A study by researchers from Harvard, published in Environmental Science & Technology shows that sprinkling charged water nanoparticles onto fruits and vegetables and food production surfaces could eliminate potential food-borne microorganisms. Currently, the popular methods for sterilizing fresh farm produce is either by spraying chlorine or using quarternary ammonium compounds or UV irradiation, which destroys bacteria instantly. However, they could leave behind residues that ruin the food’s taste and are potential irritants.
“Using nanoscale water droplets to inactivate pathogenic bacteria is an innovative approach, and these early results show its effectiveness and great potential for improving the microbial safety of food supply as well as the sanitation of food processing surfaces,” Hongda Chen, acting deputy director at the US Department of Agriculture’s National Institute of Food and Agriculture, wrote to The Scientist.
Researchers from the Harvard School of Public Health led by Philip Demokritou, devised a technique which employs Engineered Water Nanostructures (EWNS) produced by electrospraying of water vapor. EWNS possess unique properties; they are 25 nm in diameter, remain airborne in indoor conditions for hours, contain Reactive Oxygen Species (ROS) and have very strong surface charge (on average 10e/structure).
The device contains a gold-plated electrode, which is cooled to condense water on its microsized tip. A second concentric electrode hovers 5 millimeters below. When activated, electric charges build in the water, drawing liquid toward the circular electrode. Surface tension, however, grips the droplets to the gold tip, until the strain becomes too much, and an aerosolized mist of water nanoparticles spews forth. During the process, some water reacts with air molecules to produce reactive oxygen species (ROS), which shatters the microbes’ membranes.
They tested this technology by placing cherry tomatoes and stainless steel cutting boards inside a chamber, and exposed them to commonly occurring foodborne microbes such as E.coli, Salmonella enterica and Listeria innocua. They were exposed to nanobombs and in each case, they achieved disinfection which were comparable to those achieved using existing technologies. Depending on the bacterium and the surface type, the bacterial concentrations were reduced by values ranging between 0.7 to 1.8 logs.
Consumers today have become very picky about the food they consume, and the trend is more towards, chemical-free, residue-free organic produce. “With this method, there are no residues to worry about, and in 3-4 hours, everything becomes water vapour again”, said Demokritou.