ABSTRACT A wide range of intelligent double‐layer films have been developed for food freshness monitoring. Nevertheless, it remains challenging to achieve highly sensitive monitoring and effective isolation. In this work, asymmetric double‐layer films with a Janus structure were designed. Specifically, mica nanosheets (MNs) were incorporated into gellan gum (GG) to improve the barrier properties of the resulting film. Cross‐linked bacterial cellulose ( BC ) loaded with anthocyanin (Ant) served as the indicator layer. The as‐prepared Janus film exhibited outstanding comprehensive performance, including superior mechanical and improved barrier capabilities against ultraviolet light, moisture and gas (e.g., TS: 18.23 MPa, WVP: 0.24 × 10 −9 g m m −2 Pa −1 s −1 , OP: 17.7 × 10 −3 cm 3 day −1 m −2 ). Notably, the fabricated films exhibited excellent detecting performance to biogenic amines. Even at a low concentration of 50 ppm, distinct colour variations could be clearly observed, which was attributed to their highly porous fibrous structure and high swelling index (up to 860%). Moreover, the film achieved an ultra‐high DPPH free radical scavenging rate of 92.25% ± 1.21%. Characterizations including FT‐IR, XRD and SEM verified that GG, BC and anthocyanin were combined through hydrogen bonding interactions. When applied for the freshness monitoring of shrimp samples at 4°C, the films presented obvious colour evolution, and the corresponding Δ E values showed a strong correlation with shrimp spoilage indicators (TVB‐N and pH). This work provides a novel strategy for the fabrication of high‐sensitivity pH‐responsive films with optimized barrier performance, which enables the real‐time evaluation of food quality and early warning of food spoilage.
Huang et al. (Fri,) studied this question.
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