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

Abstract

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 (Cl2; 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 Cl2 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.

Effect of gas ultrafine bubbles on the potency of antimicrobials against Escherichia coliO157:H7 biofilms on various food processing surfaces

“…In previous work by our research group, Singh et al (2021) evaluated the impact of gas UFB [denoted as micro‐nano‐bubbles (MNB)] on the efficacy of commonly used AM in the food industry and demonstrated the incorporation of CO 2 UFB improved the potency of 200 ppm chlorine (Cl 2 ) and 28.4 ppm peracetic acid (PAA) solutions against E. coli O157: H7 and Listeria monocytogenes in growth media compared to these AM solutions without UFB. Similarly, Unger et al (2023) evaluated the impact of UFB on the efficacy of AM against fresh and aged L. monocytogenes biofilms on various processing surfaces and discovered that the incorporation of air, CO 2 , and N 2 UFB in Cl 2 (50, 100, and 200 ppm) and PAA (20, 40, and 80 ppm) AM solutions resulted in significantly increased log reductions of fresh and aged L. monocytogenes biofilms on polypropylene and stainless‐steel surfaces compared with AM solutions without UFB.…”

“…A three‐strain E. coli master inoculum cocktail was then prepared by mixing equal proportions of freshly grown cultures, and biofilm were developed on polypropylene, silicone, and stainless steel coupons (7.62 × 2.54 cm 2 ) through static incubation at 25°C for 3 or 30 days by submerging in 40 mL E. coli inoculated BHI broth (9.44 ± 0.07 log CFU/mL) as described by Unger et al (2023). During biofilm development, 20 mL of inoculated BHI broth was replaced by fresh BHI broth after 36 h or every 5 days of incubation for 3‐ and 30‐day biofilms, respectively.…”

“…The UFB were generated in this research using a micro‐nanobubble generator (LEA15; Living Energies & Co., Shizuoka, Japan) and procedure as described by Unger et al (2023). Food‐grade compressed cylinders of CO 2 or N 2 gas and ambient air from the laboratory were used to generate UFB in city tap water (Pullman, WA).…”

“…Food‐grade compressed cylinders of CO 2 or N 2 gas and ambient air from the laboratory were used to generate UFB in city tap water (Pullman, WA). As shown in Unger et al (2023), the presence and mean size of UFB produced by this generator was conducted by a third‐party laboratory.…”

“…The preparation of AM solutions was performed at ambient temperature (~20°C) using the procedures described by Unger et al (2023). The AM solutions were prepared to achieve 50, 100, and 200 ppm free Cl 2 , and 20, 40, and 80 ppm PAA using city tap water (with and without UFB).…”