Synergistic design of Pickering emulsion inks of nanochitosan-alginate-beeswax for edible coating in fruit preservation

Abstract

Chitosan nanowhisker (CSW) has attracted attention as a coating agent in packaging applications because of its biocompatibility, anti-bacterial activity, and high gas barrier. However, the poor viscoelasticity of virgin CSW dispersions limits the coating process to spraying or dip-coating at very dilute concentrations. Herein, rheology-engineered CSW inks with improved coating abilities were designed, making them suitable for mass-produced coatings. Given the positive surface charge of CSW, eight types of negatively charged eco-friendly binders were selected, and their efficiency as rheological modifiers was assessed at a CSW:binder weight fraction of 1:1. Among them, three binders, sodium alginate (SA), carboxymethyl cellulose, and guar, simultaneously enhanced the viscoelasticity and homogeneity. Accordingly, the three composite inks exhibit high spreadability in practical coating. Particularly, the CSW/SA coating films exhibited remarkable mechanical properties with strength and toughness of 32.9 MPa and 1.4 MJ m−3, respectively. To apply edible coatings for fruit preservation, beeswax (BW) was mixed with CSW/SA to form Pickering emulsion inks. CSW acts as a Pickering stabilizer in the aqueous BW emulsion, affording it high dispersibility. Owing to its improved hydrophobicity, the edible CSW/SA/BW coating significantly extended the shelf life of bananas and strawberries.