The non-covalent interaction between two polyphenols and caseinate as affected by two types of enzymatic protein crosslinking

Caseinate was crosslinked by horseradish peroxidase (HRP) or microbial transglutaminase (TGase) and mixed with kaempferol and quercetin at 293-313 K (i.e. 20-40 degrees C), respectively. Generally, these two polyphenols dose-dependently induced fluorescent quenching in caseinate or its crosslinked products via a static mechanism, while enzymatic crosslinking endowed caseinate with higher affinity for the polyphenols with increased apparent binding constants [(9.94-168.77) x 10(5) versus (4.92-6.53) x 10(5) L/mol], unchanged binding site number and slightly shortened binding distance. To form protein-polyphenol complexes, hydrophobic force was the main driving force for the HRP-crosslinked caseinate and unreacted caseinate, while hydrogen-bonds and van der Waals force were the main driving forces for the TGase-crosslinked caseinate. Overall, quercetin was more potent than kaempferol to bind to the proteins, while TGase-mediated caseinate crosslinking induced the highest affinity to the polyphenols with the largest Delta G decrease. Thus, two types of crosslinking impacted the driving forces, apparent binding constant and thermodynamic indices of caseinate-polyphenol interaction.

Automated summary

The study revealed that kaempferol and quercetin caused fluorescence quenching in pure caseinate or crosslinked caseinate, while enzymatic crosslinking enhanced caseinate's affinity for these polyphenols. Different types of crosslinking impacted the driving forces, apparent binding constant, and thermodynamic indices of the caseinate-polyphenol interaction.