Flavanoid ring structure

Figure 6 The flavanoid ring structure on which condensed tannins are based...

Pongamia pinnata were rich in flavanoids compared with other semi-mangroves. Up to now, more than 50 flavaonoids have been isolated from Pongamia pinnata with the structural characteristic of furan or pyran ring parallelized with the skeleton of flavaonoids. Partial flavaonoids including flavone, flavonone, chalcone, dihydrochalcone were listed in Figure 3. 

To preserve beer colloidal stability, brewers usually remove haze-active materials [34]. To get rid of haze-active proteins, precipitation with tannic acid, hydrolysis with papain and adsorption to bentonite [35] or silica gel [36, 37] are very effective, but unfortunately in some cases, such procedures also remove foam proteins. To remove haze-active polyphenols, the most usual way is adsorption to polyvinylpolypyrrolidone-PVPP. Because of the structural analogy between these compounds and proline [38], pyrrolidone rings bind polymerized flavanoids through hydrogen and ionic bonds. 

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