Whey protein soluble aggregates from heating with NaCl: Physicochemical, interfacial, and foaming properties
ABSTRACT 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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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 · 2.58 Impact Factor
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ABSTRACT: The effects of sulphydryl (–SH) reagents on protein aggregation reactions in heated whey protein isolate (WPI) and pure α-lactalbumin (α-La) were investigated. In contrast to its previously reported effect with pure β-Lg, dihydrolipoic acid (DHLA) markedly reduced the heat stability of WPI, especially the α-La component, which aggregated much more readily in the presence of DHLA than in WPI alone. Whilst pure α-La is quite stable to heat, it is much less stable in the presence of DHLA. An effect similar to DHLA was observed with reduced glutathione (GSH). N-ethylmaleimide (NEM), and to a lesser extent, dithio(bis)-p-nitrobenzoate (DTNB), improved the heat stability of WPI; these reagents had little effect on α-La.Food Chemistry 11/2014; 163:129–135. DOI:10.1016/j.foodchem.2014.04.094 · 3.26 Impact Factor
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ABSTRACT: a b s t r a c t The foaming properties of fibrillar whey proteins were compared with those of native or denatured whey proteins and also with egg white protein. Whey protein foaming capacity and stability were related to protein concentration, pH, time of whipping, pressure and heating treatments. Foams produced from fibrils showed significant improvement in foaming capacity and stability when compared with non-fibril-lar whey proteins. Dynamic high shear (microfluidization) or moderate shear (Ultra-Turrax mixing) of fibrillar protein dispersions did not significantly affect their subsequent foaming properties. Furthermore, foams prepared with fibrillar whey protein (63% protein) had comparable capacity and stability to that from egg white protein, which is the traditional foaming ingredient in food industry. Results suggest that fibrillized whey proteins are highly effective foaming agents even at relatively low protein concentrations (1–3% w/w).