Optimization and validation of an analytical RP-HPLC method for the analysis of glucosinolates in Nasturtium officinale

Abstract

Nasturtium officinale R. Br. (watercress) is a plant that belongs to the Brassicaceae and is growing mainly in Europe and Asia. The plant contains a considerable amount of vitamins, minerals and secondary metabolites and is used in food and for its medicinal properties. These are mainly attributed to the glucosinolates which are precursors of bioactive compounds such as the isothiocyanates. Glucosinolates are sulphur containing secondary metabolites, containing a β-D-thioglucose and an aglucone. The main glucosinolate in Nasturtium officinale R. Br. is gluconasturtiin. Since the quality of a food supplement of Nasturtium officinale R. Br. depends on the content of its glucosinolates and isothiocyanates, a quantitative method was developed to analyse the glucosinolates. An existing method for the determination of gluconasturtiin [1, 2] was optimized by changing the volume of the extraction solvent, extraction time and number of extraction steps. Sinigrinemonohydrate was used as internal standard. The method was validated conform the ICH guidelines [3] on the validation of analytical methods. The standard curve of sinigrinemonohydrate was linear in the concentration range of 33.2 – 166.2 µg/mL. The mean concentration of gluconasturtiin was 8.5 mg/g lyophilized watercress. The precision of the method with respect to time (3 days) and concentration (3 concentration levels) was respectively 9.74% and 8.96%, although relatively high, it was still accepted because of the complexity of the method.