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.