Application and Mechanism of High-Sensitivity Indicator Film for Monitoring Fish Freshness

The sensitivity of freshness indicator labels/films has become an important research direction of intelligent food packaging. In this study, a high-sensitivity indicator film containing gelatin and Fe²⁺ was prepared by electrospinning using blueberry anthocyanins as the indicator and zein as the matrix for monitoring fish freshness. The validity and sensitivity of the indicator film for detecting the freshness of silver carp were tested and the potential mechanism was elucidated. The results of pH sensitivity, ammonia sensitivity and anthocyanin release showed that the addition of gelatin and Fe²⁺ improved the sensitivity of the indicator film to pH and ammonia, and contributed to better binding of the anthocyanins in the film. There was a strong correlation between the color response (P = (L* + a* + b* + R + G + B)/a*) of the film and the content of total volatile basic nitrogen (TVB-N) content in fish meat as a freshness indicator (R² > 0.98). In conclusion, the prepared indicator film can effectively monitor fish freshness, and the hydrogen bond interactions between anthocyanins and gelatin/Fe²⁺ may affect the color response characteristics and sensitivity of the indicator film.