Unveiling the geographical signature of black tea through UHPLC-quadrupole-Orbitrap Exploris HRMS analysis

Understanding the geographical differentiation of black tea is essential for exploring the influence of territory on its chemical composition. In this study, black tea (powder) samples from key tea-producing regions, including Siliguri, Assam, and Idukki (Kerala) in India, Sylhet in Bangladesh, and Kandy in Sri Lanka, were analyzed using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry. The tea extracts were analysed in full MS/ddMS² mode with heated electrospray ionization, using a non-targeted metabolomics approach. A broad range of compounds (209) including polyphenols, amino acids, organic acids and their derivatives were identified based on accurate mass measurements with mass error (±5 ppm) and retention time matching (±0.2 min). Various metabolite profiles were observed across different regional samples, with certain marker compounds identified as potential indicators of geographical origin. Principal component analysis (PCA) further confirmed clear clustering and differentiation of tea samples based on the origin, highlighting the role of regional environmental factors such as climate, soil composition, and altitude. Molecular docking and dynamics were carried out to examine the interaction of theanine and the neonatal Fc receptor (FcRn), a key regulator of IgG recycling and immune homeostasis, encoded by the FCGRT gene. Results showed that theanine forms a stable complex with the neonatal Fc receptor (FcRn) and maintained consistent hydrogen bonding, particularly with key residue Ile685, and preserved FcRn's secondary structure. Binding energy analysis (MM-PBSA) showed favourable interactions dominated by van der Waals forces, with theanine exhibiting a slightly higher binding affinity (-18.72 kcal mol^-1) than RVT-1401 (-17.82 kcal mol^-1), a therapeutic monoclonal antibody known to inhibit FcRn function. The findings have significant implications for the tea industry in quality control, authentication, traceability, and health benefits, which offer new insights into how territory shapes the chemical and potentially sensory attributes of black tea.