Effect of mild heat pre-treatment with alkaline electrolyzed water on the efficacy of acidic electrolyzed water against Escherichia coli O157:H7 and Salmonella on lettuce

Cut lettuce dip-inoculated with Escherichia coli O157:H7 and Salmonella was treated with alkaline electrolyzed water (AIEW) at 20degreesC for 5 min, and subsequently washed with acidic electrolyzed water (AcEW) at 20degreesC for 5 min. Pre-treatment with AIEW resulted in an approximate 1.8 log(10) cfu/g reduction of microbial populations, which was significantly (p less than or equal to 0.05) greater than microbial reductions resulting from other pre-treatment solutions, including distilled water and AcEW. Repeated AcEW treatment did not show a significant bacterial reduction. Mildly heated (50degreesC) sanitizers were compared with normal (20degreesC) or chilled (4degreesC) sanitizers for their bactericidal effect. Mildly heated AcEW and chlorinated water (200 ppm free available chlorine) with a treatment period of 1 or 5 min produced equal reductions of pathogenic bacteria of 3 log(10) and 4 log(10) cfu/g, respectively. The procedure of treating with mildly heated AIEW for 5 min, and subsequent washing with chilled (4degreesC) AcEW for period of 1 or 5 min resulted in 3-4 log(10) cfu/g reductions of both the pathogenic bacterial counts on lettuce. Extending the mild heat pre-treatment time increased the bactericidal effect more than that observed from the subsequent washing time with chilled AcEW. The appearance of the mildly heated lettuce was not deteriorated after the treatment. In this study, we have illustrated the efficacious application of AIEW as a pre-wash agent. and the effective combined use of AIEW and AcEW. (C) 2003 Elsevier Ltd. All rights reserved.