The effect of metal ions on the black tea cream formation by comparative analysis on chemical constituents of resoluble and irresoluble black tea cream

Black tea cream down can be separated into the resoluble (RS) and irresoluble (IS) parts. The irresoluble part hardly dissolves in boiling water after it forms in tea infusion, thus it is an indelible particle in the tea beverage industry. In the current work, we qualitatively and quantitatively analyzed the differences of chemical composition between these two parts. The results showed that the irresoluble cream down contained theaflavins and caffeine, but only dissolved in DMSO rather than boiling water. The irresoluble cream down contained higher levels of Al, Ca, Fe, and Cu mineral elements than resoluble cream down. The elemental analysis also indicated that irresoluble cream down was composed of more hydrogen element than resoluble cream down. The Fourier transform infrared (FT-IR) spectroscopy analysis confirmed that the irresoluble cream down spectrum presented two critical differential absorption peaks at 2919 and 2850 cm-1, which were attributed to the saturated carbon moiety of organic compounds. Moreover, we compared the effects of four metal ions (including Al3+, Ca2+, Fe3+, and Cu2+) on the formation of cream particle, and found that Al3+ had the strongest contribution to the particle formation of cream down. Meanwhile, caffeine also contributed to the particle formation of cream down as a secondary role.