Faramarzi, Leila; Kontogeorgis, Georgios; Michelsen, Michael Locht;
The rate-based steady-state model proposed by Gabrielsen et al. (Gabrielsen, J.; Michelsen, M. L.; Kontogeorgis, G. M.; Stenby, E. H. AIChE J. 2006, 52, 10, 3443-3451) for the design of the CO2-2-amino-2-methylpropanol absorbers is adopted and improved for the design of the CO2-monoethanolamine...... impact on the model's prediction is compared. The model has been successfully applied to CO2 absorber packed columns and validated against pilot plant data with good agreement....
The geometric structure and isomerization of the 2-methylpropionyl chloride molecule in the ground electronic state in gaseous phase was studied using Ab initio methods (RHF, DFT, MP2 and QCISD). The potential energy surface (PES) and regions corresponding to transitions between conformers by the rotation of the isopropyl and two methyl groups was examined in one-dimensional approximation. The influence of the atomic orbital basis set and the method on the accuracy of the calculation of PES characteristics was considered. The calculation of the energy differences of conformers (DE) using reasonable basis sets provides values in good agreement with experimental results. The values of the potential barriers to gauche → gauche and cis → gauche transitions, and also the barrier of isopropyl and two methyl groups were compared with the same values for similar molecules as 2-methylpropanol and 2-methylpropionyl fluoride. (author)
Holm, E S; Schäfer, A; Koch, A G; Petersen, M A
Sliced saveloy samples were inoculated with monocultures of four potential spoilage bacteria and studied during a four week storage period. The objective was to investigate the resulting changes in the composition of Volatile Organic Compounds (VOCs) and the sensory quality of the product. Based on the sensory scores and the VOC composition Brochothrix thermosphacta, Chryseomonas luteola and Carnobacterium maltaromaticum were found to have a high spoilage potential in saveloy samples subjected to consumer simulated storage during the fourth week. Inoculation with Leuconostoc carnosum only resulted in a low level of spoilage. The sensory changes in the saveloy samples were modeled based on the VOC composition using Partial Least Squares Regression. The changes in the six sensory descriptors were closely related to the amount of diacetyl, acetoin, 2- and 3-methylbutanol, 2- and 3-methylbutanal and 2-methylpropanol found in the samples. These compounds are therefore potentially important for the shelf-life of sliced saveloy. PMID:23261532
Activities of the enzymes of the Ehrlich pathway and formation of branched-chain alcohols in Saccharomyces cerevisiae and Candida utilis grown in continuous culture on valine or ammonium as sole nitrogen source.
Derrick, S; Large, P J
Valine aminotransferase, a key enzyme in both biosynthesis and breakdown of branched-chain amino acids, showed consistently higher activity in Candida utilis grown in continuous culture than in Saccharomyces cerevisiae, while pyruvate decarboxylase and alcohol dehydrogenase, the other two enzymes of the Ehrlich pathway of branched-chain alcohol formation, were lower in activity. By spheroplast lysis, it was shown that valine aminotransferase followed the distribution of pyruvate decarboxylase in being located in the cytosol. Replacement of ammonium as nitrogen source by valine during conditions of carbon or nitrogen limitation caused increased specific activities of these three enzymes in S. cerevisiae, but (with one exception) decreased those of C. utilis. Of the metabolites accumulating in the culture medium, little or no ethanol or branched-chain alcohols were present during carbon-limited growth of either organism, but the change to nitrogen limitation resulted in increases in concentration of 20- to 100-fold in pyruvate, acetate and non-pyruvate keto acids as well as the accumulation of branched-chain alcohols in both organisms, and of ethanol, ethyl acetate and glycerol in S. cerevisiae. When valine was the limiting nitrogen source, there was an increase in non-pyruvate keto acids and a 10- to 16-fold increase in 2-methylpropanol. Total branched-chain alcohols formed under nitrogen limitation were 2-fold higher in S. cerevisiae than in C. utilis, irrespective of nitrogen source. Accumulation of branched-chain alcohols, ethanol, acetate and glycerol was also observed during carbon-limited growth of S. cerevisiae with valine as nitrogen source at dilution rates above the critical rate for transition to respirofermentative growth. Less than 70% of the valine carbon metabolized during growth of S. cerevisiae and only 15% of that used during growth of C. utilis was recovered in identified metabolic products. Even allowing for losses by volatilization during