Determination of kinetics of non-enzymatic browning of tomato paste during storage at different temperatures

In this study, non-enzymatic browning kinetics of tomato pastes was investigated during storage at 20, 30 and 40°C. For this purpose, samples were taken out periodically (each month) over a 12 month period of storage and analysed for ascorbic acid, hydroxy metil furfural (HMF) and color changes. As expected, the ascorbic acid contents of paste samples decreased rapidly as the storage temperature and time increased. Analysis of kinetics data suggested a zero-order reaction for the degradation of ascorbic acid during storage with the reaction rate constants (k values) of 52.69, 83.45 and 128.58 mg/100 g month at 20, 30 and 40°C, respectively. The activation energy (Ea) for the ascorbic acid degradation was 34.41 kJ/mol and Q10 values were 1.58 and 1.54 at 20-30°C and 30-40°C, respectively.While the HMF contents of tomato pastes decreased during the initial period of storage, the formation of HMF began to increase as the storage time increased. The formation of HMF was also fitted to a zero-order kinetic model with the reaction rate constants (k values) of 4.572, 8.877 and 24. 557 mg/100 g at 20, 30 and 40°C, respectively. The activation energy for the HMF formation was 63.91 kJ/mol and Q10 values were 1.94 at 20-30°C and 2.77 at 30-40°C.The color change was also fitted to a zero-order kinetic model during storage. The color of samples were significantly affected by the storage temperature. The Q10 values were 2.84 and 2.49 at 20-30°C and 30-40°C, respectively and the activation energy was 74.52 kJ/mol.Results from this study showed that the HMF content of paste samples increased while the ascorbic acid content and color quality decreased significantly as the storage temperature increased. Thus, the storage temperature of tomato paste and other tomato products should be as low as possible in order to protect their quality.Key Words: Tomato paste, storage, non-enzymatic browning, ascorbic acid, HMF, color change, kinetic, Q10