Electrospinning of myoglobin incorporated polyvinyl alcohol/pullulan film as intelligent freshness indicator: Fabrication, characterization and indicating salmon freshness

Raw salmon is highly susceptible to spoilage during storage, while the resulting quality deterioration is not always visually apparent. Therefore, an intelligent indicator capable of monitoring salmon freshness in real time is highly desirable. In this study, an intelligent freshness indicator was developed by electrospinning polyvinyl alcohol/pullulan (PVA/PUL) nanofibers incorporated with myoglobin as a natural chromogenic agent. The 0.4% myoglobin/PVA/PUL nanofibers showed a smooth, continuous, and uniform morphology with an average fiber diameter of 149.43 ± 26.41 nm, and responded effectively to hydrogen sulfide (H 2 S) released during salmon spoilage, exhibiting an irreversible color change. During refrigerated storage of salmon, the K-value increased to 19.89%, 39.32%, and 61.72% on days 2, 4, and 7, corresponding to the primary freshness endpoint, secondary freshness endpoint, and complete spoilage point, respectively. Consistently, the indicator exhibited visible discoloration at these key storage stages, with the film color changing from red to red-brown and then to brown-green as freshness decreased. In addition, the increases in total volatile base nitrogen (TVB-N) and spoilage bacteria further confirmed the progressive deterioration of salmon during storage. This study provides a simple and intuitive method for detecting the freshness of salmon and other aquatic products, which is crucial for protecting consumer safety.