Application of Water-assisted Pulsed Light Treatment to Decontaminate Raspberries and Blueberries from Salmonella

We developed and evaluated a small scaled-up water-assisted pulsed light (WPL) system, in which berries were washed in a flume washer while being irradiated by pulsed light (PL). Hydrogen peroxide (H2O2) was used in combination with PL as an advanced oxidation process and chlorine wash was used as a control. The effects of organic load, water turbidity, berry type and PL energy output on the inactivation of Salmonella using the WPL system were investigated. The combination of WPL and 1% H2O2 (WPL-H2O2) was the most effective treatment which reduced Salmonella on raspberries and blueberries by 4.0 and >5.6logCFU/g, respectively, in clear water. When high organic load and SiO2, as a soil simulator, were added in wash water, the free chlorine level in chlorinated water decreased significantly (P<0.05); however, no significant difference (P>0.05) was observed for the decontamination efficacy of 1-min WPL-H2O2 treatment. Even in the presence of high organic load and water turbidity, no viable bacterial cells were recovered from the wash water, which showed that WPL-H2O2 could effectively prevent the risk of cross-contamination during treatment. Taken together, 1-min WPL treatment without H2O2 could provide a chemical free alternative to chlorine washing with similar and in some cases significantly higher bactericidal efficacy. Compared with chlorine washing, the combination of WPL and H2O2 resulted in significantly higher (P<0.05) reduction of Salmonella on berries, providing a novel intervention for processing of small berries intended for fresh-cut and frozen berry products.