Physicochemical and rheological evaluation of TiO2/chitosan-carboxymethylcellulose hydrogels used for Cavendish banana preservation

In this study, TiO 2 particles were synthesized using three methods: hydrothermal (Ti(h)), sol-gel (Ti(s)), and precipitation (Ti(p)). The TiO 2 particles were incorporated into hydrolyzed chitosan-carboxymethylcellulose (CS-CMC) matrices to form composite hydrogels. The TiO 2 /CS-CMC hydrogels were characterized and evaluated as active coatings for preserving Cavendish bananas. FTIR confirmed the presence of functional groups and Ti O vibrations, indicating partial interaction between TiO 2 and the binary biopolymer matrix. X-ray diffraction revealed coexistence anatase and rutile TiO 2 phases in all hydrogels. DLS and SEM analyses showed that hydrothermal synthesis produced a unimodal distribution of relatively small, well-dispersed particles, while the sol-gel and precipitation methods resulted in bimodal distributions with larger agglomerates. All hydrogels exhibited Newtonian behavior. However, viscosity decreased with increasing TiO 2 particle size in the following order Ti(h)/CS-CMC > Ti(s)/CS-CMC > Ti(p)/CS-CMC. The average pH at the point zero charge of hydrogels was 5.4. In the preservation test, the Ti(h)/CS-CMC hydrogel showed the best performance, reducing the weight loss of the bananas by approximately 40% compared to uncoated bananas and preserving them better than the other groups for 10 days. This performance is attributed to the combination of higher viscosity and homogeneous TiO 2 dispersion, which enhanced the barrier properties while allowing the fruit to breathe. The highest antimicrobial activity was observed in the Ti(s)/CS-CMC and Ti(p)/CS-CMC hydrogels, particularly against S. aureus , which showed the largest inhibition zones compared to the Ti(h)/CS-CMC hydrogel. In contrast, all hydrogels exhibited similar inhibition zones (∼7 mm) against E. coli . Overall, the results highlight that the interplay among synthesis method, particle dispersion, electrostatic interactions, and rheology is critical for designing TiO 2 /CS-CMC hydrogel coatings with improved barrier and antimicrobial functions for postharvest fruit preservation.