Development of plant-derived polyphenols-loaded protein films for topical application

This study aimed to develop gelatin/sodium caseinate films containing quercetin or rutin and to evaluate their physicochemical, antioxidant, and in vitro release properties for potential topical application. Films were prepared at a gelatin-to-sodium caseinate mass ratio of 1:0.5, with glycerol at 30% and either flavonoid (quercetin or rutin) at 1%, 3%, or 5% (w/w, relative to the total protein mass). SEM revealed irregular surfaces and crystal-like domains within the matrix. No new bands or pronounced shifts were observed in the ATR-FTIR spectra, possibly suggesting the lack of new covalent bonds forming between the flavonoids and the protein matrix. However, noncovalent interactions cannot be excluded. Opacity increased with flavonoid loading, whereas moisture content, solubility, and swelling ratio were only slightly affected, possibly due to low nominal flavonoid loading and limited aqueous solubility. Water vapor permeability and mechanical properties showed limited changes: relative to the unloaded film, water vapor permeability increased, and tensile strength decreased significantly only at 5% rutin, while elongation at break increased significantly only at 1% rutin. The pronounced DPPH radical-scavenging activity of both flavonoids was largely retained after incorporation, remaining high at all loadings (82.46 ± 1.38%-85.20 ± 1.29%). Cumulative release from the 5% quercetin and 5% rutin films reached 52.67 ± 3.05% after 300 min and 53.91 ± 3.04% after 450 min, respectively. The first-order model provided the best fit for both release profiles. These findings support further development of gelatin/sodium caseinate films as potential prolonged-release carriers for topical flavonoid delivery.