Zahnley and Davis 9 in this laboratory subsequently modified this method by correcting for tyrosine absorption. One of the methods for the determination of protein-bound tryptophan discussed here is that proposed by Gaitonde and Dovey 8 in which they proposed a method in which the reaction with ninhydrin in a mixture of formic and hydrochloric acid for 10 minutes at 100☌ transforms tryptophan to a yellow product (λ max = 390 nm ε = 7120). Here, tryptophan refers to l-tryptophan and the isomeric form produced during food processing and by microbes is designated as d-tryptophan. This overview consists of the following 3 parts: (a) the evaluation of selected reported analytical methods used to determine the tryptophan content of pure proteins and protein-containing foods, including high-tryptophan corn, rice, and soybean varieties being developed using plant genetic engineering methods (b) the human nutritional function and safety of dietary tryptophan and the assessment of the replacement of d-tryptophan produced during food processing for the l-isomer in mice and (c) brief descriptions of some of the reported health-promoting aspects of tryptophan, tryptophan-containing foods, and foods with added (supplemented) tryptophan. There is, therefore, a need for alternate quantitative methods to assess the multiple functions of tryptophan in proteins, foods including dietary supplements, and in animal and human fluids and tissues (reviewed in the works by Friedman and Finley, 2 Finley et al, 3 Friedman and Cuq, 4 Cuq and Friedman, 5 Molnár-Perl 6, 7). Structures of l- and d-tryptophan and 8 bioactive metabolites.īecause the indole ring of tryptophan is degraded under the acid condition used for protein hydrolysis, tryptophan cannot be analyzed by standard amino acid analysis methods. The collated information and suggested research need will hopefully facilitate and guide further studies needed to optimize the use of free and protein-bound tryptophan and metabolites to help improve animal and human nutrition and health. The described findings are not only of fundamental scientific interest but also have practical implications for agriculture, food processing, food safety, nutrition, and animal and human health. Tryptophan can also facilitate the diagnosis of certain conditions such as human cataracts, colon neoplasms, renal cell carcinoma, and the prognosis of diabetic nephropathy. Dietary tryptophan and its metabolites seem to have the potential to contribute to the therapy of autism, cardiovascular disease, cognitive function, chronic kidney disease, depression, inflammatory bowel disease, multiple sclerosis, sleep, social function, and microbial infections. Also covered are the nutritional values of tryptophan-fortified infant formulas and corn-based tortillas, safety of tryptophan for human consumption and the analysis of maize (corn), rice, and soybean plants that have been successfully genetically engineered to produce increasing tryptophan. ![]() Analytical methods include the use of acid ninhydrin, near-infrared reflectance spectroscopy, colorimetry, basic hydrolysis acid hydrolysis of S-pyridylethylated proteins, and high-performance liquid and gas chromatography-mass spectrometry. This brief integrated overview surveys and interprets our current knowledge of the reported multiple analytical methods for free and protein-bound tryptophan in pure proteins, protein-containing foods, and in human fluids and tissues, the nutritional significance of l-tryptophan and its isomer d-tryptophan in fortified infant foods and corn tortillas as well the possible function of tryptophan in the diagnosis and mitigation of multiple human diseases. After consumption, it is metabolically transformed to bioactive metabolites, including serotonin, melatonin, kynurenine, and the vitamin niacin (nicotinamide). ![]() Tryptophan is an essential plant-derived amino acid that is needed for the in vivo biosynthesis of proteins.
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