Evaluation of heat and oxidative damage during storage of processed tomato products. II. Study of oxidative damage indices

Tomato products (pulp, puree and paste) submitted to accelerated aging (30, 40 and 50 ◦C for 3 months) were studied to evaluate variations in the kinetics of the degradation of antioxidants and antioxidant activity. The carotenoids lycopene and β-carotene, ascorbic acid, rutin and total phenolics were analysed. The antioxidant activity was measured using (a) the xanthine oxidase (XOD)/xanthine system, which generates superoxide radicals and hydrogen peroxide, and (b) the linoleic acid/CuSO4 system, which promotes lipid peroxidation. The ascorbic acid content decreased even at 30 ◦C, following pseudo-first-order kinetics, with an activation energy of 105 200 Jmol−1 for tomato pulp and 23 600 Jmol−1 for tomato paste. The lower the initial ascorbic acid content, the higher was the degradation rate. Variations in phenolic compounds occurred at 40 ◦C and higher, following pseudo-zero order kinetics. The antioxidant activity of the hydrophilic fraction of the tomato products depended on both antioxidant degradation and the Maillard reaction and could not be described by a kinetic model. The β-carotene content decreased even at 30 ◦C, whereas the lycopene content was stable in all samples. The antioxidant activity of the lipophilic fraction of the tomato products decreased following pseudo-first order kinetics, with an activation energy of 22 200 Jmol−1 for tomato pulp and 20 200 Jmol−1 for tomato paste. It is concluded that significant ‘oxidative damage’ can occur in tomato products during their commercial shelf-life.