A total of 27 yeast strains belonging to the groupsCandida, Saccharomyces, andKluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45°C.
K. marxianus andK. fragilis were found to be the best ethanol producing organisms at the higher temperature tested and, so, were selected for subsequent
simultaneous saccharification and fermentation (SSF) studies. 相似文献
The hydrolysis of chromate ion was studied potentiometrically in a concentration cell fitted with hydrogen electrodes by titrating basic NaCl–Na2CrO4 solutions with standardized HCl against a NaOH reference solution. The temperature was varied from 25 to 175°C at 25° intervals at the following ionic strengths (I): 0.1140, 0.2346, 0.5337, 0.9988, 2.940, and 5.239 (NaCl). Depending on the ionic strength, the molality of total chromium was varied from 0.001 to 0.100. The resulting titration curves could be resolved best in terms of three equilibria involving the formation of HCrO
4–
(aq), Cr2O3– (aq), and CrO3Cl– (aq). The equilibrium quotients for all three reactions were fitted as a function of temperature and ionic strength, and the molal thermodynamic parameters that were computed from these relationships are tabulated at specific ionic strengths over the experimental temperature range. 相似文献
The classic kinetic model for cellulose hydrolysis is often referred to as pseudo-homogeneous, a term revealing the insight that the process is actually heterogeneous. During the past 10–15 yr, the shortcomings of this
model have been demonstrated in various studies and the interest in the heterogeneous aspects has increased. The present work
presents a simplistic model in which the intrinsic, heterogeneous hydrolysis and transport rates are coupled by the assumption
of a constant glucosidic surface concentration. The mechanisms affecting these two rates are largely unknown, but the model
serves as a guideline for further exploration of the process. 相似文献
Homogeneous solutions are formed from equimolar amounts of Ce(NH4)2(NO3)6 and EDTA. These solutions hydrolyze single-stranded DNA far more efficiently than double-stranded DNA. In contrast, Ce(IV) hydroxide gel, obtained in the absence of EDTA, hydrolyzes both single-stranded and double-stranded DNAs at almost the same rates. In order to achieve this substrate-specificity sufficiently, the mole ratio of EDTA to Ce(NH4)2(NO3)6 must be 1.0 or greater. By using this remarkable specificity of Ce(IV)/EDTA complex, gap-site in substrate DNA is selectively hydrolyzed. The scission-site is modulated by use of appropriate combination of oligonucleotide additives. The reactions have been kinetically analyzed. 相似文献
19F and 31P NMR spectroscopy were used to study the kinetics of the hydrolysis of LiPF6 in the homogenous solvent system propylene carbonate (PC)—dimethyl carbonate (DMC)—H2O. It was found that the main products of the hydrolysis are HF, LiPO2F2 and Li2PO3F. The content of POF3 and PF5 was negligibly low. We set up a hypothesis that the main factor determining the rate of the process is the so-called ‘secondary’ catalytic effect, caused by solvated H+ ions. 相似文献
The historical importance of pregastric enzymes in cheese-making is reviewed and the potential for extending their use is discussed in terms of requiring an understanding of their physicochemical parameters. Commericial extracts from the tongues and epiglotti of suckling lambs and calves and adult goats have been processed to yield partially purified samples of the primary pregastric lipase (PGL). The N-terminal sequence and molecular weight of lamb PGL have been determined.
The activity of lamb and goat PGLs against tributyrin has been determined over a range of pH and temperature values. Optimum conditions were pH 6.4, 43°C, and pH 6.0, 52°C, for lamb and goat PGL respectively. The possible influence of the development of a ruminant multi-chambered stomach on the difference in optimal temperature is discussed. A lengthening of the carboxylic acid chain of homoacid triglycerides causes a decrease in hydrolytic activity of lamb PGL but in all cases only a single free fatty acid was released. Against a series of 4-nitrophenylalkanoate esters, maximum activity was observed against the decanoate ester but, in contrast to hydrolysis of the acetate ester which exhibited full Michaelis-Menten kinetics with increasing substrate concentration, activity against the decanoate ester was restricted to the monomeric substrate. Taurocholate inhibits the activity of lamb PGL at concentrations >8 mM. Values of pK2 equal to 6.69 and 7.92 respectively have been determined for lamb PGL.
Attempts to interesterify coconut oil and cocoa butter, and tributyrin and tricaprylin, catalysed by calf PGL were unsuccessful, although positive results obtained using Candida cylindracea encourage further investigation of alternative methods for immobilizing the PGL. Finally, anhydrous milk fat has been hydrolysed by calf, lamb and goat PGLs and the differences in relative amounts of released free fatty acids have been used to explain the differences in taste which arise when Parmesan cheese is produced using different sources of PGL. 相似文献
The hydrolysis-condensation pathways of Mn2Sb4(OEt)16 in various ethanol-toluene solvents have been studied for h < 1.5 (h = H2O/Mn2Sb4(OEt)16). The hydrolysis was performed by slow addition of H2O diluted with the ethanol-toluene solvent. Mn2Sb4(OEt)16 and its hydrolysis products were studied by FT-IR spectroscopy, SEM-EDS and single-crystal X-ray diffraction. The hydrolysis pathway for a given h-value was found to depend on the solvent composition. In ethanol-rich solvent mixtures, Mn7Sb4O4(OEt)18(HOEt)2 was obtained in maximum yield at h = 1.14, and in toluene-rich solvents, Mn8Sb4O4(OEt)20 was obtained in maximum yield at h = 1.0. In both cases, the remaining Sb was found as nonhydrolyzed Sb(OEt)3. The structures of the heterometallic ethoxides Mn2Sb4(OEt)16, Mn7Sb4O4(OEt)18(HOEt)2 and Mn8Sb4O4(OEt)20 have been determined earlier by single-crystal X-ray diffraction. According to FT-IR evidence the molecular structures of the latter two are retained almost intact in solution, whereas the first one changes appreciably. The hydrolysis products of Mn2Sb4(OEt)16 are compared with those of Ni2Sb4(OEt)16, and the structural and compositional changes in different solvents and at different h-values are discussed. 相似文献
Yellow poplar wood sawdust consists of 41% cellulose and 19% hemicellulose. The goal of pressure cooking this material in
water is to hydrate the more chemically resistive regions of cellulose in order to enhance enzymatic conversion to glucose.
Pretreatment can generate organic acids through acid-catalyzed degradation of monosaccharides formed because of acids released
from the biomass material or the inherent acidity of the water at temperatures above 160°C. The resulting acids will further
promote the acid-catalyzed degradation of monomers that cause both a reduction in the yield and the formation of fermentation
inhibitors such as hydroxymethyl furfural and furfural. A continuous pH-monitoring system was developed to help characterize
the trends in pH during pretreatment and to assist in the development of a base (2.0 M KOH) addition profile to help keep
the pH within a specified range in order to reduce any catalytic degradation and the formation of any monosac-charide degradation
products during pretreatment. The results of this work are discussed. 相似文献