Preparation and Physicochemical Characterization of Gelatin–Aldehyde Derivatives

The present study aimed at preparing novel free-radical scavenging and water-soluble compounds derived from gelatin. Specifically, gelatin−syringaldehyde, gelatin−anisaldehyde, and gelatin−vanillin were synthesized and thoroughly studied for their physicochemical properties. In particular, the compounds were characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Notably, as demonstrated by thermogravimetry and differential scanning calorimetry, all three derivatives exhibited higher thermal stability than gelatin itself. Free-radical scavenging activities of the examined compounds were explored by (i) a standard spectrophotometric ABTS assay and (ii) an assay of oxidative degradation of hyaluronic acid monitored by rotational viscometry. We found that gelatin and gelatin−syringaldehyde demonstrated the highest efficacy in scavenging •OH radicals, whereas gelatin−anisaldehyde was the least effective. The efficacy of scavenging alkyloxy- and alkylperoxy-type free radicals via hydrogen-atom-transferring property was in the following order: gelatin > gelatin−vanillin > gelatin−syringaldehyde > gelatin−anisaldehyde. Electron-donor properties determined using the ABTS assay revealed the following order in one-electron reduction of ABTS•+: gelatin > gelatin−anisaldehyde > gelatin−vanillin > gelatin−syringaldehyde.