Why can you use Na2CO3 to remove tannins from tea?

Tannins are polyphenolic compounds that are found in many plants, including tea leaves. They can contribute to the astringent and bitter taste of tea, and can also bind to proteins and minerals, making them less bioavailable. Na2CO3 can be used to remove tannins from tea by forming insoluble complexes with them. This process is known as chelation. The Na2CO3 solution is added to the tea, and the tannins bind to the sodium ions to form sodium tannate. This complex is insoluble in water, so it precipitates out of the solution and can be filtered out. By removing the tannins, the tea becomes less astringent and bitter, and the bioavailability of the proteins and minerals in the tea is increased.