Antimicrobial effect of blue LED in acidic foods

YUK Hyun-Gyun (Group Leader, Chemistry)

July 14, 2015

14 Jul 2015 NUS food scientists discovered that the antibacterial effect of blue LEDs could be enhanced by acidic or alkaline pHs that are found in different foods. Building on their previous novel findings (Ghate et al, 2013), a team led by Prof YUK Hyun-Gyun and his students from the Food Science & Technology Programme in the Department of Chemistry, NUS has now elucidated the role of pH in the efficacy of light emitting diodes (LEDs) against foodborne pathogens (Ghate et al, 2015). Prof Yuk’s team had previously shown that blue LEDs can effectively inhibit four major foodborne pathogens – Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes and Staphylococcus aureus. The present study went one step further and tried to understand the effect of the extracellular environment on this antibacterial effect.

The team tested the effect of blue and green LEDs on the four pathogens at five different pH values – 4.5, 6, 7.3, 8.0 and 9.5, at a temperature of 15 °C, up to a dosage of nearly 600 J/cm²(see Figure). It was observed that the extracellular pH significantly brought about a distinction in the susceptibility of the pathogens to the blue LEDs. Moreover, the team found out that these deadly bacteria were more susceptible to an acidic pH than a neutral pH,demonstrating the potential of 461 nm LEDs in preserving acidic foods. This was the first study to show the influence of the extracellular environment on the antibacterial effect of LED.

This study provides valuable new knowledge towards understanding the effect of pathogens to LEDs under different conditions and towards designing decontamination systems using LEDs.

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The figure shows the effect of the LEDs on L. monocytogenes at 15 °C, at a pH of 4.5. [Image credit: Yuk HG]

References

1. Ghate VS, Ng KS, Zhou W, Yang H, Khoo GH, Yoon WB, Yuk HG. “Antibacterial effect of light emitting diodes of visible wavelengths on selected foodborne pathogens at different illumination temperatures.” International Journal of Food Microbiology. 166 (2013) 399.

2. Ghate VS, Leong AL, Kumar A, Bang WS, Zhou W, Yuk HG. “Enhancing the antibacterial effect of 461 and 521 nm light emitting diodes on selected foodborne pathogens in trypticase soy broth by acidic and alkaline pH conditions” Food Microbiology. 48 (2015) 49.