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Exploration of reaction mechanisms of anthocyanin degradation in a roselle extract through kinetic studies on formulated model media
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Effect of oxygen, polyphenols and metals was studied on degradation of delphinidin and cyanidin 3-O-sambubioside of Hibiscus sabdariffa L. Experiments were conducted on aqueous extracts degassed or not, an isolated polyphenolic fraction and extract-like model media, allowing the impact of the different constituents to be decoupled. All solutions were stored for 2 months at 37 degrees C. Anthocyanin and their degradation compounds were regularly HPLC-DAD-analyzed. Oxygen concentration did not impact the anthocyanin degradation rate. Degradation rate of delphinidin 3-O-sambubioside increased 6-fold when mixed with iron from 1 to 13 mg.kg(-1) but decreased with chlorogenic and gallic acids. Degradation rate of cyanidin 3-O-sambubioside was not affected by polyphenols but increased by 3-fold with increasing iron concentration with a concomitant yield decrease of scission product, protocatechuic acid. Two pathways of degradation of anthocyanins were identified: a major metal-catalyzed oxidation followed by condensation and a minor scission which represents about 10% of degraded anthocyanins.
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