Shape, Shell, and Vacuole Formation during the Drying of a Single Concentrated Whey Protein Droplet (original) (raw)
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Morphology development in single drop drying for native and aggregated whey protein dispersions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2019
Native and aggregated whey proteins (WP) are used in food and pharmaceutical applications as stabilizers, thickeners and carriers. For increasing shelf-life and facilitating transportation, WP are transformed into powders by spray-drying. Powder functional properties strongly depend on the final particle morphology. Focusing on colloidal aspects of drying, the goal of this work is to: (i) investigate morphology development during single drop drying of native and aggregated whey protein dispersions; (ii) use structure-mechanical parameters to predict the final morphology. Results showed evaporation rate and morphology development characteristic times are not affected significantly by colloidal size. However, the final morphology of particles depends on WP colloidal size. For small colloids, particles are shriveled, while their shape is cup-like for larger colloids. Structure-mechanical parameters allowed predicting a buckled/shriveled morphology in agreement with experimental observations. Specifically, predictions anticipated the formation of a solid shell at the particle surface, which is compressed during drying, as a result of colloidal interactions being dominated by van der Waals forces. This work provides a rationalization of morphology development of WP particles. In addition, the work suggests that the elasticor gelformation, that is governed by the permeation, may be very different depending on the permeability of the proteins gel. The collapse from a dispersion to an elastic gel may be responsible for the shriveled to buckled transition. The work shows that diverse final morphologies can be achieved using same drying conditions and composition, while only changing the degree of colloidal aggregation.
Impact of spray-drying conditions on the particle size of microparticulated whey protein fractions
Dairy Science & Technology, 2013
The particle size of microparticulated whey proteins is decisive for the sensory properties and applicability of these products in foodstuffs. The impact of spray-drying conditions on the particle size of whey microparticles was studied. Solutions of 10% (w/w) whey proteins in native mixed form (ratio of α-La/β-Lg, 20:70) and isolated form were microparticulated in a scraped surface heat exchanger with a denaturation degree of 90% or higher and were dried using a lab-scale spray dryer. The effect of drying temperatures on the particle size was evaluated for the powder form as well as after reconstitution in distilled water to the original solids content, following a multilevel factorial design with variation of the inlet (180-210°C) and outlet (75-105°C) temperatures in the dryer. A slight increase in particle size was observed in the powders independent of the inlet and outlet drying temperatures, which was reversible after dissolution in water. Residual water content of the powder was reduced, independent of the protein composition, as the outlet temperature during drying was increased. Scanning electron microscope micrographs of the obtained powders showed spherical particles with morphological differences depending on the protein composition of the solutions. The results were validated at pilot scale using a spray dryer with centrifugal disc atomisation.
Development of stickiness of whey protein isolate and lactose droplets during convective drying
Chemical Engineering and Processing, 2007
The stickiness development of droplets of whey protein isolate (WPI), lactose and their mixture solutions was determined using an in situ stickiness testing device at 24, 65 and 80 • C. Stainless steel, Teflon, glass and polyurethane probes were used. At room temperature, the presence of 0.5-1% (w/w) WPI greatly lowered the observed tensile strength of water and lactose solutions due to surface adsorption and led to a weakening of the cohesive strength. At elevated temperatures, lactose droplets remained sticky showing cohesive failure until the surface was completely covered with a thin crystal layer. WPI droplets formed a thin, smooth skin immediately on coming in contact with drying air. This surface became non-sticky early in the course of drying due to the transformation of the surface to a glassy state. The skin forming and surface active nature of WPI was exploited to minimize the stickiness of honey in a pilot scale spray drying trial. Replacement of 5% (w/w) maltodextrin with WPI raised the powder recovery of honey solids from 28% to 80% in a pilot scale drying test. At elevated temperature the magnitude of stickiness on probe materials was in the order of glass > stainless steel > polyurethane > Teflon. The Teflon surface offered the lowest stickiness both at low and high temperatures making it a suitable material to minimize stickiness through surface coating.
2020
Pattern formation in drying protein droplets continues to attract considerable research attention because it can be linked to specific protein-protein interactions. An extensive study of the drying evolution and the final crack patterns are presented, highlighting the concentration dependence (from 1 to 13 wt%) on two globular proteins, lysozyme (Lys) and bovine serum albumin (BSA), in de-ionized water. The drying evolution starts with a constant contact radius mode and shifts to a mixed mode where both fluid front and contact angle changes. The contact angle monotonically decreases, whereas, the fluid front exhibits two regimes: an initial linear regime and a later nonlinear regime. Unlike the linear regime, the non-linear regime is faster for Lys droplets. This results in the formation of a "mound"-like structure in the central region. A new feature, a "dimple" is observed in this mound which is found to be dependent on the initial concentration. The different ...
