posted on 2024-03-12, 18:43authored byTomás Herraiz, Antonio Salgado
β-Carbolines (βCs) are bioactive indole alkaloids
found
in foods and in vivo. This work describes the identification, formation,
and occurrence in foods of the βC with a furan moiety flazin
(1-[5-(hydroxymethyl)furan-2-yl]-9H-pyrido[3,4-b]indole-3-carboxylic acid). Flazin was formed by the reaction
of l-tryptophan with 3-deoxyglucosone but not with 5-hydroxymethylfurfural.
Its formation was favored in acidic conditions and heating (70–110
°C). The proposed mechanism of formation occurs through the formation
of intermediates 3,4-dihydro-β-carboline-3-carboxylic acid (imines),
followed by the oxidation to CO in the carbohydrate chain
and aromatization to βC ring with subsequent dehydration steps
and cyclization to afford the furan moiety. Flazin is generated in
the reactions of tryptophan with carbohydrates. Its formation from
fructose was higher than from glucose, whereas sucrose gave flazin
under acidic conditions and heating owing to hydrolysis. Flazin was
identified in foods by HPLC-MS, and its content was determined by
HPLC-fluorescence. It occurred in numerous processed foods, such as
tomato products, including crushed tomato puree, fried tomato, ketchup,
tomato juices, and jams, but also in soy sauce, beer, balsamic vinegar,
fruit juices, dried fruits, fried onions, and honey. Their concentrations
ranged from not detected to 22.3 μg/mL, with the highest mean
levels found in tomato concentrate (13.9 μg/g) and soy sauce
(9.4 μg/mL). Flazin was formed during the heating process, as
shown in fresh tomato juice and crushed tomatoes. These results indicate
that flazin is widely present in foods and is daily uptaken in the
diet.