Efficient Production of Plat-form [sic] Organic Acids from Ligocellulosic and Algal Biomass Carbohydrates PDF Download

Author: Shao Heng
Publisher:
ISBN:
Category : Biomass conversion
Languages : en
Pages : 155

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Book Description
Lignocellulosic biomass, such as agricultural and forest residues, is an inexpensive feedstock for bio-based products. Cost-effective production of bio-based products from lignocellulosic biomass requires simple conversion steps to break down carbohydrates to component mono-saccharides, and fermentation and/or chemical conversion of the sugars to final products. Lactic acid is one potential value-added product that could be produced economically from lignocellulosic biomass, if both the hexose and pentose sugars - derived from the cellulose and hemicellulose fractions, respectively - can be utilized completely with high efficiency. However, most natural lactic acid bacteria (LAB) cannot utilize xylose efficiently: the isomerization of xylose to xylulose in the phosphoketolase (PK) pathway constitutes a bottleneck step. Fortunately, it is possible to overcome this bottleneck via exogenous isomerization of xylose, thus allowing the microorganism to utilize xylulose as a viable alternative substrate for xylose. In this study, it has been demonstrated that this new approach could significantly improve the lactic acid yield. Lactobacillus pentosus and Lactobacillus casei (subspecies rhamnosus) were used in the fermentation of hexose, xylose, and xylulose to lactic acid. With L. pentosus, no preferential utilization of xylulose over xylose was seen, when both sugars were present in the medium. Sodium tetraborate and isomerization buffers, added to the fermentation broth to promote exogenous isomerization of xylose, strongly inhibited the growth of L. pentosus, which, in turn, led to poor utilization of xylulose. In contrast, with L. casei more robust growth and superior lactic acid yield were achieved from both glucose and xylulose, following exogenous isomerization with negligible xylose left at the end of fermentation. These results confirmed that, unlike L. pentosus, the exogenous isomerization additives do not inhibit L. casei and it is possible to maximize the utilization of both C6 and C5 sugars for lactic acid production by L. casei via the approach proposed in this study. In addition to lactic acid, succinic acid is a very important intermediary chemical building block that could constitute a viable alternative for petroleum-based bulk chemical precursors. Bio-based succinic acid produced from lignocellulosic biomass via microbial fermentation of the carbohydrate-derived sugars has the potential to reduce the cost of the product. However, inhibitors generated during the pretreatment and saccharification of biomass, especially lignin-derived phenolic compounds, could adversely affect the growth of succinic acid-producing microbes. Actinobacillus succinogenes - a promising strain that could be utilized for commercial succinic acid production - is strongly inhibited by the toxic compounds generated during pretreatment. In this study, some inexpensive commercially available enzymes were used to digest the chemical bonds between the glycoprotein in the cell wall and the polysaccharides of microalgae, which enabled the release of intracellular lipids and sugars. After removing the lipids using solvent extraction, the residue of the microalgae and the sugars remaining in the solution were successfully used as carbon and nitrogen sources for A. succinogenes fermentation for producing succinic acid. As such, the new process for fractionating microalgae developed in this study could significantly reduce the production costs of lipids and other bio-based products, because it allows the maximum utilization of every component in the micro-algal biomass.