Adsorption Of Whey Proteins Research Articles

Sequential adsorption of whey proteins and low methoxy pectin at the oil-water interface: An interfacial rheology study

Protein-polysaccharide bilayers have attracted a growing interest in the design of emulsion stabilizers with improved performance. An in-depth understanding of their interfacial properties helps rational interfacial engineering. Here, the sequential adsorption of whey protein isolate (WPI) and low methoxy pectin (LMP) at the oil-water interface as a function of pH was investigated with a modified drop tensiometer allowing external phase exchange. Residual WPI in the bulk phase could accumulate at the interface (i.e. pre-formed WPI film at pH 7.0) when the pH was adjusted to be close to its iso-electric point, leading to reduced interfacial tension and increased surface concentration. However, the interfacial tension was hardly influenced by successive pH changes and LMP addition if the excess protein was washed away beforehand. A maximum interfacial viscoelasticity was reached when the pH was close to the isoelectric point of WPI, corresponding to the minimum hydration degree. Whereas the deposition of LMP onto a protein-coated oil-water interface significantly increased the interfacial viscoelasticity, its magnitude was largely dependent on the pH conditions. Besides, a more linear rheological response of the bilayer structures than of the single WPI layer was observed during the large amplitude oscillatory cycles.Moreover, the adsorbed LMP at acidic pH conditions exhibited pH-responsive desorption upon exposure to neutral pH, as evidenced by the restored interfacial viscoelasticity as well as by in situ quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The more rigid and thicker WPI/LMP bilayers (visualized by cryo-scanning electron microscopy) not only effectively prevented the aggregation of emulsion droplets during storage, but also showed outstanding mechanical properties to prevent droplet coalescence.

Effect of ionic strength on the sequential adsorption of whey proteins and low methoxy pectin on a hydrophobic surface: A QCM-D study

The effect of ionic strength on the sequential adsorption of whey protein isolate (WPI) and low methoxy pectin (LMP) onto a hydrophobic surface was investigated through a real-time QCM-D technique. A gold sensor was hydrophobically modified to simulate the oil-water interface. At neutral pH, whey proteins readily adsorbed onto the hydrophobic surface and formed a viscoelastic, heterogeneous layer. With increasing ionic strength of the continuous phase, the protein layer became more compact and less hydrated. A similar but stronger effect was observed upon switching the pH from 7.0 to 4.5 (i.e. close to the iso-electric point of WPI). The sequential adsorption of LMP onto the pre-formed protein layer was studied at pH 4.5 over a wide range of ionic strengths (from 7 to 500 mM). The enhanced frequency and dissipation shifts indicated the adsorption of LMP, as well as changes in interfacial viscoelasticity. Especially, a non-monotonic ionic strength dependency (i.e. maxima at 20 mM after rinsing) was observed for both frequency and dissipation shifts, which suggested that the added salt facilitated the electrostatic deposition of LMP. However, the much smaller shifts at higher ionic strength (e.g. up to 500 mM) were mainly due to less hydration of the adsorbed LMP layer rather than an appreciably reduced LMP adsorption. Similarly, upon exposure of the pre-formed mixed layer (at pH 4.5 with an ionic strength of 20 mM) to higher ionic strengths (up to 500 mM), most of the LMP remained adsorbed, even at the highest ionic strength considered. The obtained results provide interesting insights in the characteristics of protein-polysaccharide bilayers which are known to be promising emulsion stabilizers.

Electrostatic interaction between whey proteins and low methoxy pectin studied by quartz crystal microbalance with dissipation monitoring

