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 beta-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 beta-acids, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 100 mu g/mL and 400 mu g/mL, respectively, against E. coli, and MIC and MBC of 50 mu g/mL and 200 mu g/mL, respectively, against S. aureus. Release experiments with beta-acids indicated that nanosilica promoted cumulative and delayed release of beta-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 beta-acids led to disruption of membrane integrity and cell death. Molecular docking study of beta-acids was performed against beta-lactamases, FabI, FabH from both E. coli and S. aureus. This study lays the foundation for further exploration of the antibacterial mechanism of hops beta-acids and points towards the possibility of using beta-acids-loaded hydrogel films as an antiseptic material in the food industry.