D- and L-lactic acid production from fresh sweet potato through simultaneous saccharification and fermentation

The aim of this study was to develop a bioprocess for L- and D-lactic acid production from raw sweet potato through simultaneous saccharification and fermentation by Lactobacillus paracasei and Lactobacillus coryniformis, respectively. The effects of enzyme and nitrogen source concentrations as well as of the ratio of raw material to medium were investigated. At dried material concentrations of 136.36-219.51 g L-1, yields of 90.13-91.17% (w/w) and productivities of 3.41-3.83 g L-1 h(-1) were obtained with lactic acid concentrations as high as 198.32 g L-1 for L-lactic acid production. In addition, D-lactic acid was produced with yields of 90.11-84.92% (w/w) and productivities of 2.55-3.11 g L-1 h(-1) with a maximum concentration of 186.40 g L-1 at the same concentrations of dried material. The simple and efficient process described in this study will benefit the tuber and root-based lactic acid industries without requiring alterations in plant equipment. (C) 2013 Elsevier B.V. All rights reserved.