LC-HRMS and FTIR-based metabolomics analysis and xanthine oxidase inhibitory evaluation of Sida rhombifolia with different drying methods

Sida rhombifolia, known as Sidaguri in Indonesia, has been widely used in traditional medicine because of its bioactive metabolites, particularly flavonoids and steroids. Several factors, including the drying method, can affect the composition and concentrations of metabolites in plants. This study aimed to profile the metabolites and evaluate the xanthine oxidase inhibitory activity of S. rhombifolia dried by different methods. Three drying methods were used: air drying (AD), oven drying (OD), and sun drying (SD). Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and Fourier transform infrared (FTIR)-based untargeted metabolomics were used to profile the metabolites in S. rhombifolia. The FTIR spectra of samples dried by different methods showed similar patterns, with peaks at 3398, 2935, 2856, 1728, 1456, and 1164 cm−1. Metabolite profiling of S. rhombifolia using liquid chromatography–tandem mass spectrometry (LC–MS/MS) identified 24 putative metabolites, with 20, 15, and 16 metabolites found in the AD, OD, and SD extracts, respectively. The principal component analysis demonstrated the separation of S. rhombifolia into groups based on drying method differences. These differences account for 95% (LC–MS/MS) and 99% (FTIR) of the total variance explained. Evaluation of xanthine oxidase inhibition revealed that S. rhombifolia inhibited the enzyme by 22.81% (AD), 35.97% (OD), and 45.93% (SD) at an extract concentration of 50 ppm. The drying method affected the metabolite profile with regard to both the functional groups and amounts of metabolites. Furthermore, the results showed that the xanthine oxidase inhibitory activity depended on the S. rhombifolia drying method and conditions.