Background: Tyrosinase is a copper-containing enzyme, which is widely distributed in microorganisms, animals and plants. It is also a key enzyme in melanin biosynthesis, which plays a crucial role in determining the color of mammalian skin and hair. In addition, unfavorable enzymatic browning of plant-derived foods by tyrosinase causes a decrease in nutritional quality and economic loss of food products. Objectives: In the present study the activity of this enzyme was examined against quersetin and kaempferol as two potentially flavonoid inhibitors. Materials and Methods: In this work, the effects of quercetin and kaempferol as propolis-derived compounds on activity of mushroom tyrosinase (MT) were studied. These flavonoids showed inhibitory activity on catecholase and cresolase reactions in presence of caffeic acid and p-comaric acid, respectively. The inhibition mode of quercetin and kaempferol were competitive towards both catecholase and cresolase activities of the enzyme. Results: The inhibition constants (Ki) were determined as 0.072 and 0.112 mM for catecholase activity, and 0.016 and 0.06 mM for cresolase activity, respectively. Conclusions: In general, quercetin and kaempferol can be used as good candidates in melanogenesis inhibition. Moreover they should be considered as good blockers of enzyme activity in hyper pigmentation and clinical application.

Inhibition of tyrosinase activity can control fruit browning and preserve the flavor and nutritional value of food. The impacts of fulvic acid (FA) and humic acid (HA) on tyrosinase activity were investigated utilizing circular dichroism (CD) and fluorescence spectroscopy, molecular docking (MD), and molecular dynamics simulations. HA and FA demonstrated a mixed type of inhibition with K i 2.02 and 5.2 μM, respectively. The thermodynamic parameters displayed that the hydrogen bond and hydrophobic force play a major role in the FA-tyrosinase and HA-tyrosinase interaction, respectively.Fluorescence experiments demonstrated changes in tyrosinase tertiary structures.HA could not destroy the tyrosinase secondary structure significantly, however, FA has a significant influence on the tyrosinase secondary structure. The molecular dynamics findings demonstrated the minimal fluctuations and the lowest flexibility in the complex amino acids in the HA-tyrosinase and FA-tyrosinase interaction. Altogether, HA and FA could be utilized in food industries as an accessible natural source for tyrosinase inhibition. Practical applicationsRecently, the investigation of tyrosinase inhibitors from the biosphere for hindrance of undesired browning in the food industry has increased considerably. Mushroom tyrosinase is a suitable model for kinetic research owing to its availability as well as close conformational similarity to tyrosinase in a mammal. Natural sources and their effective compounds could have wonderful potential on tyrosinase activity and structure, thus, in this study, the interactions between tyrosinase and fulvic acid (FA) and Humic acid (HA) were investigated. Previously, it has been shown that HA and FA have antioxidant properties and they can improve the quality of food via retarding lipid oxidation. Altogether, further investigations are warranted to draw firm conclusions, HA and FA could be utilized in food industries not only as antioxidant agents but also as an accessible natural source for tyrosinase inhibition.