Blue light-emitting diodes (LEDs) show promise as a chemical-free way to preserve food, according to new research.
The LEDs work best in cold temperatures of 4 degrees C and 15 degrees C (about 39–57 F) and mildly acidic conditions of around pH 4.5, said the scientists.
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.
The findings appear in the journal Food Microbiology.
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 start a process within the cells that ultimately causes the cells to die.
Existing studies on the antibacterial effect of LED illumination mostly evaluated its efficacy by adding photosensitizers to the food samples, or by using very close distance of less than 2 cm (about 3/4 of an inch) between the bacterial suspension and LED light source. These conditions would not be viable for application on food preservation.
The team, led by assistant professor Yuk Hyun-Gyun of the Food Science and Technology Program at the National University of Singapore Faculty of Science, is the first to show that factors such as temperature and pH levels, which are typically related to food products, can affect the antibacterial effect of LEDs.
Listeria, Salmonella, and E. Coli
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.
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.
“Taken together, our two studies point to a potential for preserving acidic foods in combination with chilling temperatures without chemical treatments,” said Yuk. “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.”
The team’s findings have potential for food chillers or cold supply chain to preserve fresh-cut fruits, ready-to-eat seafood such as sushi and smoked salmon, as well as chilled meat products. This technology can also be useful for retail settings such as food courts and supermarkets, as well as for food suppliers.
“The next step for us is to apply this LED technology to real food samples such as fresh-cut fruits, as well as ready-to-eat or raw sea foods and meats products, to investigate whether LED illumination can effectively kill pathogenic bacteria without deterioration of food products,” said Yuk.
The team is also looking into using the LED technology to help preserve or enhance the nutrition of vegetables during storage, Yuk said.