Discovery of the Potential Marker Compounds for Stored White Tea by a Metabolomics Approach

Importance of the Topic

Traditional white teas develop unique sensory and health-promoting properties when stored over extended periods. However, reliable chemical markers that reflect aging progress and quality remain scarce. Identifying robust nonvolatile biomarkers enhances quality control, product authentication and understanding of biochemical transformations in white tea during storage.

Study Objectives and Overview

This study applied a non-targeted metabolomics workflow to two Chinese white tea subtypes (Bai Hao Yin Zhen and Bai Mu Dan) harvested from 2000 to 2015. The primary goals were to profile changes in nonvolatile metabolites across storage durations, discover potential chemical markers of aging, and elucidate their biochemical origins.

Methodology

Tea samples were dried, powdered and extracted with 70% methanol. Quality control pools were injected every ten samples to monitor analytical reproducibility. Data acquisition employed UHPLC separation followed by high-resolution Q-TOF mass spectrometry in positive ESI mode. Molecular feature extraction and alignment were performed in Agilent Profinder, and chemometric analysis (PCA, PLS-DA, hierarchical clustering) was carried out using Agilent Mass Profiler Professional. Tentative identification combined exact mass, MS/MS interpretation with a metabolite database search, and confirmation against authentic standards.

Used Instrumentation

• Agilent 1290 Infinity II UHPLC with built-in degasser, temperature-controlled autosampler and column compartment
• ZORBAX Eclipse Plus C18 column (150×3.0 mm, 1.8 µm) at 40 °C
• Agilent 6540/6545 Q-TOF LC/MS with Dual Jet Stream ESI source
• Agilent MassHunter Profinder, Mass Profiler Professional and Qualitative software

Main Results and Discussion

Chemometric analysis revealed clear clustering by tea subtype and gradual separation by storage duration. A total of 2 584 features passed quality filters; 125 differential compounds were tentatively identified, including flavan-3-ols, glycosides, amino acids, phenolics and organic acids. Seven novel 8-C N-ethyl-2-pyrrolidinone substituted flavan-3-ols (EPSFs) emerged only in aged samples. Their abundance increased significantly after four years, while levels of theanine and precursor flavan-3-ols declined. Correlation patterns and in vitro reactions supported a conversion pathway from theanine and catechins to EPSFs under storage conditions.

Benefits and Practical Applications

• EPSFs serve as promising chemical markers for assessing white tea aging and authenticity.
• Quality control protocols can incorporate these markers to monitor storage performance.
• Insights into precursor–product relationships inform processing and storage optimization.

Future Trends and Opportunities

Further research may explore EPSF formation kinetics under controlled conditions and extend marker validation to diverse tea origins. Integrating metabolomics with proteomics or sensory evaluation could deepen understanding of flavor and health-related changes. Development of rapid assays (e.g., targeted LC–MS/MS or immunoassays) for EPSFs may support industrial quality monitoring.

Conclusion

This work demonstrates a comprehensive metabolomics approach to uncover nonvolatile transformations in white tea during long-term storage. The identification of seven novel EPSFs and their correlation with precursor depletion provides reliable markers for tea aging. These findings advance both fundamental knowledge of tea chemistry and practical tools for quality assessment.

Reference

1. Dai W. D. et al. J. Agric. Food Chem. 2018,66,7209–7218.
2. Mao J. T. et al. Cancer Prev. Res. 2010,3(9),1132–1140.
3. Ning J. M. et al. Eur. Food Res. Technol. 2016,242(12),2093–2104.
4. Dai W. et al. Food Res. Int. 2017,96,40–45.
5. Yang C. et al. Agilent Application Note 5994-0866 EN, 2019.