Characterisation of spray-dried emulsions with mixed fat phases

Fat encapsulation in spray-dried protein-stabilised emulsions is known to depend on the choice of protein, the emulsion droplet size, and the melting point of the fat. However, the fat encapsulation may also depend on the fat crystal habit. Fats may crystallise in three different forms , β′ and β, of which the β-form is thermodynamically stable. The -form is obtained in rapidly cooled fats, and it can then transform into the β′-form during storage, and this crystal form is finally transformed into the β-form. In order to investigate the effect of different fat phases on the spray-dried emulsions, two solid fats were studied: fully hardened rapeseed oil (β-stable) and fully hardened palm oil (β′-stable). The solid fats were used on their own or in mixtures with rapeseed oil, in order to provide fat phases with different properties. The emulsion composition was chosen as to mimic the composition of whole milk, i.e. 40% lactose, 30% sodium caseinate and 30% fat on a dry weight basis. The dried powders were stored under dry conditions at 4 or 37 °C in order to investigate the changes in the fat crystals and surface composition of the powders with time. The surface composition was analysed using electron spectroscopy for chemical analysis. Evaluation of the data showed that surface coverage of fat varied depending on the composition of the fat phase. The ratio of lactose to protein remained constant, which implies that the fat was present as ‘islands’ on a surface composed of lactose and protein. The hardened palm oil crystallised initially in the - or β′-form (depending on the ratio of hardened fat to oil), and during storage, the crystal form gradually changed into the β′-form. In powders containing hardened rapeseed oil only the stable β-form was found, even in fresh samples. The surface coverage of fat was reduced after storage, whereas the ratio of lactose to protein at the surface remained unchanged. The emulsion droplet size in emulsions prepared at a low homogenisation pressure was considerably increased after spray-drying and reconstitution, whilst the emulsion droplet size was well preserved in emulsions prepared at high homogenisation pressure.     

Solid-state characterization of spray-dried ice cream mixes

The main physicochemical properties of spray-dried ice cream mixes (i.e. surface composition, wettability, flowability and microstructure) were analyzed. Emulsions contained 19-44% milk fat on a dry basis and included mixes with no added emulsifier and/or sucrose. The time necessary for complete wetting of the powders correlated with the amount of surface free-fat measured by means of solvent extraction. Non-micellar casein (sodium caseinate) showed to be a better co-encapsulant than micellar casein (skim milk) as demonstrated by surface fat coverage measured by electron spectroscopy for chemical analysis (ESCA). Emulsifiers influenced the fat surface composition of the powders by reducing the amount of surface protein due to their lower interfacial tension. Surface fat caused an initial overestimation of the particle size of the powders due to fat-related caking. Powders showed no flow before and after surface fat extraction which was attributed to fat-related caking and very small particle size (<80 microm), respectively.     

Effects of spray drying on physicochemical properties of milk protein-stabilised emulsions

The effect of spray drying and reconstitution has been studied for oil-in-water emulsions (20.6% maltodextrin, 20% soybean oil, 2.4% protein, 0.13 M NaCl, pH 6.7) with varying ratios of sodium caseinate and whey protein, but with equal size distribution (d₃₂=0.77 μm). When the concentration of sodium caseinate in the emulsion was high enough to entirely cover the oil–water interface, the particle size distribution was hardly affected by spray drying and reconstitution. However, for emulsions of which the total protein consisted of more than 70% whey protein, spray drying resulted in a strong increase of the droplet size distribution. The adsorbed amount of protein ranged from 3 mg m⁻² for casein-stabilised emulsions to 4 mg m⁻² for whey protein-stabilised emulsions with a maximum of 4.2 mg m⁻² for emulsions containing 80% whey protein on total protein, which means that for all these emulsions about one quarter of the available protein was adsorbed at the oil–water interface. The adsorbed amount of protein was hardly affected by spray drying. After emulsion preparation casein proteins adsorbed preferentially at the oil–water interface. As a result of spray drying, the relative amount of β-lactoglobulin in the adsorbed layer increased strongly at the expense of _s1-casein and β-casein. Percentages of _s2-casein and κ-casein in the adsorbed layer remained largely unchanged. The changes in the protein composition of the adsorbed layer as a result of spray drying and reconstitution were the largest when beforehand hardly any whey protein was present in the adsorbed layer and hardly any sodium caseinate in the aqueous phase. Apparently, during spray drying conditions have been such that β-lactoglobulin could unfold, aggregate, and react with other cystein-containing proteins changing the particle size distribution of the emulsions and the composition of the adsorbed layer. It seemed, however, that non-adsorbed sodium caseinate in some way was able to protect the adsorbed casein proteins from being displaced by aggregating whey protein.     

