Preparation, characterization and tomato preservation applications of gelatin-polyvinyl alcohol composite films with temperature and pH responsive properties

In recent years, the construction of responsive nano-antimicrobial films has been a hot topic in reducing microbial resistance and food preservation. However, the non-degradable and mono-responsive nature of most films limits their application. In this study, silica nanoparticles were modified by imine bonding and poly-N-isopropyl acrylamide (PNIPAM), and citral (CIT) was added as an active substance to construct temperature- and pH-responsive nanoparticles (HMSS-NH₂-CIT-PNIPAM, abbreviated as HNCP). It was then added to a gelatin (GEL)/polyvinyl alcohol (PVA) film to produce a degradable GP/HNCP composite film. The films were also evaluated for their physical properties, release characteristics, and tomato preservation. The tensile strength of the film was increased by 39.26 % as compared to the control. And the films had a good elongation (253.0 ± 4.53 %). The TGA results showed that the loading of CIT in HNCP was 42 % and the composite membrane could sustain the release for 120 + h under combined pH and temperature (pH 5.8/37 °C) stimulation. In addition, in tomato preservation experiments, tomatoes treated with GP7 composite film extended shelf life by 3-4 days compared with the control group. The biodegradability and good cytocompatibility of the composite membrane were demonstrated by degradation rate and MTT experiments. Therefore, GEL/PVA/HNCP smart response composite film is a smart antimicrobial packaging material with wide application prospects.