Preparation and Performance Characterization of Eggshell Membrane Enzymatic Hydrolysate/Chitosan Composite Film

Eggshell-membrane-based films with antimicrobial and antioxidant functions can be used to preserve food to reduce economic losses and increase the comprehensive use of eggshell waste. We used biological enzymes to hydrolyze eggshell membranes, investigated the effects of hydrolysis conditions on lysozyme activity and the DPPH· scavenging rate of the enzyme solution. We prepared active packaging films via compositing the lyophilized material obtained from the enzyme solution of eggshell membrane and freeze-drying (enzymolysis of eggshell membrane (E-ESM)) with chitosan. Our aim was to investigate the effects of E-ESM on the chitosan film structure and properties and apply the film in preserving strawberry. The lysozyme activity and DPPH· clearance of the enzymatic solution of eggshell film were 2.26 U/mL and 38.23%, respectively, after 9 U/mg alkaline protease enzyme digestion at 50 ℃ for 4 h. The film prepared with E-ESM and chitosan in a 3:5 (v/v) ratio showed appropriate mechanical properties (tensile strength 11.32 MPa and fracture elongation 11.75%), UV-blocking ability (UV transmittance 42%), water vapor permeability ((8.89±0.6)×10−11 g·m/(m2·s·Pa)), and oxygen transmittance ((2.12±0.6)×10−5 g·mm/(m2·s)). The film inhibited 83.33% and 80.85% of Staphylococcus aureus and Escherichia coli in experiments, respectively. Cell survival and biocompatibility were above 90% after 8 days of storage at 24 ℃. The weight loss rate (29.06%) in the experimental group was 15.43% lower than that of the control group. The malondialdehyde content (911.78 µmol/L) was 6.96% lower than that of the control group, and 74.82% of the VC content (57.27 mg/100 g) was retained compared with that of the control group, with a pH of 3.77 and brix of 11.03°Brix. The composite film was able to effectively extend the shelf-life of strawberries by 4~6 days and could be used as an active food packaging film.