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-CPC) of EGCG-CAF mixed aqueous solutions was assayed through a turbidity assay performed at 25 degrees 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 x 10(5) Da, and of metal ions (K+, Mg2+, Ca2+, and Al3+) were respectively introduced into the mixed solution to study their effects on C-CPC. On the basis of the changed C-CPC, 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 Al3+ is the strongest, followed by that of Ca2+.