Antioxidant profiling and quality assessment of Lithocarpus polystachyus sweet tea using LC-ECD and LC-MS/MS

Abstract This study used liquid chromatography-electrochemical detection (LC-ECD) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to screen and characterize the antioxidant components of sweet tea ( Lithocarpus polystachyus ), and to evaluate the quality of the samples from different origins. First, the total phenolic and flavonoid content of sweet tea, as well as the in vitro antioxidant activity, including ABTS and DPPH radical scavenging capacities and ferric reducing ability, were determined. Samples from different origins demonstrated potent antioxidant activity, with correlation coefficients exceeding 0.8 between total phenolic content and antioxidant activities. Then, the fingerprints of sweet tea were generated by LC-ECD and 22 common peaks were identified by LC-MS/MS, with most of them being phloretin derivatives. The clustering heat map revealed differences in the content of sweet tea from various regions, with major compounds identified as trilobatin, phlorizin, 3-hydroxyphlorizin, and its isomer. Furthermore, grey relational analysis confirmed a strong association between different compounds (protocatechuic acid, epicatechin, 3-hydroxyphlorizin, isoquercitrin, and trilobatin) and antioxidant activity, with trilobatin showing the highest contribution, reaching a correlation of 0.9. Finally, 11 phenolic compounds were quantitatively determined. This study screened and identified the major antioxidant components of sweet tea using LC-ECD and LC-MS/MS, providing guidance for its quality control.