This study compared a mathematic model, non-destructive headspace analysis and gas chromatographic methods to monitor the oxygen concentration in modified atmosphere packaged soy bread with and without calcium propionate as a chemical preservative. The bread samples were packaged in low density polyethylene pouches with air as a control or flushed with 20% carbon dioxide:80% nitrogen mixture. Mold and yeast and aerobic plate counts in the bread were monitored when stored at 23 +/- 2 degrees C and 38 +/- 2% relative humidity. At 0, 2, 4, 6, 8, 10 and 12 days, samples were removed and the mold and yeast, aerobic plate count, non-destructive and destructive headspace oxygen contents determined. A mathematical model demonstrated that evolution of the package headspace gas composition resulted from the package permeation and respiration of the micro organisms. The mathematical model, non-destructive and gas chromatographic analytical methods can be used to predict the oxygen content in the headspace of the soy bread. (C) 2007 Elsevier Ltd. All rights reserved.