Development of a Novel Film Based on Casein/Modified Tragacanth Gum Enriched by Carbon Quantum Dots for Shelf-Life Extension of Butter

Abstract

Casein proteins were cross-linked with dialdehyde tragacanth gum (DTG) to create a film with improved physico-mechanical properties. The DTG/casein film with a 2:1 ratio exhibited good physical and barrier properties, such as tensile strength (TS) (12.92 MPa), water contact angle (WCA) (73.2°), water vapor permeability (WVP) (2.1 × 10 − 10 g·mm/h·mm²·Pa), and water solubility (WS) (22.3%). Carbon dot (CD) nanoparticles were synthesized from milk permeate using a hydrothermal method. CDs (5 to 50% w/w) were incorporated into the optimal cross-linked casein films to create casein-based nanocomposites. Adding CDs (up to 15% w/w) increased the film’s tensile strength by 36%. Scanning electron microscopy (SEM) confirmed the homogeneous distribution of 5% CD in the films without aggregation. The hydrophilicity of the films increased with the addition of CDs. Additionally, incorporating CDs significantly reduced UV transmission, with a 99.09% reduction in UV-C and a 97.46% reduction in UV-A. The CD-added nanocomposite films demonstrated potent antioxidant activity, increasing DPPH scavenging from 18.1 to 94% and ABTS scavenging from 16.4 to 89.3%. No cytotoxicity was observed in normal cells (HUVEC) even after 72 h of exposure. Coating butter products with the composite films for 60 days resulted in decreased peroxide value (PV) and thiobarbituric acid reactive substances (TBARS), indicating an oxidation–reduction process. These findings highlight the potential of cross-linked casein films with CDs to extend the shelf life of food products in the food industry.