The effects of sanitizing hurdles against foodborne pathogens during blueberry processing

Abstract

Frozen berries are a minimally processed food; therefore, the blueberry industry established a sanitizing regimen, such as using hypochlorite solution (NaOCl) and chlorine dioxide (ClO2) before freezing and storage to ensure food safety. The Code of Federal Regulation (CFR) requires that the application of NaOCl or ClO2 in wash water shall be followed by either potable water rinse, blanching, cooking, or canning. Currently, no study investigated the effect of a post-rinse treatment on the efficacy of sanitizer treatment prior to freezing blueberries. This study aimed to examine the effect of post-treatment water rinsing before freezing blueberries on the antimicrobial efficacy of sequential treatments of NaOCl and ClO2 against Shiga toxin-producing E. coli (STEC), Listeria monocytogenes, and Salmonella enterica. To imitate an industrial blueberry washing line, potable water rinse, ClO2 (3 or 15 ppm), and NaOCl (200 ppm) were prepared. Sequential treatments of first 200 ppm NaOCl and then either 3 or 15 ppm ClO2 were sprayed onto the berries in sweeping passes lasting approximately 7 s for each sanitizer. To investigate the impact of potable water rinse on sanitizer efficacy, half of the treatments received an additional 15-sec rinse after sanitizer treatment prior to freezing (−20 °C) for 7 days. For Listeria, the microbial reduction from the combination treatment of NaOCl and ClO2 (3 ppm and 15 ppm) was significantly greater than that from the untreated control, just rinsing and freezing. With NaOCl alone, Listeria monocytogenes demonstrated a 5.5 log CFU/g reduction; in comparison, Salmonella and STEC demonstrated a 3.0 and 2.6 log CFU/g reduction, respectively. For Salmonella and STEC, combination treatments of NaOCl and ClO2 demonstrated significant reduction compared to untreated control and just rinsing. Post-treatment rinsing and increased ClO2 concentration did not significantly impact log reduction. Post-treatment freezing doubled the antimicrobial effect to approximately 5.0 log CFU/g reduction in Salmonella and STEC. This study demonstrates the cumulative antimicrobial effect of physical and chemical processes of produce washing and that the FDA-required potable water rinse did not impact sanitizer efficacy.