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.
Steam-jet agglomeration consists in steam-wetting of the surface of fine primary particles, colliding the sticky particles and consolidating the agglomerates by drying in order to obtain the desired ...properties. The aim of this work was to evaluate the influence of the steam/powder ratio and drying time on growth mechanisms and skim milk agglomerate properties. We demonstrated a predominant influence of the steam/powder ratio on the growth mechanisms and agglomerate properties due to the contribution of the steam flow rate. Moreover, the drying time was identified as a key process parameter to control the final water content, rehydration and mechanical properties of the agglomerates.
Highlights
A steam-jet agglomeration pilot plant was developed to study the agglomeration of skim-milk powders.
The growth mechanisms and agglomerates properties depended on the steam/powder ratio, through the contribution of the steam flow rate.
The drying time was identified as a key process parameter to control the final water content, rehydration and mechanical properties of the agglomerates.
To study the effects of whey constituents on lactose crystallisation, a model based on population balance and taking into account mutarotation was implemented. Outputs were the nucleation constants ...(B0, kn0) and the growth rate constants (kg0, g0). Batch crystallisation of a lactose solution (70 g 100 g−1 water) was studied with and without addition of various organic acids, salts, galactose and proteins. Kinetics and crystal size distributions were monitored using refractometry and laser light scattering. Factorial analysis of the results highlighted that the presence of organic acids (lactate, citrate) leads to faster crystallisation and confirmed the fact that whey proteins are slowing down the crystal growth step. The results of this study make a contribution towards a better understanding of lactose crystallisation.
The most frequently used technique for dehydration of dairy products is spray drying. This is an effective method for preserving biological products as it does not involve severe heat treatment and ...it allows storage of powders at an ambient temperature. Due to the variety and complexity of the concentrates to be dried, a more rigorous understanding of spray drying based on physico-chemical and thermodynamic properties has now become necessary. However, the current state of the art and knowledge do not allow determination of the parameters of spray drying of dairy products. The only way to determine these parameters is to perform several complex and expensive experiments with spray dryer pilots. In this study, a new method was developed to evaluate the ratio of bound to unbound water by using drying by desorption. The results, combined with thermodynamic and physico-chemical parameters (such as, absolute and relative humidity of air, total solids and temperature of concentrate, and air flow rate), provide more precise determination of certain spray drying parameters such as inlet air temperature and mass flow rate. More than 50 experiments were performed to correlate calculated and measured parameters in a pilot plant (Bionov) using water, skim milk, infant formula milk, caseinate maltodextrin and other food concentrates. The results showed that the difference between the calculated and measured inlet air temperature was less than 5%, the determination coefficient being close to 0.96.
The economic value of this system is obvious, because it is easy to anticipate the spray drying parameters by using a controller integrating the water availability of the concentrate and certain thermodynamic parameters. Software based on this step was developed (SD
2P
®, spray drying parameter simulation and determination) and registered at the APP (Association pour la Protection des Programmes).
► Experimental determination of droplet drying behavior of 50
wt.% skim milk droplets. ► Important kinetics data for modeling of industrial spray drying processes. ► Extension of the Reaction ...Engineering Approach (REA) to high solids concentration. ► Behavior of the activation energy at high initial solids concentration.
Drying kinetics data are of paramount importance for simulating industrial spray drying operations. This study reports for the first time the drying kinetics of skim milk droplets with 50
wt.% initial solids, as typically encountered in practice. The changes in droplet temperature, moisture content, and diameter were experimentally determined using glass-filament single droplet drying technique. Enhanced effects of drying temperature on droplet shrinkage were observed. Experimental data were correlated using the Reaction Engineering Approach (REA) with the master activation-energy curve providing a good description to the drying histories. Activation energy curves obtained here were compared with previous data from lower initial concentrations, as well as the plot obtained using a preliminary desorption method. The outcomes support the suitability of REA to interpret the drying behavior of skim milk with high initial solids level, which is the norm for practical spray drying of milk with feed concentration of around 50
wt.%.
The spray drying of milk proteins usually leads to dry particles of which the final shape can influencesphysical and functional properties of powders. The aim of this study was to understand the ...mechanismsof particle formation by considering the mechanical properties of materials making up the two mainclasses of milk proteins: whey proteins and casein micelles. The progressive solidification of the interfaceof the droplet during drying time was studied by high speed camera and fluorescence microscopy, indifferent experimental conditions. The mechanical properties of the final protein materials were thencharacterized by micro indentation testing. The drying dynamics of whey protein and casein micelledroplets showed different timescales and mechanical lengths, whatever the drying conditions and thedroplet configurations, leading to typical mechanical instability at the surface i.e. buckling and fracture.The interface of casein micelles reached solegel transition earlier estimated at around 156 g.L 1following by elastic and plastic regimes in which the shell distorted and buckled to form a final wrinkledparticle. In contrast, the interface of whey proteins became elastic at only half the drying time estimatedat around 414 g.L 1, retaining a spherical shape, which finally fractured at the end of drying. The mechanicaldifference between the two plastic shells might be explained by the behaviour of proteins injamming conditions. Analogous behaviour could be discussed between the casein micelles and soft anddeformable colloids on the one hand, and between whey proteins and hard spheres on the other.
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).
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°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.
This paper presents a dimensional analysis (DA) § approach of the atomisation process using a bi-fluidnozzle, allowing to predict droplet sizes of model solutions and skimmed milk concentrates in ...largeranges of operating conditions. Experimental results confirmed the atomisation mechanism describedin the literature, by underlining that the spraying operation is controlled by the coupling of liquid physicochemicalproperties (viscosity, surface tension, density) and operating conditions (air pressure andliquid flow rate). It was also highlighted that droplet coalescence occurs from a certain distance to thenozzle, counteracting the atomisation mechanism and leading to a reincrease in the droplet size whenmoving away from the nozzle. Consequently, the modelling of droplet size by DA was improved by adaptingthe model coefficients of the dimensionless process relationship to the involved mechanisms: eitheratomisation only close to the nozzle outlet or atomisation followed by droplet coalescence at longer distanceto the nozzle.
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