Effects of ultrasound, irradiation, and acidic electrolyzed water on germination of alfalfa and broccoli seeds and Escherichia coli O157:H7

The ability of power ultrasound, acidic electrolyzed water (AEW), and gamma irradiation to inactivate Escherichia coli O157:H7 inoculated onto alfalfa and broccoli seeds was examined. The treatment conditions under which the alfalfa and broccoli seeds treated with sterile deionized water (SW), AEW, ultrasound cleaning tank (UST), ultrasound probe (USP), and irradiation (IR) would retain a germination percentage of >85% were first determined for each disinfection hurdle. E. coli O157:H7 inactivation tests were then conducted with the experimental conditions determined in the germination tests to find out the maximum inactivation ability of each disinfection hurdle. AEW treatment at 55 oC for 10 min reduced E. coli O157:H7 population by 3.4 and 3.3 log CFU/g for the alfalfa and broccoli seeds, respectively. IR at 8 kGy resulted in a 5-log reduction with seed germination of >85% for both seed types, but a reduction in the length and thickness of the sprouts was observed. None of the ultrasound treatments achieved over a 2-log reduction in E. coli O157:H7 population without lowering the germination to below 85%. The results of this study demonstrated that AEW and ultrasound, when applied individually or in combination with thermal treatment at 55 oC, were not able to deliver a satisfactory inactivation of E. coli O157:H7. A combination of several hurdles must be used to achieve a complete elimination of E. coli O157:H7 cells on alfalfa and broccoli seeds.