UV-Curable choline chloride and bromophenol red covalent functionalized chitosan antibacterial and pH-sensitive hydrogels

Food safety and food freshness issues have become important concerns for consumers and hydrogels with high antibacterial efficiency, low toxicity and pH-sensitive colorimetric intelligence are one of candidates to meet the requirement of food package and food spoilage monitoring. Nevertheless, hydrogels prepared only by assembling the ingredients with non-covalent interactions through time-consuming molding process usually encounter drawbacks such as relatively poor mechanical properties, stability and thermal stability, which always restrict their further applications. To overwhelm these shortcomings, UV-curable choline chloride (ChCl) and bromophenol red (BR) covalent functionalized antibacterial and pH-sensitive cross-linked hydrogels (UV-hydrogels) were developed in this paper. The UV-hydrogels possessed good thermal stability because the initiated thermal decomposition temperature (Td5) is in the range of 135.8-184.7 degrees C. The DMA analysis revealed that the UV-hydrogels are with good mechanical properties because the elongation at break is in the range of 117-525% and the tensile strength is in the range of 0.8-2.7 MPa. The UV-hydrogels with BR groups exhibited naked eye visible color variation from yellow to dark blue-green with the variation of the pH values from 2 to 14. The antibacterial efficiency of the UV-hydrogels against S. aureus, E. coli and M. albican increased with the increment of covalent-grafted ChCl amount. Cytotoxicity assay demonstrated that the UV-hydrogels are low toxicity against L929 cells. The experiment of monitoring freshness of beef denoted the UV-hydrogels have potential application in animal-derived high protein food packaging and freshness monitoring.