Propolis manipulates the performance and application potential of TG-crosslinked dual protein composite edible film

Propolis, an edible natural functional substance with effective antioxidant and antibacterial properties, has the potential to enhance the preservation capabilities of protein-based films. Therefore, this study aims to evaluate the performance of a transglutaminase (TG) crosslinked whey protein concentrate (WPC) and egg white protein (EWP) composite film incorporated with ethanol-propolis extract (EPE) and its application in preserving tomatoes. The composite films were characterized by water vapor permeability (WVP), tensile strength, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), and antibacterial activity. The addition of 5 mg/g EPE significantly enhanced the performance of the composite film compared to without EPE films, resulting in a 65 % increase in tensile strength (from 2.8 to 4.6 MPa), a 35 % reduction in WVP (2.34 × 10⁻¹⁰ g/s•m•Pa), a 19 % decrease in the content of random coils, and a 37 % increase in the content of β-sheet. Furthermore, the addition of EPE enhanced the antibacterial activity of the composite film, particularly against Salmonella typhimurium. In the preservation experiment, the decay rate of cherry tomatoes coated by composite film with the 10 mg/g EPE on the 14th day was 55 %, which was 11 % lower than that coated by composite film without EPE. Therefore, the incorporation of EPE can alter the overall performance of the TG-crosslinked WPC/EWP composite film and enhance its effectiveness in preserving tomatoes.