Variations in the Components and Antioxidant and Tyrosinase Inhibitory Activities of Styphnolobium japonicum (L.) Schott Extract during Flower Maturity Stages

Styphnolobium japonicum (L.) S chott is widely cultivated in China, and its flowers and flower buds (FFB-SJ) are commonly used as traditional Chinese medicine. This work aimed to assess variations in the chemical components and antioxidant and tyrosinase inhibitory activities of S. japonicum extract during five flower maturity stages (ES1–ES5). The results showed that the contents of total flavonoids, rutin, and narcissin were highest at ES1, whereas the contents of quercetin and isorhamnetin were highest at ES3. ES1 presented considerable antioxidant activities in terms of reducing power (RP) and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH . ) and hydroxyl radical ( . OH) scavenging capacity, whereas ES3 showed excellent tyrosinase inhibitory activity and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical (ABTS .+ )- and O 2 .− -scavenging capacity. Rutin and quercetin are the main bioactive components of FFB-SJ with antioxidant and tyrosinase inhibition, and the immature flower buds of S. japonicum (S2 and S3) with excellent biological activities and relatively high extract yields were the best for product development.