Assembly of mutations for improving thermostability of <Emphasis Type="Italic">Escherichia coli</Emphasis> AppA2 phytase |
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Authors: | Moon-Soo Kim Jeremy D Weaver Xin Gen Lei |
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Institution: | (1) Agrotechnology and Food Sciences Group, Wageningen University and Research Centre, P.O. Box 17, 6700 AA Wageningen, The Netherlands;(2) Purac Biochem, P.O. Box 21, 4200 AA Gorinchem, The Netherlands |
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Abstract: | Conventional processes for lignocellulose-to-organic acid conversion requires pretreatment, enzymatic hydrolysis, and microbial
fermentation. In this study, lime-treated wheat straw was hydrolyzed and fermented simultaneously to lactic acid by an enzyme
preparation and Bacillus coagulans DSM 2314. Decrease in pH because of lactic acid formation was partially adjusted by automatic addition of the alkaline substrate.
After 55 h of incubation, the polymeric glucan, xylan, and arabinan present in the lime-treated straw were hydrolyzed for
55%, 75%, and 80%, respectively. Lactic acid (40.7 g/l) indicated a fermentation efficiency of 81% and a chiral l(+)-lactic acid purity of 97.2%. In total, 711 g lactic acid was produced out of 2,706 g lime-treated straw, representing
43% of the overall theoretical maximum yield. Approximately half of the lactic acid produced was neutralized by fed-batch
feeding of lime-treated straw, whereas the remaining half was neutralized during the batch phase with a Ca(OH)2 suspension. Of the lime added during the pretreatment of straw, 61% was used for the neutralization of lactic acid. This
is the first demonstration of a process having a combined alkaline pretreatment of lignocellulosic biomass and pH control
in fermentation resulting in a significant saving of lime consumption and avoiding the necessity to recycle lime. |
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Keywords: | Lime-treated wheat straw Simultaneous saccharification and fermentation Lactic acid Calcium hydroxide pH control |
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