Identification of phenolic compounds from purple pepper (Capsicum annuum L.) and their radical scavenging activities

Peppers (Capsicum spp.) are widely consumed vegetables belonging to the Solanaceae family in Korea. Recently, purple peppers have been cultivated due to consumer interest in healthy functional compounds such as phenolic compounds, flavonoids, and anthocyanin. This study investigated metabolomic discrimination of 6 pepper cultivars (cheongyang, green pepper, twist, cucumber pepper, red pepper, and purple pepper) by liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry (LC-ESI-QToF-MS) untargeted metabolomic analysis. LC-MS results indicated that monomeric diterpene capsianoside, flavonoid glycosides, and nasunin were identified as the main compounds in purple pepper. Six compounds were purified and isolated from purple peppers using ODS and silica gel column chromatography. These isolated compounds were determined to be 4’-trans-p-coumaroyl rutinosyl 2-(O-galloyl)-6-(O-β-glucopyranosyl)-4-hydroxyphenyl acetate (1), delphinidin 3-[4-(p-coumaroyl)-rutinoside]-5-glucoside (2), (8R)-isodehydrodiconiferyl alcohol 4’-β-D-glucopyranoside (3), apigenin 6-C-β-D-glucopyranoside-8-C-α-L-arabinopyranoside (4), quercetin 3-rutinoside (5), and isorhamnetin 3-rutinoside (6) by MS and NMR experiments. Compounds 1, 2, and 5 had strong radical-scavenging activities. These results provide useful information about the bioactive compounds of purple pepper.