Inactivation of Escherichia coli O157:H7 and Salmonella on Fresh Blueberries Using Pulsed Light Technology

Introduction: The consumption of fresh blueberries and their products are on the rise in the U.S. In recent years, the role of these berries as a source of outbreaks of both bacterial and viral pathogens has been well documented. Therefore, effective intervention method is needed for decontamination of these small fruits.

Purpose: This study was conducted to evaluate the inactivation of Escherichia coli O157:H7 and Salmonella on fresh blueberries using dry and wet pulsed light (PL) treatments.

Methods: Fresh blueberries (~5 g) were spot-inoculated on the skin or calyx of berries with E. coli O157:H7 or Salmonella spp. to a final level of ca. 7 log CFU/g. Inoculated berries were either treated with PL directly (dry PL treatment) or immerged in agitated water during the PL treatment (wet PL treatment) for 5 - 60s. Populations of surviving E. coli O157:H7 and Salmonella from the samples and water were enumerated and analyzed.

Results: Significant color change of blueberries was observed for dry PL treatments but the presence of water prevented the color change in wet PL treatments. Generally, both dry and wet PL treatments were significantly more effective than chlorine washing. The population of E. coli O157:H7 on calyx and skin of blueberries were reduced by 3 and > 5.7 log CFU/g, respectively, after 60-s wet PL treatment. Similar reductions were also achieved for Salmonella. No viable bacterial cells were recovered from water samples after 5-s wet PL treatment, indicating that wet PL treatment can potentially prevent cross-contamination during the processing.

Significance: These results indicate that dry and wet PL treatments could be promising alternatives to traditional chlorine washing for fresh-cut or frozen berry products to avoid the use of chemicals, although the impact of dry PL treatment on the color change of blueberries needs to be further evaluated.