National University of Singapore (NUS) scientists have demonstrated that blue light-emitting diodes (LEDs) have strong antibacterial effects 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. The finding suggests a new chemical-free food preservation method that would be very effective on acidic foods such as fresh-cut fruits and ready-to-eat meats at their nominal colder temperatures.
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Bacterial cells contain light sensitive compounds that absorb light in the visible region of the electromagnetic spectrum (400-430 nm), the wavelength of blue LED light. Exposure to illumination from blue LEDs can therefore begin a process within the bacterial cells that ultimately causes them to die.
Existing studies on the antibacterial effect of LED illumination mostly evaluated its efficacy by adding photosensitisers to the food samples, or by using very close distance of less than 2 cm between the bacterial suspension and LED light source. These conditions would not be viable for application on food preservation.
The NUS team, led by assistant professor Yuk Hyun-Gyun, from the Food Science and Technology Programme at the NUS Faculty of Science, is the first so far to show that factors such as temperature and pH levels, which are typically related to food products, can affect the antibacterial effect of LEDs.
In this study, the team placed three major foodborne pathogens--Listeria monocytogenes, Escherichia coli O157: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.
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. Since November 2012, we have also been collaborating with the Agri-Food & Veterinary Authority (AVA) to apply this LED technology to fresh-cut vegetables to determine whether LED will help preserve or improve the nutritional quality of vegetables during storage," added Yuk.
As part of this three-year study, AVA has been studying the effects of LEDs on some key quality parameters of vegetables (vitamin C, chlorophyll, and beta-carotene) to investigate if the quality of the vegetables under this LED treatment will be maintained. The results will be available once the study is complete.
SOURCE: National University of Singapore;http://news.nus.edu.sg/press-releases/9188-nus-study-shows-potential-of-blue-leds-as-novel-chemical-free-food-preservation-technology