Fortifying food

Two images of the nisin PLA polymer, outer surface (left) and cross-sectional (right) views. Nisin is evenly distributed, ensuring its slow but continuous release.

By | January 1, 2008

<figcaption>Two images of the nisin PLA polymer, outer surface (left) and cross-sectional (right) views. Nisin is evenly distributed, ensuring its slow but continuous release. Credit: Courtesy of Tony Jin</figcaption>
Two images of the nisin PLA polymer, outer surface (left) and cross-sectional (right) views. Nisin is evenly distributed, ensuring its slow but continuous release. Credit: Courtesy of Tony Jin

Food scientist Tony Jin's dissertation had something most don't: A picture of a Jack in the Box restaurant. While completing his master's degree in food engineering at the University of Missouri in 1993, the restaurant chain had an outbreak of Escherichia coli. He chose his degree because he wanted to protect food from pathogens, and that outbreak sealed his fate, so to speak.

More than 20 years later, the food industry remains vulnerable. In October, Jin learned that meat processor Topps had issued one of the largest beef recalls ever (more than 20 million pounds) due to contamination by E. coli, forcing the largest supplier of frozen hamburgers to shut its doors. This recall occurred one year after contaminated spinach sickened 205 people, killing three. These outbreaks are part of what gets Jin to work every day. "I wish I could go faster to do a better job to protect our citizens," he says.

Jin now presides over a lab in the US Department of Agriculture's eastern regional research center in Wyndmoor, Pa., where he works on antimicrobial coatings for film and liquid containers. As he and I talk, a small cabinet jiggles four bottles, emitting a hum that underscores our conversation. Jin explains that the liquid sloshing inside the bottles contains microbes, and insides of the bottles are coated with an antimicrobial film he designed.

When Jin arrived at the USDA facility, his first projects focused on pectin, a gelling agent derived from plants most commonly used in making jams and jellies. It is also an antimicrobial agent, which he thought might work as an edible film to protect food from E. coli. Early tests showed that pectin films protected against Lysteria monocytogenes and L. plantarum. But Jin soon figured out that edible films wouldn't be enough. "I realized we would still need regular packaging for film-wrapped foods," he says. So he turned his focus to polylactic acid, a biodegradable polyester derived from cornstarch with antimicrobial properties, which he could incorporate into regular packaging.

To give packaging extra antimicrobial effects, Jin sprays coatings and containers with polylactic acid and nisin, a polypeptide bacteriocin also derived from cornstarch, to knock out L. monocytogenes. In July, he presented a paper at a food science conference that showed his PLA/nisin polymer protected against L. monocytogenes and the virulent form of E. coli.

Jin is one of a group of investigators using science to improve food's appearance and longevity, with techniques ranging from edible lids on yogurt to high gloss on chocolates. Michael Chikindas, a food scientist at Rutgers University, says that nisin and polylactic acid make "a very promising matrix," and Jin's "engineering and chemistry are outstanding." Chikindas' team at Rutgers, led by Kathryn Urich, is adding antimicrobials derived from substances like thyme and clove directly to food, to block the formation of microbial biofilms on food surfaces.

In his current experiments, Jin is adding his PLA/nisin film to the insides of bottles of egg white and orange juice, and to the packaging surrounding sliced turkey. If his preliminary tests go well, he'll begin testing his films in larger quantities, and over longer periods. For that, he'll need some new equipment: During a tour of the facility, he walks into a noisy room full of working industrial machinery. There, like someone standing next to a new car in his driveway, Jin points with pride to an empty space which, if all goes well, will house a new bottling machine, capable of bottling three liters of liquid per minute.


Avatar of: anonymous poster

anonymous poster

Posts: 1

February 1, 2008

I'm all for keeping foods from spoiling but how do these materials selectively target microbes? If humans don't have the features that target the microbes, do we know that the materials won't have some other effect on humans?
Avatar of: Herman Rutner

Herman Rutner

Posts: 6

February 7, 2008

The cited container preservatives, individually or in combination, appear quite safe for use on packaging, some even when transferred to food, like nisin, that is also found in milk. \nHowever, also desirable is preserving the packaged food item itself, e.g. by means of non-toxic volatile anti-microbials like lactic acid, acetic acid or propionic acid, slowly released as vapors from the coatings of polylactide or chitosan and permeating the packaging. If desired, such water soluble additives/coatings could also be easily washed off the food item prior to cooking or consumption.\nHerman Rutner, consultant

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