Evaluating a Combined Method of UV and Washing for Sanitizing Blueberries, Tomatoes, Strawberries, Baby Spinach, and Lettuce

Abstract

We assessed a fresh produce decontamination system using a combined method of UV and washing (water-assisted UV [WUV]) in different scales. The system used tap water to wash fresh produce while exposing it to UV light. First, the reduction of Salmonella in tap water under UV treatment (1 to 1,740 mJ/cm2) was determined. Increasing the UV dose significantly (P < 0.05) increased the Salmonella reduction in wash water, and UV intensity of more than 2 mW/cm2 could reduce Salmonella in tap water to below 1 CFU/mL given enough processing time (more than 1 min; UV dose of 120 mJ/cm2). Then, the decontamination effectiveness of a small WUV system was tested on blueberries (50 g). Blueberries were spot or dip inoculated with a Salmonella cocktail and treated by the small WUV system (200 mL of water). In general, WUV treatments achieved significantly better Salmonella inactivation than tap water wash; tap water wash (10 min) and 2 mW/cm2 WUV treatment (with a UV dose of 1,200 mJ/cm2) reduced populations of spot-inoculated Salmonella on blueberries by 2.44 and 5.45 log, respectively. Compared with spot-inoculated Salmonella on blueberries, dip-inoculated Salmonella was more difficult to be inactivated by WUV treatments. Then, the decontamination effectiveness of WUV treatments was tested on blueberries (170 g), tomatoes (290 g), strawberries (170 g), baby spinach (60 g), and lettuce (60 g) using a larger WUV system. In general, 10 min of 29 mW/cm2 WUV treatment (a high UV dose of 17,400 mJ/cm2) resulted in significantly better Salmonella inactivation than tap water wash (for 10 min) regardless the inoculation method, agreeing with the results of the small-scale study. For both spot- and dip-inoculated lettuce, no significant difference (P > 0.05) in Salmonella inactivation by WUV treatments was observed when the quantity of lettuce increased from 50 to 100 g.

Strategies for Microbial Decontamination of Fresh Blueberries and Derived Products

“…This work also highlighted the difficulty of using UV in eliminating microorganisms present on rough surfaces such as the blueberry calyx, in which the reductions after all treatments were <2 log PFU/sample [83]. This result confirms what other researchers have reported-a greater reduction of pathogens on the skin than on the blueberry calyx after application of UV together with chemical methods [52,86,87]. On the other hand, Huang et al [88] proposed WUV (23-28 mW/cm 2 ) combined with PAA (80 ppm) for 2 min as recommended treatment for fresh blueberries due to its great efficiency in reducing Salmonella in water with elevated turbidity conditions.…”

“…Furthermore, at low UV doses, injured cells can be gradually recovered during storage. As regards the effect of UV on sensory quality, several studies have found no significant changes in the colour or texture of blueberries [84][85][86].…”

The utilization of vaporized ethyl pyruvate for decontamination of lettuce from E. coli O157:H7

“…This means that lowering the bacterial density in a specific region could potentially be a more feasible task. Nonetheless, another study indicated that the inoculation method did not significantly affect the effectiveness of UV application on the reduction of bacteria (Guo et al, 2019). In addition, the initial number of microorganisms attached to the lettuce samples was high.…”