Measurement and Correlation Solubility of Sodium Succinate in Binary Mixed Solvents of Water + (Methanol or Ethanol) Mixtures

The solubility of sodium succinate in binary solvent mixtures was measured by an analytical stirred-flask method in the temperature range 278.15–318.15 K at atmospheric pressure. It was found that the solubility of sodium succinate in the system increased with increasing temperature and decreased with the increasing mass fractions of methanol or ethanol. The modified Apelblat equation, the Buchwski–Ksiazaczak λh equation and the combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R–K) equation were proposed for correlating the experimental data. The modified Apelblat equation was found to regress the solubility data much better than the Buchwski–Ksiazaczak equation and the CNIBS/R–K equation in a binary solvent system. The dissolution enthalpy and dissolution entropy of sodium succinate were calculated from the solubility data, using the Van’t Hoff equation. The experiment results and correlation models could be used as essential data in the purification of sodium succinate.     

Stability and rheology of emulsions containing sodium caseinate: combined effects of ionic calcium and alcohol

We have investigated the combined effect of ionic calcium and ethanol on the visual creaming behavior and rheology of sodium caseinate-stabilized emulsions (4 wt% protein, 30 vol% oil, pH 6.8, mean droplet diameter 0.4 microm). A range of ionic calcium concentrations, expressed as a calcium/caseinate molar ratio R, was adjusted prior to homogenization and varying concentrations of ethanol were added shortly after homogenization. A stability map was produced on the basis of visual creaming behavior over a minimum period of 8 h for different calcium/caseinate/ethanol emulsion compositions. A single narrow stable (noncreaming) region was identified, indicating limited cooperation between calcium ions and ethanol. The shear-thinning behavior of the caseinate-stabilized emulsions is typical of systems undergoing depletion flocculation. Addition of calcium ions and/or ethanol was found to lead to a pronounced reduction in viscosity and the onset of Newtonian flow. The state of aggregation was correlated with emulsion microstructure from confocal laser scanning microscopy. Time-dependent rheology (18 h) with a density-matched oil phase (1-bromohexadecane) revealed that the visually stable emulsions were time-independent low-viscosity fluids. Surface coverage data showed that increasing amounts of caseinate were associated with the oil-water interface with increasing R and ethanol content. A decrease in free calcium ions in the aqueous phase with moderate increases in R and ethanol content was observed, which is consistent with greater calcium-caseinate binding (aggregation). Ostwald ripening occurred at the high-ethanol emulsion compositions that were stable to depletion flocculation. While the coarsening rate was low, this can account for the cream plug formation observed during gravity creaming experiments. The caseinate emulsion with no ionic calcium or ethanol exhibits depletion flocculation from excess nonadsorbed caseinate submicelles. Addition of calcium ions reduces the submicelle number density via specific calcium-binding in the aqueous phase (fewer, larger calcium-caseinate aggregates) and at the droplet surface (increased surface coverage). Nonspecific ethanol-induced (calcium-dependent) caseinate submicelle aggregation in the bulk phase and on the droplet surface (increased surface coverage) culminates in a reduction in the number density of caseinate submicelles. A narrow window of inhibition of depletion flocculation occurs in systems containing both calcium ions and ethanol, both species combining to aggregate the protein and so reduce the density of free submicelles.     

