Color degradation kinetics and rheological characteristics of onion puree

Kinetics of color degradation and theological characteristics of onion puree were investigated at selected temperatures. The color degradation followed first-order reaction kinetics. The tristimulus color combination La/b adequately described the degradation. Dependence of the rate constant during thermal treatment obeyed the Arrhenius relationship. The activation energy was estimated to be 27.6 kJ/mol. Onion puree exhibited shear-thinning behavior with yield stress. The power law model described well the relationship of shear stress and shear rate over a temperature range of 40 degrees C to 90 degreesC. Variation of the flow behavior index (n) with temperature was not consistent and ranged between 0.127 and 0.216 Both the consistency index (K) and apparent viscosity (eta) decreased with increase in temperature, and the activation energies of flow were found to be in the range of 13.32 to 14.3 kJ/mol.