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Sensory evaluations by healthy individuals were conducted on cobalt-60 irradiated retail dairy products which were to be incorporated into the low microbial diets of immunosuppressed patients. Irradiation (40 kGy at -78°C) caused little change in product color or texture, but generally there was a decrease in overall acceptability and an increase in off-flavor and aftertaste. Modified atmosphere packaging (nitrogen, helium, or air) or antioxidant addition (ascorbyl palmitate or a combination of butylated hydroxyanisole and butylated hydroxytoluene) prior to irradiation were effective in preserving specific sensory attributes, which in some cases resulted in improved overall acceptability (helium packed peppermint ice cream; ascorbyl palmitate treated strawberry yogurt bars) when compared to untreated irradiated products.

The effect of low temperature ( -78°C) gamma irradiation was investigated on microbial populations in selected dairy products to determine the irradiation dosage needed to produce commercially sterile dairy products for immunosuppressed patients. 40 kGy irradiation was sufficient to sterilize ice cream and frozen yogurt, but not mozzarella or Cheddar cheeses. Up to 8 wk continued incubation of the 40 kGy irradiated products at 7°C or 35°C resulted in no resuscitative growth in ice cream or yogurt, but identifiable growth in the cheeses. The 12D for B. cereus preinoculated into cheese and ice cream was 43-50 kGy.