Flavonoid composition of orange peel and its association with antioxidant and anti-inflammatory activities

- Alkaline hot water increased the yield of orange peel extract.
- Orange peel extract have higher anti-inflammatory activity than their equivalent flavonoid mixtures.
- Nobiletin is a good marker for anti-inflammatory potential of orange peel extract.
- Xinhui and Sichuan nchenpi have higher bioactivities than conventional chenpi.

Dried citrus peel derived from Citrus reticulata, also called “chenpi”, possesses a complex mixture of flavonoids and has a history of traditional use to treat a variety of digestive disorders. We compared three sources of conventional chenpi from California (USA), Guangxi, Zhejiang, and two sources of “nchenpi”, which contain greater nobiletin content, from Sichuan and Xinhui (China). Xinhui orange peel extract (OPE) had highest content of polymethoxylated flavones, along with greatest capacity to scavenge 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 2,2-diphenyl-1-pcrylhydrazyl (DPPH), and 2,2′-azobis-2-methyl-propanimidamide, dihydrochloride (AAPH) radicals and nitric oxide (NO). OPE also had higher NO, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) inhibitory activity than an equivalent mixture of flavonoids (P < 0.05). In conclusion, nobiletin is a good chemical marker for assessing the anti-inflammatory potential of OPE from different sources. Obtaining “nchenpi” from either Sichuan or Xinhui provided potentially superior health benefits compared to conventional chenpi sources.