Designing double-layer smart packaging with sustained-release antibacterial and antioxidant activities for efficient preservation and high-contrast monitoring

In this study, a double-layer intelligent packaging, which is designed by a layer-by-layer casting strategy, is employed for efficient food preservation and high contrast monitoring. Specifically, novel zein/tannic acid (TA) composite colloidal particles (ZTs) were prepared by manipulating the non-covalent interaction between zein and TA using an easy antisolvent method. The stable oregano essential oil (OEO) Pickering emulsion (ZTOEO) with varying concentrations of ZTs (0.1%–1.0%) was successfully prepared. The optimized ZTOEO, containing 0.8% ZTs, was then integrated into the emulsified hydrophobic layer of the konjac glucomannan (Kgm) matrix. Finally, the carrageenan (Car) matrix containing alizarine (Al) as an indicator was added to construct the bilayer structure. The outer Car/Al layer serves as an acid/base responsive indicator layer, while the inner Kgm/ZTOEO layer functions as a high-barrier bacteriostatic layer. The double-layer Kgm/ZTOEO-Car/Al is integrated through intermolecular hydrogen bonding and dehydration condensation. Kgm/ZTOEO-Car/Al exhibits excellent slow-release antibacterial and antioxidant activity, with a sensitive, repeatable and accurate visual response to pH/NH3. The composite film demonstrates good mechanical strength, thermal stability, light blocking, and water vapor and oxygen permeability. The individual inner Kgm/ZTOEO film effectively prolonged the shelf-life and quality of fruits, which the double-layer Kgm/ZTOEO-Car/Al film showed minimal changes in TVB-N (16.65 mg/100 g) even after monitoring and maintaining the shrimp freshness for 48 h. It can be easily processed on a large scale into packaging bags and indicator labels. This packaging is expected to be an eco-friendly, low-cost, bacteriostatic, suitable for applications requiring real-time monitoring and maintenance of fruit/seafood freshness. [Display omitted] •An antibacterial, antioxidant and slow-release bilayer intelligent packaging was designed.•Novel zein/tannic acid (TA) composite colloidal particles (ZTs) were prepared.•Outer Car/Al layer serves as an acid/base responsive indicator layer.•Inner Kgm/ZTOEO layer functions as a high-barrier bacteriostatic layer.