Abstract: In this study, a novel intelligent gel label for the real-time monitoring of the freshness of fresh-cut netted melon was fabricated using carrageenan, sodium carboxymethylcellulose and xanthan gum as the matrix materials and bromothymol blue (BTB) as the chromogenic indicator. The color of the gel label changed from blue to yellow-green, yellow-brown and orange-yellow according to the CO2 concentration inside the package, which could reflect the freshness of fresh-cut netted melon. The morphology and structure of the gel label were characterized using scanning electron microscopy (SEM), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetry (TG). The results showed the microstructure of the gel labels did not change with the addition of sodium carboxymethylcellulose and xanthan gum, which indicated the three components were well compatible, while the thermal stability of the gel label was improved with the addition of BTB. The gel label showed excellent color stability during storage at 4 or 25 ℃ and its color changed obviously with the storage of fresh-cut netted melon at 4 ℃. The correlation analysis showed a significant correlation between the label’s color difference and the CO2 concentration in the package as well as the pH and total aerobic plate counts of fresh-cut netted melon. This gel label had excellent pH sensitivity and thus could be used as an effective method for monitoring the freshness of fresh-cut netted melon.

Key words: intelligent gel label; fresh-cut netted melon; freshness; non-destructive monitoring