The antioxidative effects in vegetables were reported to be mostly due to phenolic compounds.The effective antioxidant activity in sweet potato extract due to the synergistic effect of phenolic components such as chlorogenic acid, isochlorogenic acid with amino acids. A recent study found that phenols, flavonoids, and anthocyanins of sweet potato flours were positively correlated with the DPPH radical scavenging effects (Huang et al., 2006).