Chlorophyll is a green pigment found in plants that has antioxidant activity.

In addition to giving green vegetables their color, chlorophyll is a proven anti-mutagen that guards against the alteration of cellular DNA. Chlorophyll is believed by some researchers to block initiation, the first step in the transformation of normal cells to cancerous ones.

References

Waters MD, Stack HF, Jackson MA, Brockman HE, De Flora S Activity profiles of antimutagens: in vitro and in vivo data.Mutat Res 1996 Feb 19;350(1):109-29).