Antagonistic effect of acetic acid and salt for inactivating Escherichia coli O157:H7 in cucumber puree

Aim: This study was conducted to investigate the effects of acetic acid alone or combined with salt for inhibiting Escherichia coli O157:H7 in cucumber puree during storage time at 5 and 22°C. Methods and Results: Samples at various concentrations were prepared by the addition of acetic acid (0%, 0·25%, 0·5%, 0·75%, 1%, 2%, 2·5%, or 3%) along with NaCl (0% or 3%) and pureed cucumber (50% or 94%). The effect of storage temperature (5 and 22°C) on the survival of E. coli O157:H7 was also tested. The numbers of E. coli O157:H7 were reduced as the amount of acetic acid increased (P < 0·01) and rate of reduction was more rapid at 22°C than at 5°C. Combinations of acetic acid and salt were less effective at killing E. coli O157:H7 in simulated pickled cucumber samples stored at 5 and 22°C than did treatment of acetic acid alone. The concentration of pureed cucumber affected the reduction rate of E. coli O157:H7. When stored at 5°C, E. coli O157:H7 survived for up to 23 days in a mixture of 94% cucumber puree, 1% acetic acid, and 3% NaCl. Conclusions: There was the antagonistic effect of acetic acid and 3% NaCl with regard to the reduction of E. coli O157:H7. Significance and Impact of the Study: Our results suggest that pickled cucumbers prepared with at least 2% acetic acid and stored at room temperature (22°C) after 3 days storage can free from E. coli O157:H7 without heating.