Investigation on chemical methods of analysis for glucosinolates in rapeseed

During the period 1985-1986 a study was done on request by the European Commission to select methods for the determination of glucosinolates (GSL) in rapeseed with low GSL content ("00"-rapeseed). Several methods have been studied. The ISO 5504 did not determine the indolyl GSL which is one of the disadvantages of this procedure. Other methods for the determination of individual GSL in rapeseed have also been examined, methods which include the indolyls and have not the disadvantages of molecular shifts which occur after hydrolysis with the myrosinase enzyme. The different methods were compared with each other and with methods which determine the total GSL content like palladium test or glucose determinations. Finally we concluded that the HPLC separation of desulfated GSL offers a reliable method for the control of rapeseed varietles on the content of the different GSL. However for analysing Brassica seed residues intended for animal feed this method is less suitable since it only determines the intact glucosinolates in the seed. The calculation of the HPLC results needs calibration factors being the reelprocal value of the molar extinction coefficients in the ultraviolet range. These molar extinction coefficients have been determined by comparing the results with gaschromatography. For the indolyl-GSL a calibration factor relative to the internal standard sinigrin is ëstablished of 0.21 at 226 nm and for progoitrin of 1.37. To the EC Commission the HPLC method for the determination of the desulfo glucosinolates is proposed as reference method for the control on "00" rapeseed.