Reducing Non-O157 Shiga Toxin-producing E. coli on Fuji Apple by Cinnamon Oil

Introduction: Non-O157 Shiga Toxin-producing E. coli (STEC) has gained increasing awareness due to several recent outbreaks in which fresh produce is the main vehicle contributing to the transmission of non-O157 STEC to humans. Compared to E. coli O157:H7, currently far less attention has been paid to intervention of non-O157 STEC on produce; on the other hand, due to rising health concern about chemical sanitizers, intervention using natural compounds is gaining public interest. Cinnamon is a commonly used spice reported to have antimicrobial activity. 

Purpose: To evaluate the efficacy of cinnamon oil washing in reducing non-O157 STEC on Fuji apples. 

Methods: Unwaxed Fuji apples were cleaned, air dried and dip inoculated in 10⁷ CFU/ml non-O157 STEC three strain cocktail (O26:H11, O121:H19, and O145:NT) solution.  Surface-inoculated apples were air dried for 1 h, then washed with phosphate buffered saline (PBS), 0.5%, and 1.0% cinnamon oil solution for 30 s and 60 s. Residual bacteria on apples as well as in washing solutions were enumerated onto LB plate. 

Results: Dip inoculation resulted in ~6.8 log CFU non-O157 STEC per apple, and PBS wash (control) resulted in ~1-log reduction. Inhibitory effect of cinnamon oil against non-O157 STEC on apple is time and dose dependent: 60 s washing in 1% cinnamon oil solution achieved about 3-log CFU reduction per apple, which is 2 log more reduction than that of PBS wash; 60 s wash in 0.5% cinnamon oil or 30 s wash in 0.5% and 1.0% cinnamon oil solution resulted in ~2.0 or 1.5-log reduction per apple, respectively. In addition, ~6 log CFU/ml of non-O157 STEC were detected in spent PBS wash solution, while it was under detection level in wash solution with cinnamon oil.

Significance: Cinnamon oil has the potential to be used as an alternative sanitizer in fresh apple industry.