Application of different drying methods and their influence on the physicochemical properties of tomatoes

This paper presents the results of research on the influence of selected drying methods and parameters on the physicochemical properties of tomatoes. The samples were subjected to the process of convection and vacuum drying at the temperature of 60 and 80 °C for 2 and 4 h, and then their physical properties (colour, weight loss, water activity, dry matter content) and chemical properties (extract content, total acidity, total antioxidant activity, vitamin C, lycopene, total phenols, flavonoids and their losses during drying) were compared with a control sample. Both drying method, temperature and time had a significant effect on colour of the tomatoes after drying. Lightness for convective drying for 4 h was significantly lower at 80 °C compared with 60 °C (32.21 and 36.58 respectively). The smallest content of ascorbic acid was recorded for samples dried under convection conditions for 4 h at 80 °C (5.68 mg). In addition, the amount of lycopene dropped drastically for samples dried under vacuum and convection for 4 h at 80 °C (1.51 and 1.10 mg respectively). On the basis of the obtained results, it was found that a properly conducted drying process and well-chosen temperature and time parameters contribute to the reduction of antioxidant losses as well as colour changes of the final product. It is recommended to dry tomato samples at a temperature no higher than 60 °C in vacuum to avoid browning reactions which influence on the colour of the tomatoes, as well as high losses of antioxidants.