Influence of whey protein aggregation on the residence time distribution in a tubular heat exchanger and a helical holding tube during heat treatment process (original) (raw)
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International Dairy Journal
Microparticulation of whey proteins at low concentration (2%, w/v), was examined in a pilot plant tubular heat exchanger (THE). Turbulent flow in combination with moderate temperatures (85 C) was used in the heating section to prevent fouling, whereas the flow was varied from laminar to turbulent in the holding section of the THE. The logarithm of the formal rate of denaturation of b-lactoglobulin (b-Lg) k f was À5.4 to À2.5 depending on the temperature. Variation of flow velocity in the holding section had a negligible impact on denaturation degree of b-Lg and particle size of agglomerates. A high increase of elastic modulus, G 0 , of agglomerates was combined with only bisection of water holding capacity. Advanced modifications of particle structure and properties are supposed to be achievable by more freedom in control of flow character at a heating section of a THE for example through application of direct heat transfer principles.
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...
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 dairy science, 2016
Fouling of plate heat exchangers (PHE) is a severe problem in the dairy industry, notably because the relationship between the build-up of protein fouling deposits and the chemical reactions taking place in the fouling solution has not yet been fully elucidated. Experiments were conducted at pilot scale in a corrugated PHE, and fouling deposits were generated using a model β-lactoglobulin (β-LG) fouling solution for which the β-LG thermal denaturation reaction constants had been previously determined experimentally. Then 18 different bulk temperature profiles within the PHE were imposed. Analysis of the fouling runs shows that the dry deposit mass per channel versus the ratio R=kunf/kagg (with kunf and kagg representing, respectively, the unfolding and aggregation rate constants computed from both the identification of the β-LG thermal denaturation process and knowledge of the imposed bulk temperature profile into the PHE channel) is able to gather reasonably well the experimental f...
Chemical Engineering Science, 2007
The influences of calcium concentrations (70.88 mg/l), Reynolds number and temperature (60.96 • C) upon the deposit structure and the rate of growth deposition have been investigated in a plate heat exchanger. This was done from in situ measurements of the deposit electrical conductivity via implementation of stainless steel electrodes in channels combined with assessments of deposit thickness. Calcium ions affect structures of deposits and increase the rate of deposit growth upon heated surfaces. This was attributed to the formation of weaker size aggregates at higher calcium concentrations and a higher number of calcium bindings, which reinforce adhesion forces between protein aggregates. Structures and appearances of deposits also were affected by flow rates whatever the calcium concentrations. Deposit growth rate was enhanced by increasing flow rate below a critical Reynolds number comprised between 3200 and 5000. On the contrary, above the critical Reynolds number, a limitation of the deposit and/or an escape of the deposit from the fouled layer into the core fluid occurred, caused by the predominance of particle breakage on the deposit formation. Fouling tended to be reduced at higher flow rate. It was noteworthy that rates of growth decrease during fouling experiments which may be explained by an increase in local shear stresses leading to particle breakage. ᭧
A Kinetic Study on the Heat-Induced Changes of Whey Proteins Concentrate at Two pH Values
Food and Bioprocess Technology
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 sensorial and nutritional quality of milk. The heat-induced changes on dispersions of whey proteins concentrate were monitored by measurement of thiol availability, protein solubility, and turbidity at pH 6.6 and 7.5. The fractional conversion model was used to quantitatively describe the effect of different temperature–time combination on denaturation mechanism. The results demonstrate that heat-induced changes of WPC greatly influence their solubility, expressed as degree of denaturation at pH 4.6 and were related to the heating conditions. The denaturation mechanism involved a number of consecutive conformational changes in the molecules. A curvature in Arrhenius plots was observed around 75 °C, indicating changes in the reaction mechanism. The deflection of Arrhenius plot reflects the generally accepted two-step denaturation/aggregation process of whey proteins.
Two-Way Coupling of Fluid-Flow, Heat-Transfer and Product Transformation during Heat Treatment of Starch Suspension inside Tubular Exchanger, 2013
When a liquid product is subjected to thermal treatment under continuous flow, its transport properties can evolve as a consequence of changes occurring on the product constitution (continuous phase, particles...). This two-way coupling is implicitly considered when the residence time distribution (RTD) associated with the product is studied through experimental work. For a number of liquid food products, there is experimental evidence that the minimum residence time decreases as the transformation state progresses. In this study, modeling work is employed for assessing the influence of transformation on the RTD associated with a starch suspension under continuous heat treatment. After including the impact of starch granules swelling on the suspension viscosity, the minimum residence time decreases from 55 % to 41 % of the mean value. The role played by the transformation in driving the RTD cannot be neglected if the transport properties evolve with the product transformation state. Keywords: fluid flow, heat transfer, starch granule swelling, heat exchanger, residence time distribution, computational fluid dynamics
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...
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.