Melanin plays an important role in protection the skin against ultraviolet light injury and is responsible for skin color. However, overproduction and accumulation of melanin result in several skin disorders including freckles, melasma, age spots and other hyperpigmentation
syndrome. Tyrosinase (monophenol, L-dihydroxyphenylalanine (L-DOPA): oxygen oxidoreductase EC 1.14.18.1) is the key enzyme in the first two steps of melanin biosynthesis, in which L-tyrosine is hydroxylated to L-DOPA (o-diphenol product), and L-DOPA is further oxidized into the corresponding o-quinone. It has been reported that microphthalmia-associated transcriotion factor (MITF) and other enzymes such as tyrosinase related protein-1 (TRP-1) and tyrosinase related protein-2 (TRP-2) also contribute to the production of melanin. Recently, melanogenesis inhibitors have been increasingly applied in skin care cosmetics for the prevention
of hyperpigmentation. In addition, melanogenesis is reported to produce hydrogen peroxide (H2O2) and other reactive oxygen species (ROS) which makes the melanocytes under high-grade oxidative stress. It is well known that ROS play a significant role in the regulation of the melanogenesis, while ROS scavengers and inhibitors of ROS generation may down-regulate UV-induced melanogenesis. Therefore, antioxidants such as ascorbic derivatives
and reduced glutathione (GSH) have been applied as inhibitory agents of melanogenesis.
Magnolia grandiflora L. (Magnoliaceae) is widely used as a traditional medicine for the treatment of diarrhea, abdominal diseases, rheumatic arthritis, heart disturbances,high blood pressure, epilepsy, infertility and fever. The aqueous extracts of flowers and leaves have been reported to exhibit cardiovascular effects and was also use is an anticonvulsant in rat. Chemical studies on M. grandiflora L. and other plants of the same genus, such as
M. officinalis, have reported the presence of magnolol and honokiol, which exhibit muscle relaxant activity, inhibitory effects on skin tumour promotion and antimicrobial properties [17]. It is interesting to find that M. grandiflora L. contains a number of sesquiterpene lactones which possess anti-inflammatory properties and used for treatment of pain. A number of biologically active alkaloids, sesquiterpenes, phenolic constituents, glycosides and other compounds have been isolated from this species. However, scientific studies of the antimelanogenic and antioxidant properties of this medicinal plant are lacking.