An evaluation of the potential of combination processes involving heat and irradiation for food preservation

Effects of combined heating and gamma radiation on Clostridium sporogenes spores and Salmonella seftenberg were examined. The order in which irradiation and heat were applied had a profound effect on the survival of the organisms. Heating of C.sporogenes spores at 95 degrees Celsius had very little effect on their sensitivity to subsequent irradiation, but irradiation of the spores at 0 degrees Celsius increased their sensitivity to subsequent heat treatment and thus reduced their heat D10 values (time required to activate the spores to 10% of their initial number). This radiation-induced heat sensitivity increased with the increase in radiation dose. The Z values (change in temperature required for a tenfold change in D10 values) of the spores were found to increase with the increase in pre-irradiation dose. Radiation-induced heat sensitivity was found to persist for at least 35 days in spores irradiated in frozen or freeze-dried states in distilled water or in phosphate buffer suspensions, and for at least 14 days in a number of food slurries. In phosphate buffer and nutrient broth suspensions, the radiation-heat synergism decreased with increasing pH of the media from pH 4.7 to pH 7.5. However, the effect of pH on synergism was less pronounced in spores suspended in some food slurries. Preliminary results indicate that pre-irradiation of S. senftenberg at 0.5 kGy did not change the heat sensitivity of this organism at 52 degrees Celsius, but when radiation and heat were applied simultaneously, synergistic inactivation was observed even at 50 degrees Celsius. Practical implications of these results are discussed