The research, part of a bigger project to develop nano-composite films, funded by the USDA, tackles the growing problem of waste generated by plastic packaging materials.
Dr. Reza Tahergorabi, assistant research professor, North Carolina A&T State University, said wheat starch, wheat gluten, soy and whey proteins have often been used to develop biodegradable packaging systems but they can create allergenic problems if the compounds migrate onto edible products.
“There are no such issues with sweet potato starch and it is an inexpensive and readily available vegetable, cultivated for its nutritious value,” he said.
The research involved montmorillonite (MMT) layered nanoclay and thyme essential oil which was incorporated into a sweet potato starch film to improve its physical and mechanical properties.
The MMT weight percent relative to the sweet potato starch was constant at 3% and was activated by three levels of thyme essential oil: 0.5%, 1% and 1.5%.
The researchers then investigated the impact of the MMT nanoclay and oil on the physical, mechanical and barrier properties of the starch films.
They found incorporating MMT into sweet potato starch film greatly improved the firmness, water gain and water vapor permeability of the films.
Thyme essential oil
The combined effect of MMT and thyme essential oil improved the tensile strength, elongation and tri-stimulus color values of the film.
“The eventual target audience would include the food industry particularly fresh produce industry as well as food packaging industry,” said Tahergorabi.
The research found the developed film exhibited good film formability but the physico-mechanical characteristics of the film needed to be improved, so adequate amounts of MMT were added to the sweet potato starch.
“Up to 5% of MMT improved these properties. We have tested different concentrations and found that addition of 3% of MMT will result in stronger film for packaging,” added Tahergorabi.
“At the end, thyme essential oil as an antibacterial agent was incorporated in the film. In vitro studies have shown that thyme essential oil has a strong antibacterial effect. Addition of the oil did not deteriorate the texture and film formability.
“The major impact of this project is that the developed biodegradable film could be used for the packaging of different types of fresh fruits and vegetables to replace some existing plastics.”