Copper-Induced Interactions of Caffeic Acid and Sinapic Acid to Generate New Compounds in Artificial Biological Fluid Conditions

Active ingredients may be ingested through foods, and they can cause several interactions in the human body. Although drug–drug or drug–food interactions are evaluated before the approval of medicines, several functional food interactions are not well-documented because of the wide range of possible combinations of interactions. In this study, we examined the chemical reactions between hydroxycinnamic acids (HCAs), a group of polyphenols, and metal ions in artificial gastric juice or artificial intestinal fluid. Caffeic acid (CaA) and sinapic acid (SA) reacted with copper ions under artificial intestinal fluid conditions and produced new compounds. The triple interactions of CaA or SA with iron and copper ions were also examined. Relative to the initial compounds, CaA and SA derivatives produced by condensation exhibited an increased antioxidant and a decreased prooxidant activity. This study revealed a new food ingredient interaction pattern in which new compounds are produced under biological conditions.