Nanoparticle Combats Listeria by 3 Weeks

WEST LAFAYETTE, Ind.Researchers at Purdue University have developed a nanoparticle that can hold and release an antimicrobial agent that could be sprayed directly onto food or packaging to extend the shelf life of products at risk from Listeria monocytogenes by up to 21 days.

Researchers altered the surface of a carbohydrate found in sweet corn called phytoglycogen, which led to the creation of several forms of a nanoparticle that could attract and stabilize the food-based peptide nisin for up to three weeks.

Controlling Listeria at deli counters is especially problematic because meat is continually being opened, cut and stored, giving Listeria many chances to contaminate the food. Nisin alone is only effective at inhibiting Listeria for a few days in many foods.

"People have been using nisin for a number of years, but the problem has been that it is depleted quickly in a food system," the authors wrote in the Journal of Controlled Release. "This nanoparticle is an improved way to deliver the antimicrobial properties of nisin for extended use."

The team used two strategies to attract nisin to the phytoglycogen nanopoarticles. First, they were able to negatively charge the surface of the nanoparticle and use electrostatic activity to attract the positively charged nisin molecules. Second, they created a partially hydrophobic condition on the surface of the nanoparticle, causing it to interact with partially hydrophobic nisin molecules. When the particles are hydrophobic, or repel water, they become attracted to each other.

"Both strategies may work together to allow nanoparticles to attract and stabilize nisin," they wrote."This could substantially reduce the depletion of nisin in various systems."

They said a solution containing the nanoparticles and free nisin could be sprayed onto foods or included in packaging. The solution requires a balance of free nisin and nisin on the nanoparticles.

"When you reduce the amount of free nisin, it will trigger a release of more nisin from the nanoparticles to re-establish the equilibrium," they said. "There will be a substantial amount of nisin preserved to counteract the Listeria."