May 26, 2022

New projects eye blue light, bubbles and smartphone-based infrared in produce safety

Antimicrobial blue light, ultra-fine bubbles and smartphone-based infrared cameras may seem unrelated, but each technology is part of a Center for Produce Safety-funded proof-of-concept research project.

The principal investigators leading the studies will be among those presenting final reports at the Center for Produce Safety’s Research Symposium, June 21-22, in La Jolla, California.

Antimicrobial blue light

During the one-year project, Francisco Diez-Gonzalez, Ph.D. and director of the University of Georgia Center for Food Safety, looked at antimicrobial blue light as a potential sanitation tool for Listeria monocytogenes in processing and packing plants.

Francisco Diez-Gonzalez, University of Georgia

Although the technology has seen some use in hospitals, Diez-Gonzalez said few studies have examined potential agricultural applications.

Joining him in the project, titled “Control of Listeria monocytogenes in processing/packing plants using antimicrobial blue light (aBL),” was co-principal investigator Govindaraj Dev Kumar, Ph.D., also with UGA’s Center for Food Safety.

Visible to the naked eye, the blue light tested was in the 400-470 nanometer wavelength range and had a bluish to purplish tint. The light oxidizes large biomolecules, such as DNA, within bacterial cells, inactivating and eventually killing them, Diez-Gonzalez said.

The researchers applied a cocktail comprising five Listeria monocytogenes strains from fresh produce environments to obtain dried cells or biofilms on the surface of stainless-steel coupons — or small plates. They then exposed the coupons to various blue light doses measuring microbial inactivation.

Based on the results, Diez-Gonzalez said antimicrobial blue light using LEDs appears to be a promising intervention. In fact, he said the results were so positive he applied for a U.S. Department of Agriculture National Institute of Food and Agriculture grant to expand work to include other pathogens. The USDA recently awarded Diez-Gonzalez a three-year, $599,000 NIFA grant.

“What I envision is you would have some large hanging lamps that would be turned on during the night after the packing plant was cleaned, and they could enhance the sanitation and control of listeria,” he said. “We still have to figure out quite a few challenges, but it’s very simple and doesn’t have the complications of many other, more sophisticated technologies.”

Ultra-fine bubble technology

Abhinav Upadhyay, Ph.D., with the University of Connecticut, joked that a YouTube search for a better way to bathe a dog prompted him to explore bubble technology for produce.

The project, titled “Application of ultra-fine bubble technology to reduce Listeria monocytogenes contamination of fresh produce,” looked at using ozone bubbles 1 micrometer or less — smaller than the naked eye can see.

“This is super new for the produce industry and food safety in general,” Upadhyay said. “But it’s been used in the auto industry to make engines more efficient.”

He said he’s also interested in ozone because it breaks down within about 20 minutes, leaving no residue.

Upadhyay measured the efficacy of the ultra-fine bubble technology applied to wash water to inactivate listeria on apples, celery and romaine lettuce.

The treatments involved various durations from 30 seconds to 3 minutes with and without chlorine — a common packinghouse wash water sanitizer — at 200 parts per million. The treatments also were applied to water at 4 ℃ (39 ℉) and 25 ℃ (77 ℉) with and without agitation to simulate a hydrocooling bath and a normal dump tank, respectively.

Because of varying surface properties among the produce types, Upadhyay found different results. But he did not see a color change among the treated items. In addition, Upadhyay tested listeria survival in the wash water.

He said he hoped to secure additional funding to expand the research to look at ultra-fine ozone bubbles in combination with other common sanitizers used in produce facilities as well as to measure potential effects on produce shelf life.

Smartphone-based infrared cameras

The old adage that a picture is worth a thousand words also appears true for monitoring produce cooling and storage conditions, said Kevin Mis Solval, Ph.D., with the UGA’s Food Science and Technology.

The military and construction industries already use thermal imaging technology, but he said his project is the first he’s aware of examining its use for produce.

Mis Solval and co-principal investigator Govindaraj Dev Kumar, Ph.D., compared two Android-based and two iOS-based infrared cameras to type-K thermocouples connected to a data acquisition system in the project, titled “Using low-cost smartphone-based infrared cameras to evaluate cooling and storage conditions of fresh produce.”

The relatively low-cost cameras were plugged into smartphones and used proprietary phone apps to process the images and provide real-time results.

The researchers imaged surface temperatures of lettuce heads incubated at 42 ℃ (104 ℉) to simulate postharvest field conditions. They also imaged heads after immersion in 5 ℃ (41 ℉) water for 30 minutes to mimic hydrocooling.

In addition, they imaged heads stored at different locations in a simulated cooler to measure variations in cold air distribution. Similar experiments were also performed with cantaloupes.

The researchers compared their results against a professional-grade infrared camera as well as the thermocouples.

Mis Solval said the advantages of the smartphone-based technology include that it is contactless, non-destructive and gives a broad picture of temperature variations within an area, such as a cooler in real-time.

“You get the whole picture, the whole temperature profile of the produce,” he said. “It gives you a better idea of the conditions of these commodities both before hydrocooling and after hydrocooling. The whole idea is to provide the industry with a practical tool — something they can implement tomorrow. People don’t realize that a smartphone is a supercomputer with interesting capabilities that can be used to benefit the produce industry.”

— Center for Produce Safety




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