Separation and identification of glucosinolates of vegetable turnip rape by LC/APCI-MS and comparison of their contents in ten cultivars of vegetable turnip rape (Brassica rapa L.)

Abstract

Eight major glucosinolates (GSLs) were identified in ten cultivars of vegetable turnip rape (Brassica rapa L.) by LC/APCI-MS. The GSLs indentified included five alkenyl GSLs (progoitrin, glucoraphanin, sinigrin, gluconapin, and glucobrassicanapin), two indolyl GSLs (4-hydroxyglucobrassicin and glucobrassicin), and one aromatic GSL (gluconasturtiin). The total GSL content in the ten cultivars ranged from 36 to 187 mmol kg-1 DW. The content of indolylglucosinolate (GSL) ranged widely from 0.4 to 8.2 mmol kg-1 DW, which accounted for 0.5 to 10.2%, respectively, of the total GSL content. Although the total GSL content was affected by the harvest dates, the proportion of individual GSLs did not change significantly. Furthermore, the proportion of the individual GSL content between edible parts and seeds in vegetable turnip rapevaried considerably, especially for gluconapin and glucobrassicanapin. Among them, the sum of the contents of gluconapin and glucobrassicanapin accounted for more than 65% of the total GSL content in nine vegetable turnip rape cultivars except for cv. Husanohana in which the percentages of gluconapin and glucobrassicanapin of total GSL was less than 53%. The proportion of progoitrin as a percentage of the total GSL content was markably different between vegetable turnip rape and rapeseed (B. napus L.), namely 1 and 48%, respectively. As a result, it was difficult to predict the individual GSL content in edible parts compare to those in the seeds analyzed.