Janus biopolymer nanocomposite coating with excellent antibacterial and water/oxygen barrier performance for fruit preservation

Fruit freshness is strongly influenced by the storage environment (water, oxygen), cellular respiration and microorganisms. Applying a biomass-based coating onto fruit surface is a facile and sustainable method to effectively slow down the decay rate and extend the freshness period of fruit. Inspired by the asymmetric characteristics and functionalizations of Janus structure, we developed a facile strategy to fabricate Janus biopolymer composite coating by combining modified quaternized chitosan (QCS) with aldehyde carbox-ycellulose nanofibres (ACCNF). Through a simple layer-by-layer self-assembly process, a Janus QCS/ACCNF composite coating can be easily and conformally generated on different fruit, where the outer QCS layer with positively-charged quaternary ammonium groups acts as an antibacterial barrier to effectively inhibit the growth of various microorganisms while the inner ACCNF layer strongly adheres to fruit surfaces and provides buffering effect to reduce the damage to fruit during vibration and collision. Moreover, a dense QCS/ACCNF interfacial layer is formed between QCS and ACCNF layers through strong electrostatic interaction and Schiff base reaction. This interfacial layer not only further enhances the mechanical properties of the coating, but also reduces its water and oxygen permeation, thus effectively reducing the dehydration shrinkage and oxidative deterioration of the coated fruits. The fruit preservation experiments, using mango, banana and loquat as model fruits, demonstrated this Janus QCS/ACCNF coating could confer the coated fruit with excellent antibacterial and oxygen/water permeation properties and significantly extend the freshness period of these fruits by 5-10 days, exhibiting great potential for its practical applications in fruit preservation.