Electrostatic interaction between proteins and polysaccharides has attracted considerable attention in the design of fluid interfaces with improved performance, e.g. by sequential adsorption. Here, a real-time quartz crystal microbalance with dissipation monitoring (QCM-D) was used to investigate the sequential adsorption of whey proteins and low methoxy pectin (LMP) as a function of pH. A gold sensor was hydrophobically modified to mimic the oil-water interface. At neutral pH, whey proteins adsorbed onto the hydrophobic surface and formed a viscoelastic film, where most of the adsorption is irreversible. The protein film reversibly became more rigid around its isoelectric point (IEP, pH 5.0) due to structural rearrangements. Interfacial complexation of LMP and the pre-adsorbed WPI occurred over a wide pH range (3.0–6.5), but the adsorbed amount of LMP was pH-dependent. Adsorption of LMP increased the viscoelasticity of the pre-adsorbed WPI layer by electrostatic complexation. Especially, some trapped liquid could be released from the interfacial structure due to the relatively strong interaction (e.g. at pH 4.0). After switching to pH 7.0, the adsorbed LMP was fully detached from the protein layer, suggesting its pH-response behavior. The results indicated that QCM-D is ideally suited to investigate the effect of changing environmental conditions (such as pH) on the characteristics of the adsorbed layer, and to study the interaction between different components by sequential adsorption.

Preparation of mesoporous activated carbon from defective coffee beans for adsorption of fresh whey proteins

Whey protein has high biological value and functional properties. Therefore, it is necessary to develop methods to recover this valuable protein and minimize the environmental impacts. Adsorptive processes using alternative adsorbents from agroindustrial waste increase the number of alternatives for adequate final disposal of the waste and add value. The aim of this study was to develop a mesoporous activated carbon (AC) from defective coffee beans (DCB) for the adsorption of fresh whey protein. The morphological structure of the adsorbent produced was characterized, and both Raman spectroscopy, FTIR and thermal analyses were performed; and the effect of pH on the adsorption capacity (q, mg g-1) was evaluated. The characterization showed that: the AC exhibited a porous size between 33 and 43 Å, corresponding to mesoporous materials; the crystallite size (La) of AC was estimated at 9.31 ± 0.14 nm; the highest adsorption capacity value (239.1781 mg g-1) was achieved at pH 2.5 and 25ºC; and the point of zero charge of the adsorbent was at pH 2.0. The pseudo first-order model fit best to the experimental results (R2 > 0.99) of whey protein adsorption onto activated carbon, and the Langmuir model was the most appropriate to represent the experimental data, with a maximum adsorption capacity of 378.4380 mg g-1, demonstrating the potential of AC obtained from DCB to adsorb fresh whey protein.

Improvement of the viability of probiotics (Lactobacillus acidophilus) by multilayer encapsulation

ABSTRACT: This study produced pectin microcapsules containing Lactobacillus acidophilus by external ionic gelation, followed by the adsorption of whey protein and pectin to form multilayers. The viability of free and microencapsulated lactobacilli was evaluated after in vitro exposure to gastrointestinal conditions. They were also assessed by heat treatment, and stability was examined at -18 °C, 5 °C and 25 °C for 120 days. Exposure to different pHs, simulating passage through the gastrointestinal tract, showed that treatment of the microcapsules with only pectin (LA/P0) and with one and two layers of whey protein (treatments LA/P1 and LA/P3, respectively), were able to protect Lactobacillus acidophilus , with microcapsules increasing the release of probiotics from the stomach into the intestines. Free cells showed a decrease in their counts over the course of the simulated gastrointestinal system. Regarding heat treatments, microcapsules with a layer of whey protein (LA/P1) maintained the viability of their encapsulated Lactobacillus acidophilus (9.57 log CFU/g-1). The best storage viability was at -18 °C, with a count of 7.86 log CFU/g-1at 120 days for microcapsule LA/P1,with those consisting of two layers of whey protein (LA/P3)having a 6.55 log CFU/g-1 at 105 days. This study indicated that external ionic gelation was effective and could be used for the production of pectin microcapsules, with multilayer whey protein promoting greater protection and viability of Lactobacillus acidophilus.

