Multifunctional chitosan-based film loaded with hops β-acids: Preparation, characterization, controlled release and antibacterial mechanism

The broad-spectrum bacteriostatic properties of hops (Humulus lupulus L.) components have been widely recognized. In this study, chitosan was selected as raw material, and silane was introduced by covalent and non-covalent bonding to yield a chitosan-based hydrogel film loaded with hops β-acids. The structure of the obtained film was explored by Fourier infrared transform spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Mechanical performance assay revealed that the tensile strength (TS) of the film increased to 4.14 MPa after modification with silicon. The film had an inhibitory effect on Escherichia coli and Staphylococcus aureus after loading with hops β-acids, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 100 μg/mL and 400 μg/mL, respectively, against E. coli, and MIC and MBC of 50 μg/mL and 200 μg/mL, respectively, against S. aureus. Release experiments with β-acids indicated that nano-silica promoted cumulative and delayed release of β-acids due to the formation of covalent bonds with silicon. In addition, the obtained film displayed a remarkable ability to block ultraviolet rays. Results of antibacterial activity assay and SEM observations revealed that β-acids led to disruption of membrane integrity and cell death. Molecular docking study of β-acids was performed against β-lactamases, FabI, FabH from both E. coli and S. aureus. This study lays the foundation for further exploration of the antibacterial mechanism of hops β-acids and points towards the possibility of using β-acids-loaded hydrogel films as an antiseptic material in the food industry.