Interactions of cinnamaldehyde and its metabolite cinnamic acid with human serum albumin and interference of other food additives

•Binding ability of cinnamaldehyde (CNMA) is stronger than cinnamic acid (CA).•STD-NMR and docking studies indicated CNMA and CA bound to site I and site II of HSA, respectively.•Microenvironments of amino acid residues and secondary structure of HSA change with the addition of ligands.•Four kinds of food additives disturb the binding constant of the two systems. Considering the adverse effect of food additives on humans, thorough research of their physiological effects at the molecular level is important. The interactions of cinnamaldehyde (CNMA), a food perfume, and its major metabolite cinnamic acid (CA) with human serum albumin (HSA) were examined by multiple-spectroscopies. NMR analysis revealed CNMA and CA both bound to HSA, and STD-NMR experiments established CNMA and CA primarily interacted with site I and site II of HSA, respectively. The ligands caused strong quenching of HSA fluorescence through a static quenching mechanism, with hydrophobic and electrostatic interaction between CNMA/CA and HSA, respectively. UV–vis absorption and CD results showed ligands induced secondary structure changes of HSA. Binding configurations were proved by docking method. Furthermore, binding constants of CNMA/CA–HSA systems were influenced by the addition of four other food additives. These studies have increased our knowledge regarding the safety and biological action of CNMA and CA.