Color degradation kinetics and rheological characteristics of onion puree

Kinetics of color degradation and theological characteristics of onion pure e were investigated at selected temperatures. The color degradation followe d first-order reaction kinetics. The tristimulus color combination La/b ade quately described the degradation. Dependence of the rate constant during t hermal treatment obeyed the Arrhenius relationship. The activation energy w as estimated to be 27.6 kJ/mol. Onion puree exhibited shear-thinning behavi or with yield stress. The power law model described well the relationship o f shear stress and shear rate over a temperature range of 40 degrees C to 9 0 degreesC. Variation of the flow behavior index (n) with temperature was n ot consistent and ranged between 0.127 and 0.216 Both the consistency index (K) and apparent viscosity (eta) decreased with increase in temperature, a nd the activation energies of flow were found to be in the range of 13.32 t o 14.3 kJ/mol.