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The evaporation of colloidal solutions is frequently observed in nature and in everyday life. The investigation of the mechanisms taking place during the desiccation of biological fluids is currently a scientific challenge with potential biomedical and industrial applications. In the last few decades, seminal works have been performed mostly on dried droplets of saliva, urine and plasma. However, the full understanding of the drying process in biocolloids is far from being achieved and, notably, the impact of solute properties on the morphological characteristics of the evaporating droplets, such as colloid segregation, skin formation and crack pattern development, is still to be elucidated. For this purpose, the use of model colloidal solutions, whose rheological behavior is more easily deducible, could represent a significant boost. In this work, we compare the drying of droplets of whey proteins and casein micelles, the two main milk protein classes, to that of dispersions of silica particles and polymer-coated silica particles, respectively. The mechanical behavior of such biological colloids and model silica dispersions was investigated through the analysis of crack formation, and the measurements of their mechanical properties using indentation testing. The study reveals numerous analogies between dairy and the corresponding model systems, thus confirming the latter as a plausible powerful tool to highlight the signature of the matter at the molecular scale during the drying process.

The purpose of this study was to improve understanding of the structural and functional property changes that milk-protein concentrates undergo during production, particularly how the manufacturing route (heat treatment position and intensity), standardization (in osmosed water or ultrafiltrate permeate) and formulation (casein:whey protein (Cas:WP) ratio) influence the physico-chemical characteristics—hygroscopicity, particle size, sphericity, density and evolution of browning during storage. To obtain a comprehensive understanding of the parameters responsible for the distinctive characteristics of different powders, a multifactorial approach was adopted. Hygroscopicity depended mainly on the standardizing solution and to a lesser extent the Cas:WP ratio. The particle size of the heat-treated casein-dominant powders was up to 5 μm higher than for those that had had no heat treatment regardless of the standardizing solution, which also had no influence on the sphericity of the powder particles. The density of the powders increased up to 800 kg·m−3 with a reduced proportion of casein, and lactose and whey proteins participated in browning reactions during storage at 13 °C. In increasing order, the modality of heat treatment, the standardizing solution and the Cas:WP protein ratio influenced the key characteristics. This work is relevant for industrial applications to increase control over the functionalities of powdered products. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Dairy powders are mainly produced by droplet spray drying, an articulated process that enables the manufacture of high added-value goods with a long shelf life and well-preserved functional properties. Despite the recent advances, a full understanding of the mechanisms occurring at the droplet scale in drying towers and, consequently, of the impact of process parameters and processed fluid characteristics on the powder properties is far from being achieved. In the wake of previous studies based on a laboratory scale approach, in this work, we provided a global picture of the drying in droplets of dairy protein mixes, i.e., whey proteins and casein micelles, which represent crucial dairy powder ingredients. Using profile visualization and optical microscopy, we explored the shape evolution in droplets with a range of protein contents and compositions typical of commercial powder production. The observation favored the evaluation of the specific role of each protein on the evaporation dynamics, and led to the construction of a phase diagram predictive of the dry droplet shape starting from the characteristics of the initial protein dispersions. Our outcomes represent a further step shedding light on the paradigm linking the physics of drying at the microscale and the nutritional properties of complex dairy powders. [ABSTRACT FROM AUTHOR]

The evaporation of a colloidal dispersion is characterized by solute accumulation at the air-liquid interface, leading to the gradual formation of a gelled skin. The development of this layer, from preliminary colloid deposit to complete solidification, affects overall drying process and final sample morphology. Despite, progress in the last decades, the mechanisms governing skin formation in drying colloidal suspensions have not yet been fully clarified, especially in complex polydisperse systems. In this work, we investigate this open question in droplets consisting of the two main milk proteins, i.e. whey proteins and casein micelles. Using complementary experimental approaches, we evaluate skin rheological behavior during the different stages of the evaporation process, highlighting the specific role of each colloid. Our results are interpreted in the light of drying-induced protein stratification, whose evidence is provided by the direct observation of dry skin section structure. This study contributes to the understanding of the competitive drying mechanisms occurring in binary colloidal systems. Moreover, our outcomes are potentially valuable for the optimization of milk powder production in dairy industry. [Display omitted] [ABSTRACT FROM AUTHOR]

