Now, scientists report that they have developed a packaging film coated with clay nanotubes packed with an antibacterial essential oil. The film provides a one-two punch, preventing over-ripening and microbial growth, which could help improve the shelf life of perishables.
The researchers present their results this week at the 254th National Meeting & Exposition of the American Chemical Society (ACS), the world's largest scientific society.
"Food packaging that is capable of interacting with food can contribute to safety and prevent economic losses from spoilage," said Dr. Hayriye Unal with Sabanci University in Turkey. "Specialized films that can preserve a wide array of foods are highly sought after."
People have been trying to preserve fruits, vegetables and meats since ancient times, ranging from the traditional methods of salting or fermenting to the more modern methods of canning, freezing or wrapping in plastic films.
According to the U.S. Department of Agriculture, about 30-40% of the food farmers in the country produce goes to waste. This sometimes occurs when people just don't have enough time to eat all of the fresh food they buy, but other times food spoils at the grocery store because consumers avoid purchasing fruits, vegetables and meats with visible imperfections.
Over the past two decades, scientists have been developing alternative ways to preserve food, with an extensive focus on packaging, according to the ACS news release. Numerous issues, primarily the versatility of the materials, have hindered progress.
"While companies can already make many films that prevent fruit and vegetables from drying out, incorporating additional properties in the same film is a challenge," Unal said.
Bacterial contamination and permeability to both oxygen and water vapor are major issues scientists are addressing. Another challenge is to prevent too much ethylene from building up around foods. Ethylene is a compound naturally released by fruits and vegetables that aids in the ripening process, but an excess of ethylene trapped underneath the packaging film can cause food to over-ripen and rot.
To meet the demand for multifunctional packaging, Unal's team started with a polyethylene film. To scavenge for ethylene and provide a gas barrier, the group incorporated clay "halloysite nanotubes," which are small, hollow cylinders. The nanotubes prevent oxygen from entering the film and prevent water vapor and other gases from escaping. In addition, they keep ethylene from building up by absorbing it.
The researchers loaded these nanotubes with a natural antibacterial essential oil found in thyme and oregano called carvacrol and coated the inner surface of the packaging film with the loaded nanotubes to kill microbes.
The team wrapped tomatoes, bananas and chicken in the film to test its effectiveness over varying amounts of time compared to foods wrapped in plain polyethylene. After 10 days, tomatoes wrapped with the new film were better preserved than the control vegetables. In addition, the new film helped bananas stay firmer and keep their vibrant yellow color after six days compared to the control fruit. Chicken enveloped with the experimental film and refrigerated for 24 hours showed significantly less bacterial growth than chicken in plain polyethylene.
Still, Unal said, moving this technology to the industry will require some additional work. As a next step toward that effort, her team will test the new film to make sure it is safe and nontoxic.
Unal's work was funded by the Scientific & Technological Research Council of Turkey.
ACS, a not-for-profit organization chartered by Congress, provides access to chemistry-related information and research through its multiple databases, peer-reviewed journals and scientific conferences. ACS does not conduct research but publishes and publicizes peer-reviewed scientific studies.