Through modelling of modified atmosphere packaging (MAP) systems, it is possible to predict evolution of gas composition in the package headspace and ease the selection of favorable packaging conditions for the optimal preservation of the packaged product. However, it is necessary to adequately describe the associated phenomena: product respiration and gas exchange through the package. In this work, a mathematical model was established to describe the evolution of the O-2 and CO2 concentrations in a MAP system, considering packages with perforations and of variable volume and validated for tomato. Respiration rates of the packed product were described using Michaelis-Menten kinetics while gas exchange through the packaging films and the perforations was described with Fick equations of diffusion. The influence of temperature in these kinetics was considered to follow Arrhenius' law. In order to validate the model proposed, an experiment was conducted packaging tomatoes in PP, PLA and LDPE perforated bags for 12 days at 13.5 degrees C. The prediction capacity of the model agrees with the experimental data, with a coefficient of determination (R-2) equal to 0.89-0.98 for O-2 concentrations and 0.83-0.97 for CO2 concentrations. The model was used to define the required package surface area or perforation diameter to achieve a specific O-2 concentration in the headspace. (C) 2015 Elsevier Ltd. All rights reserved.