Effects of Tea-Polysaccharide Conjugates and Metal Ions on Precipitate Formation by Epigallocatechin Gallate and Caffeine, the Key Components of Green Tea Infusion.

The mechanism of tea-infusion precipitation is not clear. Epigallocatechin gallate (EGCG) and caffeine (CAF) are the core components of green tea infusion precipitate. The critical precipitation concentration ( C) of EGCG-CAF mixed aqueous solutions was assayed through a turbidity assay performed at 25 °C and verified by a differential-scanning calorimeter (DSC) for reliability. Different concentrations of the green tea polysaccharide conjugate fraction (gTPC-D), with a molecular weight of 2.32 × 10 Da, and of metal ions (K, Mg, Ca, and Al) were respectively introduced into the mixed solution to study their effects on C. On the basis of the changed C, the clarification-precipitation phase diagrams of the mixed aqueous solutions were constructed. By calculating the integral area of the clarification phase, it was determined that the four metal ions and gTPC-D could accelerate precipitate formation with a dose-response relationship; among the metal ions, the effect of Al is the strongest, followed by that of Ca.