The effect of temperature and shear upon technological properties of whey protein concentrate: Aggregation in a tubular heat exchanger (original) (raw)
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Le Centre pour la Communication Scientifique Directe - HAL - Université Paris Descartes, 2011
The aim of this study was to describe a thermal aggregation process at laboratory scale by using an experimental process simulator. This device is able to impose fast variations of temperature and shear in the same range as in industrial equipments. Thermally-induced aggregation was studied on 1lactoglobulin (1-lg) solutions. We observed the influence of a moderate shear and of treatment duration, on the final product characteristics: aggregate size and concentration and residual native fraction. The first results provide information about the shear influence on 1-lactoglobulin denaturation/aggregation during thermo-mechanical process: shear has no effect on the aggregated fraction but has a significant influence on the size distribution. The higher is the shear rate during heating, the higher is the concentration of large particles (20-1000 µm). These results are discussed in regards to the theoretical aspects of particles motion in suspension and the role of both perikinetic (Brownian motion) and orthokinetic (shear) collisions on 1-lactoglobulin denaturation and aggregation.
2011
The aim of this study was to describe a thermal aggregation process at laboratory scale by using an experimental process simulator. This device is able to impose fast variations of temperature and shear in the same range as in industrial equipments. Thermally-induced aggregation was studied on β- lactoglobulin (β-lg) solutions. We observed the influence of a moderate shear and of treatment duration, on the final product characteristics: aggregate size and concentration and residual native fraction. The first results provide information about the shear influence on β-lactoglobulin denaturation/aggregation during thermo-mechanical process: shear has no effect on the aggregated fraction but has a significant influence on the size distribution. The higher is the shear rate during heating, the higher is the concentration of large particles (20-1000 μm). These results are discussed in regards to the theoretical aspects of particles motion in suspension and the role of both perikinetic (Br...
Journal of Food Engineering, 2012
The residence time distribution (RTD) of a whey protein (WP) suspension flowing through a heat treatment system was studied. The experimental system is the tubular heat exchanger and the helical holding section of a laboratory scale thermal process. RTD was measured in isothermal conditions at 60°C, a temperature involving no WP aggregation, and at 87°C, temperature at which WP aggregates. Two flow rates (20 L/h and 49 L/h) were tested with two different lengths of holding tube in order to maintain the same order of magnitude of the holding time. Methylene blue was used as tracer and spectrophotometer analysis were performed to determine the outlet concentration. These investigations yielded to great differences between the RTD in aggregation and no aggregation conditions. The minimum residence time is shorter when WP aggregation occurs due to the modification of the velocity field inside the tubular devices with the local enhancement of the viscosity. Fitting the experimental results with a new compartment model based on the generalized convection model give very good agreement contrary to the more classical RTD models. This RTD model could be used in combination with a population balance model in order to predict the WP aggregates size dispersion.
Foods
The influence of thermomechanical treatment (temperature 60 °C–100 °C and shear rate 0.06 s−1–50 s−1) and mixing ratio of β-lactoglobulin (βLG) and α-lactalbumin (αLA) (5:2 and 1:1) on the denaturation and aggregation of whey protein model systems with a protein concentration of 60% and 70% (w/w) was investigated. An aggregation onset temperature was determined at approx. 80 °C for both systems (5:2 and 1:1 mixing ratio) with a protein concentration of 70% at a shear rate of 0.06 s−1. Increasing the shear rate up to 50 s−1 led to a decrease in the aggregation onset temperature independent of the mixing ratio. By decreasing the protein concentration to 60% in unsheared systems, the aggregation onset temperature decreased compared to that at a protein concentration of 70%. Furthermore, two significantly different onset temperatures were determined when the shear rate was increased to 25 s−1 and 50 s−1, which might result from a shear-induced phase separation. Application of combined t...
International Journal of Food Studies, 2020
A computational fluid dynamics model was designed to study the problem of thermal processing of a liquid food product containing whey proteins within a heat exchanger consisting of heating, holding and cooling tubular sections. This physical problem is associated with strong coupling between the phenomena of fluid flow, heat transfer, and thermal denaturation-aggregation of whey proteins. Our primary objective was to investigate the two-way coupling between these phenomena within the heat exchanger. This was carried out by analyzing the model predictions of velocity, temperature and product properties at both axial and radial directions. Attention was focussed on the whey proteins present in a cream cheese formulation. The thermal denaturation-aggregation kinetics was supposed to follow that of the beta-lacto-globulin, which plays a major role in fouling when milk derivatives are submitted to thermal processing in heat exchangers. Model predictions demonstrated that the apparent vis...
