Rapid analysis of the chemical composition of black tea leaves using vibrational spectroscopy techniques

  • Stephanie Heaney

Student thesis: Doctoral ThesisDoctor of Philosophy


The introduction of rapid methods to monitor tea quality during the oxidation stage in black tea manufacturing is essential for increasing the sustainability of tea production. During this significant stage, the catechins in the tea leaves are converted to theaflavin and the thearubigin compounds and their ratios at the end point of this process plays a major role in the quality of the final product. The implementation of rapid techniques to monitor this process would ultimately increase quality assurance standards resulting in higher yields to quality tea. Fulfilling this challenge requires the exploration of rapid analytical methods and their ability to provide essential information of the chemical compounds, which are associated with tea oxidation status.

This thesis explores the use of vibrational spectroscopy techniques and chemotic methods for the rapid analysis of chemical components which can indicate tea quality and oxidation status to ultimately enhance process control in tea manufacturing. Initially, Near-Infrared (NIR) and Mid-Infrared (MIR) were investigated to explore their potential to classify a variety of tea samples by a range of tea quality attributes. The use of NIR and MIR as off-line methods for monitoring oxidation status was assessed by oxidising teas for various times and collecting the spectral fingerprints of these samples after drying. An oxidation unit which was connected toa portable NIR sensor was used to instantly collect spectra of tea during oxidation. This data was used to explore the ability of NIR to rapidly predict oxidation status of teas during this processing.

The findings from the research demonstrates that vibrational spectroscopy techniques coupled with chemometric analysis can predict important quality compounds associated with oxidation when tea has been dried (off-line) and during processing (on-line). The results demonstrate potential for methods to be developed and scaled up for application in black tea manufacturing to aid to oxidation control and ultimately produce higher quality yields of sustainable tea.
Date of AwardJul 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorTassos Koidis (Supervisor) & Sally Redfern (Supervisor)

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