INACTIVATION OF ESCHERICHIA-COLI O157-H7 IN APPLE JUICE BY IRRADIATION

Three strains (932, Ent-C9490, and SEA13B88) of Escherichia coli O157: H7 were used to determine the effectiveness of low-dose gamma irradiat ion for eliminating E. coli O157:H7 from apple juice or cider and to c haracterize the effect of inducing pa-dependent, stationary-phase acid resistance on radiation resistance. The strains were grown in tryptic soy broth with or without 1% dextrose for 18 h to produce cells that were or were not induced to pa-dependent stationary-phase acid resista nce. The bacteria were then transferred to clarified apple juice and i rradiated at 2 degrees C with a cesium-137 irradiator. Non-acid-adapte d cells had radiation D values (radiation doses needed to decrease a m icrobial population by 90%) ranging from 0.12 to 0.21 kGy, D values in creased to 0.22 to 0.31 kGy for acid-adapted cells. When acid-adapted SEA13B88 cells were tested in five apple juice brands having different levels of suspended solids (absorbances ranging from 0.04 to 2.01 at 550 nm), radiation resistance increased with increasing levels of susp ended solids, with D values ranging from 0.26 to 0.35 kGy, Based on th ese results, a dose of 1.8 kGy should be sufficient to achieve the 5D inactivation of E, coli recommended by the National Advisory Committee for Microbiological Criteria for Foods.