Starch gelatinisation in Couette-Taylor flow apparatus

Abstract

In this paper starch gelatinisation in Couette-Taylor flow (CTF) apparatus (equipped with a water heat jacket) has been investigated. CTF (characterised by the presence of Taylor vortices) provides good environment for gelatinisation, e.g. effective mixing, fast heat transfer, positive influence on starch rheological properties. During experiments starch gelatinisation degree and starch swelling has been studied. It was accompanied by temperature measurements performed along the apparatus. Additionally, starch gelatinisation was investigated by computer simulation. A complete starch gelatinisation was obtained for the shortest investigated residence time in the apparatus when the temperature in the heat jacket was above 85 °C. Nevertheless, it seems that it is still possible to reduce a residence time value, as well as, the value of T hj , but it may require some acceleration of rotor rotation. The swelling degree of gelatinised starch increased with growing values of residence time, rotor rotation and process temperature. Heat transferred could be affected by the structure of the Taylor vortex flow. No significant destruction of starch granules was observed during the treatment in Couette-Taylor flow apparatus. A quite satisfactory agreement between computer simulation and experiments results was achieved.

Thermal treatment of starch slurry in Couette-Taylor flow apparatus

“…For this purpose an aluminium vessel (with a thin wall) was used. The outside of the vessel was covered with a layer of ice (1 cm thick), whose temperature was about -5 C (Hubacz and Buczyńska 2011). The sample taking procedure was a continuous process, during which starch dispersion gathered in the vessel was gently stirred and mixed with a new portion of the dispersion of high temperature.…”

“…Although it was believed that dissolved starch was mostly in the form of amylose, some shorter or less branched molecules of amylopectine can be also possibly detected using this method. It is worth remembering that this procedure should not be confused with procedure of DSG measurement (Baks et al 2007;Hubacz and Buczyńska, 2011), which was also based on the amylose-iodine complex formation. The concentration of amylose (or dissolved starch) in the supernatant was the result of amylose leaching from the starch granules and the water absorption by the granules (i.e.…”

“…The hydrodynamics of the flow during starch gelatinization was calculated using steady state NavierStokes equations adapted for a 2D axisymmetric swirl model (see Hubacz and Buczyńska, 2011). The 2D axisymmetric swirl model is based on the assumption that there is no circumferential gradient in the flow, although, there may be non-zero circumferential or swirl velocity.…”

“…The 2D axisymmetric swirl model is based on the assumption that there is no circumferential gradient in the flow, although, there may be non-zero circumferential or swirl velocity. In addition to this, energy and species transport equations were solved (see Hubacz and Buczyńska, 2011). These equations were included into the model in order to calculate rheological properties of starch slurry, which was modelled using a power-law equation (see Hubacz et al, 2013):…”

“…Additionally, in order to ensure good heat transfer conditions and to avoid separation of the starch from the water phase, an agitation of the slurry is needed (Sakonidou et al, 2003). In such a context, Couette-Taylor flow (CTF) apparatus was proposed for wheat starch processing (Hubacz and Buczyńska, 2011;Hubacz et al, 2013;Masuda et al, 2013). This type of apparatus consists of two cylinders with the inner one (rotor) rotating, while the fluid flows in the gap between these cylinders.…”