Granulation of whey permeate (WP) and demineralised whey (DW) superconcentrates was evaluated by addition of powder using a high-shear mixer during which consumption of electrical current was monitored. Granulation of DW required 50% more energy than that of WP and the resulting DW granules were larger (∼2×) indicating greater resistance to fragmentation. Furthermore, addition of whey protein isolate (WPI) into the back-mix powder resulted in more efficient granulation (reduced energy, finer granules etc.) of superconcentrated WP. This was linked to the higher water-holding capacity of WPI and a simple model based on protein content was proposed to predict occurrence of granulation. This study sheds light on granulation behaviour under these conditions. Interestingly, while high cohesiveness of superconcentrates, which is related to protein content, has been previously shown to negatively impact granulation, increasing the protein content of the granulating powder was shown here to have positive effects, which offers great potential for design of formulated products. [Display omitted] • Protein content plays a key role in determining granulation efficiency. • High protein content in superconcentrates negatively affects granulation. • High protein content in the back-mixed powder improves granulation efficiency. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Hypothesis The effective contribution of interfacial properties to the rheology of foams is a source of many open questions. Film dynamics during topological T1 changes in foams, essentially studied for low molecular weight surfactants, and scarcely for proteins, could connect interfacial properties to protein foam rheology. Experiments We modified whey protein isolate (WPI), and its purified major protein β-lactoglobulin (β-lg) by powder pre-conditioning and dry-heating in order to obtain a broad variety of interfacial properties. We measured interfacial properties, film relaxation duration after a T1 event and bulk foam rheology. Findings We found that, for β-lg, considered as a model protein, the higher the interfacial elastic modulus, the longer the duration of topological T1 changes and the greater the foam storage and loss moduli and the yield stress. However, in the case of the more complex WPI, these correlations were less clear. We propose that the presence in WPI of other proteins, lactose and minerals modify the impact of pre-conditioning and dry-heating on proteins and thereby, their behaviour at the interface and inside the liquid film. [ABSTRACT FROM AUTHOR]

Abstract In the present work, we investigated the effects of powder dry-heating parameters on whey protein foams stability, especially against drainage. To this aim, whey protein isolate solutions were prepared at various pH (3.5, 5.0, 6.5), with or without a prior dialysis step to reduce the lactose content, freeze-dried, adjusted to various levels (0.12, 0.23, 0.52) of powder water activity a w and dry-heated at 70 °C for up to 125 h. Protein solutions were then reconstituted at pH 7.0 and foams prepared by air bubbling. An original approach was followed to study the foam stability against drainage, involving monitoring of the liquid fraction as a function of both height in the foam column and time, and analysing the whole set of time and height liquid fraction profiles using multivariate statistics. The effects of dry-heating parameters were markedly interdependent, resulting in complex effects on foam stability. However, the results suggest that dry-heating at pH 3.5 increased foam stability. Moreover, the a w adjustment step, though consisting in a two-week pre-conditioning at room temperature, also had a significant effect on the foam stability, of the same order of magnitude as dry-heating effects. Highlights • We monitored drainage using time and height liquid fraction profiles. • Multivariate statistics allow comparison of foam stabilities. • Storage of powders prominently impacted foam stability. • Powder dry-heating parameters caused complex effects on foam stability. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of lactose on the ageing-induced structural changes through a varying lactose content in whey protein powders. In this scope, four powders differing in their lactose content (0.1–16 w/w %) were stored at 40 °C and 60 °C for up to 3 months and sampled periodically. A small variation in lactose content of WPI powders was found to affect the level of structural and functional changes during powders ageing. At a higher lactose content (2.6 w/w %), proteins were more rapidly lactosylated and aggregated, with a higher rate than the control WPI powder; whereas at a lower content (0.1 w/w %) the rate of lactosylation and aggregation was considerably limited. These results highlighted the great contribution of the Maillard reaction during ageing of WPI powders. Reducing lactose content in the WPI powders is a promising way to extend their stability among storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Denaturation/aggregation of whey proteins was modified by increasing concentration. • Non-cumulative effect of heat treatment on whey protein denaturation/aggregation. • Whey protein/casein micelles co-aggregation was promoted in the absence of lactose. • No correlation between whey protein denaturation and casein micelles aggregation. • Rennet gel firmness and firming rate were reduced by increasing protein denaturation. Dairy ingredients with highly concentrated protein contents are high added value products with expanding market. The manufacture of such ingredients includes a succession of unit operations of which heat treatment is a key step to guarantee the microbial safety, that induces major changes in protein structures and thus ingredients functionalities. However, due to an incomplete understanding of phenomena taking place at high protein concentrations, shedding light on their mechanisms is a scientific challenge as well as an industrial need. In this study, the influence of heat treatment (74 °C/ 30 s) of highly concentrated milk protein systems (up to 20 % w/w) on protein denaturation/aggregation and enzymatic coagulation properties was studied using an original semi–industrial approach. 10 % w/w protein solutions constituted with whey protein and casein micelles at milk ratio, standardized in osmosed water or ultrafiltration permeate were used. These protein solutions were processed in different ways prior the manufacture of powders: heat treatment of the 10 % w/w protein solution before vacuum evaporation, heat treatment of the 20 % w/w protein solution after vacuum concentration, two consecutive heat treatments before and after vacuum evaporation. A fourth powder was prepared from unheated 10 % w/w protein solution. An increase in protein concentration led to a higher heat-induced protein denaturation. This phenomenon was reduced when increasing the lactose content. The effect of heat treatment on the extent of protein denaturation was not cumulative. At high protein concentration, interactions between κ-casein and whey protein were modified compared to milk, as mainly micelle-bound aggregates were formed at pH about 6.7. This phenomenon was enhanced at low ionic strength and lactose content. Our study showed that the enzymatic coagulation properties of reconstituted protein powders could be correlated with their physico–chemical compositions. An increase in protein denaturation disrupted the gel reorganization and led to the formation of weaker gels but did not interfere on the micelles aggregation phase and the early gelation. On the contrary, an increase in ionic strength and lactose content led to higher gel time. [ABSTRACT FROM AUTHOR]

