Statistical analysis of the results revealed that light accounted for the greatest systematic variation of the relative levels of free radicals in peanuts, oatmeal and muesli, whereas the oxygen availability had the largest influence on the formation of hexanal. The opposite was observed for pork scratchings, where oxygen had the most significant effect on the formation of radicals. It is concluded that ESR and headspace-GC complement each other in detecting the oxidative changes.