Development of a rheological method to characterize palm oil crystallizing under shear

Abstract

To follow palm oil crystallization under shear, a new rheological method was developed. This method can be split up into two parts: In the first part, continuous shear is applied for a pre-defined period and crystallization is monitored by measuring the apparent viscosity as a function of isothermal time under shear. In the second part, shear is halted and oscillation is applied during 30 s, thus recording moduli and phase angle. These moduli and phase angle are then characteristic of a sample crystallized under shear during this pre-defined period. After repeating this procedure for increasing shearing periods in the first part, complex modulus and phase angle were plotted as a function of isothermal time under shear. The thus obtained results were compared with crystallization data obtained via time-resolved X-ray diffraction and polarized light microscopy

Influence of shear flow on polymorphic behavior and microstructural development during palm oil crystallization

“…Conversion factors for shear rate (4.500) and shear stress (48,600 m -3 ) were determined by the manufacturer by performing a calibration with both Newtonian and non-Newtonian oil. This geometry is described in detail elsewhere [17,18].…”

“…The crystallization of palm oil was followed at four temperatures (18,20,22 ). Figure 1 shows SAXS patterns of palm oil crystallized at 18 7C without and with shear and crystallized at 25 7C without shear.…”

“…In this part of the study, palm oil (IV 51) was crystallized at four different crystallization temperatures (18,20,22 and ) for three different isothermal shear periods (1, 15, 30 min: step c), followed by further crystallization without shear. During the shear step (step c), the crystallization process was monitored by apparent viscosity measurement.…”

“…The following time-temperature program was applied: -heating to 70 7C, holding isothermally for 10 min to erase all crystal memory; -cooling at 10 7C/min to the desired crystallization temperature (18,20,22 or 25 7C);…”

Effect of frying on the rheological and chemical properties of palm oil and its blends

“…For a better perception, a table (Table 2) on viscosity of different blends (before frying) at various temperature is included which was first appeared as a predecessor of this study (Siddique et al 2010). This might be due to the presence of fat crystals that coalesce together and need more time for destruction while it increases the friction between the layers and results in the sharp increase in viscosity (Vaclavik and Christian 2003;Graef et al 2008). One the probable explanation for this observation might be because at relatively low temperature there are fat crystals present in the oil samples.…”