The spray drying of milk proteins usually leads to dry particles of which the final shape can influences physical and functional properties of powders. The aim of this study was to understand the mechanisms of particle formation by considering the mechanical properties of materials making up the two main classes of milk proteins: whey proteins and casein micelles. The progressive solidification of the interface of the droplet during drying time was studied by high speed camera and fluorescence microscopy, in different experimental conditions. The mechanical properties of the final protein materials were then characterized by micro indentation testing. The drying dynamics of whey protein and casein micelle droplets showed different timescales and mechanical lengths, whatever the drying conditions and the droplet configurations, leading to typical mechanical instability at the surface i.e. buckling and fracture. The interface of casein micelles reached sol–gel transition earlier estimated at around 156 g.L −1 following by elastic and plastic regimes in which the shell distorted and buckled to form a final wrinkled particle. In contrast, the interface of whey proteins became elastic at only half the drying time estimated at around 414 g.L −1 , retaining a spherical shape, which finally fractured at the end of drying. The mechanical difference between the two plastic shells might be explained by the behaviour of proteins in jamming conditions. Analogous behaviour could be discussed between the casein micelles and soft and deformable colloids on the one hand, and between whey proteins and hard spheres on the other. [ABSTRACT FROM AUTHOR]

The drying of milk concentrate dropletsusually leads to specificparticle morphology influencing their properties and their functionality.Understanding how the final shape of the particle is formed thereforerepresents a key issue for industrial applications. In this study,a new approach to the investigation of droplet–particle conversionis proposed. A single droplet of concentrated globular proteins extractedfrom milk was deposited onto a hydrophobic substrate and placed ina dry environment. Complementary methods (high-speed camera, confocalmicroscopy, and microbalance) were used to record the drying behaviorof the concentrated protein droplets. Our results showed that whateverthe initial concentration, particle formation included three dynamicstages clearly defined by the loss of mass and the evolution of theinternal and external shapes of the droplet. A new and reproducibleparticle shape was related in this study. It was observed after dryinga smooth, hemispherical cap-shaped particle, including a uniform proteinshell and the nucleation of an internal vacuole. The particle morphologywas strongly influenced by the drying environment, the contact angle,and the initial protein concentration, all of which governed the durationof the droplet shrinkage, the degree of buckling, and the shell thickness.These results are discussed in terms of specific protein behaviorsin forming a predictable and a characteristic particle shape. Theway the shell is formed may be the starting point in shaping particledistortion and thus represents a potential means of tuning the particlemorphology. [ABSTRACT FROM AUTHOR]

Abstract: 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 (B 0, k n0) and the growth rate constants (kg 0, g 0). 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. [Copyright &y& Elsevier]

Whey protein fractal aggregates reveal different texturizing properties depending on their size. This study characterize the effect of three process parameters (flow regime, heating residence time (RT h) and heating temperature) on the size and shape of aggregates formed at a semi-industrial scale using a dynamic tubular heat exchanger, and identify the mechanisms involved in their formation. The study showed that physicochemical parameters are not the unique levers to modulate agregates properties but process parameters are also efficient. Asymetrical-Flow-Field-Flow-Fractionation was used to highlight the significant increase of aggregate size produced under transient regime conditions compared to laminar and turbulent regimes. Even larger aggregates were obtained while increasing the heating temperature from 80 to 85 °C since the unfolding aggregation of protein was controlled by the aggregation step. Moreover, RT h showed no effect on aggregate formation. This study paves the way to the control of aggregate properties obtained in a continuous dynamic mode. • Whey protein fractal aggregates were produced in continuous mode at pilot scale. • Transient regime led to larger aggregates compared to laminar and turbulent flow. • Larger fractal aggregates were obtained while increasing the heating temperature. • Heating residence time showed no effect on the size and shape of aggregates formed. • Formation of fractal aggregates is governed by the association of reactive species. [ABSTRACT FROM AUTHOR]