Flavonoid contents and antityrosinase activity in various parts of Dendrobium 'Sonia Jo Daeng' and Dendrobium 'Khao Sanan' at different growth stages

Dendrobium 'Sonia Jo Daeng' (DSJD) and D. 'Khao Sanan' (DKS) are widely known as cut orchids of Thailand. Several researches indicated that various parts of orchids contain high phenolic and flavonoid contents. Thus, the flavonoid contents and antityrosinase activity in various parts of DSJD and DKS at different growth stages were evaluated. The analyses were performed in roots, leaves, pseudobulbs, flowers, and peduncles of 1- and 4-year-old plants of both cultivars. The results showed that various parts of both orchids contained different flavonoid contents and antityrosinase activity. In DSJD, total flavonoid contents (6.34±0.41 mg QE g^‑1 DW) were the highest in leaves of 4-year old plants consistent with the antityrosinase activity (55.33±7.44% tyrosinase inhibition). Moreover, high contents of total flavonoids were observed in pseudobulbs (5.52±0.19 mg QE g^‑1 DW), flowers (5.47±0.20 mg QE g^‑1 DW), and peduncles (3.59±0.20 mg QE g^‑1 DW) of 1-year-old DKS and also in pseudobulbs (3.38±0.15 mg QE g^‑1 DW), and peduncles (3.50±0.07 mg QE g^‑1 DW) of 4-year-old plants. These results are in agreement with the antityrosinase activity which was found the highest in peduncles of 1- and 4-year-old plants (38.72±3.52 and 42.44±4.17% tyrosinase inhibition, respectively). Therefore, leaves of 4-year-old DSJD are a rich source of flavonoids and had highest antityrosinase activity. Taken together, this finding suggested that flavonoids play an important role in inhibition of tyrosinase activity which could be further useful as anti-melanogenesis in cosmetic industry.