Antagonistic interaction of phenols and alkaloids in Sichuan pepper (Zanthoxylum bungeanum) pericarp

The pericarp of Zanthoxylum bungeanum (PZB) is rich in phenols and alkaloids as a potential source of antioxidants, also known as Huajiao or Sichuan pepper in China, and is not only extensively used as a pungent culinary spice but also as a traditional medicinal plant due to its remedial properties. Previous studies have shown that PZB extract is highly effective against oxidative stress-related dysfunction in vitro and in vivo. Although phenols and alkaloids are considered as the two main antioxidant components in Zanthoxylum species, the impact of species diversity and cultivation region on the antioxidant composition and radical scavenging activity (RSA) of PZB extracts remains unknown. This study aimed to compare the phenol and alkaloid compositions in PZB extracts (S1-S7) obtained from seven cultivation regions in China. Additionally, the RSA of the PZB extracts and the contribution of individual phenols and alkaloids to RSA were evaluated. Six phenols and 14 alkaloids were identified at variable content levels in the PZB extracts using HPLC-MS2. The highest total phenolic content (59.60 ± 1.48 mg g−1) was recorded in S7 (Laiwu) while S1 (Hanyuan) was the richest in total alkaloid content (189.43 ± 2.81 mg g−1). The S5 (Linxia) exhibited the highest RSA, with 50 % scavenging concentration (IC50) values of 2.62 ± 0.05 mg L−1, 1.94 ± 0.04 mg L−1 and 158.26 ± 4.34 mg L−1, after exposure to spectrophotometric, electron paramagnetic resonance spectroscopy (EPR), and cyclic voltammetric (CV) systems. However, there was no significant correlation between the component content and RSA. Interestingly, representative phenols (rutin, quercetin, and hyperoside) and alkaloids (hydroxyl-α-sanshool (α-SOH)) displayed an antagonistic effect on the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) scavenging activity, among which the impact of the quercetin-α-SOH combination was the strongest. This suggested that the interaction between phenols and alkaloids might confer important biochemical activities to PZB during processing and pharmaceutical applications.