Impact of selected dietary polyphenols on caramelization in model systems

Abstract

Polyphenols are nowadays commonly consumed as dietary antioxidants which may contribute to health benefits associated with a lower risk of cardiovascular disease and cancer. Caramelization products which contribute to food color and flavor are also reported to possess antioxidant activities. In this research, six kinds of polyphenols (phloretin, naringenin, quercetin, epicatechin, rosmarinic acid, chlorogenic acid) belonging to different polyphenol categories were investigated of their effects on the caramelization process of fructose. The fructose solution with or without polyphenol was heated at 120 °C for two hours at neutral (pH=7) or alkaline conditions (pH=10). The browning intensity (A420) of the caramelization product was found to be elevated by addition of polyphenols, especially phloretin, naringenin and epicatechin. Liquid chromatography analysis of the intermediate degradation products at 280 nm indicated that no detectable amount of furfural or 5-(hydroxymethyl)furfural was formed from fructose degradation under the conditions used. The amount of polar degradation intermediates was much higher at alkaline condition and significantly decreased upon addition of chlorogenic acid and rosemarinic acid. Besides, naringenin and phloretin were greatly consumed during caramelization process, possibly forming complex with sugar degradation intermediates. The antioxidative activity of the caramelization products was quantified by Trolox-equivalent antioxidant capacity assay. The results showed that all polyphenols tested significantly increased the antioxidant capacity of the caramelization products. When comparing the value with that of polyphenol equivalent heated alone, results were variable depending on both the pH and the polyphenol category, indicating the complexity of the interaction between polyphenol and sugar during caramelization process worthy further examination in order to provide constructive advice upon food processing.