Glucosinolates in isano (Tropaeolum tuberosum) tubers: qualitative and quantitative content and changes after maturity

Six varieties of isano (Tropaeolum tuberosum), an Andean edible tuber, were analysed. The aim was to characterise qualitatively and quantitatively their content of glucosinolates and to determine concentration changes of these compounds upon delayed harvest. Additionally, exploratory assays were carried out on the effect of postharvest cold storage of the tubers as well as of a drying process imposed on blanched tuber slices. Only one glucosinolate (p-methoxybenzyl glucosinolate) was found in the six domestic varieties analysed. Its concentration varied between 36.5 and 90.0 (mu)mol g^-1 dry matter. This range is relatively high when compared with other edible glucosinolate-containing vegetables. Dark coloured tuber varieties showed higher levels than light coloured tuber varieties at normal harvest time. Of the two varieties on which the effect of delayed harvest was studied, one showed increasing and then decreasing changes until 44 days after maturity, while the other did not show any significant change with time. Postharvest cold stored samples showed similar changes to tubers kept in soil, and glucosinolate levels in dried blanched tubers did not differ significantly from those in fresh samples. Taken together, the data indicate that the glucosinolate content of isano is highly dependent on both the variety and the time of harvest. These parameters should be taken into account when considering isano as a promising food source with medicinal properties for humans and animals, but also with possible adverse biological effects, all related to the presence of glucosinolates.