1,1-Diphenyl-2-picrylhydrazyl (DPPH) is a stable organic free radical. Its solution is characterized by the color of purplish red, and free radical scavengers can pair with its single electron and weaken
the purplish red color, so the DPPH scavenging activity can be determined by the change of its color (Sendra, Sentandreu, & Navarro, 2006).