Saturday, August 15, 2015

Emergence of LED based bacterial destruction technology- Opening up a new avenue for safeguarding foods

Technology for food preservation has evolved over a hundred years in the past and from the early findings that salt, sugar, acids can protect foods from deterioration by pathogenic microorganisms, modern food technology has been able to innovate newer processes with more reliability and assurance. Canning was considered the most trustworthy process and during various wars canned foods formed the backbone of the fighting soldiers. Emergence of technologies like irradiation, High pressure processing, controlled environment storage/packing, HTST etc are now available to the industry for different types of products. Ultimately the effectiveness and acceptability of a technology depend on its ability to preserve the quality of the food processed, achieving cent percent kill of microbes and the cost of using the technology under commercial conditions. Recent claims that blue LED rays can be an effective tool in the hands of technologists to preserve foods, offer a new option that may be acceptable to the industry. Here are more details of the same as reported recently.

"Blue LEDs in conjunction with cold temperature and acidic conditions can kill off foodborne pathogens making chemical-free preservation a possibility for a range of foods. Fresh-cut fruits and ready-to-eat meats are just some of the foods which are mildly acidic (pH 4.5) that could use this preservation technology to avoid the use of chemical preservatives and present the 'clean label' that consumers desire. A team of scientists from the National University of Singapore (NUS) has found that blue light emitting diodes (LEDs) have strong antibacterial effect on major foodborne pathogens and are most effective when in cold temperatures (between 4 and 15°C) and mildly acidic conditions of around pH 4.5. These findings were recently published in the Food Microbiology journal in June 2015. 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. Existing studies on the antibacterial effect of LED illumination mostly evaluated its efficacy by adding photo sensitisers 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. 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."

Though blue light rays are used widely for a variety of applications, its utility to food preservation is some what new deserving further development to bring it to wide scale use commercially. The major constraint has been that photo sensitizers are required to activate the kill effect of the blue rays. Also the efficiency of blue rays depends largely on the distance between the food sample and the source of the light. Though cold temperature and pH conditions can enhance the kill effect, how suitable equipment can be designed for large scale commercial application needs to be addressed. If these problems are overcome, blue ray technology may find wide applications in future in the industry, retail stores and domestic refrigerators, especially to protect cut fruits and vegetables, meat cuts and other perishable foods


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