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

Abstract

Phragmites australis straw (PAS) is an abundant and renewable wetland lignocellulose. Bacillus coagulans IPE22 is a robust thermophilic strain with pentose-utilizing capability and excellent resistance to growth inhibitors. This work is focused on the process study of lactic acid (LA) production from P. australis lignocellulose which has not been attempted previously. By virtue of thermophilic feature of strain IPE22, two fermentation processes (i.e., separated process and integrated process), were developed and compared under non-sterilized conditions. The integrated process combined dilute-acid pretreatment, hemicellulosic hydrolysates fermentation, and cellulose utilization. Sugars derived from hemicellulosic hydrolysates and cellulose enzymatic hydrolysis were efficiently fermented to LA in a single vessel. Using the integrated process, 41.06 g LA was produced from 100 g dry PAS. The established integrated process results in great savings in terms of time and labor, and the fermentation process under non-sterilized conditions is easy to scale up for economical production of lactic acid from PAS.Obviously, SSCF is at the heart of the integrated process and the robust thermophilic strain with pentose-utilizing capability and excellent resistance to growth inhibitors is essential. Processes 2018, 6, x FOR PEER REVIEW 2 of 9 Author Contributions: Conceptualization, Y.Z.; methodology, M.L. and T.N.; validation, Z.N.; writing-original draft preparation, Z.N.; writing-review and editing, Y.Z.; funding acquisition, Y.Z. and Z.N.

L-(+)-Lactic Acid from Reed: Comparing Various Resources for the Nutrient Provision of B. coagulans

“…However, since no standard has yet been provided for P. australis by the National Institute of Standards and Technology (NIST), method errors cannot be excluded [38]. Nevertheless, as can be seen in Table 1, our data lies well within the range of earlier reported values concerning the lignocellulose composition of P. australis analyzed according to NREL guidelines [14,39]. Sodium hydroxide (NaOH) and sulfuric acid (H 2 SO 4 ) were chosen as chemical agents for affecting the lignocellulose structure of reed, employing concentrations ranging from 0.5%-4%.…”

“…The LA titer achieved in this study is comparable to results from other studies describing the fermentation of pretreated reed. Besides SSF trials, Zhang et al [14] conducted a batch experiment on the filtrated supernatant of acid pretreated reed. Modified MRS medium was added as a rather costly source of nutrients, containing various compounds such as peptone, beef extract and yeast extract.…”

“…Regarding reed, few studies focus on the production of LA: Perttunen et al [13] utilized hemicellulose liquor from reed, which occurred as a by-product in the pulping process for fermentation by L. pentosus. Zhang et al [14] pretreated reed with sulfuric acid and compared separate and integrated fermentation strategies by employing B. coagulans IPE22. The best result was attained by a simultaneous saccharification and co-fermentation approach (SSCF), leading to an LA-titer of 35.05 g L −1 after a course of 55 h [14].…”

“…Zhang et al [14] pretreated reed with sulfuric acid and compared separate and integrated fermentation strategies by employing B. coagulans IPE22. The best result was attained by a simultaneous saccharification and co-fermentation approach (SSCF), leading to an LA-titer of 35.05 g L −1 after a course of 55 h [14]. Reports on other grassy crops like corn stover are more frequent in the literature.…”

Heterologous expression and biochemical characterization of a thermostable xylulose kinase from Bacillus coagulans IPE22

“…However, its thermo‐stability and kinetic parameters have not been evaluated. In our previous study, the strain B. coagulans IPE22 was isolated and displayed outstanding feature to ferment xylose at high temperatres . Inuterestingly, B. coagulans IPE22 metabolizes xylose faster than glucose and the strain's growth can be improved significantly in xylose medium .…”