Monascus purpureus CWT715 is a strain of red yeast rice that can scavenge free radicals when fermented with residual sorghum from Kinmen sorghum liquor waste (KSL). This study used KSL as the primary nutrient source in the production of metabolites from M. purpureus CWT715, whose antioxidant activity was tested on mouse embryonic liver cells (BNL CL.2). Image analysis of a comet assay was performed to evaluate DNA strand breaks, and thiobarbituric acid-reactive substance (TBARS) analysis was used to measure lipid peroxidation. The results demonstrate that, compared with the control, M. purpureus CWT715 pretreated with 100 mu g/ml of fermentation broth reduced DNA damage by 61% and lipid peroxidation by 51%. Thus, KSL shows considerable potential as an antioxidant in functional foods. This is the first report on the use of Monascus species in the conversion of KSL to produce antioxidants. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.