ARS | Publication request: The efficacy of sanitizer and ultrasound combined treatments on reduction of Escherichia coli O157:H7 surrogate population on spinach

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: May 12, 2007
Publication Date: July 28, 2007
Citation: Zhou, B., Feng, H., Luo, Y. 2007. The efficacy of sanitizer and ultrasound combined treatments on reduction of Escherichia coli O157:H7 surrogate population on spinach. [abstract]. Annual Meeting of the Institute of Food Technologists.

Technical Abstract: The recent outbreak of Escherichia coli O157:H7 infections on bagged spinach reaffirmed the importance and challenges of produce safety. Current washing processes in industrial scale operations can only achieve 1- to 2-log CFU/g reduction in microbial populations. More effective post-harvest intervention technologies are needed for assuring the microbial safety of fresh and fresh-cut produce. The use of a sanitizer in combination with other disinfection factors, such as ultrasound, may provide a means to enhance sanitation efficacy. This study was undertaken to determine the effects of selected sanitizers, with or without ultrasound, on the reduction of E. coli 87-23 tox-O157:H7 populations on spinach. Fresh spinach was spot-inoculated with 0.1mL phosphate buffered saline (pH 7.0) containing 108 E. coli cells, and was air-dried for 12 hours at 22°C. The inoculated samples were treated with water, chlorine (200 mg/L), acidified sodium chlorite (ASC) (200mg/L), peroxyacetic acid (POAA, 80 mg/L), acidic electrolyzed water (80 mg/L free chlorine), and a new washing solution (NWS) (0.6%), as well as the combination of these sanitizers with ultrasound (21.2 kHz) for 2 min at room temperature. Treated and untreated spinach was homogenized in sterile peptone water (pH 7.4), serially plated on tryptic soy agar containing 50µg/ml nalidixic acid, and incubated at 37°C for 24 hours. The ASC and the NWS reduced E. coli populations by 2.2- and 2.8-logs over that of the water wash, respectively, while the reduction from other sanitizers was about 1 log cycle. Ultrasound treatment enhanced the reduction of E. coli cells from spinach by 1 log cycle in all treatments except the NWS. The highest E. coli reduction was 4.5 logs and was achieved with the NWS and ultrasound combined treatment. The combination of a selected sanitizer with ultrasound can potentially be used to enhance the microbial safety of leafy green produce.