Inactivation of Escherichia coli O157:H7 on Apples by Caprylic Acid

摘要

The efficacy of caprylic acid as a wash treatment for reducing E. coli O157:H7 on apples was investigated. Apples inoculated with a five-strain mixture of E. coli O157:H7 (10 CFU) were subjected to 9 washing in sterile deionized water (control) or deionized water containing 50 mM, 75 mM, or 100 mM caprylic acid for 5 or 10 min at 24 C (treatment) with gentle shaking. Immediately after washing in caprylic acid solution or water, apples were transferred to separate Whirl-Pak bags containing 50 ml of sterile Tryptic Soy Broth (TSB) and agitated at 200 rpm for 2 min. One ml of wash suspension from each bag was serially diluted (1:10) with 9ml of sterile PBS and 0.1-ml portions from appropriate dilutions were spread plated on duplicate Tryptic soy agar pates. The plates were incubated at 37 C for 24 h before counting the colonies. Immersion of apples in caprylic acid solutions (50, 75, or 100 mM) for 5 or 10 min significantly reduced (P < 0.05) E. coli O157:H7 population, in comparison to that on apples soaked in sterile water (control). Moreover, no E. coli O157:H7 was detected in caprylic acid wash solution, whereas a substantial population of the pathogen survived in the control wash water. Results indicate that caprylic acid treatment could effectively be used to kill E. coli O157:H7 on apples, but sensory and quality characteristics of apples treated with caprylic acid need to be determined.