Antioxidative Activities of Natural Hydroxy-Bearing Cinnamaldehydes and Cinnamic Acids: A Comparative Study

Purpose: To determine the potent antioxidants among six hydroxy-bearing cinnamaldehyde compounds and their corresponding acids. Methods: The antioxidative activities were evaluated by scavenging 2, 2’-diphenyl-1-picrylhydrazyl (DPPH) free radicals and anti-hemolysis of human red blood cells (RBCs). Fourier transform infrared spectrometry（FT-IR, nuclear magnetic resonance (NMR）and mass spectrometer(MS) evaluations were used to determine the synthesized compounds. Results: The scavenging ability of the compounds on DPPH radicals was in the following rank order: caffeic aldehyde (F) ≈ caffeic acid (C) vitamin C (Vc) o-coumaraldehyde (D) p-coumaric acid (B) p-coumaraldehyde (E) ≈o-coumaric acid. Inhibitory ability against 2′-Azobis(2-methylpropionamidine) dihydrochloride (AAPH)-induced erythrocyte hemolysis was ranked as follows: o-coumaraldehyde (D) p-coumaraldehyde (E) ≈ caffeic aldehyde (F) caffeic acid (C) ≈o-coumaric acid (A) p-coumaric acid (B) Vitamin C. The corresponding inhibition time (tinh ) of D and Vc was 63.6, and 23.7 min, respectively. Conclusion: Cinnamaldehydes demonstrated superior antioxidative activities to their corresponding acids. DPPH scavenging ability correlated directly with the number of hydroxyl groups on the catechol ring while the degree of lipophilicity of the compounds may be proportional to their anti-hemolytic activity.