Oxidative polymerization process of hydroxytyrosol catalysed by polyphenol oxidases or peroxidase: Characterization, kinetics and thermodynamics

Hydroxytyrosol oligomer prepared by bioenzyme shows stronger health-promoting properties than its monomer. However, the polymerization process carried out by laccase, tyrosinase or horseradish peroxidase is still lacking in term of product characterization, kinetics and thermodynamics. To achieve these aspects, ATR-FT-IR, NMR, the Michaelis-Menten equation and isothermal titration calorimetry were explored. The results showed that the identified polymers presented a C-C bond and a degree of polymerization less than six. Laccase showed the greatest affinity to hydroxytyrosol via comparison of K-m and V-m. All of these polymerization processes were spontaneous and exothermic behaviuors ranging from 30 to 50 degrees C, and were driven by hydrogen bonds, van der Waals interactions and hydrophobic interactions. Furthermore, circular dichroism spectroscopy was used to reveal the enzymatic structural changes during the catalysis, which showed that beta-sheet levels for laccase, ahelix levels for tyrosinase, and the a-helix and random coil levels for horseradish peroxidase were dramatically decreased.

Automated summary

The hydroxytyrosol oligomer prepared by bioenzyme exhibits stronger health-promoting properties compared to its monomer. However, the polymerization process carried out by laccase, tyrosinase or horseradish peroxidase lacks sufficient product characterization, kinetics and thermodynamics. Further investigations using ATR-FT-IR, NMR, Michaelis-Menten equation and isothermal titration calorimetry revealed that the identified polymers had a C-C bond and a degree of polymerization less than six. The polymerization processes were found to be spontaneous and exothermic behaviors driven by hydrogen bonds, van der Waals interactions and hydrophobic interactions. Circular dichroism spectroscopy showed significant enzymatic structural changes during the catalysis, with beta-sheet levels for laccase, alpha-helix levels for tyrosinase, and a decrease in alpha-helix and random coil levels for horseradish peroxidase.