Figure 4. Assay of black tea. (A) Standard curve with increasing amounts of black tea in solution measured in the presence of 1 M HCl at 415 nm. Mean ± SD of 5 assays. The amount of black tea polyphenols is unknown, but the figures shown are based on the volume of tea stock solution (2 g in 100 mL water) and published figures suggesting 1 mg polyphenol per mL tea (Bravo, 1999). (B) Assay of black tea and salivary protein added sequentially to hydroxyapatite. Total amounts of protein added were: parotid saliva only (S), 400 µg; histatin (H) fraction, 1.7 µg; and proline-rich protein (P) fraction, 100 µg. Mean ± SD of 3 assays. Saliva first, then tea sequentially (S/T); histatin first, then tea sequentially (H/T); proline-rich proteins first, then tea sequentially (P/T). ^aS/T and P/T were statistically significantly greater than black tea alone (p < 0.05, paired t test).