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Biomedical subjects

N P Nghiem

Publications and source records attributed to N P Nghiem.

4 recordsLinked to original sources
PubMed2000

Ethanol production from glucose and xylose by immobilized Zymomonas mobilis CP4(pZB5).

Fermentation of glucose-xylose mixtures to ethanol was investigated in batch and continuous experiments using immobilized recombinant Zymomonas mobilis CP4(pZB5). This microorganism was immobilized by entrapment in kappa-carrageenan beads having a diameter of 1.5-2.5 mm. Batch experiments showed that the immobilized cells cofermented glucose and xylose to ethanol and that the presence of glucose improved the xylose utilization rate. Batch fermentation of rice straw hydrolysate containing 76 g/L of glucose and 33.8 g/L of xylose gave an ethanol concentration of 44.3 g/L after 24 h, corresponding to a yield of 0.46 g of ethanol/g of sugars. Comparable results were achieved with a synthetic sugar control. Continuous fermentation experiments were performed in a laboratory-scale fluidized-bed bioreactor (FBR). Glucose-xylose feed mixtures were pumped through the FBR at residence times of 2-4 h. Glucose conversion to ethanol was maintained above 98% in all experiments. Xylose conversion to ethanol was highest at 91.5% for a feed containing 50 g/L of glucose and 13 g/L of xylose at a dilution rate of 0.24/h. The xylose conversion to ethanol decreased with increasing feed xylose concentration, dilution rate, and age of the immobilized cells. Volumetric ethanol productivities in the range of 6.5-15.3 g/L.h were obtained. The improved productivities achieved in the FBR compared to other bioreactor systems can help in reducing the production costs of fuel ethanol from lignocellulosic sugars.

Aldose-Ketose Isomerases↗
PubMed1999

Ethanol production from corn starch in a fluidized-bed bioreactor.

The production of ethanol from industrial dry-milled corn starch was studied in a laboratory-scale fluidized-bed bioreactor using immobilized biocatalysts. Saccharification and fermentation were carried out either simultaneously or separately. Simultaneous saccharification and fermentation (SSF) experiments were performed using small, uniform kappa-carrageenan beads (1.5-2.5 mm in diameter) of co-immobilized glucoamylase and Zymomonas mobilis. Dextrin feeds obtained by the hydrolysis of 15% drymilled corn starch were pumped through the bioreactor at residence times of 1.5-4 h. Single-pass conversion of dextrins ranged from 54-89%, and ethanol concentrations of 23-36 g/L were obtained at volumetric productivities of 9-15 g/L-h. Very low levels of glucose were observed in the reactor, indicating that saccharification was the rate-limiting step. In separate hydrolysis and fermentation (SHF) experiments, dextrin feed solutions of 150-160 g/L were first pumped through an immobilized-glucoamylase packed column. At 55 degrees C and a residence time of 1 h, greater than 95% conversion was obtained, giving product streams of 162-172 g glucose/L. These streams were then pumped through the fluidized-bed bioreactor containing immobilized Z. mobilis. At a residence time of 2 h, 94% conversion and ethanol concentration of 70 g/L were achieved, resulting in an overall process productivity of 23 g/L-h. At residence times of 1.5 and 1 h, conversions of 75 and 76%, ethanol concentrations of 49 and 47 g/L, and overall process productivities of 19 and 25 g/L-h, respectively, were achieved.

Journal Article↗
PubMed1986

The X-ray crystal structure of DL-(1,3,5/2,4)-1,2,3,4-tetraacetoxy-5-(acetoxymethyl)cyclohexane.

The crystal and molecular structure of the pseudo-sugar DL-(1,3,5/2,4)-1,2,3,4-tetraacetoxy-5-(acetoxymethyl)cyclohexane ("pseudo-beta-DL-glucopyranose pentaacetate") has been determined by X-ray diffraction and statistical-phasing procedures. The data were refined to R = 0.049 and Rw = 0.054 over 1543 reflections with I greater than 3 sigma(I). The racemic crystals are monoclinic, space group P2(1)/c, a = 11.580(2), b = 8.276(1), c = 22.031(2) A, beta = 104.33(1) degrees, Dc = 1.26 g/cm3, with four molecules in the unit cell. The ring has a 4C1(D), 1C4(L) conformation, with puckering amplitude of 0.582(4) A, a pseudorotation angle of -168.35 degrees, and a gg orientation about the C-5-C-6 bond.

Carbohydrate Conformation↗