Impact of gas ultrafine bubbles on the efficacy of commonly used antimicrobials for apple washing

Ultrafine bubble (UFB) technology is a novel tool in food safety with potential to improve the efficacy of antimicrobials during produce washing. This research investigated the impact of incorporating gas (air and CO2) UFBs on the potency of chlorine (Cl-2; 100 and 200 ppm) and peracetic acid (PAA; 40 and 80 ppm) antimicrobial solutions against Escherichia coli O157:H7 and Listeria monocytogenes on inoculated Gala apples. Apples were dip inoculated with either E. coli or L. monocytogenes, and dried at room temperature for 1 hr. Apples were then treated by dipping into Cl-2 or PAA solutions with or without UFBs (CO2 or air) for 1 or 2 min. Apples were then transferred into bags containing Dey-Engley neutralizing broth, and hand massaged for 90 s. Log reductions for respective antimicrobial treatments were calculated by subtracting post-antimicrobial treatment bacterial populations from the initial bacterial populations on inoculated apples. Incorporation of CO2 UFBs in antimicrobial solutions resulted in significantly greater E. coli and L. monocytogenes reductions (2.1 and 2.4 Log CFU/apple, respectively) on apples compared to solutions without UFBs (1.4 and 1.9 Log CFU/apple, respectively). However, incorporation of air UFBs resulted in similar log reductions of E. coli and L. monocytogenes (1.9 and 2.2 Log CFU/apple, respectively) on apples compared to antimicrobials with CO2 UFBs and without UFBs. The 2 min treatment time for various antimicrobials resulted in significantly greater L. monocytogenes reductions (2.4 Log CFU/apple) compared to 1 min (2.0 Log CFU/apple), but no differences were observed for E. coli.