No Chemicals Needed: Preserve Food With Blue Light

Scientists in Singapore have demonstrated that blue light, coupled with mildly acidic conditions and cool temperatures, has a strong antibacterial effect. This opens the door to using blue light emitting diodes (LEDs) as a novel means of food preservation, without the need for any additional chemical inputs.

Fresh fruit: these fruit could potentially be preserved using only blue light and taking advantage of their natural acidity. Photo by Bill Ebbesen.Fresh fruit: these fruit could potentially be preserved using only blue light and taking advantage of their natural acidity. Photo by Bill Ebbesen.

LEDs have risen to prominence in the lighting industry thanks primarily to their low energy consumption and high durability. They have become the de facto option for environmentally conscious consumers everywhere as well as finding use in the electronics and agricultural business due to their narrow emission spectra and the ease with which they can be integrated with existing infrastructure. Now, a new arena stands to benefit from the development of LEDs, that of food preservation.

About a decade ago, the antibacterial properties of LEDs – particularly those in the blue region of the spectrum – were discovered. The process involved is termed photodynamic inactivation. Bacterial cells contain light-sensitive molecules that absorb blue light. This energetic absorption leads to the formation of reactive oxygen species which ultimately react toxically with various cell components and cause eventual cell death. This is similar to the dreaded “free radicals” found in our own bodies that we are all anxiously consuming pomegranates and acai berries to avoid. But in the case of harmful bacteria on our food, cell death is the desired outcome.

The researchers from the Food Science and Technology Programme at the National Univerity of Singapore tested the process on three major foodborne pathogens – Listeria, Salmonella and E. coli O157:H7 while varying the acidity of the conditions. According to the Center for Disease Control, in 2009-2010 (the most recent year on record) 29,444 cases of foodborne illnesses were confirmed in the US. Of these, Salmonella was responsible for 30% of reported cases as well as nearly half of those illnesses that required hospitalization. While Listeria was not among the most common pathogens, those who were exposed to this bacteria were the most likely to require hospitalization. Among the recorded deaths from foodborne illness over this time frame, these pathogens were the top three causes. This data clearly demonstrates the importance of targeting these particular organisms.

Salmonella: an electron microscope image shows Salmonella (red) invading human cells.Salmonella: an electron microscope image shows Salmonella (red) invading human cells.

The results showed that moderately acidic conditions led to most effect bacteria destruction. Coupled with the group’s previous analysis of temperature, which found that cool temperatures between 4 and 15 °C, this work clarified the ideal conditions for the use of blue LEDs in food preservation. Conveniently, mildly acidic conditions are found in fresh fruit and raw meat and fish, all of which are regularly kept chilled throughout the supply chain. The researchers thus suggest that this technology could be easily implemented to already existing infrastructure. For example, the refrigerated trucks already used to transport fresh fruit and meat could be outfitted with blue LED lights to maintain food safety.

The potential benefit to this research is obvious as customers increasingly covet “natural” foods and reject the notion of chemical treatments. Manufacturers are scrambling to meet these demands without putting consumer safety at risk. As team leader Assistant Professor Yuk Hyun-Gyun summarizes, "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."

Via Science Daily, the National University of Singapore, and Food Microbiology.