Structural, physico-mechanical, and bio-functional properties of whey protein isolate-based edible films as affected by enriching with nettle (Urtica dioica L.) leaf extract

In this study, antioxidant and antibacterial edible films based on whey protein isolate (WPI) and nettle leaf extract (NLE) were developed. NLE at different concentrations (0, 10, 30, and 50%) was added to the WPI film-forming solution and the bioactive films were produced by the casting method. The results showed that the addition of NLE into the WPI films increased their thickness and elongation, whereas decreased their moisture content, water solubility, water vapor permeability, and tensile strength. The results also indicated that the enriching of WPI films with NLE increased their darkness, yellowness, and greenness. The FTIR spectroscopy showed that the hydrogen bonds were formed in the film matrix between WPI and NLE. The XRD analysis also showed that these interactions have been taken place in the amorphous phase. The total phenolic content and antioxidant activity (free radical scavenging activity and reducing power) of WPI were also significantly increased by enriching with NLE. The NLE-enriched films also showed antibacterial activity against Staphylococcus aureus and Escherichia coli. Generally, the findings of this work suggested that the incorporation of NLE into the WPI-based films can lead to the production of eco-friendly antioxidant and antibacterial biopolymer-based food packaging systems.