d- and l-lactic acid production from fresh sweet potato through simultaneous saccharification and fermentation

•A method for l- and d-lactic acid production from fresh sweet potato.•The method produced l-lactic acid at 122.91–198.32gL−1 with yields over 90% (w/w).•The method produced d-lactic acid at 122.49–186.40gL−1 with yields of 90.11–84.92% (w/w).•This study would benefit the tuber and root-based lactic acid industries without alteration of plant equipment. 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 136.36–219.51gL−1, yields of 90.13–91.17% (w/w) and productivities of 3.41–3.83gL−1h−1 were obtained with lactic acid concentrations as high as 198.32gL−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 2.55–3.11gL−1h−1 with a maximum concentration of 186.40gL−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.