Analysis, nutrition, and health benefits of tryptophan

Authors: Friedman, Mendel

Submitted to: International Journal of Tryptophan Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2018
Publication Date: 9/26/2018
Citation: Friedman, M. 2018. Analysis, nutrition, and health benefits of tryptophan. International Journal of Tryptophan Research. 11:1-12. https://doi.org/10.1177/1178646918802282.
DOI: https://doi.org/10.1177/1178646918802282

Interpretive Summary: This manuscript was prepared in response to an invitation by the Editor to contribute to a special issue of the International Journal of Tryptophan Research. The nutritionally essential amino acid tryptophan contributes to protein synthesis and the regulation of numerous physiological mechanisms. These include serving as a precursor for the neurotransmitter serotonin and the vitamin niacin. It is therefore important to be able to analyze tryptophan levels accurately and sensitively but unfortunately this is not straightforward; protein-bound tryptophan is degraded in the acid hydrolysis used for analysis of all amino acids. A number of methods have therefore been developed that can overcome this problem. including the acid ninhydrin method that might be preferable over basic hydrolysis as well as the near-infrared reflectance spectroscopy assay, widely used to analyze large numbers of samples from plant breeding and plant engineering programs. Because tryptophan seem safe to consume, and is used to fortify foods such as infant formulas and corn flour tortillas, and they have potential health benefits, a major challenge is to foster the further development. via plant molecular genetic engineering the creation of high-tryptophan, as well as high-lysine and high-methionine cereals and legumes. The protein quality of such transgenic foods might approach that of the much more expensive meat, so they have the potential to alleviate malnutrition at an affordable cost. Moreover, because, after consumption, tryptophan is reported to mitigate the course of multiple chronic diseases, there is an urgent need for additional clinical studies designed to investigate the possible therapeutic potential of inexpensive, high-tryptophan foods. Such studies should include the evaluation of the functions of tryptophan metabolites resulting from tryptophan-gut-microbiota interactions on the causes and prevention of human diseases.

Technical Abstract: Tryptophan is an essential plant derived amino acid that is needed for the in vivo biosynthesis of proteins. After consumption, it is metabolically transformed to bioactive metabolites, including serotonin, melatonin, kynurenine, and the vitamin niacin. This 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. Analytical methods include the use of acid ninhydrin, near-infrared reflectance spectroscopy (NIRS), colorimetry, basic hydrolysis; acid hydrolysis of S-pyridylethylated proteins, and high-performance liquid and gas chromatography-mass spectrometry. Also covered are the nutrition of tryptophan-fortified infant formulas and corn flour based tortillas, the safety of tryptophan for human consumption and the analysis of maize (corn), rice, and soybean plants that have been successfully genetic engineered to produce increasing tryptophan content? 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. Tryptophan can also facilitate the diagnosis of certain conditions such as human cataracts, colon cancer, renal cell carcinoma, and the prognosis of diabetic nephropathy. 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. The collated information and suggested research needs 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.