Formation of thiazolidine-4-carboxyiic acid (thioproline), an effective nitrite-trapping agent in human body, in Parkia speciosa seeds and other edible leguminous seeds in Thailand

The amounts of thioproline, an effective nitrite-trapping agent in the human body, in various edible leguminous seeds have been determined. Thioproline in uncooked Parkia spedosa, the most popular seeds eaten in the south of Thailand, was undetectable but increased markedly to 0.14 ±0.02 mmmol/100 g after boiling. The formation of thioproline was effectively inhibited by the addition of N-ethylmaleimide, a thiol-trapping agent. The uncooked Parkia speciosa seeds contained substantial amounts of formaldehyde and thiol compounds and the amounts decreased after boiling. The contents of thioproline in other uncooked edible leguminous seeds, Parkia javanica and Archidendron clypearia, were 0.006 ± 0.002 and 0.31 ± 0.11 mmol/100 g, respectively and increased to 0.54 ± 0.2 and 2.95 ±0.8 mmol/100 g after boiling. Archidendron jirringa and Leucaena leucocephala, both uncooked and boiled, showed no detectable amount of thioproline.