The objective of this foundational study was to develop and evaluate the efficacy of an affordable hyperspectral imaging (HSI) system to identify single and mixed strains of foodborne pathogens in dairy products. This study was designed as a completely randomized design with three replications. Three strains each of Escherichia coli O157:H7 and Listeria monocytogenes were evaluated either as single or mixed strains with the HSI system in growth media and selected dairy products (whole milk, and cottage and cheddar cheeses). Test samples from freshly prepared single or mixed strains of pathogens in growth media or inoculated dairy products were streaked onto selective media (PALCAM and/or Sorbitol MacConkey agar) for isolation. An isolated colony was selected and mixed with 1 ml of HPLC grade water, vortexed for 1 min, and spread over a microscope slide. Images were captured at 2000× magnification on the built HSI system at wavelengths ranging from 400 nm to 1100 nm with 5‐nm band intervals. For each image, three cells were selected as regions of interest (ROIs) to obtain hyperspectral signatures of respective bacteria. Reference pathogen libraries were created using growth media, and then test pathogenic cells were classified by their hyperspectral signatures as either L. monocytogenes or E. coli O157:H7 using k‐nearest neighbor (kNN) and cross‐validation technique in R‐software. With the implementation of kNN (k = 3), overall classification accuracies of 58.97% and 61.53% were obtained for E. coli O157:H7 and L. monocytogenes, respectively.

Aim To study the impact of incorporating micro‐nano‐bubbles (MNBs) in commonly used food antimicrobials (AMs) against Escherichia coli O157:H7 (EC) and Listeria monocytogenes (LM). Methods and Results Air, carbon dioxide (CO2) and nitrogen (N2) were used to incorporate MNBs in city water. AM solution (with or without MNBs) of 9 ml was individually taken into sterile test tubes and mixed with 1 ml of inoculum grown in brain heart infusion (BHI) broth to get the net AM concentrations of 28·4 ppm peracetic acid (PAA), 200 ppm chlorine (Cl2), 5·4% citric acid (CA) and 4·5% lactic acid (LA). After treatment time of 1·5 and 3·0 min, 1 ml of sample was neutralized using Dey–Engley neutralizing broth and plated on BHI agar. For EC, Cl2‐CO2 solutions resulted in significantly greater log reductions (5·2 logs) compared to that of Cl2 solutions without MNBs (3·8 logs). For LM, PAA‐CO2 solutions resulted in significantly greater log reductions (4·4 logs) compared to that of PAA solutions without MNBs (1·7 logs). Conclusions This study demonstrated that the efficacy of Cl2 and PAA AM solutions could be increased by incorporating CO2‐MNBs against EC and LM in microbiological growth medium. Significance and Impact of the Study Incorporation of CO2‐MNBs in AM solutions could increase the efficacy of AMs against pathogens on/in food matrices, which should be tested in future research.

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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.

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Ultrafine bubbles (UFB) are a novel concept that has the potential to enhance the potency of antimicrobials to eliminate biofilms. This study investigated the impact of incorporating gas (air, CO2, and N2) UFB on the potency of chlorine (Cl2; 50, 100, and 200 ppm) and peracetic acid (PAA; 20, 40, and 80 ppm) antimicrobial (AM) solutions against fresh (3 days) and aged (30 days) Listeria monocytogenes biofilms on polypropylene, silicone, and stainless steel surfaces. Listeria monocytogenes biofilms were statically grown on polypropylene, silicone, and stainless steel coupons (7.62 × 2.54 cm) at 25°C for 3 or 30 days, by immersing in a three‐strain cocktail of L. monocytogenes in brain heart infusion (BHI) broth. The coupons were treated by submerging in AM solutions with or without UFB for 1 min, then swabbed into Dey‐Engley neutralizing broth and enumerated on BHI agar. Incorporation of air, CO2, and N2 UFB in AM solutions resulted in significantly increased log reductions (0.4–1.5 logs) of fresh and aged L. monocytogenes biofilms on polypropylene and stainless steel surfaces, whereas incorporation of CO2 UFB in AM solutions resulted in ~1 log greater reductions of fresh and aged L. monocytogenes biofilms on silicone surfaces compared with AM solutions without UFB. This study also demonstrated that 200 ppm Cl2 was most effective against fresh and aged L. monocytogenes biofilms on polypropylene, silicone, and stainless steel surfaces compared with 50 ppm Cl2, 20 ppm PAA, and 40 ppm PAA.

No abstract

Ultrafine bubble technology is a novel concept in food safety that can improve the potency of antimicrobials against biofilms. This study was conducted to evaluate the impact of gas (air, CO2, or N2) ultrafine bubbles incorporation in 100 and 200 ppm chlorine (Cl2) solutions to inactivate fresh Listeria monocytogenes biofilms on stainless steel. Listeria monocytogenes biofilms were grown on stainless steel coupons through static incubation at 37°C for 72 hr by immersing in L. monocytogenes inoculated brain heart infusion (BHI) broth. The coupons were treated by dipping in water or Cl2 solutions with or without ultrafine bubbles for 1 min. Random pre‐determined areas on coupons were swabbed into Dey–Engley neutralizing broth before and after treatments and enumerated using BHI agar. Air and CO2 nanobubbles in 100 ppm Cl2 resulted in greater log reductions (5.0 and 4.9 log CFU/cm2, respectively) in L. monocytogenes biofilms compared with 100 ppm Cl2 without gas ultrafine bubbles (3.7 log CFU/cm2). Incorporation of air, CO2, and N2 ultrafine bubbles in water and 200 ppm Cl2 did not have any impact on the efficacy of biofilm inactivation.