Food Science + Engineering = Safer Food

PurdueAgricultures

Food science + engineering = safer food

Common Denominators

By Brian Wallheimer

Arun Bhunia is not an engineer, although scientists confuse him with one sometimes at conferences.

This mistaken identity can be traced to a decade ago, when a group of engineering students and postdocs approached him about using lasers to detect bacteria. Bhunia, a microbiologist in Purdue University's Department of Food Science, had never thought about pathogen detection using a laser, and he wasn't sure it was possible.

But he was intrigued. Bhunia had hit dead ends in research before, so he decided to see what he could do with a bunch of engineers. "Before I came to Purdue, I was doing pathogen detection work," he says. "But you could only go so far before your expertise was no longer enough."

Bhunia and the engineering students who worked with former head of Mechanical Engineering E. Dan Hirleman gathered in Bhunia's lab and pointed the laser at bacteria. They watched the light scatter after it passed through the bacterial colonies. Based on what they saw, it seemed that different bacteria produced different patterns of scattered light.

To be sure, they contacted J. Paul Robinson, a professor of biomedical engineering, and Bartek Rajwa, a research assistant professor, both experts in image analysis.

Working together, the group, which now includes research assistant professor of mechanical engineering Euiwon Bae, found that bacteria do scatter light in different and predictable ways. A library of the images could be built, and food safety inspectors could use a laser-based device to quickly test samples to detect harmful pathogens, such as E. coli and Salmonella.

Bhunia now speaks regularly at conferences about the BARDOT (Bacterial Rapid Detection using Optical Scattering Technology) light-scattering device. Based on his work with Robinson, Rajwa and others, Bhunia can talk with confidence about some of the engineering components of the project, which is why he's mistaken for an engineer.

"I have to be able to talk about all aspects of the device. My engineering knowledge is limited, but I know a lot more now than I did before this project," Bhunia says.

The Early Years

The BARDOT light-scattering project is one of the successes to come out of Purdue's Center for Food Safety Engineering, which marked its 10th anniversary this year. And it perfectly illustrates the mission of the center: to

bring together chemists, biologists, engineers and other scientists to improve food safety through advancements in the detection and control of foodborne pathogens and chemical hazards.

Today, at a university that has an entire physical section of campus—Discovery Park—designed to foster interdisciplinary research, that seems like a no-brainer: together, scientists can do more than the sum of their parts.

But Rich Linton remembers what it was like convincing researchers of that a decade ago. "People were in their silos. There was an effort to integrate research across disciplines. I remember those first meetings with people from various fields. We didn't even speak the same language," says Linton, who directed the center until this past summer, when he left for Ohio State University. "We started the center when it was really unpopular to bring together different disciplines. We had to convince people it was a good thing to work together."

Bringing in Engineers

Linton did that in the beginning by finding a common denominator—Michael Ladisch. As an agricultural and biological engineer, Ladisch had worked with more traditional food scientists as well as engineers.

Back then, Ladisch was interested in developing a device that could use antibodies to detect proteins present in human disease. Linton asked him instead to look for pathogens in food and to head a team of engineers and food microbiologists, including Bhunia and Rashid Bashir, a former Purdue electrical engineer now at the University of Illinois.

The group developed a chip the size of a postage stamp that can detect foodborne pathogens within hours. The device takes a microliter of fluid—much less than a drop—and concentrates the cells. Those cells are run through microscopic channels where antibodies attach to any pathogenic bacteria present. A change in conductivity of the chip alerts scientists to the bacteria.

The project required Bhunia's knowledge of antibodies, Bashir's ability to microfabricate the chip and Ladisch's expertise to assemble the components and test the chip's abilities.

"If we'd done it in food science, it would have been just about the food component," Ladisch says. "Had the technology been done just in engineering, it would have only addressed the engineering concerns. The center really brings out the best in Purdue Agriculture and engineering. It's one way of translating fundamental science and technology into real-world applications."