Heat-induced changes in some technological properties of whey proteins concentrate
Whey protein concentrate (WPC) is used as food ingredients due to their commercially important functional properties. The effects of heat treatment on the components of milk are very important for the final product character, since they undergo modifications that affect sensory and nutritional quality of milk. As foodstuffs they are applied not only because of their functional properties, but also because of their high nutritive value. Improvements in functional properties may be achieved by modifying the protein structure by chemical, enzymatic or physical treatments. Functional properties of whey proteins such as solubility, viscosity, water-holding capacity, gelation, adhesion, emulsification and foaming are affected by their structure and mainly reflect the functionality of β-lactoglobulin as the most abundant protein. The objective of this work was to evaluate the effect of heat treatment on dispersions of whey proteins concentrate on some technological properties. The heat ind...
Thermal Aggregation of Whey Protein Isolate Containing Microparticulated or Hydrolyzed Whey Proteins
Journal of Agricultural and Food Chemistry, 1997
Thermal aggregation from 25 to 97°C (0.8°C/min heating rate) of diluted whey protein isolate (WPI) containing microparticulated WPI (µWPI) or specific WPI tryptic hydrolysate was studied at pH 6.0 using a spectrophotometric method. Mixed WPI solutions containing above 3.75% µWPI displayed faster thermal aggregation at lower heating temperatures of protein species than the control WPI solutions (no µWPI added), with a shift of aggregation mechanism from predominantly homogeneous to biphasic. Interactions between whey proteins and soluble/insoluble whey protein microparticles were thought to be at the origin of the shift. Results also showed that the presence of 20-40% WPI tryptic hydrolysate into the WPI solutions improved whey protein thermal aggregation at pH 6.0. Such a result could not be ascribed only to protein-peptide interactions because hydrolysate promoted an initial acidification of WPI solutions from 6.9 to 5.4 (20% hydrolysate added) or to 4.6 (20% hydrolysate added), which contributed to whey protein isoelectric precipitation and formation of whey protein aggregates.
Journal of Dairy Research, 2005
Microfiltration and ultrafiltration were used to manufacture skim milks with an increased or reduced concentration of whey proteins, while keeping the casein and milk salts concentrations constant. The skim milks were heated on a pilot-scale UHT plant at 80, 90 and 120 °C. The heat-induced denaturation and aggregation of β-lactoglobulin (β-lg), α-lactalbumin (α-la) and bovine serum albumin (BSA) were quantified by polyacrylamide gel electrophoresis. Apparent rate constants and reaction orders were calculated for β-lg, α-la and BSA denaturation. Rates of β-lg, α-la and BSA denaturation increased with increasing whey protein concentration. The rate of α-la and BSA denaturation was affected to a greater extent than β-lg by the change in whey protein concentration. After heating at 120 °C for 160 s, the concentration of β-lg and α-la associated with the casein micelles increased as the initial concentration of whey proteins increased.
Food and Bioprocess Technology, 2013
Upon ultrasonic treatment at 20 kHz, protein aggregates in a dairy whey solution were broken down. In addition, when sonication was applied to a heated solution of denatured and aggregated proteins, there was a dramatic reduction in viscosity and aggregate size, which was maintained after re-heating. This observed heat stability may be due to shear forces that are induced by acoustic cavitation. To determine whether high shear mixing or homogenisation is able to cause similar effects to that of acoustic cavitation, sonication, high shear mixing and homogenisation were performed on 5 wt% whey protein concentrate solutions at identical energy density levels, which was based on the power drawn in each system. Homogenisation provided similar particle size and viscosity reductions as sonication while high shear mixing was less efficient in decreasing particle size. Cavitation was shown to be absent in both the mixing and homogenisation configurations, indicating that the shear forces generated are responsible for the observed particle size and viscosity reduction. In addition, heat stability was achieved in all systems indicating that a combination of heat treatment and any method that generates high shear forces can be used to improve the heat stability of whey proteins.
Modulation of rheological properties by heat-induced aggregation of whey protein solution
Food Hydrocolloids, 2011
Heat-induced protein aggregation at low protein concentrations generally leads to higher viscosities. We here report that aggregated protein can yield weaker gels than those from native protein at the same concentration. Aggregated protein was produced by heating a solution of whey protein isolate (WPI) at 3% and 9% w/w. The higher protein concentration resulted in a larger aggregate size and a higher intrinsic viscosity. The protein fraction in native WPI had the smallest size and the lowest intrinsic viscosity. The same trend was observed for the shear viscosity after concentrating the suspensions containing aggregates to around 15% w/w. Suspensions containing aggregates that were produced from a higher concentration possessed a higher viscosity. After reheating the concentrated suspensions, the suspension from the 9% w/w aggregate system produced the weakest gel, followed by the one from 3% w/w, while the native WPI yielded the strongest gel. Reactivity of the aggregates was also an important factor that influenced the resulting gel properties. We conclude that aggregation of whey protein solution is a feasible route to manipulate the gel strength of concentrated protein systems, without having to alter the concentration of the protein.