Characterization of phenolic compounds in rooibos tea

Area of Science:

• Phytochemistry
• Natural Product Chemistry

Background:

• Rooibos (Aspalathus linearis) is a popular herbal tea rich in polyphenols.
• Understanding the chemical composition of rooibos is crucial for its health benefits.
• Previous isolation methods may not be efficient for large-scale polyphenol extraction.

Purpose of the Study:

• To develop and validate a robust method for isolating polyphenols from rooibos.
• To obtain pure flavonoids for structural elucidation.
• To investigate the chemistry of dihydrochalcones and related compounds in rooibos.

Main Methods:

• Two-step isolation process involving multilayer countercurrent chromatography (MLCCC) and preparative high-performance liquid chromatography (HPLC).
• Purity and identity confirmation using Nuclear Magnetic Resonance (NMR) spectroscopy, HPLC-diode array detector (DAD), and gas chromatography-mass spectrometry (GC-MS).
• Chemical transformation studies including oxidation of aspalathin and degradation of flavanone-C-glycosides.

Main Results:

• Successful isolation of polyphenols, including known and potentially novel structures, in gram quantities.
• Confirmation of isolated compound identities through advanced spectroscopic and chromatographic techniques.
• Demonstration of the chemical conversion of dihydrochalcone aspalathin to flavanone-C-glycosides and subsequently to flavones isoorientin and orientin.

Conclusions:

• The combined MLCCC and HPLC strategy is effective for isolating and purifying rooibos polyphenols.
• This methodology facilitates the characterization of complex polyphenol structures.
• The study provides insights into the chemical reactivity and interconversion of key rooibos constituents.