Identification, structure elucidation, and isomer differentiation of phenolic compounds of Chinese pepper cultivars by UPLC-ESI-Q-TOF-MS and their antioxidant activity

A total of 43 compounds, including phenolic acids, flavonoids, lignans, and diterpene, were identified and characterized using UPLC-ESI-Q-TOF-MS coupled with UNIFI software. The identified flavonoids were mostly isomers of luteolin, apigenin, and quercetin, which were elucidated and distinguished for the first time in pepper cultivars. The use of multivariate data analytics for sample discrimination revealed that luteolin derivatives played the most important role in differentiating pepper cultivars. The content of phenolic acids and flavonoids in immature green peppers was generally higher than that of mature red peppers. The pepper extracts possessed significant antioxidant activities, and the antioxidant activities correlated well with phenolic contents and their molecular structure. In conclusion, the findings expand our understanding of the phytochemical components of the Chinese pepper genotype at two maturity stages. Moreover, a UPLC-ESI-Q-TOF-MS in negative ionization mode rapid methods for characterization and isomers differentiation was described.