Functional properties of corn starch films incorporated with carbon quantum dots for potential active packaging applications

Incorporating carbon quantum dots (CQDs) is promising to enhance the limited functional properties of starch films for active food packaging applications. This study developed corn starch films containing different CQD concentrations via solvent casting. CQD inclusion improved mechanical properties, with optimal tensile strength and Young's modulus at 1.0 wt% CQDs, exhibiting 96.8 and 171.6% improvements, respectively, ascribed to strong interfacial interactions between CQDs and starch matrix. The maximum degradation temperature increased by 3.83 °C at 3.0 wt% CQDs. Ultraviolet-blocking capabilities were enhanced, with transmittance at 280 nm reduced by 88.29% for films with 5.0 wt% CQDs. However, water vapor permeability increased by 27.43% due to the hydrophilicity of CQDs. Antimicrobial analysis via disc diffusion exhibited no zones of inhibition against Staphylococcus aureus and Escherichia coli, likely due to CQD immobilization within the dense starch matrix, restricting their diffusion into agar medium. However, antioxidant activity was significantly enhanced, reaching a 12.82-fold improvement at 5.0 wt% CQDs. Overall, 1.0 wt% CQDs is considered the most suitable concentration for practical applications. It optimized mechanical integrity, whereas relatively small gains in thermal and active properties at higher concentrations were offset by compromised structural resistance. Films with 1.0 wt% CQDs better maintained the firmness and pH of cherry tomatoes during 6-day storage compared to neat starch films. Driven by their antioxidant and UV-blocking capabilities, these findings demonstrate the potential of starch/CQD films as eco-friendly active food packaging materials to improve the quality attributes and shelf-life of fruit, helping to solve food safety and security issues.

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