Surface composition of spray-dried milk protein-stabilised emulsions in relation to pre-heat treatment of proteins

Several important technical properties of spray-dried food powders depend on particle-liquid interactions (e.g. wettability, dispersability) and particle-particle interactions (e.g. flowability). It can be assumed that the chemical composition of the surface layer of the particles to a large extent determine these properties. The present study has been aimed to investigate the relation between the surface composition of spray-dried milk protein-stabilised emulsions and pre-heat treatment of the proteins. Solutions of WPC were heat-treated at low (60-90 degrees C) and high (140 degrees C) temperature and the degree of denaturation was determined, prior to the preparation of emulsions with rapeseed oil. The surface composition of the dry powders were established by using ESCA (electron spectroscopy of chemical analysis). The emulsions were characterised by droplet size distribution before spray drying and after dissolution of the powders. Also free fat extractions and estimations of wettability (dissolution rates) were performed. The powder surface coverage of protein decreased with increasing degree of protein denaturation before the emulsification, whereas the emulsion droplet size increased both before spray drying and after reconstitution of powders. The free fat extraction as well as the dissolution rate, whereof the latter decreased with increasing surface fat coverage, correlated well with the fat coverage of the powder surface.     

Determination of fat in dairy products using pressurized solvent extraction

Gravimetric fat data were obtained for a wide range of dairy products with fat contents ranging from 0.5 to 83% using pressurized solvent extraction at elevated temperatures and pressure (80-120 degrees C; 10.3 MPa). Extraction performance was sensitive to solvent composition, temperature, and sample matrix. By optimizing solvent mixtures, sample-solvent contact times of 8-10 min were sufficient for high recoveries from all products tested. The most successful solvents with regard to speed of extraction, selectivity, and recovery (average recovery, %) were various mixtures of hexane (or petroleum ether)-dichloromethane-methanol for dried cream (99.8%), dried whole milk (99.6%), dried buttermilk (98.2%), dried skim milk (97.0%), dried whey protein concentrate (97.5%), casein (95.0%), and caseinate (102.1%); petroleum ether-acetone-ethanol or petroleum ether-acetone-isopropanol for cheddar-type cheese (99.4%); petroleum ether-acetone for butter (99.9%); petroleum ether-acetone-isopropanol for cream (100.3%); and petroleum ether-isopropanol for liquid milks (99.0%). Relative standard deviations for repeatability were obtained for dried whole milk (0.2%), dried whey protein concentrate (0.7%), cheese (0.3%), butter (0.1%), and ultraheat treated (UHT) milk (0.7%). Solvent removal and drying of extracts with a heated block evaporator saved time compared with conventional drying ovens. Estimated savings in labor (50-75%) and solvents (80%) were substantial compared with the manual Mojonnier methods.     

Dissolution kinetics of oxidic nanoparticles: The observation of an unusual behaviour

The solubility of nanoparticles was measured in aqueous solution as a function of time, and oxides of aluminium, silicon, titanium, and zirconium were investigated. Our solubility results show a maximum at the beginning of the dissolution process, whereas over time, the solubility levels are shown to decrease. Depending on the special conditions the solubility maximum may exceed the long-time solubility of the nanoparticles by several orders of magnitude. This behaviour is called as kinetic size effect. The extent of the effect depends on the size, surface tension and mass of the particles exposed to dissolution. It will always be of practical interest if a larger quantity of nanoparticles is brought into contact with a solvent, even when the equilibrium solubility data appears negligible. A rigorous thermodynamic and kinetic analysis of a colloidal system, which includes nucleation, particle growth, Ostwald ripening, and dissolution of particles, shows at least a qualitative agreement between all the experimental results and model calculations.     

Elucidating the relationship between the spreading coefficient, surface-mediated partial coalescence and the whipping time of artificial cream

We studied the whipping of artificial creams composed of a blend of sunflower oil and hydrogenated palm fat stabilized by protein or a mixture or protein and low molecular weight (lmw) surfactant. It was found that an increased whipping speed, decreased protein concentration, and the addition of lmw surfactant leads to shorter whipping times. Further, shorter whipping times were observed for WPI-stabilized cream compared to cream stabilized by sodium caseinate. In all cases, the decrease in whipping time was due to a decrease in the length of the second stage of whipping, the stage characterized by the adhesion of fat droplets to the air bubble surface. The decrease in whipping time could be accounted for by considering the influence of the experimental variables on the fraction of bubble surface area at which fat droplet spreading is possible. The same changes in parameters that promote droplet spreading at the air/water interface cause a decrease in the whipping time of our model creams. Correlating the whipping time of cream with the spreading behavior of fat droplets at the air/water interface represents a new insight into the mechanisms involved in the whipping of cream.     

