From leather waste to smart packaging: Collagen hydrolysate- and anthocyanin-based biocomposite films for the real-time monitoring of raw food freshness

The precise and timely assessment of food freshness is pivotal for safeguarding food quality. Here, multifunctional biofilms were fabricated using hazardous leather waste-chrome shaving dust (CSD)-derived collagen hydrolysate (CH), sodium alginate (SA), and glycerol (G), loaded with onion peel anthocyanin (OPA) and dahlia flower anthocyanin (DFA), respectively. After successful removal of chromium (98.54%) and confirming the absence of toxic chromium (VI), CH at varying concentrations (5-20%) was utilized to prepare biocomposite films. Assessment of visual (ΔL and ΔRGB), physicochemical, and mechanical properties confirmed the suitability of the C10SAG/OPA and C10SAG/DFA films for further evaluation. The film formation mechanism was investigated through FTIR and FE-SEM analyses. The C10SAG/OPA and C10SAG/DFA films exhibited comparable thermal stability up to 300 °C, effective UV-shielding at 450 nm and 380 nm, acceptable water vapor permeability of 5.657 × 10-9 g/mhPa and 6.262 × 10-8 g/mhPa, respectively. Furthermore, clear zones of inhibition against Bacillus subtilis and Escherichia coli demonstrated the potent antimicrobial activity of the films. Across a pH range of 2-12, the C10SAG/OPA film transitioned from brownish yellow to dark brown, while the C10SAG/DFA film shifted from reddish pink to dark green. Both films exhibited remarkable ammonia-responsive colorimetric behavior, enabling real-time visual monitoring of milk and shrimp freshness through easily distinguishable color changes. This work pioneers a circular bioeconomy strategy by transforming hazardous leather- and agro-waste into smartphone-assisted, intelligent, and biodegradable packaging films for sustainable food freshness monitoring.