Whey Protein Soluble Aggregates from Heating with NaCl: Physicochemical, Interfacial, and Foaming Properties

Department of Food Science, Nestlé Research Center, Vers-chez-les-Blanc, CH-1000 Lausanne 26, Switzerland.
Langmuir (Impact Factor: 4.46). 04/2007; 23(8):4155-66. DOI: 10.1021/la0632575
Source: PubMed


Whey protein isolate was heat-treated at 85 degrees C for 15 min at pH ranging from 6.0 to 7.0 in the presence of NaCl in order to generate the highest possible amount of soluble aggregates before insolubility occurred. These whey protein soluble aggregates were characterized for composition, hydrodynamic diameter, apparent molecular weight, zeta-potential, surface hydrophobicity index, activated thiol group content, and microstructure. The adsorption kinetics and rheological properties (E', etad) of these soluble aggregates were probed at the air/water interface. In addition, the gas permeability of a single bubble stabilized by the whey protein soluble aggregates was determined. Finally, the foaming and foam-stabilizing properties of these aggregates were measured. The amount of whey protein soluble aggregates after heat treatment was increased from 75% to 95% from pH 6.0 to pH 7.0 by addition of 5 mM to 120 mM NaCl, respectively. These soluble aggregates involved major whey protein fractions and exhibited a maximum of activated thiol group content at pH > 6.6. The hydrodynamic radius and the surface hydrophobicity index of the soluble aggregates increased from pH 6.0 to 7.0, but the molecular weight and zeta-potential decreased. This loss of apparent density was clearly confirmed by microscopy as the soluble aggregates shifted from a spherical/compact structure at pH 6.0 to a more fibrillar/elongated structure at pH 7.0. Surface adsorption was faster for soluble aggregates formed at pH 6.8 and 7.0 in the presence of 100 and 120 mM NaCl, respectively. However, interfacial elasticity and viscosity measured at 0.01 Hz were similar from pH 6.0 to 7.0. Single bubble gas permeability significantly decreased for aggregates generated at pH > 6.6. Furthermore, these aggregates exhibited the highest foamability and foam liquid stability. Air bubble size within the foam was the lowest at pH 7.0. The coarsening exponent, alpha, fell within predicted values of 1/3 and 1/2, except for very dry foams where it was 1/5.

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    • "Extensive research have been dedicated to reduce milk fouling deposition on hot processing surfaces by modifying thermal parameters, adding inhibiting chemicals fouling and modifying the design of the processing equipment. Reducing fouling is related to the control and understanding of β-lactoglobulin (β-lg) denaturation reaction, since, accounting for half of the whey proteins in cow milk (Ayadi et al. 2004, 2007; Schmitt et al. 2007), it is predominant in the fouling phenomenon of milk derivatives. Under heat treatment, β-lg loses its tertiary structure and becomes reactive by exposing a free thiol. "
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    ABSTRACT: Using a developed laboratory scale device, different heat treatment conditions were applied on camel and cow milks. After each fouling experiment, photos of stainless steel plates were taken and dry deposit weights were determined. The thermal behaviour of camel and cow proteins was studied by electrophoresis (SDS-PAGE), differential scanning calorimetry (DSC) and free thiol groups concentrations evolution. The obtained results have shown that heating both camel and cow milks at 70°C for 2h generate deposit formation. The fouling rate was more important when heating camel milk than after heating cow milk for all heat conditions except at 90°C for 2h. Electrophoresis patterns indicated that after heating camel milk at 90°C, α-lactalbumin (α-la), camel serum albumin (CSA) and κ-casein bands decreased. Bovine serum albumin (BSA) disappear from the electrophoresis patterns after heating cow milk at 70°C while β-lactoglobulin (β-lg) and α-la bands disappeared only at 90°C. DSC thermograms of camel milk showed that the denaturation temperature of camel proteins is 77.8°C, lower than that of cow proteins which is 81.7°C. The results of free thiol groups evolution versus temperature and heating time showed that camel proteins denaturation starts between 70 and 80°C. However, for cow milk, the whole denaturation phenomenon happens after heat treatment at 70°C for 30min.
    Food and Bioprocess Technology 08/2015; DOI:10.1007/s11947-015-1529-5 · 2.69 Impact Factor
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    • "Schmitt et al. [11] reported that in the absence of added salt stable suspensions of spherical particles with a radius of about 60 nm formed in solutions of 10 g/L WPI during heating at pH 6.0, whereas at pH 6.6 and pH 7.0 small curved strands were formed. The ␨potential of the two types of aggregates was similar, but the surface hydrophobicity was lower for the spherical particles. "
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    ABSTRACT: Whey proteins spontaneously form spherical particles when heated in aqueous solutions at conditions where their net charge density is below a critical value. The particles are microgels consisting of a hydrated crosslinked network of proteins with a diameter between 100nm and 1μm. Stable suspensions of these microgels can be formed in a narrow range of conditions when the protein charge density is low enough to induce their formation, but high enough to inhibit further association into larger clusters or macroscopic gels. The formation of microgels and their application to stabilize emulsions and foams; form core-shell particles; form gels; or modify the texture of polysaccharide solutions and gels are reviewed. Copyright © 2015 Elsevier B.V. All rights reserved.
    Colloids and surfaces B: Biointerfaces 06/2015; DOI:10.1016/j.colsurfb.2015.05.055 · 4.15 Impact Factor
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    • "The third is an ion-induced conformational change, which leads to altered hydrophobic interactions and aggregation at elevated temperatures (Kinsella and Whitehead, 1989; Wang and Damodaran, 1991). The latter indicates that calcium acts principally on BLG aggregation (Mulvihill and Donovan, 1987; Petit et al., 2011) by both increasing the size of aggregates (Allen and Smith, 2001; Schmitt et al., 2007) and lowering the BLG denaturation temperature, which in turn, favours aggregate formation (De Wit, 1990; Simmons et al., 2007). Its role in BLG unfolding is limited to the reinforcement of the native BLG tertiary structure (Petit et al., 2011). "
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    ABSTRACT: Fouling and cleaning with a whey protein concentrate solution in a plate heat exchanger were investigated with a varying calcium concentration (from 70 to 87.5 mg L−1) and under a wide range of hydrodynamic conditions for a bulk fouling fluid temperature, ranging from 60 and 96 °C. This work demonstrates that increasing the calcium concentration in whey protein concentrate contributes to the amount of fouling and affects the thermal conductivity of the deposit. It was also observed that the fluid flow regime during fouling, impacts the deposit growth, modifies the structure of fouled layers and has a significant consequence on cleaning behaviour. Finally, a dimensional analysis together with experimental measurements, allowed a relationship to be established enabling prediction of the amount of dry mass deposited locally as a function of the known calcium content, Reynolds number and bulk fluid temperature.
    Journal of Food Engineering 02/2015; 147:68–78. DOI:10.1016/j.jfoodeng.2014.09.020 · 2.77 Impact Factor
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