Abstract
Tryptophan is essential amino acid and precursor for many neurotramsmiters that must be obtained from dietary proteins. However, its free form is easily absorbed and could increase the availability of this amino acid to the brain. Because of free tryptophan interaction with human health simple, eco-friendliness and low-cost method of determination are still needed. In this study, new and simple procedure for free tryptophan determination using capillary isotachophoresis is discussed. The method validation pointed good linearity, satisfactory selectivity, accuracy (recoveries varied from 98.4 to 100.1%), intra- and inter-day precision (coefficent of variation was < 5% for each standard solution and < 6% for real samples) and no matrix effect. The proposed procedure was successfully applied to analyse free tryptophan in beer samples and found contents varied from not detected to 40.74 ± 0.27 mg L−1. The obtained results were compared with chromatographic determination after derivatization with 2-chloro-1,3-dinitro-5-(trifluoromethyl)benzene and pointed better selectivity and accuracy of isotachophoretic procedure with similar precision. Due to the simplicity and flexibility, the proposed procedure is suitable for tryptophan analysis in complex matrices.
Highlights
Tryptophan (Trp) is large neutral amino acid (LNAA) and precursor for brain neurotransmitters
Hirokawa et al (1991) studied the dilution and elongation of ITP zones by carbonate ions from the terminating electrolyte and concluded that in the analysis of amino acid anions, under pH between 8 and 10, the carbonate zone migrates before the sample zones
The following parameters were evaluated in the validation procedure of chosen system of electrolytes: selectivity of the ITP determination, precision and accuracy, linearity, limit of detection (LOD) and limit of quantification (LOQ) and matrix effect
Summary
Tryptophan (Trp) is large neutral amino acid (LNAA) and precursor for brain neurotransmitters (serotonin, melatonin, tryptamine, quinolinic acid and kynurenic acid). According to Friedman (2018), dietary Trp and its metabolites may contribute to the therapy of many diseases, cognitive function, depression, sleep and social function This hypothesis is still under discussion (Soh and Walter 2011). The main source of this amino acid is protein-based food including meats, dairy products, fruits and seeds (Jenkins et al 2016). The protein-rich diet results in an increase of tyrosine content in relation to other LNAA and reduces the available tryptophan for transport across the blood-brain barrier, whereas carbohydrate-rich food with high-glycaemic index is found to increase the availability of tryptophan (Markus 2008; Jenkins et al 2016).
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