Hydrocyclone fractionation of chickpea flour and measurement of physical and functional properties of flour and starch and protein fractions
Tabaeh Emami, Seyed Shahram
Chickpea grain contains a high amount of starch and valuable protein. Many grain legumes (pulses) can be processed by pin milling and air classification with high separation efficiency. However, chickpea exhibits low separation efficiency because it has a relatively high fat content compared to other pulses. Therefore, the main goal of this research was to improve the starch-protein separation from chickpea flour in order to increase the economic value of chickpea grain.The chemical composition of pin-milled chickpea flour was determined. The functional and physical properties of chickpea flour affecting starch-protein separation were determined. No chemical interactive force was detected between starch granules and protein particles. Therefore, a physical separation technique, i.e. applying centrifugal force in a hydrocyclone, was employed to separate starch granules from protein particles. Using a hydrocyclone, centrifugal force was applied to chickpea flour particles. Chickpea flour was suspended in two different media, isopropyl alcohol or deionized water. In both media, high inlet pressure resulted in smaller geometric mean diameter of particles collected in the overflow and underflow. Isopropyl alcohol as a medium resulted in particles with smaller geometric mean diameter than did deionized water. Starch and protein separation efficiencies were higher at greater inlet pressures. The application of a double-pass hydrocyclone process increased the purity of starch in the underflow and of protein in the overflow, although this process reduced separation efficiencies. Starch granules and protein particles were separated at higher purities in deionized water than in isopropyl alcohol. Separation in deionized water resulted in higher starch separation efficiency and lower protein separation efficiency than did separation in isopropyl alcohol. This difference was due to the difference in density and viscosity of the two media. The higher viscosity of isopropyl alcohol reduced the likelihood of starch granules reaching the inner hydrocyclone wall. Thus, some starch granules were retained in the overflow instead of in the underflow. Additionally, the centrifugal force and drag force applied to the chickpea flour particles differed between the two different media. Hydrocyclone operation resulted in higher centrifugal force and lower drag force in deionized water than in isopropyl alcohol. Since the drag force in isopropyl alcohol was higher than that in deionized water, some small starch granules were diverted to the overflow which caused reduction of protein purity. The use of pH 9.0 and defatting of chickpea flour improved both starch and protein separation efficiencies. Chickpea flour in deionized water at a feed concentration of 5% yielded a pumpable slurry which was delivered efficiently to the hydrocyclone at an inlet pressure of 827 kPa Fractionation of starch and protein from chickpea flour in deionized water using an integrated separation process resulted in starch and protein fractions containing 75.0 and 81.9% (d.b.) starch and protein, respectively. This process resulted in starch and protein separation efficiencies of 99.7 and 89.3%, respectively. Experiments were also conducted to determine the physical and functional properties of chickpea flour and starch and protein fractions. Thermal conductivity, specific heat, and thermal diffusivity were determined and the polynomial linear models were fitted very well to experimental data. Internal and external friction properties of chickpea flour and starch and protein fractions were determined. Samples were subjected to uniaxial compression testing to determine force-time relationships. The samples’ particles underwent rearrangement rather than deformation during compression. The asymptotic modulus of samples was also computed, and it was linearly related to maximum compressive pressure. The functional properties of fractionated products were highly affected by the separation process. The water hydration capacity of starch fraction increased, whereas the emulsion capacity and foaming capacity of starch and protein fractions were reduced, compared to that of chickpea flour.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentAgricultural and Bioresource Engineering
ProgramAgricultural and Bioresource Engineering
SupervisorTabil, Lope G.
CommitteeMeda, Venkatesh; Kushwaha, Radhey Lal; Baik, Oon-Doo; Tyler, Robert T. (Bob)