A Novel Hydrophobic Film-Based SiO₂@nylon with Colorimetric Sensor Array for Silver Salmon Freshness Visualization

This study aims to develop a novel hydrophobic film based on a nylon film substrate, SiO2 sol (tetraethyl orthosilicate and trimethylethoxysilane), eight porphyrins, and eight pH indicators for monitoring salmon freshness. The hydrophobic properties of the film were verified by using scanning electron microscope (SEM), atomic force microscope (AFM), Fourier transform infrared spectrometer (FTIR), and contact angle (WCA). The total volatile base nitrogen (TVB-N) and gas chromatography–mass spectrometer (GC-MS) results for silver salmon were collected throughout the storage period. The accuracy and sensitivity of the colorimetric sensor array (CSA) were subsequently validated. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were employed to analyze the color difference maps. The results were generated before and after the sensor array’s response, allowing differentiation between various freshness levels of silver salmon. The K-nearest neighbor (KNN) algorithm achieved a recognition rate of 93% for the prediction set, and the linear discriminant analysis (LDA) model demonstrated a recognition rate of 95 and 93.3% accuracy for calibration and prediction sets, respectively. This development of the CSA with a hydrophobic substrate effectively identified changes in the freshness of silver salmon during storage. Thus, this novel hydrophobic substrate is suitable for detecting food freshness, which could be applied to other types of meat freshness.