Preparation and characterization of antifungal coating films composed of sodium alginate and cyclolipopeptides produced by Bacillus subtilis

Abstract

We report the inclusion of cyclolipopeptides (CL) from Bacillus subtilis in the production of an easily removed alginate coating for the preservation of vulnerable berries. The sodium alginate-CL (SA-CL) coating films exhibited potent antifungal and freshness-maintaining properties during the storage of blueberries, the 3% CL-added film decreased total fungal count to 2.5 × 10³ cfu/g at the end of the storage. The SA-CL films had poor mechanical properties (i.e., tensile strength and elongation at break), low water vapor permeability and high water solubility. The addition of CL (3%) decreased the tensile strength and elongation at break of the SA-CL film to 0.37 mPa and 2.57%, respectively, and increased the water solubility to 28.92%. But the water vapor permeability of the 3% film was lowered to 398.10 g/m²/day. These results implied the film was suitable for the coating of vulnerable berries. Further research revealed that ionic and hydrogen bonding interactions between CL and alginate stabilized the network of the coating film while the fatty acid moiety weakened the strength and crystallinity and restricted the water transfer of the coating film. Our findings provide an effective route to an easily washed alginate coating film through inclusion of amphiphilic antifungal substances.

Keywords: Active package; Antifungal film; Blueberries; Edible film; Iturin; Postharvest preservation.