Bioscience Evidence 2024, Vol.14, No.3, 98-109 http://bioscipublisher.com/index.php/be 101 have shown moderate activity in suppressing α-glucosidase, a key enzyme involved in carbohydrate metabolism (Li et al., 2023). The identification of these minor constituents provides new insights into the hypoglycemic effects of R. glutinosa and its potential for developing α-glucosidase inhibitor drugs. Furthermore, the antioxidant activity of R. glutinosa has been linked to its diverse phytochemical profile, with certain samples exhibiting high levels of catalpol, rehmaionoside A, and rehmannioside D, which contribute to its strong antioxidant properties (Liu et al., 2020). In summary, the chemical composition of Rehmannia glutinosa is complex and diverse, with iridoid glycosides, phenethyl alcohol glycosides, polysaccharides, and various minor constituents playing crucial roles in its bioactivity. These compounds collectively contribute to the plant's therapeutic potential, making it a valuable resource in traditional and modern medicine. 4 Analytical Techniques for Component Identification 4.1 Chromatographic methods 4.1.1 High-performance liquid chromatography (HPLC) High-Performance Liquid Chromatography (HPLC) is a widely used technique for the separation, identification, and quantification of components in complex mixtures. In the context of Rehmannia glutinosa, HPLC has been employed to analyze various bioactive compounds, ensuring the quality and consistency of the herbal material. The technique's high resolution and sensitivity make it ideal for detecting minor components and impurities, which is crucial for both research and clinical applications. 4.1.2 Gas chromatography-mass spectrometry (GC-MS) Gas Chromatography-Mass spectrometry (GC-MS) combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. This method is particularly useful for analyzing volatile and semi-volatile compounds. In studies involving Rehmannia glutinosa, GC-MS has been used to profile the metabolic components and to understand the pharmacokinetics of the herb in biological systems. For instance, the UPLC-Q-TOF/MS technique, which is closely related to GC-MS, has been applied to analyze the metabolic profiles of bioactive components in Rehmannia glutinosa, providing insights into their absorption and metabolism in both normal and CKD rats (Tao et al., 2018). 4.2 Spectroscopic methods 4.2.1 Nuclear magnetic resonance (NMR) Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. NMR provides detailed information about the molecular structure, dynamics, reaction state, and chemical environment of molecules. In the study of Rehmannia glutinosa, NMR can be used to elucidate the structures of complex polysaccharides and other bioactive molecules, contributing to a better understanding of their functional properties and potential therapeutic effects. 4.2.2 Infrared spectroscopy (IR) Infrared Spectroscopy (IR) is another essential tool for the identification of chemical compounds based on their vibrational transitions. Fourier Transform Infrared Spectroscopy (FTIR) has been specifically utilized to analyze the chemical composition of Rehmannia glutinosa and its extracts. FTIR, combined with second derivative spectrum and thermal analysis, has proven effective in distinguishing subtle differences in the chemical components of various types of Rehmannia glutinosa, thereby aiding in quality control and standardization of the herbal material (Zhang et al., 2022). 4.3 Other analytical approaches In addition to chromatographic and spectroscopic methods, other advanced analytical techniques have been employed to study the bioactive components of Rehmannia glutinosa. For example, Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI-MSI) combined with machine learning has been used to visualize the spatial distribution of oligosaccharides in processed Rehmannia glutinosa. This approach not only helps in understanding the metabolic changes during processing but also aids in the standardization and
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