blue LEDsAn NUS study has shown the potential of blue LEDs as a novel chemical-free food preservation technology.Photo credit: Gussisaurio, Wikimedia CommonsA team of scientists from the National University of Singapore (NUS) has found that blue light emitting diodes (LEDs) have a strong antibacterial effect on major foodborne pathogens, and are most effective when in cold temperatures (between 4°C and 15°C) and mildly acidic conditions of around pH 4.5.

This opens up novel possibilities of using blue LEDs as a chemical-free food preservation method. Acidic foods such as fresh-cut fruits and ready-to-eat meat can be preserved under blue LEDs in combination with chilling temperatures without requiring further chemical treatments that are commonly needed for food preservation.


Enhancing blue LEDs’ ability to deactivate bacteria

While LEDs are most commonly known as an energy-saving light source, they have also been known to have an antibacterial effect. Bacterial cells contain light sensitive compounds that adsorb light in the visible region of the electromagnetic spectrum (400-430 nm), which is mainly blue LED light. Exposure to illumination from blue LED light can hence start off a process within the cells that ultimately causes the cells to die.



In this study, the team placed three major foodborne pathogens – Listeria monocytogenesEscherichia coliO157:H7 and Salmonella Typhimurium – under blue LED illumination, and varied the pH conditions from acidic to alkaline. The team found that higher bacterial inactivation was achieved at acidic and alkaline pH conditions than when neutral. In particular, acidic conditions were more detrimental than alkaline conditions for L. monocytogenes. For E. coli O157:H7 and S. Typhimurium, alkaline conditions were most detrimental although acidic conditions were also sufficiently effective in deactivating them.

A previous study in 2013 by the same team had also looked at the effect of temperature on blue LED’s ability to deactivate bacterial cells and found the antibacterial effect to be most enhanced in chilling temperatures.

Asst Prof Yuk said, “Taken together, our two studies point to a potential for preserving acidic foods in combination with chilling temperatures without chemical treatments. This could meet the increasing demand for natural or minimally-processed foods without relying on chemicals such as acidulants and artificial preservatives to preserve food products.”



Collaborating with the Agri-Food & Veterinary Authority



“AVA hopes that the research will affirm the potential of LED as a food preservation technique that can help reduce food loss in Singapore’s fresh produce industry,” said Miss Khoo Gek Hoon, Director, Post-Harvest Technology Department, AVA.