The inhibition mechanisms between asparagus polyphenols after hydrothermal treatment and tyrosinase: A circular dichroism spectrum, fluorescence, and molecular docking study

Asparagus contains high quantity of polyphenols, including gallic acid, coumaric acid, chlorogenic acid, quercetin, p-hydroxybenzoic acid, rutin, trans-4-hydroxycinnamic acid, and ferulic acid. An understanding of the antityrosinase capacity and polyphenols changes during hydrothermal treatments was crucial for the development of asparagus. The results show that hydrothermal treatments (HT) enhance the total polyphenols in asparagus, and HT-160 has the highest total polyphenol contents (5.321 mg/g·dw) and tyrosinase inhibitory rate (95.87%). Rutin content reach 1754.01 μg/mL at 140°C. Increased polyphenols caused 7.5%, 4.8%, 2% decrease in α-helix, β-sheet, β-turn and a 7.4% increase in random coil using circular dichroism spectra. The fluorescence quenching of tyrosinase by HT samples (HT-80, HT-100, HT-120, HT-140, and HT-160) was accompanied by bigger ranges of red shift. Molecule docking analysis indicated that antityrosinase capacity was attributed to the capacity of polyphenols to bind to protein molecules and change the microenvironment of tryptophan or tyrosine residues. Conventional hydrogen bond, van der Waals, π-π stacked, π-σ interaction, and π-alkyl interactions were generated between asparagus polyphenols (ASP) and residues. As a promising inhibitor of tyrosinase, ASP could be employed as a potential agent to reduce food browning.