Characterization of film-forming solutions and films incorporating free and nanoencapsulated tea polyphenol prepared by gelatins with different Bloom values

Abstract

Gelatin film-forming solutions and their films incorporating tea polyphenol (TP) and TP-loaded chitosan nanoparticles (TP-CSNs) were prepared from gelatins with different Bloom values (100, 150 and 225). Gelatins with higher Bloom values had more α- and β-chains as well as more triple-helix structures. Gelatin film-forming solutions and films with higher Bloom values showed superior physical and mechanical properties. TP significantly decreased the surface tension, but increased the viscosity of film-forming solutions. TP-CSNs showed relatively insignificant effects on the surface tension and viscosity of solutions. Incorporation of TP resulted in a dramatic increase in tensile strength of films (P < 0.05), whereas the gel strength of gels had negligible increases (P > 0.05) in value. The addition of TP-CSNs led to significant enhancements in tensile strength and stiffness of films, especially for the 100 Bloom value sample (P < 0.05). In comparison, the gel strength of gels was significantly decreased (P < 0.05) for all Bloom values. Both TP and TP-CSNs enhanced the extensibility and toughness of the 225 Bloom value gelatin film due to the presence of high triple-helix content. SEM results showed that the presence of TP led to more compact microstructures of gelatin gels and films. In addition, the TP-CSNs were uniformly distributed within the three-dimensional network matrix of gels and within the cross-section matrix of films, without obvious aggregation.