Characterization of Cassava Starch Processed in an Internal Mixer

An internal mixer connected to a torque rheometer was used to investigate the effect of moisture content (13.2 to 46.8 g.100g(-1)), rotation speed (13.2 to 46.8 rpm) and processing temperature (53.2 to 86.8 degrees C), applying a factorial central composite design, on the specific mechanical energy (SME), pasting viscosity and crystallinity of cassava starch. Torque values were highly significant for the three variables, showing decrease with increasing moisture, temperature and rpm. The highest cold viscosity (CV) was obtained at 13.18 g.100g(-1) moisture, 86.87 degrees C and 30 rpm due to increased rupture of starch granules caused by processing at lower moisture condition. Peak viscosity (PV) values were higher than CV values which indicated that the processing was not able to destroy completely the molecular integrity of the starch granules. Smaller setback (SB) at high temperature and rpm and low moisture showed possible starch depolymerization causing loss of recrystallization capacity. Processing under low moisture content resulted in reduction of crystallinity. The results showed that the effect of moisture was more pronounced than rotation speed and processing temperature of cassava starch.