Challenges of developing a valid dietary glucosinolate database

Glucosinolates are a group of important cancer chemo-preventive sulfur-containing compounds in cruciferous vegetables. To estimate their dietary intake, there is a great need to develop a valid glucosinolate database. The aim of this study was to investigate the key challenges in developing such database. First, three commonly used enzyme deactivation methods (blanching, steaming and microwaving) were compared with samples of raw untreated broccoli and kale. Steaming and microwaving were found to effectively deactivate myrosinase, both led to significantly higher glucosinolate values that blanching (∼15-50% higher). Glucosinolates in untreated broccoli was similar to that of blanching broccoli, while glucosinolates were not detected in untreated kale. Heat treatment was also shown to alter the profiles of individual glucosinolate. Quantification of total glucosinolates of four common vegetables was compared by the two most commonly used analytical methods (ISO 9167-1 method and cyclocondensation method). Except for kale, the results from ISO 9167-1 were much higher (∼6-8 fold) than that from cyclocondensation method in other three vegetables. In conclusion, the sample preparation procedure, analytical method for quantification and the compounds to be measured must be considered and validated in order to develop a valid dietary glucosinolate database.