pH-responsive cellulose nanomaterial films containing anthocyanins for intelligent and active food packaging

A combination of cellulose nanocrystals (CNCs) and nano-fibrillated cellulose (NFC) was used as a sustainable substrate to immobilize anthocyanins in red cabbage extract (RCE) and prepare a pH-sensitive packaging film. The incorporation of RCE in the CNC/NFC suspension changed the morphology and increased the steady-state viscosity and storage modulus of the suspension. Three rheological models (i.e., Power-law, Herschel–Bulkley, and Nasiri–Ashrafizadeh) fitted the relationship between shear stress and shear rate for each suspension. The incorporation of RCE to the CNC/NFC suspension altered the physical, optical, and mechanical properties of the films and acted as a free radical scavenger. The incorporation of 50 wt% RCE in the CNC/NFC film enhanced its elongation at break by around 855%. With the enhanced film flexibility, its tensile strength, however, declined. The developed indicator film contained 30 wt% RCE demonstrated an optimum physical, mechanical, and optical properties with the lowest response time to alkaline pH, which has a great potential as a pH-sensitive film for use in the seafood packaging industry.Graphical abstractThe develop halochromic CNC/NFC films containing anthocyanins provide a sensitive way for monitoring the freshness of packaged seafood products.