The antioxidant activity of tomato : 4. Effects of storage on oxidative and heat damage

Three commercial tomato products (tomato pulp, tomato puree, and tomato paste) were subjected to accelerated aging tests (3 months at 40°C) to evaluate the kinetics of variation of heat damage indexes (5-hydroxymethyl-2- furfural [HMF] and color [?E]) and oxidative damage indexes (lycopene, β-carotene, ascorbic acid, total phenolics, antioxidant activity of hydrophilic and lipophilic fractions). Experimental data were processed to obtain rate constant values. HMF formation followed zero-order kinetics in tomato puree, and paste, and first-order kinetics in tomato pulp, to a final value of nearly 160, 200, and 495 mg/kg dw in tomato pulp, puree, and paste. Significant colour changes were only observed in tomato concentrate. Ascorbic acid decreased in all products according to pseudo-first-order kinetics, with a higher rate in tomato paste and puree. A slight increase in total phenolics was observed in all products during storage. Lycopene concentration was very stable in all products, whereas β-carotene decreased at the same rate in all products, to a final 30-40% reduction. The antioxidant activity of the hydrophilic fraction decreased, to a final reduction of 35-40% in all samples. The antioxidant activity of the lipophilic fraction also decreased, although to a smaller extent, to a final reduction of about 30% in the three products. Reduction of antioxidant activity can be ascribed to the loss in ascorbic acid and β-carotene.