Reduction of Listeria monocytogenes and Salmonella Typhimurium on Blueberries through Brief Exposure to Antimicrobial Solutions Coupled with Freezing

Abstract

This study evaluated the efficacy of different brief-exposure antibacterial washes (≤3 min) coupled with frozen storage against Listeria monocytogenes and Salmonella Typhimurium on blueberries. Inoculated berries where treated with sodium hypochlorite (NaOCl, 200 ppm), chlorine dioxide (15 ppm), ozone (3 and 5 ppm), or lactic acid (2%) for short exposure times (10 s, 1 min, or 3 min), and antibacterial effectiveness was determined with or without an additional freezing hurdle (−12°C, 1 week). Wash treatments alone resulted maximum log reductions from 1.0 to 2.8, while the additional freezing step increased this to a range from 3.7 to 6.6. The greatest reduction of L. monocytogenes (6.6 log) and Salmonella Typhimurium (5.3 log) was observed after freezing combined with 3 min of exposure to 2% lactic acid or 200 ppm of NaOCl, respectfully. After treatment, no residue was measured by the methodologies used. However, lactic acid treatment resulted in changes of color and aroma. In conclusion, wash treatments of blueberries using short exposure times had antimicrobial effectiveness (1.0 to 2.8 log reductions) and can be enhanced by coupling with freezing. HIGHLIGHTS

Integrity of the Escherichia coli O157:H7 Cell Wall and Membranes After Chlorine Dioxide Treatment

“…As an antimicrobial agent, ClO 2 washes have been previously demonstrated to effectively reduce levels of pathogenic bacteria including, but not limited to, Shiga toxin-producing Escherichia coli, Salmonella enterica, Listeria monocytogenes, Pseudomonas aeruginosa, Staphylococcus aureus, and Yersinia enterocolitica on a variety of produce (Gómez-López et al, 2009;Wu, 2016;Praeger et al, 2018;Tadepalli et al, 2018;Bridges et al, 2019). Nevertheless, information regarding how ClO 2 affects bacterial cells is limited.…”

Fundamental Differences in Inactivation Mechanisms of Escherichia coli O157:H7 Between Chlorine Dioxide and Sodium Hypochlorite

“…Stock solutions of NaClO and ClO 2 were prepared as described previously (Tadepalli et al, 2018;Bridges et al, 2019). In short, working solutions of 500, 1,000, and 2,000 ppm NaClO were made by diluting bleach solution (6% NaClO) with sterile deionized (DI) water on the day of experimentation.…”

“…A stock solution of ClO 2 was generated using a dry media method provided by ICA TriNova, LLC (Forest Park, GA, United States). The generated ClO 2 stock solution was diluted with DI water to generate working solutions of 25, 50, and 100 ppm ClO 2 on the day of experimentation, and ClO 2 was measured by the DPD (N, N-diethyl-r-phenylenediamine) method using a Hatch DR 900 colorimeter as utilized in previous studies (Wu and Kim, 2007;Tadepalli et al, 2018;Bridges et al, 2019).…”

“…Treatment of Escherichia coli O157:H7 With Sodium Hypochlorite or Chlorine Dioxide and Measurement of Viability Due to the fact that NaClO and ClO 2 are known to have different oxidative strengths and dissimilar antibacterial efficacies at comparable concentrations, treatment concentrations and times were selected based on commonly utilized conditions in published literature and preliminary trials aimed at achieving similar ranges of E. coli O157:H7 reduction (Tadepalli et al, 2018(Tadepalli et al, , 2019Bridges et al, 2019). One milliliter of NaClO solution (500, 1,000, or 2,000 ppm) or ClO 2 solution (25, 50, or 100 ppm) was added to 9 ml of ∼8 log CFU/ml E. coli O157:H7 culture to make final concentrations of 50, 100, or 200 ppm NaClO and 2.5, 5, or 10 ppm ClO 2 .…”

An innovative water-assisted UV-C disinfection system to improve the safety of strawberries frozen under cryogenic conditions

“…This problematic has led to scientists and industries to find problem-solving approaches, mainly focused on introducing disinfection and sanitizing methods and preservation procedures in fruit produce workflow that sufficiently reduce levels of potential microbial contaminants, previous to frozen storage (Leistner, 2000). Indeed, some berries (strawberries and blueberries) picked for frozen processing are usually hulled in the field, transported to the processing facility, and washed with sodium hypochlorite (NaClO) solutions (50 to 200 ppm) to remove debris (e.g., twigs and rocks) with subsequent frozen storage, improving the advantages of freezing over refrigeration in terms of food safety and the extension of the fruit shelf-life (Bridges et al, 2019).…”