KINETIC PARAMETER-ESTIMATION FOR QUALITY CHANGE DURING CONTINUOUS THERMAL-PROCESSING OF GRAPEFRUIT JUICE

Reaction order, activation energy (E(a)) and average rate constant (k(av)) were evaluated by dynamic modeling for color degradation of grapefruit juice during thermal processing. Simulated aseptic conditions were: 85-135 degrees C, 40-175 sec processing time, and average velocities 5-30 cm/sec. Quality was assessed by nonenzymatic browning index (NEBI) and 5-hydroxymethyl-furfural (HMF). Average values for reaction-order and energy of activation were: 0 and 21.4 kcal/g-mol (NEBI) and 0.3 and 23.2 kcal/g-mol (HMF), respectively. These values were compared with those contained in the deformed ellipsoid which define the 90% joint confidence interval of all possible parameter combinations. Based on initial and final concentrations, the method can predict effects of processing on liquid foods.