Diffusing wave spectroscopy study of the colloidal interactions occurring between casein micelles and emulsion droplets: comparison to hard-sphere behavior

Understanding the underlying processes that govern interparticle interactions in colloidal systems is fundamental to predicting changes in their bulk properties. In this paper we discuss the colloidal behavior of casein micelles and protein-stabilized fat globules individually and in a mixture. The colloidal interactions were observed by transmission diffusing wave spectroscopy. The turbidity parameter, l*, and the diffusion coefficients of the samples studied were measured experimentally and compared to the theoretically calculated parameters for a hard-sphere system. The light scattering properties of casein micelles (volume fraction phi = 0.1-0.2) dispersed in milk permeate showed no deviation from the theoretically predicted model. Whey protein isolate (WPI)-stabilized emulsions (phi = 0.025-0.1) prepared either in milk permeate or in 5 mM imidazole buffer at pH 6.8 showed a behavior identical to that of the hard-sphere model. Similarly to the WPI-stabilized fat globules, the sodium caseinate (NaCas)-stabilized emulsions (phi = 0.025-0.1) prepared in milk permeate also showed resemblance to the theory. In contrast, NaCas-stabilized emulsions prepared in 5 mM imidazole buffer exhibited some discrepancy from the theoretically calculated parameters. The deviation from theory is attributed to the enhanced steric stabilization properties of these droplets in a low ionic strength environment. When recombined milks made from concentrated milk and WPI- and NaCas-stabilized droplets prepared in permeate (phi = 0.125-0.2) were studied, the experimental data showed a significant deviation from the theoretical behavior of a hard-sphere model due to mixing of two different species.     

Ostwald ripening of protein-stabilized emulsions: effect of transglutaminase crosslinking

Ostwald ripening in n-alkane oil-in-water emulsions stabilized by sodium caseinate at neutral pH has been studied by monitoring time-dependent changes in the number-average droplet diameter and the droplet-size distribution. In qualitative agreement with theory, the destabilization rate has been shown to increase with reduction of the n-alkane chain length and on addition of ethanol to the aqueous phase. Replacement of caseinate by β-lactoglobulin also leads to improved stability, but addition of calcium ions does not. The potential use of transglutaminase-induced crosslinking of adsorbed protein as a way of inhibiting the Ostwald ripening of caseinate-stabilized emulsions has been examined. It is shown that enzymic crosslinking before emulsification can lead to a modest reduction in the coarsening rate at long storage times. Crosslinking of caseinate after emulsification produces enhanced stability at short times, but there is a catastrophic loss of stability at long times due to droplet coalescence.     

Structure, dynamics, and optical properties of concentrated milk suspensions: an analogy to hard-sphere liquids

A systematic study of the effects of volume fraction increment on the optical properties, the structure, and the dynamics of the casein micelles and fat droplets in milk was performed using diffusing wave spectroscopy. Four types of milk were investigated, NIDO full fat milk, fat-free milk, whey and fat-free milk, and finally lactose and fat-free milk. Independent measurements to calculate the dependence of the viscosity and the index of refraction of the milk serum and casein micelles as a function of the volume fraction were also performed. We compare the experimentally determined quantities photon transport mean free path (l*) and self-diffusion coefficient D(s) with the predictions from theoretical calculations using classical colloidal models such as a hard-sphere fluid. We demonstrate that all types of milk with and without fat content behave, structurally, like colloidal hard-sphere systems up to volume fractions well over 45%. In the case of dynamic measurements, both lactose- and fat-free and whey- and fat-free milk behave also like hard-sphere systems whereas fat-free milk and fat-containing NIDO milk deviate slightly at volume fractions over 35%. Finally, a comparative measurement and theoretical calculation of the casein micelle's size was performed.     

