Glucosinolates in vegetative tissues and seeds of twelve cultivars of vegetable turnip rape (Brassica rapa L.)

Abstract

Total glucosinolate (GSL) content of edible parts, such as flower buds, leaves, and stems of vegetable turnip rape (Brassica rapa L.) was determined and compared among twelve cultivars consisting of eight early types and four medium or late types. The average dry weight of the edible parts in the medium or late types was 2-fold higher (3.20 g) than that of the early types (1.61 g). The relative proportion of each edible part to the dry weight in the early types was approximately 31, 35, and 35% for the flower buds, leaves, and stems, respectively. However, in the medium or late types, the leaf proportion was six times higher than that of the flower buds. Two GSL compounds, gluconapin, and glucobrassicanapin, were mainly found in all the edible parts. The relative proportion of gluconapin to the total GSL content was higher than that of glucobrassicanapin in the early types, but the reverse was observed in the medium or late types. The total GSL content of edible parts, recalculated by using the percentage of dry weight to the sum weight, ranged from 60 to 80 mmol kg−1 DW in all the cultivars, except for ‘Syunrai’ (30 mmol kg−1 DW) and ‘No. 88’ (31 mmol kg−1 DW). The high-pressure liquid chromatography (HPLC) profile patterns of the seeds and vegetative tissues were similar, with different amounts, particularly gluconapin. A nonsignificant positive correlation was observed between the total GSL content in the seeds and vegetative tissues (R 2 = 0.1758). Although gluconapin was the only GSL to be found in the seeds, both gluconapin and glucobrassicanapin occurred in the edible parts.