Caseinate-Induced Competitive Displacement of Whey Protein from Interfaces

The caseinate-induced competitive displacement of whey protein from planar air-water interfaces was investigated based on atomic force microscopy (AFM) imaging and that from the surfaces of oil droplets immersed in aqueous solution based on AFM force spectroscopy. After the addition of sodium caseinate to the sub-phase, the surface pressure of planar interfacial films of pre-adsorbed whey protein increased from 8 mN/m to up to 21 mN/m. The thicknesses of interfacial films were uniform and remained to be approximately 2 nm at relatively low surface pressures up to 18 mN/m, while they became uneven at higher surface pressures and increased to up to 7.1 nm, presumably due to the compression of interfacial whey protein networks by adsorbed caseinate. The rigidity of oil droplets coated with protein adsorbed to their surfaces was then evaluated based on the slope of approximately linear force-distance curves obtained by pressing an oil droplet against another. The adsorption of whey protein to oil droplet surfaces increased droplets’ rigidity. The subsequent addition of caseinate to the bulk solution surrounding oil droplets coated with pre-adsorbed whey protein further increased droplets’ rigidity. The present results suggest that caseinate adsorbed to an interface to which whey protein had adsorbed in advance did not completely expel pre-adsorbed whey protein molecules into the aqueous phase but caused a compaction of interfacial whey protein networks and thereby strengthened the interfacial film.

Adsorption behavior of β-lactoglobulin onto polyethersulfone membrane surface

The adsorption of whey protein onto polyethersulfone (PES) membrane was investigated by static adsorption experiments to understand fouling mechanism and optimize the process condition to minimize the membrane fouling. Adsorption isotherm was applied to calculate the isotherm parameters such as adsorption capacity (KF) and surface heterogeneity (1/n). The KF values increased about 3.7 times at pH 3.0, 1.5 times at pH 5.2, and 2.3 times at pH 9.0 compared to that at pH 7.0. The hydrophobic interaction by dissociation of dimer structure of β-lactoglobulin to monomer structure at acidic and alkaline conditions showed the greatly increasing of the amount of protein adsorption by the protein and membrane interaction which might form the strong and rigid protein layer on the polymeric membrane surface. The addition of salt reduced the protein adsorption on PES membrane because of the interactions between charged protein molecules and salt ions.

Preparation of activated carbons from cocoa shells and siriguela seeds using H3PO4 and ZnCL2 as activating agents for BSA and α-lactalbumin adsorption

The aim of this work was to prepare activated carbons from cocoa shells and siriguela seeds and to evaluate the whey protein adsorption on produced activated carbon. The residues were impregnated with ZnCl2 and H3PO4. DTA/TG and FTIR were performed with this material. Carbonization was performed under nitrogen flow for 40min at 500 °C and the obtained activated carbons were washed, dried and stored. The resulting carbons were characterized regarding their textural properties. Additionally, an adsorption study was performed, using BSA and α-lactalbumin. The activated carbons showed surface areas higher than 642 m2·g−1. Impregnation with H3PO4 was more effective in modifying the structure of the precursors and carbon textural properties and this action was favorable for the adsorption of the protein α-lactalbumin. Impregnation with ZnCl2 resulted in activated carbons which were more effective in the adsorption of BSA. In both cases, use of the siriguela seed as a precursor in the production of activated carbon was favorable. The pseudo second-order model was fitted satisfactorily to the time equilibrium experimental data, for both proteins. The Toth model represents most efficiently α-lactalbumin adsorption experimental data and the Langmuir model was considered the most satisfactory for the adsorption of BSA.

Modeling of adsorption process of whey proteins in tanks shaken

It was developed a numerical procedure for the solution of the mass transfer model of adsorption in stirred tanks that considers intraparticle diffusion, mass transfer resistance in the liquid film at the particle surface and local equilibrium. The model was capable of simulating quickly, with a simulation time varying from 10 seconds to 47 seconds, the simultaneous adsorption of whey proteins, α-lactalbumin (α-la) and β-lactoglobulin (β-lg), by an ionic exchange resin. The comparison of experimental and simulated kinetic curves showed that the model is adequate for the study of these systems. From the developed model some simulations were made to study the effect of the mass transfer parameters, diffusion coefficient and mass transfer coefficient, in the adsorption kinetics of proteins α-la and β-lg.

