An untargeted UPLC-MS-based metabolomics approach towards quality control of bush tea (Athrixia phylicoides DC.) from South Africa

Bush tea (Athrixia phylicoides, Asteraceae), an indigenous South African shrub, is widely consumed as a caffeine-free herbal tea. Infusions of the aerial parts are used as a traditional medicine by many ethnic groups [1]. The economic success of other indigenous South African teas has stimulated an interest in the commercialisation of bush tea. This study was aimed at determining the extent of phytochemical variation within the species, and to identify biomarkers for quality control. Samples (N = 48) of A. phylicoides were collected from different regions of South Africa. The ultra-performance liquid chromatography-quadrupole time-of-flight-mass spectrometry (UPLC-QToF-MS) profiles of the methanol extracts of aerial parts were obtained. Principal component analysis (PCA) and supervised orthogonal projections to latent structures-discriminant analysis (OPLS-DA) models were constructed from the data. It was found that 44.3% (R² X_cum= 0.443) of the variation in the data (two principal components) was explained by the model. The profiles of samples from Mpumalanga and Limpopo were alike, but differed from the majority of samples KwaZulu-Natal Province, which displayed more variation. The OPLS-DA scores plot revealed clustering according to the province of origin, since the KwaZulu-Natal samples were separated along PC2 (R²X = 0.214), while the Limpopo and Mpumalanga samples separated along PC1. An S-plot was used to extract biomarker compounds for each of the three provinces. Two of these compounds were isolated from the dichloromethane extract of a batch sample using silica gel column chromatography and identified as p-hydroxyphenylpropan-3-ol coumarate [2] (1) and 5-hydroxy-6,7,8,3',4',5' hexamethoxyflavon-3-ol [3] (2), using accurate mass data from UPLC-QToF-MS analysis. The isolated compounds, previously identified in A. phylicoides, may be used as biomarkers for quality control, once quality aspects of samples from each of the clusters have been investigated.

Acknowledgements: We are grateful to the Tshwane University of Technology, SAMRC Herbal Drugs Research Unit and the National Research Foundation for financial support.

Keywords: Athrixia phylicoides, herbal tea, chromatography, isolation, quality control, UPLC-QToF-MS; metabolomics.

References:

[1] Roberts M. Indigenous Healing Plants, 1^st edition. Southern Book Publishers, Halfway House, South Africa.1990.

[2] Bohlmann F, Zdero C. Neue norkauren- und thymol-derivate aus Athrixia-arten Phytochemistry. 1977; 16: 1773 – 1776

[3] Mavundza EJ, Tshikalange TE, Lall N, Mudau FN, Hussein AA. Antioxidant activity and cytotoxicity of three flavonoids from Athrixia phylicoides ethanol extract. J Med Plants Res 2010; 4: 2584 – 2587