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

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 (Delta E); 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 degrees C. The order of reaction and the constants E-a and k(O) of the Arrhenius equation were determined. All the colour parameters followed an apparent first order kinetics, with the exception of Delta E, 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(O) of 11.3 and 1.28 min(-1) for both phases, respectively. The parameter 'b' (E-a = 20.5 kcal mol; ln k(O) = 22.2 min(-1)) was more sensitive to temperature changes than the parameter 'a' (E-a = 9.79 kcal mol; ln k(O) = 9.10 min(-1)), and other colour parameters. The 'a/b' ratio showed an E-a = 6.86 kcal mol (In k(O) = 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(O) of 10.2 kcal mol and 12.9 min(-1) for Delta E, 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. (C) 1997 Elsevier Science Limited. All rights reserved.