Changes in the surface protein of the fat globules during ultra-high pressure homogenisation and conventional treatments of milk

Disruption of fat globules upon homogenisation provokes a reduction of their size and a concomitant increase in their specific surface area. In order to overcome this phenomenon, the milk fat globule membrane (MFGM) adsorbs non-native MFGM proteins. The aim of the present study was to examine the effects of UHPH conditions (temperature and pressure) on the milk fat globule and the surface proteins by comparison with conventional treatments applied in the dairy industry. Transmission electron microscopy and SDS-PAGE revealed major differences. In UHPH-treated milk, casein micelles were found to be adsorbed on the MFGM in a lesser extent than in conventional homogenisation–pasteurisation. However, greater adsorption of directly bonded casein molecules, released by UHPH through the partial disruption of casein micelles, was observed especially at high UHPH pressures. Adsorption of whey proteins on the MFGM of conventionally homogenised–pasteurised milk was mainly through intermolecular disulfide bonds with MFGM material, whereas in UHPH-treated milk, disulfide bonding with both indirectly and directly adsorbed caseins was also involved.

Application of Kevin—Voigt Model in Quantifying Whey Protein Adsorption on Polyethersulfone Using QCM-D

The study of protein adsorption on the membrane surface is of great importance to cheese-making processors that use polymeric membrane-based processes to recover whey protein from the process waste streams. Quartz crystal microbalance with dissipation (QCM-D) is a lab-scale, fast analytical technique that can precisely monitor and quantify the amount of proteins adsorbed onto the polymer surface in real time. The ability of the software that accompanies the instrument to predict the minute amount of the mass of the protein on the surface and the structural properties of the adsorbed protein requires a suitable viscoelastic model to convert the data of frequency and dissipation shift responses generated from the QCM-D apparatus into the mass and viscoelastic properties of the proteins adsorbed on the surface at given times. In this study, data recorded by a QCM-D apparatus were fitted into the Kevin—Voigt model, to quantify the whey protein adsorption on the polyethersulfone membrane surface.

Kinetics of adsorption of whey proteins and hydroxypropyl-methyl-cellulose mixtures at the air–water interface

The aim of this research is to quantify the competitive adsorption of a whey protein concentrate (WPC) and hydroxypropyl-methyl-cellulose (HPMC so called E4M, E50LV and F4M) at the air–water interface by means of dynamic surface tensiometry and Brewster angle microscopy (BAM). These biopolymers are often used together in many food applications. The concentration of both protein and HPMC, and the WPC/HPMC ratio in the aqueous bulk phase were variables, while pH (7), the ionic strength (0.05 M) and temperature (20 °C) were kept constant. The differences observed between mixed systems were in accordance with the relative bulk concentration of these biopolymers ( C HPMC and C WPC) and the molecular structure of HPMC. At short adsorption times, the results show that under conditions where both WPC and HPMC could saturate the air–water interface on their own or when C HPMC ⩾ C WPC, the polysaccharide dominates the surface. At concentrations where none of the biopolymers was able to saturate the interface, a synergistic behavior was observed for HPMC with lower surface activity (E50LV and F4M), while a competitive adsorption was observed for E4M (the HPMC with the highest surface activity). At long-term adsorption the rate of penetration controls the adsorption of mixed components. The results reflect complex competitive/synergistic phenomena under conditions of thermodynamic compatibility or in the presence of a “depletion mechanism”. Finally, the order in which the different components reach the interface will influence the surface composition and the film properties.

Whey protein–carboxymethylcellulose interaction in solution and in oil-in-water emulsion systems. Effect on emulsion stability

