Percorrer por autor "Martinez, Alfredo"
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- D-Lactic acid production from Cistus ladanifer residues: Co-fermentation of pentoses and hexoses by Escherichia coli JU15Publication . Alves Ferreira Caturra, Júnia Aparecida; Carvalheiro, Florbela; Duarte, Luís C.; Ferreira, Ana R. P.; Martinez, Alfredo; Pereira, Helena; Fernandes, M. C.ABSTRACT: n this study, glucan-rich solids, and xylose-rich hydrolysates obtained from Cistus ladanifer distillery residues (CLR) were used for D-lactic acid (D-LA) production by the D-lactogenic Escherichia coli strain JU15. Firstly, hemicellulosic hydrolysates obtained by the autohydrolysis process were submitted to dilute sulfuric acid catalysed post-hydrolysis. The influence of operational conditions on oligosaccharides hydrolysis was assessed by the combined severity parameter (CS) in the range of 1.1-2.3. The optimum post-hydrolysis conditions were found for CS of 1.6 (300 mM H2SO4, 15 min, 121 degrees C). Subsequent detoxification procedures on post hydrolysed liquors were carried out, where 9.1% (w/v) powdered activated charcoal enabled a full removal of furfural, 5-hydroxymethylfurfural (HMF), and phenolic compounds together with a reduction of acetic acid (37%), and formic acid (27%). Diverse fermentation modes using detoxified and non-detoxified hydrolysates, as well using previously NaOH delignified glucan-rich solids alone (SHF or SSF) or together with pentoses liquors (SSCF) (5% loading) were performed. For all the tested conditions, both hemicellulose-and cellulose-derived sugars can be efficiently used as the carbon source to produce D-lactic acid by E. coli JU15 with a D-LA yield always surpassing 92 g(D-LA)/100 g sugars.
- D-lactic acid production from hydrothermally pretreated, alkali delignified and enzymatically saccharified rockrose with the metabolic engineered Escherichia coli strain JU15Publication . Fernandes, M. C.; Alves Ferreira Caturra, Júnia Aparecida; Duarte, Luís C.; Pereira, Helena; Carvalheiro, Florbela; Martinez, AlfredoABSTRACT: Rockrose lignocellulosic residues (RR) were selectively fractionated for hemicellulose separation using autohydrolysis, followed by an alkaline treatment to solubilize the lignin. The cellulose-enriched solids were used to study the effect of solid loading (SL: 2-10%) and enzyme dosage (ED: 6.34-23.66 FPU/g dry biomass) on saccharification using a Doehlert experimental design, followed by fermentation with the metabolic engineered Escherichia coli strain JU15 to produce D-lactic acid (DLA). Pretreatment increased glucan content and enzymatic digestibility up to 84%. A significant positive effect of SL and ED was found for glucose production, but SL negatively impacted glucose yield. DLA concentrations and productivity varied from 8.85 to 32.98 g/L and 1.11 to 2.17 g/(Lh), respectively. Overall process efficiency strongly depended on saccharification yield and varied from 33 to 71%. These results indicate that sequential autohydrolysis, delignification, and fermentation of RR may be a potential relevant strategy for D-lactic production in the biorefinery framework.