Abstract
Tryptophan (TRP) is an essential amino acid which cannot be synthesized by humans and animals, but has to be supplied by exogenous sources, notably through the diet. The bulk of dietary TRP flows into the synthesis of body’s proteins, but the TRP metabolism also involves several biochemical reactions (i.e., serotonin and kynurenine pathways). Defects in the TRP transport mechanism or catabolism are related to a large number of clinical abnormalities. Therefore, dietary TRP intake is necessary not only for the body’s growth but also for most of the body’s metabolic functions. Among protein-based foods, milk proteins provide a relatively high amount of TRP. In this paper, a rapid chromatographic method for TRP determination in yoghurt, by ultra high performance liquid chromatography on a reversed-phase column with fluorescence detection (280 nm Ex; 360 nm Em), is provided. A linear gradient elution of acetonitrile in water allowed TRP analysis in 8.0 min. The limit of detection and limit of quantification of the method were 0.011 ng/µL and 0.029 ng/µL, respectively, using 5-methyl-l-tryptophan as the internal standard. The analytical method was successfully applied to commercial yoghurts from different animal species, and the TRP values ranged between 35.19 and 121.97 mg/100 g (goat and cow Greek type yoghurt, respectively).
Highlights
Tryptophan (TRP) is an essential amino acid needed for normal growth, and is involved in the synthesis of different bioactive compounds, such as nicotinamide, melatonin, tryptamine, kynurenine, 3-hydroxykynurenine, and quinolinic and xanthurenic acids [1].In lower organisms, TRP is formed through the condensation of serine with an indole group by the action of tryptophan synthase [2]
Partial disruption of TRP can occur during hydrolysis: these losses can be corrected based upon the recovery of an internal standard [16], and 5-methyl-l-tryptophan (M-TRP) has been revealed as the preferred internal standard for TRP
Due to the presence of the indole ring in the tryptophan structure, which is degraded under the acid conditions generally used in the protein hydrolysis, TRP cannot be analyzed by the standard method for amino acid analysis [1]
Summary
Tryptophan (TRP) is an essential amino acid needed for normal growth, and is involved in the synthesis of different bioactive compounds, such as nicotinamide (vitamin B6), melatonin, tryptamine, kynurenine, 3-hydroxykynurenine, and quinolinic and xanthurenic acids [1]. TRP is formed through the condensation of serine with an indole group by the action of tryptophan synthase [2]. Though, TRP cannot be synthesized because they are lacking in tryptophan synthase [2]. Besides participating in the formation of the body’s proteins, TRP is involved in numerous chemical reactions. TRP transport through the cell membranes is competitively inhibited by the other large neutral amino acids (NAA), such as valine, leucine, isoleucine, phenylalanine and tyrosine [3]
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