Nanocellulose-based ammonia sensitive smart colorimetric hydrogels integrated with anthocyanins to monitor pork freshness

This study aims to develop green sustainable TEMPO-oxidized cellulose nanofibril (TOCNF)-based smart hydrogels triggered with different crosslinkers and anthocyanins (ACNs) from different sources for monitoring pork freshness. Al³⁺ was selected as an optimum crosslinker for TOCNF-based colorimetric freshness indicators (CFIs) and interestingly the resulting CFIs showed a critical color change in the neutral pH range; the pH range of the majority of animal-origin food. The response of the CFIs to ammonia was nonlinear and the limit of detection (LD) with naked eye inspection and instrumental color measurements was 150 and 50 ppm, 150 and 50 ppm, and 50 and 25 ppm for CFIs doped with Aronia, Liriope, and red cabbage ACNs, respectively. Based on the results of TVB-N, even very fresh pork comprises a considerable amount of ammonia, indicating CFIs with very low LD cannot be applicable for pork freshness evaluation. The cheap and environmentally friendly CFIs developed in this study could detect the pork warning stage and the medium fresh stages both qualitatively and quantitatively. The non-linear response of the CFIs to ammonia could indicate their potential to differentiate TVB-N mixtures contributing to the meat spoilage process. Based on these results, using a combination of resulting CFIs rather than using a single one could be a more effective tool for confrontation with complex cases like pork freshness evaluation.