The tlag of 31.66 ± 3.8 min previously observed in ultrasoundtreated
apple juice was completely eliminated in the sample subjected
to the combination process. There was a slight increase in the
D value calculated, from 9.2 ± 2.2 min in the cells subjected to ultrasound
alone, to 10.3 ± 0.3 min for cells subjected to the combined
process. The faster death rate of E. coli O157:H7 in the sample
subjected to ultrasound treatment may be due to the injury that the
cells have already accumulated in the inactivation lag phase.
Despite such observation, the t5D value calculated in the apple juice
subjected to the combination process was significantly shorter at
51.5 ± 1.5 min, compared to the 77.5 ± 7.4 min calculated for cells
subjected only to ultrasound treatment. These t5D values of E. coli
O157:H7 in apple juice subjected to ultrasound alone and to the
combination of ultrasound and UV-C were still significantly lower
than the t5D of the pathogen in the same juice subjected to UV-C
alone (319.1 min, data not presented).