Disinfection Capacity of High-Power Ultrasound Against E. coli O157:H7 in Process Water of the Fresh-Cut Industry

The fresh-cut industry must treat process water to guarantee its microbial quality before reuse or recirculation back into the processing line. In the present study, the suitability of high-power ultrasound (HPU) for disinfecting and recycling process water was evaluated. An ultrasonic horn (20 kHz) was used to inactivate Escherichia coli O157:H7 inoculated in five types of process water which showed different physical and chemical characteristics. Differences in the inactivation level of E. coli O157:H7 at different HPU densities (0.14, 0.28, 0.56, and 1.12 kW/L) with controlled (20-25 A degrees C) and uncontrolled (15-72 A degrees C, 3.6 A degrees C/min) temperature increase were studied. Results showed that the higher the power density and temperature, the higher the efficiency, reaching up to 6 log reductions of E. coli O157:H7. Alkalinity (between 0 and 253 mg HCO3 (-)/L) and organic matter concentration (between 9 and 3,525 mg O-2/L) in water did not reduce ultrasonic efficacy against E. coli O157:H7. Agglomerates > 90 mu m, which represented 34 % of those present in the process water, were reduced to only 11 % by HPU. Results indicate that HPU can be successfully applied to treat process water of the fresh produce industry because the antimicrobial efficacy was not affected by the continuous variation of the process water quality. HPU can be a suitable technology for the fresh produce industry to be able to reduce consumption of water and decrease wastewater and the generation of disinfection by-products.