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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #403196

Research Project: Elucidating the Factors that Determine the Ecology of Human Pathogens in Foods

Location: Produce Safety and Microbiology Research

Title: The effects of sanitizing hurdles against foodborne pathogens during blueberry processing

item Lacombe, Alison
item Wu, Vivian

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2023
Publication Date: 7/24/2023
Citation: Lacombe, A.C., Wu, V.C. 2023. The effects of sanitizing hurdles against foodborne pathogens during blueberry processing. Food Control. 154. Article 109981.

Interpretive Summary: Blueberries are generally safe to eat, and they offer a variety of health benefits. However, it is essential to process them properly to prevent foodborne illnesses, especially by washing them with chlorine sanitizers like bleach and chlorine dioxide. This study examines each step of the blueberry washing process to improve the reduction of foodborne pathogens. The regulation requires that the blueberries are rinsed with water after being treated with chlorine. Currently, no study investigated the effect of a post-treatment rinse on chlorine's ability to kill bacteria. We tested the impact of post-treatment water rinsing on sanitation efficacy before freezing blueberries. The results demonstrate that water rinsing did not affect the ability of chlorine to kill bacteria. However, we found that increasing the concentration of chlorine dioxide in the wash water did not necessarily increase the reduction of bacteria. Instead, combining the sanitizers with freezing doubled the removal of bacteria, which created a much larger drop in pathogens than sanitizers or freezing alone. This work will impact the industry by providing knowledge on optimizing blueberry washing.

Technical 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 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 foodborne pathogens Shiga toxin-producing E. coli (STEC), Listeria monocytogenes, and Salmonella enterica. To imitate an industrial blueberry washing line, potable water rinse, chlorine dioxide (ClO2, 3 or 15 ppm), and sodium hypochlorite (NaOCl, 200 ppm) were prepared. Sequential treatments of first 200 ppm NaOCl and then either 3 or 15 ppm ClO2 were sprayed on to the berries in sweeping passes lasting approximately 7 seconds 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 combinatorial treatment of NaOCl and ClO2 (3 ppm and 15 ppm) were significantly larger from the untreated control, just rinsing and just 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. Salmonella and STEC combinatorial 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, whereas post-treatment freezing doubled antimicrobial effect to approximately 5.0 log CFU/g reduction in for 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.