Purple tea extract-modified chitosan films with pH-responsive properties for fresh shrimp freshness monitoring

BACKGROUND Faced with the relentless depletion of fossil fuels and the global environmental crisis, the strategic utilization of abundant biomass resources has drawn significant attention, offering vast application prospects in the field of food packaging. This study pioneers an investigation into the effects of incorporating purple tea extract (PTE) in chitosan (CS) films on their fundamental physical properties and functionalization, leading to an active and intelligent CS/PTE composite film with pH-responsive characteristics and improved physical properties. RESULTS X-ray diffraction and Fourier transform infrared analyses indicate that CS and PTE interact primarily through hydrogen bonding, demonstrating high compatibility. The impact of varying PTE concentrations on the water vapor permeability, transparency, mechanical properties, antioxidant activity, antimicrobial performance, and pH responsiveness of the CS film was systematically investigated. The experimental results show that PTE significantly enhances the films’ light and water vapor barrier properties. Specifically, films containing more than 6% PTE exhibit improved antioxidant, antimicrobial, and food preservation capabilities. The resulting composite film demonstrated excellent antioxidant and antibacterial performance with a DPPH radical scavenging rate of 83.2%, and inhibitory rates exceeding 90% against Escherichia coli and Staphylococcus aureus , as well as pH-responsive color changes. CONCLUSION Overall, the CS/PTE composite film represents a highly promising active and intelligent food packaging material. It not only expands the range of naturally available materials for smart packaging films but also holds significant potential for practical applications in the food industry. © 2026 Society of Chemical Industry.