Kinetics of colour change of double concentrated tomato paste during thermal treatment

Abstract

The kinetics of the colour change of double concentrated tomato paste during heating was studied. The Hunter ‘ L’, ‘ a’, ‘ b’ tristimulus values were measured to characterise the colour, and colour difference (ΔE); saturation index (SI) and ‘ a b ’ ratio were calculated from those values. The kinetic study was performed using the capillary tube method with temperatures ranging from 70.0 to 100.0 °C. The order of reaction and the constants E a and k 0 of the Arrhenius equation were determined. All the colour parameters followed an apparent first order kinetics, with the exception of ΔE, which showed a zero order behaviour. The degradation of the colour parameter ‘ L’ followed two consecutive first order reactions, with E a values of 11.5 and 5.73 kcal mol, and ln k 0 of 11.3 and 1.28 min −1 for both phases, respectively. The parameter ‘ b’ ( E a = 20.5 kcalmol; in k 0 = 22.2 min −1) was more sensitive to /temperature changes than the parameter ‘ a’ ( E a = 9.79 kcal mol; ln k 0 = 9.10 min −1), and other colour parameters. The ‘ a b ’ ratio showed an E a = 6.86 kcal mol (ln k 0 = 5.20 min −1), smaller than that of all the other colour parameters, with the exception of ‘ L’ (second phase). Thus, ‘ a b ’ was less sensitive to changes during heating than most of the other parameters. Values of E a and ln k 0 of 10.2 kcal mol and 12.9 min −1 for ΔE, and 10.1 kcal mol and 9.28 min −1 for SI were determined. The parameters obtained permit colour change prediction in double concentrated tomato paste during thermal processing.