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Amino Acid Nitrogen (amino + acid_nitrogen)
Selected AbstractsResolution of Racemic N -Benzyl ,-Amino Acids by Liquid-Liquid Extraction: A Practical Method Using a Lipophilic Chiral Cobalt(III) Salen Complex and Mechanistic StudiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pawel Dzygiel Abstract The efficient resolution of racemic N -benzyl ,-amino acids (N -Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen,cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N -benzyl ,-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII,,,CoII) counter-extraction with aqueous sodium dithionite or L -ascorbic acid in methanol. Thereductive cleavage allowed to recover the [CoII(3)] complex in good yield, which could be easily re-oxidized to[CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N -Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N -benzyl ,-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Small intestinal digestibility of microbial and endogenous amino acids in dairy cowsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 1-2 2001M. Larsen The small intestinal digestibility of microbial amino acids and the apparent re-absorption of endogenous amino acids were estimated in three ruminal, duodenal and ileal fistulated lactating dairy cows. The cows were assigned to a 3 × 3 Latin square and fed diets low in amino acids, composed of straw, starch, molasses and urea. The treatments were three straw to concentrate ratios. The digestibilities and re-absorptions were estimated from duodenal and ileal flows of amino acids from feed, microbial and endogenous sources. The duodenal distribution of amino acids between different origins was determined by the difference method and by the amino acid profile method. The ileal distribution was estimated by a simple method where the feed fraction was estimated by the mobile bag method, the endogenous fraction as the water soluble fraction and the microbial fraction as the rest. In ileal samples, 8.0 ± 1.1, 52.2 ± 2.9 and 39.8 ± 2.6% of total amino acid nitrogen (AAN) were of feed, microbial and endogenous origin, respectively, compared with 5.1 ± 0.9, 61.6 ± 6.6 and 32.7 ± 6.9% in duodenal samples. The small intestinal digestibility of microbial AAN was estimated to be 75.1 ± 1.8% and the apparent re-absorption of endogenous AAN to be 62.3 ± 11.1%. [source] Nitrogen-to-Protein Conversion Factors for Some Cereal Products in JapanJOURNAL OF FOOD SCIENCE, Issue 3 2008S. Fujihara ABSTRACT:, To evaluate a practical method of determining more accurately conversion factors for calculating the protein contents of foods from the total nitrogen content, 19 cereal products found in Japan were analyzed for total nitrogen, amino acid nitrogen, and amide nitrogen, and then the nitrogen-to-protein conversion factors were calculated. The average conversion factors were 5.75 for rice, 5.81 for wheat, and 5.95 for others. These values, corresponding to the proportion of the amino acid residue to amino acid nitrogen recovered from 20 amino acids, were lower than the currently applied factors to these foods, except for wheat flour and amaranth. The use of this factor for estimating the protein content results in a considerable difference from the estimate based on amino acid residue concentrations, due to the wide variations in amino acid composition and to the presence of a significant level of nonprotein nitrogen. The distribution of the protein nitrogen recovered from the amino acids to total nitrogen averaged 93%. Adjusted conversion factors corresponding to the proportion of the amino acid residue to total nitrogen averaged 5.26 for rice, 5.47 for wheat, and 5.54 for other cereal products. Protein contents estimated using these factors are in good agreement with the contents defined as amino acid residues. [source] Effect of the fungal protease EPg222 on proteolysis and texture in the dry fermented sausage ,salchichón'JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 2 2005María J Benito Abstract Proteolytic activity of the fungal protease EPg222 and its effect on the texture of the dry fermented sausage ,salchichón', which has a long ripening process, was assayed. Samples with enzyme added showed a significant reduction of myofibrillar protein concentration during the ripening period, compared with a control, and proteolytic activity of the enzyme led to a higher accumulation of non-protein and -amino acid nitrogen. Analysis of volatile compounds in ripened dry fermented sausages revealed that only in EPg222 batches were branched compounds derived from amino acids catabolism detected that are associated with the flavour of dry cured meat products. The texture profile analysis showed reduction in hardness, gumminess and chewiness values in treated compared with control sausages. The effect of this enzyme could be of great interest in stimulating proteolysis, in flavour development and in reducing the hardness of dry fermented sausages produced by a long ripening process. Copyright © 2004 Society of Chemical Industry [source] | ||||||||||