Concentration available lysine

Kawamura, et a l. (58) reported that the nonreducing sugar level, available lysine, and whiteness decreased in parallel with heating time of defatted soybean flakes at 100 or 120°C. Concentrations of the three oligosaccharides (sucrose,... 

Available lysine in the model system was determined by an adaptation of the method of Kadade and Leiner (17). After preliminary rate studies the parameters chosen for measurement were pH—5,6,7,8 temperature—20, 40 and 60°C in a water bath time—usually 24 hours with samplings at 10 min and 1,2,4, and 8 or 10 hours (occasionally after 2 or 4 days 20°C) BPA concentration—1 g/L, 10 g/L carbonyl compound concentration—0.07 to 35.0 mM or carbonyl lysine—1 10 to 50 1. 

Experimental procedures employed generally were as follows The BPA solution was measured into a culture tube, the carbonyl compound at the desired concentration added and the two gently mixed. Zero time samples were withdrawn and the capped tubes were placed in a Beckman thermocirculator at the experimental temperature. Blank (no carbonyl) and control (no BPA) tubes were included with each run. Samples were withdrawn at specified intervals and assayed for available lysine. 

The decrease in available lysine due to reaction with polyphenols can occur during the preparation of protein isolates or concentrates from polyphenol-rich materials such as alfalfa leaves or sunflower seeds. 

In the advanced and late "Maillard reaction" the furosine method is not valuable since the Amadori products lead to further compounds. Therefore the amount of available lysine in severely damaged foods is underestimated. In the case of fructose rich food (e.g. special diets for diabetics or products which are sweetened with honey or concentrated fruit juice) similar false conclusions are possible since glucoselysine which is formed from fructose during the "Maillard reaction" is not a precursor for furosine. 

The factors affecting the Maillard reaction include temperature, time, moisture content, concentration, pH, and nature of the reactants. - It has been shown that, out of 21 amino acids, glycine, lysine, tryptophan, and tyrosine provide the most intense browning when exposed to five saccharides, especially a-lactose. The Maillard reaction is also responsible for the decreased availability of lysine in proteinaceous foods. 

The most frequently used protein assay is based on a method after Bradford (Bradford, 1976), which combines a fast and easily performed procedure with reliable results. However, the Bradford assay has sensitivity limitations and its accuracy depends on comparison of the protein to be analyzed with a standard curve using a protein of known concentration, commonly bovine serum albumin (BSA). Many commercially available protein assays such as those from Pierce or BioRad rely on the Bradford method. The assay is based on the immediate absorbance shift from 465 nm (brownish-green) to 595 nm (blue) that occurs when the dye Coomassie Brilliant Blue G-250 binds to proteins in an acidic solution. Coomassie dye-based assays are known for their non-linear response over a wide range of protein concentrations, requiring comparison with a standard. The dye is assumed to bind to protein via an electrostatic attraction of the dye s sulfonic groups, principally to arginine, histidine, and lysine residues. It also binds weakly to the aromatic amino acids, tyrosine, tryptophan, and phenylalanine via van der Waals forces and hydrophobic interactions. 

For a DICE analysis, two different fluorescence dyes, CyDye minimal dyes and CyDye saturation dyes, are available. CyDye minimal dyes react with an NHS-ester bond of lysine e-amino residues and enable coelectrophoresis of up to three different samples in one approach. Eor special applications, e.g., samples from microdissection, the CyDye saturation dyes allow complete 2-D analysis and quantification of protein abundance changes in scarce sample amounts. The dyes react via a maleimide group with all available cysteine residues in the protein sample, giving a high labeling concentration. 

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