4. Conclusion
We prepared 20 kinds of CA-Pro-Xaa-NH2 to show that proline had an important role in providing excellent antioxidative activity in histidine-containing CA dipeptides. Five kinds of CA-Pro-Xaa-NH2, 11, 15, 10, 2 and 20, showed slightly higher % RSA than 7 (CA-Pro-His-NH2). However, considering the results from the DPPH radical-scavenging test and lipid peroxidation inhibition test, 7 (CA-Pro-His-NH2) was the best antioxidant. From this study, we demonstrated that proline gives a critical effect on the enhanced antioxidant activity of CA-Pro-His-NH2. In addition, we found that the imidazole ring of histidine could have an optimised structure with proline to exert synergistic antioxidative activity. Further study on the structural benefits of CA-Pro-His-NH2 is under way.