β-lactoglobulin denaturation, aggregation, and fouling in a plate heat exchanger: Pilot-scale experiments and dimensional analysis

In this work, we investigated the role of four independent process parameters, namely product temperature at the heat exchanger outlet, mean residence time, temperature increase between the heat exchanger inlet and outlet, and heat effectiveness, in the protein denaturation, aggregation, and fouling of a beta-lactoglobulin (beta-lg) concentrate that was chosen as model fluid for milk derivatives. A pilot scale plate heat exchanger in countercurrent configuration, supplied with a holder, was used in order to mimic industrial process conditions. The denaturation level and aggregates size of the heat treated beta-lg concentrate at the exchanger and holder outlets, along with the fouling mass in the plate heat exchanger were simultaneously determined. The results indicated that beta-lg denaturation, aggregation, and fouling reactions were mainly governed by the temperature profile in the investigated range of operating conditions, even though a small influence of residence time and healing rate was highlighted in the less denaturing conditions. A dimensional analysis was performed to identify the key dimensionless numbers governing beta-lg denaturation, aggregation, and fouling mechanisms in the heat treatment of a beta-lg concentrate. This allowed to emphasise the major influence of the Arrhenius exponential factor of beta-lg unfolding reaction, both related to temperature and beta-lg reactivity. The first Damkohler and Reynolds numbers, related to residence time and hydrodynamic conditions in the heat exchanger, as well as the heat exchange process parameters, linked to the heat effectiveness and the bulk-wall temperature differences, had also a small impact on beta-lg chemical behaviour. Moreover, empirical relationships based only on the Arrhenius exponential factor of beta-lg unfolding reaction permitted to describe the main trends observed in denaturation levels, aggregate sizes, and fouling masses, which underlined the predominant role of temperature and beta-lg reactivity in the investigated operating conditions. This study outlines finally that fast heat treatments permit to minimise fouling issues. (C) 2013 Elsevier Ltd. All rights reserved.