The main objective of this work was to evaluate the effectiveness of pulsed light (PL) treatment for the inactivation of Escherichia coli in liquids with different levels of clarity. Nonpathogenic E. coli ATCC 25922 and pathogenic E. coli O157: H7 were used as challenge organisms. Butterfield's phosphate buffer (BPB), tryptic soy broth (TSB), apple juice, and apple cider were used as substrates. The inoculated liquids were placed in a thin layer (1.3 mm) into glass chambers (23 by 53 by 11 mm) and exposed to PL doses of up to 13.1 J/cm2. PL treatments were performed in a Xenon RS-3000C PL unit, both in static mode and under turbulence. Survivors were determined by standard plate counting or the most-probable-number technique. For static treatments, reduction levels exceeding 8.5 log were obtained in BPB for all strains and reduction levels of about 3.5 log were obtained in TSB. For apple juice, inactivation levels of 2.66 ± 0.10 log were obtained for E. coli ATCC 25922 and 2.52 ± 0.19 log for E. coli O157:H7. In cider, inactivation levels of 2.32 ± 0.16 log and 3.22 ± 0.29 log were obtained for the nonpathogenic and pathogenic strains, respectively. Inactivation kinetics was characterized using the Weibull model. Turbulent treatments resulted in 5.76 ± 0.06 log reduction in cider and 7.15 ± 0.22 log reduction in juice, which satisfies the U.S. Food and Drug Administration requirement of 5-log reduction of E. coli. These results show promise for the use of PL for the effective reduction of E. coli in apple juice and cider.

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