Abstract
This study aimed at investigating the effect of l-ascorbic acid on the Cu2+-induced oxidation of quercetin, within a pH range from 6.7 to 8.3 and temperatures varying from 53 to 87 °C. Initial examinations showed that quercetin degradation obeyed apparent first-order kinetics and it was significantly affected by temperature. Modelling of the effect of l-ascorbic acid by implementing response surface methodology suggested that l-ascorbic acid did not impact quercetin oxidation significantly (p < 0.05) and led to an empirical kinetic model based on temperature (T) and pH. Liquid chromatography–diode array–mass spectrometry analyses revealed the presence of typical quercetin degradation and oxidation products, including protocatechuic acid and 2-(hydroxybenzoyl)-2-hydroxybenzofuran-3(2H)-one. It was concluded that the formation of l-ascorbyl or other radicals (superoxide anion) may be involved in quercetin oxidation and this fact merits further attention to illuminate the possible beneficial or adverse nutritional consequences of such reactions in foods.
Highlights
Quercetin is a ubiquitous flavonoid that belongs to the subclass of flavonols and may be present in several edible fruits and vegetables [1]
Modelling of the effect of L-ascorbic acid by implementing response surface methodology suggested that L-ascorbic acid did not impact quercetin oxidation significantly (p < 0.05) and led to an empirical kinetic model based on temperature (T) and pH
Quercetin oxidative degradation leads in the formation of simple phenolics that possess uniformly low absorbance at this region of the spectrum [14]; quercetin degradation may be effectively monitored by recording A370, without perturbation
Summary
Quercetin is a ubiquitous flavonoid that belongs to the subclass of flavonols and may be present in several edible fruits and vegetables [1]. Quercetin is a well-studied molecule owed to its wide range of bioactivities, including chemopreventive action and beneficial effects against other cardiovascular degenerative diseases [2]. This particular flavonoid is notorious for its powerful antioxidant properties, which, along with other dietary antioxidants such as vitamin C, vitamin E and carotenoids, may provide effective protection against oxidative stress [3]. A quercetin dimer, generated through quercetin oxidation was shown to be a less effective antioxidant [6]. To the contrary, another quercetin oxidation product [2-(hydroxybenzoyl)-2-hydroxybenzofuran-3(2H)-one]
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