induced the formation of large particles when added in a solution of preformed aggregates of β-Lg.
Vacuum concentration and dehydration by spray drying are valuable techniques for the evaporation of water and are used to stabilize most dairy ingredients. In view of the increasing development of ...filtration processes, there is a need for the dairy industry to improve their understanding of the effects of controlling these processes on the concentration and spray drying and hence on the quality of protein powders. Several authors have reported that proteins have an important role in the mechanisms of water transfer during drying and rehydration. The residence time of the droplet and the powder in the spray dryer is so short that it is very difficult to implement studies on the mechanisms of the structural changes in the protein without fundamental research into the process/product interactions. However, many studies have reported that the main structural and functional modifications occur before spray drying; that is, during concentration by vacuum evaporation and heat treatment. Following an extensive introduction focusing on dairy powders, this article covers three significant areas: an overview of the main dairy powder processes, the properties of these powders, and the effects of the processes on powder quality.
•Droplet size varies in a complex way according to the distance to the nozzle.•Droplet size was modelled by dimensional analysis of the atomisation process.•Both the atomisation and coalescence ...mechanisms contribute to the droplet size.•Air velocity prevail in the spray characteristics.
This paper presents a dimensional analysis (DA) § approach of the atomisation process using a bi-fluid nozzle, allowing to predict droplet sizes of model solutions and skimmed milk concentrates in large ranges of operating conditions. Experimental results confirmed the atomisation mechanism described in the literature, by underlining that the spraying operation is controlled by the coupling of liquid physicochemical properties (viscosity, surface tension, density) and operating conditions (air pressure and liquid flow rate). It was also highlighted that droplet coalescence occurs from a certain distance to the nozzle, counteracting the atomisation mechanism and leading to a reincrease in the droplet size when moving away from the nozzle. Consequently, the modelling of droplet size by DA was improved by adapting the model coefficients of the dimensionless process relationship to the involved mechanisms: either atomisation only close to the nozzle outlet or atomisation followed by droplet coalescence at longer distance to the nozzle.
How the type of protein influences particle morphology remains a hot topic of debate. In this study we focused on the drying behavior of two major milk protein types; that is, whey protein and native ...micellar caseins. To improve understanding of the role of each protein in the particle-forming mechanisms, seven mixtures containing different whey proteins to caseins ratios were investigated. A monodisperse spray dryer (MDSD) was used to produce uniform particles by drying monodispersed droplets in a hot, dry air flow. Single particles were also obtained from the same material using single droplet drying in a pendant configuration. Powders were characterized according to their physical characteristics and their rehydration properties. It was demonstrated that particle morphology was mainly governed by the type of protein matrix, almost regardless of the drying kinetics, which differed considerably between MDSD and single droplet drying. Controlling product formulation thus represents a potential means by which to tune particle morphology and therefore the functional properties of powder.
•Innovative ways to agglomerate durum wheat semolina.•Agglomerates were produced by using pneumatic or mechanical mixing technologies.•The process conditions control the internal microstructure of ...the agglomerates.•A mechanistic model describes the reversible/irreversible mechanisms.
The agglomeration process controls the structure characteristics and end-use properties of the agglomerates. Understanding the mechanisms involved in the structuration of the food agglomerates still represents a real scientific stake. The objective of the present study is to improve the knowledge of the process–structure–properties relationships for the agglomeration of the durum wheat semolina. Pneumatic and mechanical agglomeration technologies were selected to generate different hydro–thermo–mechanical stresses during process. The agglomerates were characterized by their structures (electron microscopy, compactness, X-ray micro-tomography, starch gelatinization) and functional properties (colors, flowability, swelling, water solubility index). The results demonstrate specific effects of shear rate, process duration, and temperature on the physicochemical mechanisms occurring during processing. A functional mechanistic model was proposed to improve the description of the agglomeration mechanisms by considering the reversible and irreversible changes. This offers innovative potential to design new agglomeration processes by considering the physicochemical reactivity of the food powders.
One-dimensional (1-D) simulation is a useful technique for the evaluation of dryer operating parameters and product properties before conducting real spray drying trials. The main advantage of a 1-D ...simulation tool is its ability to perform fast calculations with significant simplicity. Mathematical models can be formulated using heat, mass and momentum balances at the droplet level to estimate time-dependent gas and droplet parameters. One of the purposes of this paper is to summarize key mathematical models that may be used to perform 1-D simulation for spray drying processes, predict essential product-drying gas parameters, assess the accuracy of prediction using pilot-scale spray drying data and perhaps most importantly address the main benefits and limitations of the 1-D simulation technique in relation to industrial spray drying operations. The results of a recent international collaborative study on the development of spray drying process optimization software for skim milk manufacture are presented as an example of the application of 1-D simulation in milk processing.
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