NQO1 activity in murine hepatoma hepa1c1c7 cells by A) licorice extracts from the three major species, GG, GU, and GI in comparison to hops extract. B) LigC/LigF, and LicA from licorice in comparison to XH from hops. C) Licorice bioactive constituents relative to XH, curcumin from turmeric, and sulforaphane from broccoli sprouts. D) Chemopreventive index was calculated as the ratio of a compound's LC50 over its CD value in the NQO1 activity assay. Results are shown as fold induction and are the means of three independent determinations.