Solubility, Dissolution Enthalpy and Entropy of Isoimperatorin in Ethanol?+?Water Solvent Systems from 288.2 to 328.2?K

The solubility of isoimperatorin in pure solvents and solvent mixtures was measured by UV spectrophotometry from 288.2 to 328.2?K. The solubility of isoimperatorin in binary ethanol and water solvent systems increases with temperature and with decrease of the mole fraction of water in the solvent mixture. The solubility data were correlated with a modified Apelblat equation. The enthalpy and entropy of dissolution of isoimperatorin were evaluated using the van??t Hoff equation.     

Fat retention at the tongue and the role of saliva: adhesion and spreading of 'protein-poor' versus 'protein-rich' emulsions

Fat perception of food emulsions has been found to relate to in-mouth friction. Previously, we have shown that friction under mouth-like conditions strongly depends on the sensitivity of protein-stabilized emulsion droplets to coalescence. Here, we investigated whether this also implies that oral fat retention depends in a similar manner on the stability of the emulsion droplets against coalescence. We investigate the separate contributions of droplet adhesion and droplet spreading to fat retention at the tongue, as well as the role of saliva. We perform ex vivo (Confocal Raman Spectroscopy; Confocal Scanning Laser Microscopy) experiments using pig's tongue surfaces in combination with human in vivo experiments. These reveal that protein-poor (unstable) emulsions are retained more at the tongue than protein-rich (stable) emulsions. Furthermore, the layer formed by adhering protein-poor droplets is more stable against rinsing. Saliva is found to be very efficient in removing fat and emulsion droplets from the oral surface but its role in fat retention needs further research. We relate our results to the colloidal forces governing droplet adhesion and spreading.     

Colloidal crystallization of colloidal silica modified with ferrocenyl group-contained polymers in organic solvents

Surface modification of colloidal silica with ferrocenyl-grafted polymer and colloidal crystallization of the particles in organic solvent were studied. Poly(methyl methacrylate-co-vinylferrocene)-grafted silica never formed colloidal crystals in polar solvent, such as acetone, acetonitrile, ethanol and N,N-dimethylformamide (DMF), while poly(methyl methacrylate-co-ferrocenyl acrylate)-grafted silica gave colloidal crystallization in DMF. The particles prepared by grafting of poly(N,N-dimethylacrylamide-co-vinylferrocene), with vinylferrocene (Vfc) mole fraction of 1/13 and 1/23, were observed to give the crystallization in ethanol and DMF over particle volume fraction of 0.058. Further, silica modified with copolymer of Vfc and N-vinyl-2-pyrrolidone, N-vinylcarbazole or N-isopropylacrylamide formed colloidal crystals in ethanol and DMF. Especially, poly(N-isopropylacrylamide-co-Vfc)-grafted silica, which was composed of the highest mole fraction of vinylferrocene, 1/3, afforded colloidal crystallization in ethanol over particle volume fraction of 0.053. Relatively high polar vinylferrocene copolymer grafting of silica resulted in colloidal polymerization in organic solvents.     

Correlations of Fat Content in Human Milk with Fat Droplet Size and Phospholipid Species

Fat globule size and phospholipid (PL) content in human milk (HM) were investigated. HM was classified into three groups depending on fat content (A < B < C). PL content (mg/100 g HM) was significantly higher in the C group (p < 0.05), indicating its positive relationship with HM fat content. When the PL content was normalized (mg/g fat), that of group A was significantly higher (p < 0.05) and fat droplet size in group C was slightly larger, suggesting that HM fat content is affected by fat droplet numbers to a larger extent than by fat droplet size. A correlation between PC and SM content in HM was observed regardless of fat content, while correlation between PE and either PC or SM increased in the order of C > B > A, hence the composition and content of PL species in HM varied according to its fat content.     

The migration of styrene butadiene latex during the drying of coating suspensions: when and how does migration of colloidal particles occur?

