Mixture Of Hexoses Research Articles

Characterization of Bioethanol Production from Hexoses and Xylose by the White Rot Fungus Trametes versicolor

Bioethanol production by white rot fungus (Trametes versicolor), identified from fungal mixture in naturally decomposing wood samples, from hexoses and xylose was characterized. Results showed that T. versicolor can grow in culture, under hypoxic conditions, with various mixtures of hexoses and xylose and only xylose. Xylose was efficiently fermented to ethanol in media containing mixtures of hexoses and xylose, such as MBMC and G11XY11 media (Table 1), yielding ethanol concentrations of 20.0 and 9.02 g/l, respectively, after 354 h of hypoxic culture. Very strong correlations were found between ethanolic fermentation (alcohol dehydrogenase activity and ethanol production), sugar consumption and xylose catabolism (xylose reductase, xylitol dehydrogenase and xylulokinase activities) after 354 h in culture in MBMC medium. In a medium (G11XY11) containing a 1:1 glucose/xylose ratio, fermentation efficiency of total sugars into ethanol was 80% after 354 h.

Dekkera/Brettanomyces yeasts for ethanol production from renewable sources under oxygen-limited and low-pH conditions

Industrial fermentation of lignocellulosic hydrolysates to ethanol requires microorganisms able to utilise a broad range of carbon sources and generate ethanol at high yield and productivity. D. bruxellensis has recently been reported to contaminate commercial ethanol processes, where it competes with Saccharomyces cerevisiae [4, 26]. In this work Brettanomyces/Dekkera yeasts were studied to explore their potential to produce ethanol from renewable sources under conditions suitable for industrial processes, such as oxygen-limited and low-pH conditions. Over 50 strains were analysed for their ability to utilise a variety of carbon sources, and some strains grew on cellobiose and pentoses. Two strains of D. bruxellensis were able to produce ethanol at high yield (0.44 g g(-1) glucose), comparable to those reported for S. cerevisiae. B. naardenensis was shown to be able to produce ethanol from xylose. To obtain ethanol from synthetic lignocellulosic hydrolysates we developed a two-step fermentation strategy: the first step under aerobic conditions for fast production of biomass from mixtures of hexoses and pentoses, followed by a second step under oxygen limitation to promote ethanol production. Under these conditions we obtained biomass and ethanol production on synthetic lignocellulosic hydrolysates, with ethanol yields ranging from 0.2 to 0.3 g g(-1) sugar. Hexoses, xylose and arabinose were consumed at the end of the process, resulting in 13 g l(-1) of ethanol, even in the presence of furfural. Our studies showed that Brettanomyces/Dekkera yeasts have clear potential for further development for industrial processes aimed at production of ethanol from renewable sources.

Dosage comparatif des produits issus de la dégradation alcaline des hexoses

The mixture of hexoses and carboxylic acids produced by alkaline degradation of fructose was analyzed quantitatively by high-performance liquid chromatography. A pulsed amperometric detector with two Carbopac Dionex columns in series was employed in the assay of sugars (glucose, fructose, mannose, sorbose, and psicose), while a conductimeter with an HPICE AS1 Dionex column was employed for carboxylic acids (lactic, glyceric, glycolic, formic, and acetic). This sensitive and reproducible method obviated sample pretreatment. The results were compared with those of enzymatic assays and HPLC determinations using Biorad HPX87C and HPX87P columns in series for the sugars, and an Interaction ORH 801 column for the carboxylic acids. The behaviour of fructose, glucose, and mannose in alkaline medium was compared. Keywords: hexoses, polyhydroxylic acids, isomerization, alkaline degradation, high-performance ionic liquid chromatography.

Determination of d(+)glucose, d(+)mannose, d(+)galactose or d(−)fructose in a mixture of hexoses and pentoses by use of dental plaque coupled with a glass electrode

A potentiometric sensor has been developed by coupling dental plaque with a flat-surface glass electrode. Selectivity of this electrode for hexoses and pentoses has been tested. The electrode responds linearly to β- d(+)glucose, d(+)mannose, d(+)galactose and β- d(−)fructose over a narrow concentration range between 10 −4 and 10 −3 M, but has negligible response to the other hexoses and pentoses. This “plaque” electrode, using live bacterial cells, may serve as a model for the development of other selective electrodes for carbohydrates.