Integral kinetic model for studying quercetin degradation and oxidation as affected by cholesterol during heating

Stability of iron-quercetin complexes in synthetic wine under in vitro digestion conditions

Wine is a dietary source of polyphenolic compounds with reported health benefits when moderately consumed. Several of these compounds can associate with metals forming complexes. Therefore, this work was conducted to reach a better understanding of the nature and chemical stability of wine-derived Fe(3+)-quercetin complexes in a digestion model. The stability of the complexes in a synthetic (simulated) wine was studied before and after in vitro gastric and intestinal digestions by high-performance liquid chromatography (HPLC) with UV-Vis detection. Metal determination was performed by atomic absorption spectrometry (ETAAS) to evaluate possible dissociation of complexes. During HPLC analysis all peaks eluted from the chromatographic column were collected, acidified, and analyzed by ETAAS. The results showed that complexes remain substantially stable after gastric digestion conditions, with recoveries of 84% to 90%. Although metal complexes were partially degraded during intestinal digestion, 41% to 45% of the Fe(3+)-quercetin complexes was recovered.

PRACTICAL APPLICATION

This work reveals the chemical stability of Fe3+–quercetin complexes in synthetic wines after an in vitro gastrointestinal digestion. The knowledge of this process would be useful to understand the bioavailability of these compounds.

Thermally accelerated oxidative degradation of quercetin using continuous flow kinetic electrospray-ion trap-time of flight mass spectrometry

Thermally accelerated oxidative degradation of aqueous quercetin at pH 5.9 and 7.4 was kinetically measured using an in-house built online continuous flow device made of concentric capillary tubes, modified to fit to the inlet of an electrospray ionization-ion trap-time-of-flight-mass spectrometer (ESI-IT-TOF-MS). Time-resolved mass spectral measurements ranging from 2 to 21 min were performed in the negative mode to track intermediate degradation products and to evaluate the degradation rate of the deprotonated quercetin ion, [Q-H](-). Upon heating solutions in the presence of dissolved oxygen, degradation of [Q-H](-) was observed and was accelerated by an increase in pH and temperature. Regardless of the condition, the same degradation pathways were observed. Degradation mechanisms and structures were determined using higher order tandem mass spectrometry (up to MS(3)) and high mass accuracy. The observed degradation mechanisms included oxidation, hydroxylation, and ring-cleavage by nucleophilic attack. A chalcan-trione structure formed by C-ring opening after hydroxylation at C2 was believed to be a precursor for other degradation products, formed by hydroxylation at the C2, C3, and C4 carbons from attack by nucleophilic species. This resulted in A-type and B-type ions after cross-ring cleavage of the C-ring. Based on time of appearance and signal intensity, nucleophilic attack at C3 was the preferred degradation pathway, which generated 2,4,6-trihydroxymandelate and 2,4,6-trihydroxyphenylglyoxylate ions. Overall, 23 quercetin-related ions were observed.