Abstract: In order to address the problem of insufficient sensitivity of traditional methods for the freshness monitoring of aquatic products, this study employed the amino acid-based ionic liquid glycine hydrochloride ([Gly]Cl) as a green solvent. Chitosan grafted ferulic acid (CS-g-FA) was prepared by the carbodiimide coupling method and complexed with polyvinyl alcohol (PVA) and roselle anthocyanin (RA). Subsequently, [Gly]Cl was added as a sensitizer to prepare a highly sensitive pH-responsive intelligent indicator film (PVA/CS-g-FA/G/RA). This study investigated the effects of different components on the color response characteristics, physical properties and microstructure of the indicator film, and evaluated its application performance in monitoring the freshness of Penaeus vannamei. The results demonstrated that [Gly]Cl promoted the deprotonation of RA through hydrogen bond interaction, which significantly enhanced the pH sensitivity of the indicator film. Within the characteristic pH range (pH 6–8) for the spoilage of aquatic products, the ∆E value of the PVA/CS-g-FA/G/RA film increased from 14.66 ± 0.92 to 29.65 ± 0.74. After exposure to 80 mmol/L ammonia for 90 min, the ∆E value reached as high as 30.01 ± 0.24, indicating excellent response to ammonia. After addition of [Gly]Cl, the elongation at break of the indicator film increased to (10.35 ± 0.90)%, and its water vapor permeability rose to (2.64 ± 0.50) × 107 g/(m·Pa·s), thereby facilitating the penetration of volatile alkaline substances. In addition, the indicator film displayed excellent UV barrier ability and antioxidant activity, with a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate of (86.73 ± 0.71)%, and possessed a uniform and compact microstructure. This film clearly differentiated fresh, semi-fresh and spoiled P. vannamei, its color changing gradually from deep purplish-red to deep reddish-brown and finally to deep grayish-brown. Its ∆E value showed a significantly positive correlation with total volatile basic nitrogen (TVB-N) content (R2 = 0.956 55). In summary, the PVA/CS-g-FA/G/RA film, with its outstanding environmental responsiveness and biological activity, holds broad application prospects in the field of intelligent indicator packaging for aquatic products.

Key words: ionic liquid; chitosan; ferulic acid; intelligent indicator film; visualization; freshness monitoring