The stability and degradation products of polyhydroxy flavonols in boiling water

Polyhydroxy flavonols readily degraded during thermal processing. In this study, the UPLC-Q-tof-MS/MS was applied to explore the stability of dietary polyhydroxy flavonols, myricetin, kaempferol, galangin, fisetin, myricitrin, quercitrin and rutin, in boiling water. The decomposition of flavonols was mainly caused by the heterocyclic ring C opening to form simpler aromatic compounds. The degradation products mainly included 1,3,5-benzenetriol, 3,4,5-trihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid and 2,4,6-trihydroxybenzaldehyde, etc. Compared with myricetin with a pyrogallol-type structure on the ring B, the glycoside in myricitrin slightly affects the stability. However, the glycosides in rutin and quercitrin dramatically improved the stability in water. During the boiling process, flavonols underwent a series of chemical reactions, such as hydroxylation, dehydroxylation, deglycosidation, deprotonation, and C-ring cleavage.

Automated summary

Polyhydroxy flavonols are easily degraded during thermal processing. This study used UPLC-Q-tof-MS/MS to investigate the stability of dietary polyhydroxy flavonols, including myricetin, kaempferol, galangin, fisetin, myricitrin, quercitrin, and rutin, in boiling water. The degradation of flavonols mainly resulted from the opening of the heterocyclic ring C to form simpler aromatic compounds. The degradation products included 1,3,5-benzenetriol, 3,4,5-trihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, and 2,4,6-trihydroxybenzaldehyde, among others. The presence of glycosides in myricitrin slightly affected its stability, while the glycosides in rutin and quercitrin significantly improved their stability in water. During boiling, flavonols underwent various chemical reactions, such as hydroxylation, dehydroxylation, deglycosidation, deprotonation, and C-ring cleavage.