Experimental Determination of Drying Kinetics of Skim-Milk Suspended Droplet
The article presents a detailed report of the measurements and analysis of the drying kinetics obtained using suspended droplet technic. Measurements of drying process of milk, whey and lactose solutions were performed in range of temperatures 60-140°C. The drying rate, locking point and critical moisture content of particle have been obtained on a base of recorded images and measurements of exhausted air humidity. Influence of drying air temperature on particle morphology has been observed. Highly porous, hollow particles were created in air temperatures higher than 100°C due to intensive inflation-deflation period. Smaller and compact particles were produced in low air temperatures (T g < 100°C). Dry particle structure was analyzed by X-ray computed tomography. Experimentally obtained drying curves can be used in determination of drying parameters and validation of single droplet drying models.
How surface composition of high milk proteins powders is influenced by spray-drying temperature
Colloids and Surfaces B: Biointerfaces, 2010
High milk proteins powders are common ingredients in many food products. The surface composition of these powders is expected to play an essential role during their storage, handling and/or final application. Therefore, an eventual control of the surface composition by modifying the spray-drying temperature could be very useful in the improvement of powder quality and the development of new applications. For this purpose, the influence of five spray-drying temperatures upon the surface composition of the powders was investigated by X-ray photoelectron spectroscopy. The major milk proteins were studied: native micellar casein and native whey, both more or less enriched in lactose.
Food Hydrocolloids, 2014
A mixed solution of whey protein isolate, sugar beet pectin and laccase was microemulsified as nanodroplets in a mixture of sunflower oil and span 80. The droplets were transformed into nanoparticles through laccase-induced cross-linking and in situ gelation of biopolymers. Entrapment of caffeine within the conjugate bulk gel of biopolymers postponed the gelation time indexed by dynamic rheometry and decreased the strength of the final gel. The mean size of conjugate particles was 109 nm. Scanning electron microscopy images revealed an almost spherical morphology for uniformly shaped particles. Fourier transform infrared spectroscopy suggested the cross-linking of protein and pectin with participation of ferulic acid groups of pectin. Heat scanning experiments carried out by differential scanning calorimetry indicated the transition of conjugate particles from glassy to rubbery state at lower temperatures than their parent biopolymers.
Skin layer stratification in drying droplets of dairy colloids
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021
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.
Journal of Food Engineering, 2014
A micro-fluidic-jet spray dryer was used to fabricate spray freeze dried (SFD) and spray dried (SD) uniform microparticles with feed solid content >30 wt% of reconstituted skim milk. The effects of feed solid content on the particle size, morphology, surface composition, wettability and solubility were investigated. The surface composition of SFD and SD sample was characterized via an X-ray photoelectron spectroscopy. Fat and protein was found to be over-represented on the SD particle surface, while lactose significantly declined. Such ingredient segregation was quantitatively shown to occur during atomization and continue within the drying process, i.e. atomization-induced ingredient segregation (AIIS) and drying-induced ingredient segregation (DIIS). The wettability and solubility of the spray dried samples were quantified using scaled-down GEA Niro Methods in relation to the feed solid contents.
Journal of Pharmaceutical Sciences, 2002
This work investigates the use of spray freeze-drying (SFD) to produce protein loaded particles suitable for epidermal delivery. In the first part of the study, the effects of formulation and process conditions on particle properties are examined. Aqueous solutions of trehalose produce SFD particles in the size range 20-80 mm, with a smooth, textured surface, but having high internal porosity. The latter was visualized using SEM and a novel particle embedding and sectioning technique. Use of an annealing step during the freeze-drying cycle caused the particles to shrink, reducing hereby porosity and also the measured rate of moisture uptake into these amorphous particles. SFD pure mannitol was approximately 40% amorphous, but not hygroscopic. Incorporation of dextran 37,500 into a combined amorphous trehalose/mannitol formulation led to increased particle shrinkage and lower particle porosity on annealing. The model protein trypsinogen lost approximately 15% activity during SFD of solutions containing 50 mg/mL protein, but was only marginally aggregated (1.4%). It is suggested that trypsinogen forms an irreversible partially unfolded state or molten globule on SFD/rehydration. The pure protein was also partially inactivated without aggregation during atomization into air. Surprisingly, neither activity loss nor aggregation were detected on atomization of the protein solution into liquid nitrogen. Quench-freezing of small droplets may reverse the partial unfolding of trypsinogen occurring on atomization into air. The origin of the trypsinogen inactivation during SFD must therefore be the subsequent freeze-drying step of this multistep process. Isolated freeze drying of trypsinogen produces strong aggregation and equivalent inactivation. This result suggests that trypsinogen behaves differently during freeze drying from frozen droplets and from bulk solution in a vial. In the former case the protein forms an irreversible partially unfolded state, whereas in the latter case aggregates are formed. Trypsinogen inactivation during SFD could be completely prevented by the presence of trehalose in the formulation. Electron Spectroscopy for Chemical Analysis (ESCA) showed a high surface excess of the protein in the SFD particles, which was reduced on inclusion of Polysorbate 80, but not trehalose. Taken together, these results help to elucidate the complex destabilization behavior of trypsinogen during SFD.