The occurrence of glucose-derived
β-carboline alkaloids tangutorid
E (Tan E) and tangutorid F (Tan F) as well as their dehydroxy-derivatives
(DH-Tan E/F) was investigated in a broad variety of foodstuffs by
LC–MS/MS-based stable isotope dilution analysis (SIDA). For
that purpose, the target compounds and their 13C6-stable isotope-labeled analogues were synthesized from l-tryptophan and (13C6-)d-glucose and
used to develop a rapid LC–MS/MS–SIDA method. After
validation for several food matrices, the method was applied to the
analysis of these β-carbolines in 80 food items. Quantitative
amounts were detected in 46.3, 50.0, and 42.5% of the samples regarding
Tan E, Tan F, and DH-Tan E/F, respectively, with corresponding ranges
of 0.01–6.75, 0.01–5.07, and 0.01–0.75 mg/kg;
the highest amounts were found in processed tomato products. A combination
of the obtained occurrence data in foods with average food consumption
data led to the calculation of rough estimates for the chronic daily
intake of those alkaloids, yielding values of 0.44, 0.36, and 0.13
μg/kg body weight/day for Tan E, Tan F, and DH-Tan E/F, respectively.
Evidently, the consumption of processed tomato-based products accounts
for the majority of the total daily intake of the investigated β-carbolines;
the potential bioactivities of Tan E, Tan F, and DH-Tan E/F have yet
to be investigated.
In this study, the applicability of several -carboline, imidazole, and steroidal alkaloids as biomarkers for tomato juice intake is evaluated. Methods and results: Over the course of a 2-week crossover dietary intervention study, 14 volunteers were given low and high doses of tomato juice after 3 days of avoiding tomato-based products. On the day of consumption and the following days, volunteers provided urine samples that were quantitatively analyzed by high-performance liquid chromatography-tandem mass spectrometry. Herein, glucose-derived -carboline alkaloids are determined as supporting, yet non-specific dietary biomarkers for tomato juice intake. Several imidazole alkaloids represent further biomarkers, which are shown to specifically indicate consumption of tomato juice for 24 h and partly >24 h. Additionally, steroidal alkaloids derived from esculeogenin B are determined to be specific biomarkers for tomato juice detectable for at least 48 h after consumption. The intake of low and high amounts of tomato juice is significantly distinguishable based on the urinary excretion of all determined biomarkers as well. Conclusions: The dietary intake of tomato juice is conclusively traceable based on urinary excretion of multiple -carboline, imidazole, and steroidal alkaloids, and can be determined for up to 48 h after consumption. Furthermore, different intake doses can clearly be distinguished based on their urinary excretion.
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