Biomass carbon dots and oxidized anthocyanins dual-driven strategy: enhanced collagen films for shrimp preservation and colorimetric/fluorescent freshness monitoring.

In this study, a dual-driven smart and active packaging film was developed by incorporating bovine hide/tannic acid/L-cysteine carbon dots (BTC-CDs) and oxidized Roselle extracts (ORE) into a collagen matrix, aiming to integrate active preservation with dual-mode freshness sensing. BTC-CDs were synthesized via a hydrothermal method, while ORE was prepared through laccase-catalyzed oxidation. Structural characterization revealed that BTC-CDs and ORE primarily interacted with the collagen through Schiff base covalent bonding and hydrogen bonding, resulting in a compact structure of film, which significantly enhanced the mechanical properties, UV-blocking capacity, water resistance, and thermal stability of the film, alongside excellent cytocompatibility and biodegradability. Functionally, the synergistic incorporation of BTC-CDs and ORE endowed the OC film with outstanding antioxidant activity (scavenging rates exceeding 92%) and antibacterial activity (95.3% against Staphylococcus aureus and 87.9% against Escherichia coli). It also demonstrated sensitive responsiveness to ammonia, featuring a distinguishable color transition (max sRGB = 46.57%) and an obvious fluorescence quenching (max efficiency = 89.89%). The shrimp packaging experiments demonstrated that the OC film could indicate freshness through colorimetric and fluorescent changes in practical application. Furthermore, the film effectively slowed the increases in thiobarbituric acid reactive substances (TBARS), total volatile basic nitrogen (TVB-N), and total viable counts (TVC), extended the shelf life by approximately 4 days, and alleviated the degradation of muscle microstructure, suggesting its ability to retard lipid oxidation, protein decomposition, and microbial proliferation. Overall, this study provides an effective dual-driven strategy for constructing a novel intelligent and active packaging material for high-protein foods, capable of simultaneously preserving food quality and enabling reliable freshness monitoring.