Effect of 450 nm Visible Blue Light from Light-Emitting Diode on Escherichia coli O157:H7 in Agar Gels: Optimizing the Lighting Array and Quantitative Microbial Exposure Assessment

Visible blue light emitting diodes (LED) have been studied to inactivate Escherichia coli (E. coli) O157:H7 in agar gels. The LED array was optimized to attain uniform light illumination, and the light intensity distribution was visualized through optical simulation. The uniformity of LED light intensity was assessed, and the evenly spaced array showed the best uniformity with a Petri factor of 0.99. Microbial populations in agar gels prepared with and without a dye were analyzed after light irradiation. Each segment of the gels with different heights was taken to measure microbial reduction, and the results indicated that optical properties, such as opaqueness, played an important role in microbial reduction. The agar gel without and with a dye showed a maximum reduction of <3.4 and <2.1 log CFU/g, respectively. An exposure assessment for E. coli O157:H7 was conducted based on the assumption for the agar gel product after LED illumination. The probability results indicated that a risk (>5 log CFU/g) existed mainly in the bottom layer of the sample, despite the average contamination being <5 log CFU/g. This study provides a suitable approach for designing the LED photoinactivation process and subsequent exposure assessment to avoid risk.