Multifunctional intelligent packaging films incorporated with elderberry anthocyanin for monitoring milk freshness

In this study, pH-sensitive polyphenolic elderberry fruit extract (ELPE) incorporated pullulan (PUL) and gellan gum (GG) based films were prepared. The intermolecular interactions between ELPE and polymer matrix were verified by infrared spectroscopy. The enhanced thermal stability following the introduction of ELPE was caused by the phenolic compounds present in ELPE. The incorporation of ELPE raised the thickness, water vapor permeability, and tensile strength of the films, while it decreased the moisture content, UV-Vis light transmission, and elongation at break values of the films. The film's total antioxidant capacity, the total phenolic contents, and the total monomeric anthocyanin contents were increased with increasing ELPE content. The high anthocyanin concentration in ELPE caused pH sensitivity of the films, changing from red to blue/green as the pH value was raised from 2 to 13. Also, ELPE-incorporated films showed good antibacterial activity against S. aureus and E. coli. Lastly, ELPE-incorporated films were used to monitor the freshness of milk, and as the milk spoiled after being stored at 40 degrees C for 8 h, the films changed color. The application of PUL-GG-ELPE films was suggested to be used as novel active and intelligent multifunctional food packaging materials by our findings.