Abstract: In this paper, the antioxidant and antiproliferative activity of a carotenoid and isoprenoid quinone-rich extract (B7CIQE) from Rhodococcus sp. B7740 were determined. The in vitro antioxidant activity was evaluated by β-carotene bleaching, lipid peroxidation inhibition, protein oxidation inhibition and oxidative DNA cleavage inhibition assays, and the antiproliferative activity against HepG2 human liver cancer and KB human oral cancer cells and the cellular antioxidant activity were investigated as well. Three common carotenoids from higher plants, β-carotene, lutein and lycoypene, were used as controls. The inhibition rate of β-carotene oxidation by different antioxidants was in the decreasing order of B7CIQE (70.20%) > butylated hydroxytoluene (66.70%) > epigallocatechin gallate (17.80%) > lycopene (1.90%). Peanut oil with the addition of B7CIQE had the lowest initial oxidation temperature (175 ℃) followed by β-carotene (165 ℃), lutein (162 ℃) and lycopene (160 ℃). The inhibition rate of protein oxidation was in the decreasing order of B7CIQE (25.75%) > β-carotene (24.97%) > lutein (17.94%) > lycopene (10.40%). The median effective concentration (EC50) against HepG2 cells was in the decreasing order of lutein (20.86 μg/mL) < β-carotene (124.88 μg/mL) < B7CIQE (126.34 μg/mL) < lycopene (139.24 μg/mL), whereas the EC50 against KB cells decreased in the following order: B7CIQE (25.14 μg/mL) < lutein (64.29 μg/mL) < lycopene (69.87 μg/mL) < β -carotene (149.16 μg/mL). These results demonstrated that B7CIQE had superior antioxidant activity and antiproliferative effect when compared with plant-derived carotenoids.

Key words: microbial carotenoids, microbial isoprenoid quinones, Rhodococcus sp. B7740, antioxidant activity, antiproliferative activity