Conversion of rice straw to bio-based chemicals: an integrated process using Lactobacillus brevis

Abstract

Commercialization of lignocellulosic biomass as a feedstock for bio-based chemical production is problematic due to the high processing costs of pretreatment and saccharifying enzymes combined with low product yields. Such low product yield can be attributed, in large part, to the incomplete utilization of the various carbohydrate sugars found in the lignocellulosic biomass. In this study, we demonstrate that Lactobacillus brevis is able to simultaneously metabolize all fermentable carbohydrates in acid pre-processed rice straw hydrolysate, thereby allowing complete utilization of all released sugars. Inhibitors present in rice straw hydrolysate did not affect lactic acid production. Moreover, the activity of exogenously added cellulases was not reduced in the presence of growing cultures of L. brevis. These factors enabled the use of L. brevis in a process termed simultaneous saccharification and mixed sugar fermentation (SSMSF). In SSMSF with L. brevis, sugars present in rice straw hydrolysate were completely utilized while the cellulase maintained its maximum activity due to the lack of feedback inhibition from glucose and/or cellobiose. By comparison to a sequential hydrolysis and fermentation process, SSMSF reduced operation time and the amount of cellulase enzyme necessary to produce the same amount of lactic acid.

A Process Study of Lactic Acid Production from Phragmites australis Straw by a Thermophilic Bacillus coagulans Strain under Non-Sterilized Conditions

“…The slurry of pretreated lignocellulose is directly fermented in a single vessel. Obviously, SSCF is at the heart of the integrated process and the robust thermophilic strain is also essential to establish the economical way for bio-refinery [13].…”

“…Obviously, SSCF is at the heart of the integrated process and the robust thermophilic strain is also essential to establish the economical way for bio-refinery [13]. Production of LA through integrated process was first proposed using Lactobacillus brevis [13]. However, L. brevis was mesophilic bacteria, and produced LA by heterofermentation pathway.…”

“…As a result, LA of 35.05 g/L was attained using mMRS as nutrient supplementation, and the LA yield was 41.06 g per 100 g dry PAS, respectively. Production of LA through integrated process was first proposed using Lactobacillus brevis [13]. However, L. brevis was mesophilic bacteria, and produced LA by heterofermentation pathway.…”

“…Simultaneous saccharification and fermentation (SSF) or simultaneous saccharification and co-fermentation (SSCF) is an effective way to eliminate feedback inhibition of cellulase hydrolysis, since the released glucose could be rapidly fermented to product [7]. Recently, a new integrated process was applied to produce lignocellulose-based biochemical [3,[11][12][13]. Figure 1 shows a schematic diagram of the conventional separated process and the new integrated process.…”

Engineered biosynthesis of biodegradable polymers

“…But in many LAB, sugars are sequentially metabolized and the utilization of glucose represses the utilization of other sugars [74]. A few LAB strains have demonstrated simultaneous consumption of lignocellulose-derived sugars, e.g., Lactobacillus brevis [49,75], L. plantarum [49] and novel isolated LAB strain Enterococcus mundtii [2].…”