Active-intelligent packaging film developed by gelatin-oxidized sodium alginate and blueberry anthocyanins with robust UV shielding and ammonia/pH sensitivity.

Abstract

Pure gelatin film lacks sufficient flexibility and functional properties, thus limiting its wide use as an intelligent packaging film. In this study an active-intelligent packaging film (G-OSA-BA) was prepared based on incorporating blueberry anthocyanins (BAs) with the gelatin/oxidized sodium alginate (G-OSA) matrices. The synergistic effects between the covalent crosslinking G-OSA network and the physical blending of natural anthocyanins endowed the G-OSA-BA film with excellent comprehensive performance. Notably, all the G-OSA-BA films exhibited remarkable ductility; elongation at break reached a peak value of 170.31% when adding 1.6 wt% BAs, which increased by 4.0 times compared to pure gelatin film (42.19%). Moreover, the G-OSA-BA films showed almost 100% ultraviolet-blocking capacities, strong antioxidant activity (67.35% against DPPH radical) and antibacterial activity (the maximum inhibition zone was 16.97 mm against Staphylococcus aureus (+) and 14.77 mm against Escherichia coli (-)). Furthermore, moderate dosage of BAs (1.6-2 wt%) endowed the G-OSA-BA film with significant pH/ammonia responsiveness. When applied to monitor shrimp freshness at 4 °C, the intelligent films turned from orange in fresh shrimp to green in spoiled shrimp after ~3 days. This visual change corresponded well with objective freshness metrics, as total volatile basic nitrogen levels rose from 10.91 to 34.3 mg 100 g-1. Finally, the practical packaging test showed that the shrimp's spoilage was delayed from ~2 days to nearly ~4 days at 4 °C with the G-OSA-BA film containing 1.6 wt% BAs as a wrap. The produced G-OSA-BA film, as an active-intelligent packaging film, has potential in real-time monitoring of food freshness and extension of food shelf-life aspects. © 2026 Society of Chemical Industry.