2.4. Measurement of free radical scavenging activity
The percentage of radical scavenging activity (% RSA) was determined by measuring the degree of decrease in the absorbance of the DPPH solution after adding the antioxidant. Methanolic DPPH solution (0.1 mM, 1480 μL) was mixed with 20 μL of 1.85 mM CA-Pro-Xaa-NH2 or CA dissolved in methanol in a 1.5-mL Eppendorf tube. The absorbance was measured at 516 nm after 10 min. The percentage of RSA was calculated through the following equation: