The immediate precursor of L-ascorbic acid, or vitamin C, is 2-keto-L-gulonic acid (2-KLG). This is commonly produced commercially by Ketogulonicigenium vulgate and Bacillus megaterium, using corn steep liquor powder (CSLP) as an organic nitrogen source. In this study, the effects of the individual CSLP components (amino acids, vitamins, and metal elements) on 2-KLG production were evaluated, with the aim of developing a complete, chemically defined medium for 2-KLG production. Forty components of CSLP were analyzed, and key components were correlated to biomass, 2-KLG productivity, and consumption rate of L-sorbose. Glycine had the greatest effect, followed by serine, biotin, proline, nicotinic acid, and threonine. The combination of 0.28 g L(-1) serine, 0.36 g L(-1) glycine, 0.18 g L(-1) threonine, 0.28 g L(-1) proline, 0.19 g L(-1) nicotinic acid, and 0.62 mg L(-1) biotin in a chemically defined medium produced the highest maximum biomass concentration (4.2 x 10(9) cfu mL(-1)), 2-KLG concentration (58 g L(-1)), and yield (0.76 g g(-1)) after culturing for 28 h. (C) 2010 Elsevier Ltd. All rights reserved.