Atmospheres containing 99 kPa of helium, argon, neon (for mushrooms only), nitrous oxide or nitrogen were flushed into airtight glass jars containing mushrooms or sliced apples to create anaerobic conditions at 10degreesC. Anaerobic CO2 production rates (fermentative index, FI), color, firmness, tissue ethanol and headspace ethanol in the jars of both products were measured. As compared to nitrogen, noble gases and nitrous oxide did not have any significant effect in reducing the rate of anaerobic catabolism (FI and ethanol production rate), color and firmness of either product. Increasing amounts of CO2 were confirmed to be responsible for the yellow discoloration and firmness retention of mushrooms. High correlation coefficients were obtained between combined mean values of headspace ethanol, tissue ethanol and headspace CO2 concentrations of mushrooms and sliced apples. Residual oxygen levels left in the jars and trapped in the tissues seem to be responsible for the initial rise in CO2 production of sliced apples and mushrooms and were estimated as 1.5 and 1.75 kPa, respectively.