Novel composite antimicrobial film could help combat foodborne illnesses

Researcher Abdelrahim Hassan, who was a visiting scholar in the Department of Food Science when the research was conducted, examines the novel composite film that offers antimicrobial properties and at the same time provides the strength, transparency, gas permeability and water resistance that the meat industry is looking for. Credit: Penn State

A novel composite film – created by the bonding of an antimicrobial layer to conventional, clear polyethylene plastic typically used to vacuum-package foods such as meat and fish – could help to decrease foodborne illness outbreaks, according to researchers in Penn State’s College of Agricultural Sciences.

The antimicrobial lining of the film is comprised of a pullulan-based biopolymer produced from starch syrup during a fermentation process, which is already approved for use in foods. Pullulan, a water-soluble ‘polysaccharide,’ is essentially a chain of sugar, glycerin and cellulose molecules linked together. To kill pathogens such as Salmonella, Listeria and pathogenic E. coli, the researchers infused the pullulan with Lauric arginate, made from naturally occurring substances and already approved for use in foods.

Development of the composite antimicrobial film is said to be important because of the 76 million cases of foodborne illnesses that occur each year in the US alone, resulting in 300,000 hospitalisations and 5,000 deaths, according to the US Centers for Disease Control and Prevention (CDC).

The pullulan film slows the release of the antimicrobial, disbursing it at a predictable rate to provide continuous bacteria-killing activity, explained researcher Catherine Cutter, Professor of food science. She added that without being impregnated into the film, the antimicrobial would run off the surface of a food product, such as meat; or evaporate.

The novel composite antimicrobial film stopped pathogens from growing on this ready-to-eat turkey breast. Credit: Penn State

Lauric arginate was chosen as the antimicrobial because it is said to be a remarkable, broad-spectrum antimicrobial compound that proved highly effective in killing and limiting the growth of pathogens that cause foodborne illness, noted Cutter.

“Lauric arginate is a safe, completely nontoxic ingredient,” she said. “It is hydrolysed in the human body by chemical and metabolic pathways, which quickly break it into its naturally occurring components – lauric acid and L-arginine.”

Cutter credited Abdelrahim Hassan, Associate Professor of food safety and technology at Beni-Suef University in Egypt, who spearheaded the latest study, for devising a procedure to fuse the pullulan-based antimicrobial layer to the polyethylene plastic – allowing the novel composite to be born.

“Hassan figured out a way to get the pullulan to attach to polyethylene,” Cutter said. “He modified the formulation of pullulan and changed the hydrophobicity of the plastic. These steps were important because polyethylene repels everything – nothing sticks to it. So, the challenge was, how could we get pullulan to adhere to it.”

Based on these preliminary results, Shiga toxin-producing E. coli, Salmonella spp., Listeria monocytogenes and Staphylococcus aureus were experimentally inoculated onto raw beef, raw chicken breast and ready-to-eat turkey breast, vacuum packaged with the composite antimicrobial film, sealed and placed into refrigerated storage for up to 28 days.

Hassan and Cutter reported that the composite antimicrobial film containing Lauric arginate significantly reduced foodborne pathogens on the experimentally inoculated surfaces of the raw and ready-to-eat muscle foods after refrigerated storage.

Cutter said that the findings from this research will most likely be of interest to the packaging and muscle food industries, as well as regulatory agencies that seek to reduce pathogens in the food supply. Although there was thought not long ago that biopolymers could entirely replace plastic in food packaging, Cutter stated that the composite nature of the antimicrobial film is still needed.