Rheological and physical properties of various flour extrudates at different barrel temperatures
Extrusion process is a high-temperature short time cooking process. The aim of this study was to evaluate the effect of barrel temperature and flour types on the residence time distribution, physical properties and rheological properties of various pregelatinized flour. Corn flour, rice flour, an...
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| Format: | Thesis |
| Language: | English |
| Published: |
2016
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/69454/1/FSTM%202016%2020%20-%20IR.pdf |
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| Summary: | Extrusion process is a high-temperature short time cooking process. The aim of this
study was to evaluate the effect of barrel temperature and flour types on the residence
time distribution, physical properties and rheological properties of various
pregelatinized flour. Corn flour, rice flour, and their blends with 30% potato starch
(w/w, d.b), were extruded under extrusion conditions at screw speed of 75 rpm, feed
moisture at 25% (w/w, w.b.), barrel temperature ranging from 80 °C to 140 °C and die
size of 1.88 mm. The extrudates were dried at 50 °C overnight, ground and further
analyzed. The results showed that an increase in extruder barrel temperature
significantly decreased the mean residence time (p ≤0.05), total collection time (p
≤0.05) and mean collection time (p ≤0.05) of the extrudates. Analysis on the physical
properties (expansion ratio, rehydration ratio, water absorption index, water solubility
index, color, and water activity) and the rheological properties (steady shear, dynamic
shear, and cohesiveness of powder) were done on the extrudate sample. The results
showed that increase in barrel temperature significantly increased expansion ratio (p
≤0.05), water absorption index, WAI (p ≤0.05), water solubility index, WSI (p ≤0.05),
and the yellowness, b (p ≤0.05) of the extrudates while decreased the shear thinning
behavior (n become closer to 1), and decreased the apparent viscosity of the extrusion
dispersion at shear rate 100 s-1. The addition of potato starch influences the properties
such as increases the WSI at 140°C, decreases the WAI at 140°C and decreases the
overall gel strength of the pregelatinized flours. Corn flour blended with potato starch
extrudates and rice flour extrudates were well fitted (R2 >0.8) into the Arrhenius
equation with a decreasing Ea with increasing extruder barrel temperature. All
extrudate samples showed shear thinning behavior for the dispersion and a solid-like
gel. The additional of potato starch on the extrudates extruded barrel temperature of
80 °C and 100 °C make the extrudates less frequency dependency with a moderate but
consistent G´ across the frequency range tested. The addition of potato starch caused
properties different such as an increase in WAI, WSI and decrease in overall G´ and G˝
of the pregelatinized flours. The pregelatinized flours’ cohesiveness was not affected
by barrel temperature (p >0.05). Corn flour blended with potato starch extrudates
showed a good thickening and gelling properties. Both, the effects of barrel
temperature and flour type play important roles in the rheological and physical
properties of the pregelatinized flours. |
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