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.
"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. "
[Show abstract][Hide abstract] 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
"Schmitt et al.  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. "
"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). "
[Show abstract][Hide abstract] 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.
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