Evaluation of the in vitro and in situ antimicrobial properties of chitosan-functionalised silica materials

Abstract

Using chitosan as a natural food preservative is limited given its scarce solubility at neutral and alkaline pH values. Alternatively, its covalent immobilisation on the surface of inert supports can help to avoid its limited use in the free form, while preserving its antimicrobial properties. In this work, chitosan was immobilised by surface silanisation using three organosilanes on silica supports of different sizes and distinct physico-chemical properties. After the synthesis and characterisation of materials, the antimicrobial properties of the chitosan-functionalised supports were studied by in vitro and in situ antimicrobial susceptibility tests using reference strains of foodborne and food-spoilage microorganisms. The results displayed the preservation of bioactive chitosan properties after functionalisation, and chitosan immobilisation by covalent urea bonding was the most suitable grafting methodology. Antimicrobial activity was significantly influenced by support material, particle concentration and target microorganism. Utilising chitosan-functionalised supports as food additives in apple juice reduced the microbial load of the food matrix by increasing its shelf life. Therefore, the developed antimicrobial agents proved suitable for controlling microbial contamination, which confirmed their potential use as food preservatives or food processing aids in the food industry.