Surface elemental compositions of model latex clay coatings on an impervious substrate consolidated under various conditions were measured using the XPS technique, in order to clarify when and how colloidal latex particles migrate to the surface during drying. Under similar drying conditions, surface carbon content decreased with the addition of a water-soluble polymer to the coating colors, while remaining virtually unchanged for coatings of different coat weights made with a given color, indicating that surface carbon content variation is mainly caused by migration of latex rather than of water-soluble polymer. The results also showed that for coatings made with a given suspension, surface carbon content decreased with increasing delay time between coating and heating. For coatings frozen during consolidation and dried by sublimation, surface carbon content increased with increasing drying time before freezing. These results suggest that for the model coatings studied, latex migration mainly occurs after coating application before capillary formation during the initial drying stage when coatings are in the liquid phase, contradicting both the conventional capillary transport and boundary wall migration mechanisms. An alternative mechanism which attributes latex migration to surface trapping effect and to higher Brownian mobility of the smaller latex particles compared with pigment appears to provide a systematically consistent explanation to those phenomena. The new particle migration mechanism implies that segregation of colloidal particles is a ubiquitous phenomenon that would occur not only during the drying of paper coatings but also during consolidation of colloidal films containing particles of different sizes. This is of great importance in the control of surface compositions of nanocomposite coatings.     

Dynamic self-assembly of polymer colloids to form linear patterns

A dynamic self-assembling process is reported which involves drying a droplet of positively charged colloidal suspension on a flat negatively charged hydrophilic surface. This extremely simple method affords lines of colloidal particles with regular 1.5-4.5 microm line spacing and smaller than 2 microm line width over a broad surface area. The ordered region diffracts light to display an iridescent appearance and generates first-order diffraction spots when illuminated by a He-Ne laser. A periodic stick-slip motion of the drying liquid front is observed during the drying process using optical microscopy. The periodic motion must be related to the periodic particle deposition. We propose that the simultaneous deposition of the particles at a fixed distance (i.e., the line spacing) behind the previous line of particles where the contact line is pinned is in turn responsible for the periodic stick-slip motion. The key distinguishing feature of the present system is the attractive interaction between the particles and the surface, which instigates the periodicity of the particle deposition.     

Influence of major process and formulation parameters On microfluidized fat globule size distribution and example of a practical consequences

The influence of certain process variables (pressure and temperature), as well as composition variables (fat, protein and low molecular weight emulsifier concentrations) and the emulsification process used, on the size distribution of milk fat globules was studied in a dairy oil-in-water model emulsion and in homogenized milk. In the first case, the use of a central composite experimental design allowed us to obtain two nonlinear multiple regression equations relating the volume-weighted average diameter ( _v) of the fat globules as well as the relative width of size distribution (CV) to the emulsification pressure (7.8–76.3 MPa) and temperature (35–100°C), and to sodium caseinate (0.5–3.9wt.%), butter oil (5.2–14.7 wt.%) and monoglyceride (0.08–0.88 wt.%) concentrations. These two functions, which account for 93.7 and 81.7%, respectively, of the variation in the average diameter and in the size distribution width of the microfluidized fat globules, were used to describe certain interactions between the different variables affecting the size of the microfluidized fat globules. They were also used to define the optimal conditions that correspond to the extremes of the average particle diameter and of the distribution width of the fat globules. These two functions also allowed us to predict fat globule parameters as a function of process and formulation conditions. In the second case, the microfluidization process lead to an overestimation (up to 0.3%) of the milk fat content as determined by a infrared analyser.     

含盐胶体液滴的蒸发图案形成机理

研究了聚四氟乙烯(PTFE)胶粒与NaCl混合液滴的蒸发过程及其图案形成机理. 结果表明, PTFE颗粒对接触线具有强烈的钉扎作用, 胶体液滴蒸发伴有显著的“咖啡环”效应. 由于液滴中心液相区表面张力法向分力的作用, 使得凝胶区存在辐射状应力, 进而产生从液滴边缘向中心的辐射状裂纹, 裂纹数量随胶粒的体积分数增大而减少. NaCl与PTFE胶粒的混合液滴出现了复杂多样的蒸发图案. 盐的加入抑制了向外的毛细补偿流, 从而有利于获得宏观上厚度均匀的沉积膜. NaCl与PTFE胶粒耦合形成了凹凸不平的枝晶状形貌, 这可能是释放蒸发应力的结果.