Food Chem~try25 (1987) 117-126 Kinetics and Equilibria of Tea Infusion: Part 8 The Effects of Salts and of pH on the Rate of Extraction of Theaflavins from Black Tea Leaf Michael Spiro, William E. Price, William M. Miller & Mokhtar Arami Department of Chemistry,ImperialCollegeof Science and Technology, London SW7 2AY, Great Britain (Received 1 October 1986; accepted 12 November 1986) A BS TRA C T The rates of extraction of theaflavins from sieved Kapchorua Pekoe Fannings (600-710 ~m) and from a Ceylon Broken Orange Pekoe Fine Leaf Blend have been measured at 80°C with a set of aqueous salt and buffer solutions spanning the pH range 3"1 to 8"1. There was little effect on adding 1:1 electrolytes but considerable decreases in rate occurred in the presence of cal.~ium chloride. The rate constants in acid buffers were the same as in a normal unbuffered infusion but in alkaline buffers of pH 8 they were over 50% larger. This phenomenon was quantitatively accounted for by the partial dissociation of theaflavins at higher pH and the greater diffusion coefficient of the resulting ionic salt. The relevance of these findings to tea brewing and to industrial theaflavins extraction is discussed. INTRODUCTION We reported in the preceding paper (Spiro & Price, 1987b) how the rate of extraction of caffeine from a black Kenyan CTC tea, Kapchorua Pekoe Fannings, was affected by the addition of various salts to the water. The rate was not, however, dependent on pH. We now present corresponding data for the extraction of all the theaflavins (ungallated, monogallated and digallated, together abbreviated as TF). The same sieved 600-710/~m Kapchorua leaf was used (experiments by W.E.P.) as well as Ceylon Broken 117 Food Chemistry 0308-8146/87/$03"50 © ElsevierApplied SciencePublishers Ltd, England, 1987. Printed in Great Britain