Chemical composition, antioxidant, antibacterial, and tyrosinase inhibition activity of extracts from Newhall navel orange (Citrus sinensis Osbeck cv. Newhall) peel

BACKGROUND Newhall navel orange (Citrus sinensis Osbeck cv. Newhall) is the major navel orange cultivar planted in China. Almost all Newhall navel orange peels produced in that country are currently discarded, which is not only harmful to the environment but also a waste of resources. It is therefore necessary to carry out research to explore the utilization potential of this resource. RESULTS A 95% ethanol extract (EE) of Newhall orange peel was prepared and fractionated into three subextracts: petroleum ether extract (PEE), ethyl acetate extract (EtOAcE), and water extract (WE) by simple liquid / liquid extractions. These four extracts were then subjected to antioxidant, antibacterial, and tyrosinase inhibition assays. Interestingly, EtOAcE was significantly superior to all other three extracts, exhibiting the best biological effects. The total polyphenol content (TPC), total flavonoid content (TFC), and primary individual flavonoids of these four extracts were analyzed and compared. This was followed by principal component analysis (PCA) and the Pearson's correlation test. The result indicates that the primary bioactive compounds responsible for the biological effects of the EtOAcE are sinensetin, 4 ',5,6,7-tetramethoxyflavone, nobiletin, 3,3 ',4 ',5,6,7-hexamethoxyflavone, and narirutin. In view of its easy preparation and potent biological effects, EtOAcE might demonstrate excellent application potential in various industrial areas. CONCLUSIONS This study successfully identified EtOAcE as a potent naturally occurring antioxidant, antibacterial, and tyrosinase inhibitory agent, which might add value to the utilization of Newhall navel orange peel in the food, cosmetic, and pharmaceutical industries.