Preparation of nanocellulose/tannic acid-stabilized emulsions combined synergistic co-pigments incorporated polysaccharide-based film for fresh-keeping monitoring and efficient preservation

Developing active and indicative packaging is an effective strategy for controlling and monitoring food quality. Here, a double-layer intelligent active film was fabricated. Firstly, the emulsified layer was made of carrageenan (Car) and high-stability Pickering emulsions (CTO) (named Car/CTO layer). The CTO was prepared by using the cellulose nanocrystals (CNC)-tannic acid (TA) composite (CNC/TA)-stabilized oregano essential oil. Secondly, the indicator layer was made of alginate (Alg), anthocyanin (An) and/or alizarin (Al) and co-pigment TA. The four kinds of indicator layer (Alg/Al, Alg/An, Alg/Al/An, Alg/Al/An/TA) were formed. Finally, different double-layer films were successfully developed using layer-by-layer casting strategy. In particularly, the leading role of intrinsic functional properties of TA in bilayer was explored. Results showed that CNC/TA composite endowed CTO excellent stability. Furthermore, CTO enabled controlled release of essential oil, effectively preserving fruit freshness with bactericidal rate of 98.8 % (S. aureus) and 87.6 % (E. coli). The CTO incorporation within the double-layer structure improved mechanical strength, hydrophobic and barrier properties. More importantly, the colorimetry and antibacterial properties were enhanced via dual TA strategy. The combination of natural and assisted pigments improved the sensitivity and stability by increasing the color intensity and the range of color variations. During food preservation, the co-pigment effect further strengthened the indication response. The Car/CTO-Alg/Al/An/TA film showed the smallest change in TVB-N (15.87 mg/100 g) after 48 h of maintaining shrimp freshness. In addition, the loading of functional substances had no effect on the biodegradability.