Tyrosinase Inhibitory Activity and Thermostability of the Flavonoid Complex from Sophora japonica L (Fabaceae)

Purpose: To investigate the tyrosinase inhibitory activity and thermostability of weak acid-treated Sophora japonica L. flavonoid complex (SJ-FC) in different solutions. Methods: The flavonoid complex of S. japonica was isolated and treated with weak acid to generate SJ-FC. The anti-tyrosinase activities of SJ-FC and well-known tyrosinase inhibitors were compared by mushroom tyrosinase activity assay. The thermostabilities of SJ-FC and other inhibitors in different solution environments for long-term storage were also investigated. Results: The results indicate that SJ-FC has potent tyrosinase inhibitory activity, and at a concentration of 0.1 %, SJ-DC has a tyrosinase inhibitory activity equal to that of 1 % ascorbic acid or hydroquinone. In addition, SJ-FC in both propylene glycol (PG) and glycerol solutions exhibited obvious tyrosinase inhibitory activity. Ascorbic acid and arbutin, two other tyrosinase inhibitors, exhibit < 60 % of their initial activity in both PG and H2O solutions after 6 months of storage. However, SJ-FC stored in PG and H2O solutions retained almost 100 % of its activity over a 6-month period. Conclusion: SJ-FC is an effective and stable anti-tyrosinase agent and may be used as a function agent in medicines, foods and cosmetics.