Carboxymethylcellulose (CMC) was used as coagulation aid to precipitate the whey proteins from defatted milk serum and the ability of the resulting whey protein concentrate (WPC, protein content: 63.69%) to aid in the physicochemical stabilization of oil-in-water emulsions, during ageing or following the application of heat or freeze–thaw treatment, was investigated, along with the stability of emulsion systems prepared with a commercial whey protein isolate. The stability of WPC emulsions against droplet flocculation and creaming, and to a lesser extent against droplet coalescence, depended on the presence of the CMC molecules in the emulsion continuous phase and the extent of adsorbed protein–polysaccharide interactions as affected by the emulsion pH. Studies on whey protein–CMC interaction were conducted, both in biopolymer mixture solutions and emulsion systems, by applying zeta potential measurement and viscometry techniques. These results were combined with data on protein surface hydrophobicity and on methylene blue-binding ability of CMC molecules and indicated that whey protein–CMC interaction may take place in solution, both at neutral as well as at acidic environments, leading, depending on pH, to the formation of soluble or non-soluble amphiphilic conjugates. In emulsion systems, however, conjugate formation is observed only at relatively acidic pH environments, probably because at a neutral or at a slightly acidic pH whey protein adsorption to the emulsion droplet surface and molecular unfolding does not favour protein–polysaccharide interaction.

Hydrophobic interaction adsorption of whey proteins: Effect of temperature and salt concentration and thermodynamic analysis

The adsorptive behavior of bovine serum albumin (BSA) and β-lactoglobulin (β-lg) on hydrophobic adsorbent was studied at four temperatures and different salt concentrations. The Langmuir model was fitted by experimental equilibrium data showing that an increase in temperature and salt concentration results in an increase on the capacity factor of both proteins. A thermodynamic analysis coupled with isotherm measurements showed that salt concentration and temperature affected the enthalpic and entropic behavior of the adsorption process of both proteins, mainly to the β-lg. The fast variation in the Z value for temperature over than 303.1 K suggest a great conformational change occurring in the β-lg structure, which almost duplicated the maximum adsorption capacity of this protein.

Bovine whey proteins inhibit the interaction of Staphylococcus aureus and bacteriophage K

To understand the potential use of bacteriophage K to treat bovine Staphylococcus aureus mastitis, we studied the role of whey proteins in the inhibition of the phage-pathogen interaction in vitro. The interaction of bacteriophage K and S. aureus strain Newbould 305 was studied in raw bovine whey and serum. Incubation of S. aureus with phage in whey showed that the bacteria are more resistant to phage lysis when grown in whey and also bovine serum. Whey collected from 23 animals showed a wide variation in the level of phage-binding inhibition. The role of the protein component of milk whey in this inhibition was established; treatment of the whey by heat, proteases and ultrafiltration removed the inhibitory activity. Brief exposure of S. aureus cells to whey, followed by resuspension in broth, also reduced phage binding. Microscopy showed the adhesion of extracellular material to the S. aureus cell surface following exposure to whey. Chromatographic fractionation of the whey demonstrated that the inhibitory proteins were present in the high molecular weight fraction. The adsorption of whey proteins to the S. aureus cell surface appeared to inhibit phage attachment and thereby hindered lysis. The inhibitory whey proteins are of high molecular weight in their native form and may sterically block phage attachment sites on the cell surface. These findings have implications for any future use of phage therapy in the treatment of mastitis, and other diseases, caused by S. aureus. This pathogen is predicted to be much more resistant to phage treatment in vivo than would be expected from in vitro broth culture experiments.

Whey protein adsorption onto steel surfaces—effect of temperature, flow rate, residence time and aggregation

Whey protein adsorption on stainless steel surfaces was investigated by in situ ellipsometry under well-defined flow conditions and protein solution residence times. The size distribution in solution of the protein aggregates formed under the same conditions was determined by dynamic light scattering. The adsorption was performed at 72 °C and 85 °C, which is below and above the unfolding temperature of β-lactoglobulin (75 °C). The effect of increasing the Reynolds number on the aggregation process was evident only for the longest protein solution residence time, when larger aggregates were produced. At the higher temperature, higher flow turbulence decreased the amount of protein adsorbed on the surface, which was attributed to shear-induced removal of protein from the surface. At both temperatures, longer protein solution residence times decreased both the adsorption kinetics and the amount of protein adsorbed. This could be related to the concentration of native protein available in solution. Based on the experimental results, a model of the formation of a protein monolayer and multilayers on solid surfaces was developed. The model takes into account the dependence of the adsorption process on both protein solution residence time and flow rate and predicts the evolution of adsorbed mass of protein per unit surface area with operating time. Surface-induced aggregation was identified as the main mechanism responsible for the formation of multilayers, based on experimental data. To reduce the amount of protein adsorbed/deposited on the surface an increase in protein solution residence time was found to be more effective than an increase in the Reynolds number.

