Semicontinuous Fermentation of Cassava by Streptococcus bovis Using Membrane Bioreactor to Produce Lactic Acid

The main objective of this study is to compare the production of lactic acid from cassava by Streptococcus bovis in semicontinuous system with and without membrane separation. Fermentation was run for 72 h, and membrane filtration was performed using micro filtration membrane (MF). The results obtained demonstrate that higher productivity of lactic acid was achieved using fermentation coupled with membrane separation. It was also found that dilution rate (D) of 0.02 h-1 led to slight increase in the lactic acid productivity. Despite this small increase, this investigation shows that membrane separation has the potential to improve the performance of semicontinuous fermentation system.

High Improvement in Lactic Acid Productivity by New Alkaliphilic Bacterium Using Repeated Batch Fermentation Integrated with Increased Substrate Concentration

Optically pure lactic acid (LA) is an important chemical platform that has a wide range of industrial and biotechnological applications. Improved parameters for cost effective LA production are of great interest for industrial developments. In the present study, an alkaliphilic lactic acid bacterium, BoM 1-2, was selected among 369 newly obtained bacterial isolates. It was characterized using API 50 CHL kit and identified asEnterococcus hiraeBoM 1-2 by 16S rRNA gene sequence analysis. Efficient polymer-gradeL-lactic acid production was achieved at pH 9.0 and 40°C. In batch fermentation strategy using 20 g L−1glucose, 19.6 g L−1lactic acid was obtained with volumetric productivity of 2.18 g L−1 h−1. While using 100 g L−1glucose, 96.0 g L−1lactic acid was obtained with volumetric productivity of 1.07 g L−1 h−1.The highest lactic acid concentration of 180.6 g L−1was achieved in multipulse fed batch strategy with volumetric productivity of 0.65 g L−1 h−1. To achieve higher productivity, repeated fermentation processes were applied using the two different strategies. In the first strategy, the lactic acid productivity was increased from 1.97 g L−1 h−1to 4.48 g L−1 h−1when the total of 10 repeated runs were carried out using 60 g L−1glucose, but lactic acid productivity decreased to 2.95 g L−1 h−1using 100 g L−1glucose. In second strategy, repeated fermentation coupled with gradual increase in glucose concentration from 40 to 100 g L−1was conducted for 24 runs. A dramatic increase in LA productivity up to 39.9 g L−1 h−1(18-fold compared to first run) was achieved using 40 g L−1glucose while volumetric productivity ranging between 24.8 and 29.9 g L−1 h−1was achieved using 60–100 g L−1glucose.

Isolation of lignocellulose-derived sugars, co-fermentation of lactic acid bacteria strains, and evaluation of L-lactic acid productivity

High-productivity lactic acid bacteria (LAB) strains were screened and their capability to ferment lignocellulose-derived sugars into lactic acid were evaluated. Fifteen LAB strains were successfully isolated from cow dung, haystack, and sheep manure, respectively. Four relatively good strains were selected based on Gram stain, colony morphology, and catalase activity tests. The four strains and commercial inoculants (Lactobacillus pentosus and Enterococcus faecalis) were used to ferment cellobiose/ glucose/xylose to produce high-purity L-lactic acid. One of the strains (N4) presented the highest production of L-lactic acid after fermentation for 12 h and showed a L-lactic acid production of 15.1 g/L, 18.5 g/L, and 2.8 g/L and a productivity of 1.01 g∙L−1∙h−1, 3.68 g∙L−1∙h−1, and 0.47 g∙L−1∙h−1 by metabolizing cellobiose, glucose, and xylose, respectively. Through a phylogenetic tree analysis, strain N4 was identified as Enterococcus faecium and named Enterococcus faecium N4. Enterococcus faecium N4 has a great potential to ferment lignocellulose-derived sugars into L-lactic acid.