Ethanol limiting oxygen concentrations

During the first 24-48 h of cocoa bean fermentation (phase 1), yeasts convert saccharides (sucrose, glucose and/or fructose) into alcohol (ethanol) under conditions of high carbohydrate concentrations (characteristic for the fresh cocoa pulp-bean mass), limited oxygen availability (due to tight packing... 

Cu-CuO% nanoparticles (with a content of about 10 wt.%) on titania are effective for the production of hydrogen under sacrificial conditions [176-178], A fairly low concentration of Cu (2.5 wt.%) was sufficient to allow promising H2 production from ethanol-water and glycerol-water mixtures in the case of CuO% nanoparticles encapsulated into porous titania [179]. A key limitation of this system is photocorrosion under oxidizing conditions (oxygen and carboxylic adds as by-products of partial oxidation of the sacrificial agent). However, in the presence of UV irradiation, Cu photodeposition can occur, preventing loss of Cu [179]. 

Some catabolic reactions depend upon ADP, but under most conditions its concentration is very low because it is nearly all phosphorylated to ATP. Reactions utilizing ADP may then become the rate-limiting pacemakers in reaction sequences. Depletion of a reactant sometimes has the effect of changing the whole pattern of metabolism. Thus, if oxygen is unavailable to a yeast, the reduced coenzyme NADH accumulates and reduces pyruvate to ethanol plus C02 (Fig. 10-3). The result is a shift from oxidative metabolism to fermentation. 

CSTR Substrate and nutrients including oxygen are continuously fed so as to achieve the desired steady state. The beer containing ethanol, biomass and unconsumed nutrients is removed continuously. The productivity can reach 6g/l h, about three times of a batch reactor. The yield of ethanol is limited by the inhibition effect Total productivity is also limited by low biomass concentration (10-12g/l). A sugar concentration of 10% in the feed gives the highest productivity. Two or more CSTR in series can be used. 

In view of the uncertainties inherent in Hammett indicator determinations of surface acidity by visual means, a study was made of the spectral behavior of dyes adsorbed on several silica-alumina catalysts and silica gel (62). The effects of catalyst water content, dye concentration, catalyst composition and pretreatment on the spectra of the adsorbed dyes were examined. The Hammett indicator dyes employed and their corresponding pKA values are summarized in Table II. Reference spectra were determined for the base-form of the dye in iso-octane or methylene chloride solution and for the acid-form in an aqueous sulfuric acid or ethanolic-hydrogen chloride solution. Dyes were adsorbed from isooctane solutions onto thin plates of optically transparent catalysts which were installed in evacuated cells of design similar to that shown in Fig. 4. The catalysts samples were routinely pretreated by calcination in oxygen at 500° to remove any organic contaminants, followed by evacuation at this temperature. To examine the effect of variable water content on the spectra the samples were rehydrated in an atmosphere of wateir vapor for 24 hr after pretreatment and subsequently evacuated at some lower temperature. Dye solutions were introduced through a side arm. These solutions were suitably dilute so that the absorbance due to dissolved dye was either below the limits of detection or, at... 

Strain was cultivated in 30 g xylose under oxygen limitation, it consumed three times more xylose than the control strain. Ethanol and acetate were produced at low levels and the xyHtol yield was reduced by half. The relatively poor ethanol yield and productivity were attributed to two factors. T. thermophUus XI has a temperature optimum at 85°C with an activity of 1 U mgand the enzyme has only trace activity at mesophihc temperatures, 0.04 U mg [56]. The other important factor leading to the poor performance of the strain was the formation of xylitol, primarily by the unspecific NADPH-Unked aldose reductase [37,156]. Xylitol formation has a dual effect on the ethanol yield it not only leads to loss of carbon,but it also competitively inhibits XI [157]. With increasing intracellular xyUtol concentration the apparent affinity of XI towards xylose decreases, and more xylose is chaimeled into xyUtol, imtil the NADPH pool of the cell is depleted. 

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