Lycopene is the principle pigment found in tomatoes and is important not only because of the color it imparts but also because of the recognized health benefits associated with its presence. Heating and drying of tomato products under different processing conditions to manufacture tomato juice, pulp, powder etc. may cause degradation of lycopene. For an exact calculation of the rest concentration of a nutrient in a drying process one would have to know the material temperature and water concentration at each moment and the dependence of degradation reaction rate constant on temperature and moisture content. The objective of this study was to determine a mathematical model of the reaction kinetic of lycopene degradation to describe the rate of lycopene loss in a drying process of tomato pulp. Tomato pulps with different moisture contents were heated at specified temperatures for different time periods. A mathematical model giving rate constant of lycopene degradation as a function of material temperature and moisture content was derived from the changes of lycopene concentration in equal time intervals. This model was used to simulate the lycopene loss during two drying processes of tomato pulp. The first process was the concentration of tomato pulp with total solids concentration of 14% to approximately 40% final moisture content, whereas the second one was the spray drying of tomato pulp. It was concluded that there was a close agreement between the experimental and predicted values of lycopene loss during the tomato pulp concentration confirming the validity of the proposed model for this process. However, for the spray drying process a correction coefficient was introduced in the model, due to the more intense exposure of product surface to air. (c) 2005 Elsevier Ltd. All rights reserved.