P3-53 Effect of Residual Chlorine on the Attachment and Survival of Escherichia coli O157:H7 on Spinach Surface

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Vijay Singh Chhetri , Louisiana State University AgCenter , Baton Rouge , LA
Achyut Adhikari , Louisiana State University AgCenter , Baton Rouge , LA
Introduction:  Recent foodborne disease outbreaks highlighted produce packing environment as an important source of contamination. After sanitization, produce are exposed to the environment for several minutes before packaging, which may increase the risk of cross-contamination.

Purpose: This study examined the residual chlorine level on spinach after sanitization and its effect on the attachment and die-off rate of Escherichia coli O157:H7 on the surface of the leaf.

Methods: Baby Spinach was purchased from a local retail store. The intact leaves with similar size and appearance were treated with chlorine solution (150 ppm) for three minutes. The residual chlorine level on spinach surface after the treatment was examined up to 90 minutes using DPD Colorimetric Method. A cocktail of E. coli O157:H7 (H1730, ATCC 43895, EC 4042) was inoculated on the surface (8 cm²) of the leaves immediately and 30 minutes after treatment with chlorine. The effect of residual chlorine on the attachment and die-off rate of E.coli O157:H7 was examined up to 48 hours.

Results: A rapid decline in both free chlorine (7.2 to 0.3 mg/kg) and total chlorine (10.6 to 1.5mg/kg) level was observed on spinach surface treated with chlorine within 90 minutes of storage at 4°C. The residual chlorine present in freshly treated and 30 minutes after chlorine treated samples significantly (P<0.05) reduced the E.coli O157:H7 level on spinach surface. The reduction was by 1.30 log CFU/cm² on the freshly treated samples and by 1.14 log CFU/cm² on 30 minutes after treated samples. Further reduction (2.78 log CFU/cm2) was observed on freshly treated samples after 24 hours of storage. The SR values which indicate the attachment strength of microorganisms on produce were significantly higher on chlorine treated samples than on untreated samples.

Significance:  Our study suggests that the residual chlorine on produce surfaces may minimize the survival of postsanitation microbial contamination.