Determination of Free Tryptophan in Beer Samples by Capillary Isotachophoretic Method

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.

Simple extraction procedure for free amino acids determination in selected gluten-free flour samples

“…The isotachophoretic analysis of tryptophan (Trp) was performed as described earlier [22] with the leading electrolyte (LE): 10 mM HCl + 1% hydroxyethylcellulose (HEC) + 1,3-bis[tris(hydroxymethyl)methylamino]propane (BTP), pH = 9.0 and terminating electrolyte (TE): 10 mM 6-aminocaproic acid (EACA) + 10 mM 6-aminocaproic acid (AMPD), pH = 9.0. The glutamic acid (Glu) was determined with the same LE, whereas 10 mM histidine + AMPD, pH = 9.4 was applied as TE.…”

“…Analyses were carried out on OP C-18, (5 μm particle size, 150 × 4.6 mm) column. HPLC measurements of amino acids derivative with CNBF were performed as described by Jastrzębska et al [22] and Li et al [29] using the solvent system: acetonitrile (A) and mixture of acetate buffer (0.05 mol L −1 ) + acetonitrile + triethylamine (82.8:17:0.2 v/v/v) (B). The flow rate was 0.32 mL min −1 , the detection wavelength was 260 nm and the temperature was set at 30 °C.…”

“…The reaction of amino acids with CNBF was performed by the method of Jastrzębska et al [22]. The solution of each amino acid was mixed with CNBF in the presence of borate buffer and incubated at 60 °C for 30 min.…”

“…This method is efficient in the analysis of amino acids in food samples due to the lack of a derivatisation stage and a simpler procedure of analysis than HPLC. In our previous paper, we have described the procedure of tryptophan determination in beer samples by ITP-ITP method [22]. The composition of the electrolytes (LE: 10 mM HCl + 1% HEC + BTP; TE: 10 mM EACA + AMPD), and the pH value were discussed in detail.…”

“…Because amino acids can form cations, zwitterions or anions, depending on pH, the application of capillary isotachophoresis (ITP) technique for AAs determination is possible. It is worth noting that, despite many advantages and lack of the amino acids derivatisation stage, there is limited number of publications on amino acid determination in food matrices by ITP [22,23].…”