There are many kinds of flavonoids in Traditional Chinese medicine, and the solubility is very different due to the different structure and state. Free aglycones are insoluble or insoluble in water, but easily soluble in organic solvents such as methanol, ethanol, ethyl acetate, ether, or dilute alkali solution. Some planar molecules, such as flavones, flavonols, chalcone, etc., are closely arranged among molecules, with high gravity, and are difficult to dissolve in water. In contrast, non-planar molecules, such as dihydrogen derivatives, have looser intermolecular arrangement and lower gravity, which is conducive to the entry of water molecules and more soluble in water.
The more hydroxyl groups are introduced into a flavonoid, the more soluble it is in water. Hydroxyl groups are methylated or acetylated to increase solubility in organic solvents. After flavonoid compounds are formed into glycosides, solubility in organic solvents decreases, and solubility in water increases accordingly. Moreover, the longer the sugar chain is, the greater the solubility in water will be. In addition, the different location of sugar binding also has a certain effect on the solubility of glycosides in water.
"Loquacious", its 3-0-glucoside is more water-soluble than 7-0-glucoside.
The hydrolytic enzymes of glycosides are often found in plants of Traditional Chinese medicine, so the enzymes must be inactivated when extracting flavonoids. There are many ways to inactivate enzymes, such as extracting with boiling water or ethanol of more than 70%, and adding lime when extracting.
As for the extraction method of flavonoids, according to the understanding of Nanjing Qingyun Biotechnology Xiaobian, due to the rapid development in recent years, many new ideas have been put forward, such as ultrafiltration method, ultrasonic method, supercritical C02 extraction method, etc.