Interactions of quercetin, curcumin, epigallocatechin gallate and folic acid with gelatin

Some small bioactive molecules from food show the potential health benefits, but with poor chemical stability and bioavailability. The interactions between small molecules and gelatin were investigated. Fluorescence experiments demonstrated that the bimolecular quenching constants (kq) of complexes (gelatin-quercetin, gelatin-curcumin, gelatin-epigallocatechin gallate, gelatin-folic acid) were 3.7 × 1012 L·mol−1·s−1, 1.4 × 1012 L·mol−1·s−1, 2.7 × 1012 L·mol−1·s−1 and 8.5 × 1012 L·mol−1·s−1, indicating that fluorescence quenching did not arise from a dynamical mechanism, but from gelatin-small molecules binding. Furthermore, the affinity with gelatin was ranked in the order of folic acid > quercetin > epigallocatechin gallate > curcumin. Fluorescence spectroscopy, ultraviolet and visible absorption spectroscopy, FTIR and circular dichroism showed that the interactions between small molecules and gelatin did not significantly alter the conformation and secondary structure of gelatin. Non-covalent interactions may result in the binding of gelatin with small molecules. The interactions were considered to be through two modes: (1) small molecules bound within the hydrophobic pockets of gelatin; (2) small molecules surrounded the gelatin molecule mainly through hydrogen bonds and hydrophobic interactions.