Abstract
Bioactive compounds in fruit and vegetables influence each other’s antioxidant activity. Pure standards, and mixtures of the common plant compounds, namely ascorbic acid, 5-caffeoylquinic acid, and quercetin-3-rutinoside (sum 0.3 mM), in the presence and absence of iron, were analyzed pre- and post-thermal processing in an aqueous solution. Antioxidant activity was measured by total phenolic content (TPC), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (TEAC) radical-scavenging assays. Ionic ferrous iron (Fe2+) and ferric iron (Fe3+) were measured photometrically. For qualification and quantification of reaction products, HPLC was used. Results showed that thermal processing does not necessarily lead to a decreased antioxidant activity, even if the compound concentrations decreased, as then degradation products themselves have an antioxidant activity. In all used antioxidant assays the 2:1 ratio of ascorbic acid and 5-caffeoylquinic acid in the presence of iron had strong synergistic effects, while the 1:2 ratio had strong antagonistic effects. The pro-oxidant iron positively influenced the antioxidant activity in combination with the used antioxidants, while ferrous iron itself interacted with common in vitro assays for total antioxidant activity. These results indicate that the antioxidant activity of compounds is influenced by factors such as interaction with other molecules, temperature, and the minerals present.
Highlights
In the human diet, many different plant-based products are consumed throughout the day, even within the same meal
In pomegranate–nectarine juice, between the natural phenols and ascorbic acid, the same interaction was found, while in grape juice increasing antagonistic effects by increasing ascorbic acid concentration were observed [36]. These results suggest that mixtures of ascorbic acid, 5-caffeoylquinic, and quercetin-3-rutinoside achieve the highest
Based on the above-described findings, the antioxidant activity (AOA) of ascorbic acid, 5-caffeoylquinic acid, and quercetin-3-rutinoside was influenced by their molecule structure, concentration, ratio, and interactions with other antioxidants and iron
Summary
Many different plant-based products are consumed throughout the day, even within the same meal. Many secondary plant metabolites are potent antioxidants, which help to protect biological systems from reactive oxygen species (ROS) and reactive nitrogen species (RNS) [3]. These bioactive compounds can interact with each other before consumption, resulting in numerous subsequent reaction products or complexes. A major bioactive compound, found in numerous plant species, is 5-caffeoylquinic acid (chlorogenic acid), a hydroxycinnamic acid ester of caffeic acid and quinic acid It can form ferric iron complexes, which are generally associated with a reduced absorption of non-heme iron in humans [5,6]. Iron has the capacity to accept and donate electrons readily
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