A reversed-phase high-performance liquid chromatography method for the analysis of malic, lactic, acetic, citric, succinic, propionic and butyric acids, during the incubation of Bacillus spp., was developed. All samples taken from cultivation were centrifuged (20 min, 11,500g at 5 degrees C) and filtered through a 0.45 mu m membrane filter before injection. A programme pumping phosphate buffer at pH 2.50 and acetonitrile was used to separate the compounds on a C-18 column. Various parameters affecting analysis were optimized to take less than 30 min with a good linearity (R > 0.999). Bacillus licheniformis or B. subtilis, isolated from Daqu, was inoculated to ferment a liquid culture of Daqu. Growth of bacteria and organic acid production during the fermentation were investigated. Although there were no significant differences in the production of organic acids between B. licheniformis and B. subtilis during the first 8 h, significant differences in the production rates of organic acids, except for citric acid, were observed between B. licheniformis and B. subtilis from 8 to 48 h, with the final concentration of each organic acid varying. Copyright (C) 2013 The Institute of Brewing & Distilling
