Rooibos tea: equilibrium and extraction kinetics of aspalathin

A mobile phase for the extraction of aspalathin was developed and used to study the kinetics of extraction of the compound from Rooibos tea. The rate of infusion of aspalathin into water at 80 °C was measured for Rooibos tea, using a leaf of size 1.00–1.40 mm. The first order rate constant (kobs=23.4×10−4 s−1) was determined from the rate of increase of aspalathin concentration in a tea infusion with time and the result interpreted using a steady state model. The results were compared with those of rose-hip, black and green teas. The first order rate constant for extraction of aspalathin was found to be comparable with that of l-ascorbic acid in rose-hip tea. However, the value was about five times smaller than that of flavanols from Japanese green tea and 3–10 times smaller than the extraction of caffeine from black Assam Bukial and green Chun Mee teas. The pH of the liquor at equilibrium was found to be 4.6. This value is comparable to that of both black and rose-hip tea but 20% smaller than that of green Chun Mee tea.