Effect of surface and bulk solution properties on the adsorption of whey protein onto steel surfaces at high temperature

The adsorption of whey proteins on modified and unmodified 316 2R stainless steel surfaces was studied by in situ ellipsometry under well-defined flow conditions. The effects of bulk properties, e.g. temperature, pH, protein concentration and flow rate as well as surface modification by ion implantation, sputtering, chemical vapour deposition and silica sol–gel deposition, were investigated. The surface properties were characterized in terms of wettability and roughness. The results suggest a surface-induced aggregation process given that (1) the adsorbed amount at high temperature was significantly larger than expected for a monolayer, and (2) the adsorption was lower with a larger number of aggregates in solution. The surface modifications affected the initial adsorption rate, i.e. the rate of forming the monolayer, which in turn influenced the surface induced aggregation and eventually the total amount deposited. Therefore, once the surface was fully covered with protein, the rate of deposition, which is controlled by protein–protein interactions, was less affected by the surface modifications. This work evidenced the potential of surface modification regarding the reduction of protein adsorption on steel surfaces.

Article

Carbonyl analysis was used in order to follow the main reactions involved in the process of deterioration of milk powders. This method was applied after the milk had been processed using microfiltration and ultrafiltration, freeze-drying or spray-drying. The milk powders were then stored at a temperature of 45 o C and aw ranging from 0.7, 0.11, 0.23 and 0.33 to 0.5 for a period of twenty days. Water adsorption was influenced by powder composition on one hand, with a maximum water adsorption of whey proteins at 0.20 aw, and by the physical state of molecules on the other hand. At certain conditions such as 45 o C and 0.33 aw, amorphous lactose released the water molecules and turned into crystallised lactose. All powders studied exhibited a minimum deterioration, except those rich in lactose, at 0.20 ± 0.5 aw. For the products rich in lactose this minimal deterioration was ob- served at two aw values: 0.10 and 0.30. The determination of the monolayer moisture was carried out either theoretically with the BET model or experimentally so as to predict the most favourable degree of dehydration of dehydrated products. Carbonyl / powder stability / sorption isotherm / water activity / monolayer value

Fouling of inorganic membranes by adsorption of whey proteins

The adsorption of proteins to membrane surfaces can lead to the reduction of a permeate flux and represents a serious impediment to efficient membrane filtration operations. The factors influencing protein adsorption, permeate flux and overall membrane fouling during cross-flow filtration of whey protein solutions using 50 nm pore size ultrafiltration zirconia membrane and 200 nm pore size microfiltration alumina membrane were examined in this study. The permeate flux was observed to be a function of protein concentration and transmembrane pressure and followed classic membrane filtration behavior for the membranes studied. Studies of the fouling resistances, coupled with static adsorption studies, indicated that adsorption-related pore plugging plays a significant role in the larger pore alumina microfiltration membranes.

Adsorption of whey protein isolate at the oil-water interface as a function of processing conditions: a rheokinetic study.

In this paper we present surface dynamic properties (interfacial tension and surface dilational properties) of a whey protein isolate with a high content of beta-lactoglobulin (WPI) adsorbed on the oil-water interface as a function of adsorption time. The experiments were performed at constant temperature (20 degrees C), pH (5), and ionic strength (0.05 M). The surface rheological parameters and the interfacial tension were measured as a function of WPI concentration (ranging from 1 x 10(-)(1) to 1 x 10(-)(5)% w/w) and different processing factors (effect of convection and heat treatment). We found that the interfacial pressure, pi, and surface dilational modulus, E, increase and the phase angle, phi, decreases with time, theta, which should be associated with WPI adsorption. These phenomena have been related to diffusion of the protein toward the interface (at short adsorption time) and to the protein unfolding and/or protein-protein interactions (at long-term adsorption) as a function of protein concentration in solution and processing conditions.