Chlorophyll:

Chlorophyll is one of the main pigments in olive oil. The chlorophyll content decreases as the fruit matures, so olives picked green produce a greener oil with a "grassy" flavor. According to Apostolos Kirisakis, one of the premier researchers on olive oil components, fresh olive oil contains between 1 to 10 parts per million -- miniscule compared to a portion of spinach. The olive cultivar, weather, pressing method, etc. also determine chlorophyll content. Olives are invariably pressed with some leaves still present so some of the chlorophyll comes from that source. Some producers have been know to deliberately allow leaves in the mill to increase the "grassiness" of the oil. In the light, chlorophyll will promote formation of oxygen radicals and speed up oxidation, but in the dark chlorophyll acts as an antioxidant. In current physiological studies, chlorophyll is broken down in the body and has no effect as an oxidant or antioxidant.