Dual-function biodegradable film based on gelatin-chitosan incorporating Careya sphaerica (Kradon) extract and red cabbage anthocyanins: Smart antimicrobial and pH indicator for monitoring fresh-cut pork quality

Abstract

Dual-function bilayer films were developed to simultaneously extend shelf-life and monitor freshness of fresh-cut pork through synergistic interaction of active and intelligent components. The films comprised an outer gelatin (1.5% w/v)-chitosan (1.5% w/v) layer incorporating Careya sphaerica extract (Kradon, 0–15% w/v) for antimicrobial activity, and an inner gelatin layer (2% w/v) embedded with red cabbage anthocyanins (2% w/v) as pH sensitive colorimetric indicator. Among formulations tested, the 9% C. sphaerica extract film (CR9) demonstrated the most favourable balance of physicochemical, barrier, and antimicrobial properties: water vapor transmission rate (WVTR) of 77.98 g/day·m², tensile strength of 31.85 MPa with 10.45% elongation, and water contact angles of 89.8° (outer layer) and 65.7° (inner layer). Fourier transform infrared spectroscopy (FTIR) analyses confirmed hydrogen bonding interactions between phenolic compounds and polymer matrices. The CR9 film demonstrated significant antimicrobial efficacy with 4.1 log CFU/g reduction against Staphylococcus aureus and 2.8 log CFU/g reduction against Pseudomonas aeruginosa. The anthocyanin indicator exhibited distinct pH-dependent colour transitions from red (pH 2–4, λmax = 520 nm) to blue green (pH 10–12, λmax = 603 nm), with rapid ammonia responsiveness within 10 min. Application on fresh-cut pork at 4°C extended shelf-life from 3 to 5 days, while the indicator provided real-time spoilage detection through visible colour changes (ΔE > 15) that correlated strongly with pH, total volatile basic nitrogen (TVB-N), and total plate count (TPC) (R² > 0.90). These results demonstrated the film's substantial practical utility for active preservation and intelligent quality monitoring of fresh meat products.