Improvement of l-lactic acid productivity from sweet sorghum juice by repeated batch fermentation coupled with membrane separation

In order to efficiently produce l-lactic acid from non-food feedstocks, sweet sorghum juice (SSJ), which is rich of fermentable sugars, was directly used for l-lactic acid fermentation by Lactobacillus rhamnosus LA-04-1. A membrane integrated repeated batch fermentation (MIRB) was developed for productivity improvement. High-cell-density fermentation was achieved with a final cell density (OD620) of 42.3, and the CCR effect was overcomed. When SSJ (6.77 g L−1 glucose, 4.51 g L−1 fructose and 50.46 g L−1 sucrose) was used as carbon source in MIRB process, l-lactic acid productivity was increased significantly from 1.45 g L−1 h−1 (batch 1) to 17.55 g L−1 h−1 (batch 6). This process introduces an effective way to produce l-lactic acid from SSJ.