Combined Treatment on the Inactivation of Naturally Existing Bacteria and Escherichia coli O157:H7 Inoculated on Fresh-Cut Kale

An aqueous chlorine dioxide (ClO2) treatment combined with highly activated calcium oxide (CaO) and mild heat was tested for inactivating naturally existing bacteria and Escherichia coli O157: H7 inoculated on fresh-cut kale. Kale samples were treated with different concentrations of ClO2 (10, 30, and 50 ppm), CaO (0.01%, 0.05%, 0.1%, and 0.2%), and mild heat (25 degrees C, 45 degrees C, 55 degrees C, and 65 degrees C) as well with combinations of 30 or 50 ppm ClO2 and 0.2% CaO at 55 degrees C for 3 min. An increasing concentration of ClO2 and CaO significantly reduced the microbial population compared with the control. In addition, mild heating at 55 degrees C elicited greater microbial reduction than the other temperatures. A combined treatment of 50 ppm ClO2 and 0.2% CaO at 55 degrees C reduced the population of naturally existing bacteria on kale by 3.10 log colony forming units (CFU)/g, and the counts of E. coli O157: H7 were below the detection limit (1 log CFU/g). In addition, no significant differences in the Hunter color values were evident in any treatment during storage. Therefore, a combined treatment of ClO2 and active CaO at 55 degrees C can be an effective sanitizing method to improve the microbiological safety of fresh-cut kale without affecting its quality.