Longan seed tannins as a quality tyrosinase inhibitor and browning resistance agent: Activity and mechanism

Longan seed tannins (LSTs) were separated and confirmed to be mixtures of procyanidins, ellagitannins, and gallotannins. Multiple spectroscopy methods and molecular simulation technique demonstrated that LSTs were competitive inhibitors of tyrosinase and formed stable complex with the enzyme. The LSTs influenced the micro-environment of amino acid residues in the catalytic center of tyrosinase by non-covalent interactions, and induced stretching of polypeptide framework and conformational change of the enzyme by altering its secondary structures, generating an intense inhibition in enzyme activity. Moreover, LSTs effectively prevented the enzymatic browning of apples by inhibiting the polyphenol oxidation, enhancing the anti-oxidation system, and preventing the lipid peroxidation of cell membrane. This study demonstrated that LSTs were quality tyrosinase inhibitors and browning resistance agents, and provided novel insights for understanding the suppressive mechanism of LSTs on tyrosinase and browning, as well as scientific evidence for their potential application as food preservative.