Abstract
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 viscosity of the liquid product exhibited a complex behavior along the processing unit: in addition to its dependence on local temperature, it was affected by the local degree of denaturation of whey proteins – and hence on the product history previous to this position in the heat exchanger. The numerical model was structured into a sequence of computational domains; its versatility was illustrated by changing the length of the holding section and then assessing the impact on the final degree of denaturation of the whey proteins present in the liquid product.
Highlights
Heat treatment of foods need to be optimized to promote beneficial effects and to counteract undesired effects (van Boekel et al, 2010)
Numerical modelling of thermal denaturation-aggregation SI19 objective was to investigate the two-way coupling between those phenomena; in addition, the model was employed as a tool for virtual experiments, predicting the final transformation state of the liquid product under conditions which were not considered in the implementation of the model
The concentration of native whey proteins decreases with the time, and the rate of such a decrease depends on the temperature; the local value of the denaturation ratio at a given position of the heat exchanger depends on the whole thermal and kinetics history experienced, since the inlet of the first heating section, by the fluid particles that are running at the position of the interest
Summary
Heat treatment of foods need to be optimized to promote beneficial effects and to counteract undesired effects (van Boekel et al, 2010). The study of liquid products becomes very challenging from the modelling perspective when there is two-way coupling between phenomena of fluid flow and heat transfer in the processing unit Such a coupling is relevant in the dairy industry, because it is associated with the formation of deposits of transformed product onto the heat transfer surfaces (fouling which can reduce heat transfer and add resistance to fluid flow (Goode, Asteriadou, Robbins, & Fryer, 2013; Khaldi et al., 2018; Li, Singh, & Lee, 2004). In such a coupled problem, thermal denaturation-aggregation of proteins can affect product rheology, which in turn drives the velocity field through the processing unit. Numerical modelling of thermal denaturation-aggregation SI19 objective was to investigate the two-way coupling between those phenomena; in addition, the model was employed as a tool for virtual experiments, predicting the final transformation state of the liquid product under conditions which were not considered in the implementation of the model
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