Prediction of decoloration in paprika oleoresins. Application to studies of stability in thermodynamically compensated systems.

In six paprika oleoresins, the kinetic parameters for the decoloration reaction at three temperatures have been established. The thermodynamic study shows that the decoloration reaction in each oleoresin has its own activation entropy (DeltaS) and activation enthalpy (DeltaH). The six reactions studied show a constant ratio between DeltaH and DeltaS, which means that each reaction is an isokinetic form of only one reaction affected by thermodynamic compensation. Instead of one equation per oleoresin to predict pigment concentration as a mathematical function of time and temperature, one unique equation can be obtained in which DeltaH is a function of DeltaS. The validity of this equation has been tested by comparing the actual concentration remaining during a heat treatment and the calculated one. More than 90% of the calculated concentrations are within the range of variability of the actual mean. Due to the reduction in the number of variables in thermodynamic compensated systems, a general procedure to calculate the activation entropy in isokinetic reactions is proposed.