Technology for the Real World

The Purdue scientists also work with U.S. Department of Agriculture scientists, and much of the funding comes from the USDA.

USDA scientist Shu-I Tu says the collaboration has shaved possibly years off the time it might have taken to develop technologies that can detect multiple bacterial pathogens the way the center's sensors have done.

"What we are creating is more practical for the real world," Tu says. "We're using resources to solve problems from different angles and complementing each other."

The collaboration means Purdue scientists can develop technology with those who will use it in the USDA. Devices don't have to be modified later. They're developed to handle situations and scenarios USDA scientists are seeing in the real world.

"We have a slightly different perspective on how to apply the technologies," says George Paoli, a research microbiologist and lead scientist in the Molecular Characterization of Foodborne Pathogens Research Unit at the USDA Agriculture Research Service's Eastern Regional Research Center. "The center provides a way for these things to come together that wasn't happening before."

Funding Affects Ongoing Research

The Center for Food Safety Engineering has been successful in pulling together teams of researchers, and it has also addressed another key component to any successful research project: funding.

Joseph Irudayaraj, a professor of biological engineering, is developing foodborne pathogen sensors using nanotechnology with the help of steady funding from the CFSE. Before joining the center, he heard a lot of praise for his ideas, but grants never followed.

"The funding agencies just weren't funding sensor technology at the time," Irudayaraj says. "To make any type of long-term impact, we need continued funding. The center provides the needed continuity."

With the initial funding, Irudayaraj has made progress in using nano-scopic gold and silver particles to detect 10 or fewer cells of harmful pathogens. The nanoparticles, coated with antibodies, attach to the bacteria and glow, making them visible to scientists or food safety inspectors.

The initial funding from the CFSE has led to corporate funding from a company interested in refining the technology, Irudayaraj says.

Bruce Applegate's detection work got off the ground with funding from the CFSE as well. Applegate, a food science researcher, is collaborating with Michael Kane in Computer and Information Technology and Sergei Savikhin in Physics to investigate quantitative polymerase chain reactions, which involve taking small pieces of DNA and multiplying them over and over again.

The multiplied DNA is added to a substrate or surface, which contains molecular "beacons" that search for genes found in pathogenic bacteria such as E. coli, Salmonella and Listeria. If those genes are present, the DNA binds to the molecular beacons, causing them to unfold or open.

A green light from a laser shined on the sample will reflect back green if the beacon is open, indicating the presence of harmful bacteria. If the light reflects back red, the beacon is closed, and the bacteria are not present.

"We're able to look for multiple things at once, not just one," Applegate says.

Another Applegate project involves constructing bacteriophages—viruses that infect and live off bacteria—that cause the pathogenic bacteria to glow when infected.

"You could just throw the phage in a sample, come in the next day and turn off the light in the lab," Applegate says. "If it's glowing, the pathogen is there."

Looking Ahead

This year, Lisa Mauer, a professor of food science, took over as interim director of the CFSE. One of her foremost goals is to push the commercialization of the technologies developed in the center. When that happens, she says, everyone who expects food to be safe would benefit.

"The focus in food safety for many folks has been about what happens after an outbreak; how fast can we trace back an outbreak," Mauer says. "But we are developing devices that will reduce the time it takes to initially detect these pathogens. We're moving toward stopping the outbreaks from happening in the first place."

There will also be challenges, Mauer says. As federal budgets are slashed, it's unclear whether money will be in the USDA budget to continue the collaboration.

"We have to diversify," Mauer says. "We have to find other funding opportunities."

Mauer is plunging ahead. As new faculty members arrive on campus, new opportunities arise. The Department of Food Science expects to hire two new faculty members who may become active in the center. One will take the Scholle Chair in Food Processing position once held by 2007 World Food Prize laureate Philip Nelson . Another position will have a major Extension role, focused on taking the knowledge of food safety, including that gained within the center, to those who can use it best.

"That will really expand our work. The research and outreach go hand in hand," Mauer says.

Contact Brian Wallheimer at

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