Preparation and characterisation of edible layer-by-layer coatings of sodium polyacrylate/chitosan for the preservation of strawberries

Abstract

To improve the preservation of strawberries during storage, an edible coating was prepared using a layer-by-layer self-assembly electrostatic deposition technology. Sodium polyacrylate (PAAS) was used as polyanion solution, and chitosan (CS) was used as polycation solution. The obtained coating was characterised to determine its self-repairing ability and its effect on the preservation of strawberries. The results showed that CS (9 mg/mL) and PAAS (5 mg/mL) could assemble, by hydrogen and ionic bonding, to form a new coating with no obvious pores and had a tight cross-sectional structure. The PAAS/CS self-assembled coating displayed high water resistance (water vapor transmission rate, 31.22 × 10-11 g• m/m2•s•Pa·), transparency (light transmittance, 87.5%), and excellent mechanical properties (tensile strength, 17.31 MPa; elongation at break, 13.72%). The self-repairing ability of the PAAS/CS coating upon scratching was manifested by the repair of the coating's morphology (repair rate, 81.05%), and the restoration of its mechanical properties. When compared with uncoated strawberries, PAAS/CS coating significantly reduced the weight loss rate, the rot rate during storage (p < 0.05), and the loss of anthocyanin and vitamin C. In conclusion, the PAAS/CS coating greatly improved the fresh-keeping of strawberries.