Determination of sinigrin, sinalbin, allyl- and benzyl isothiocyanates by RP-HPLC in mustard powder extracts

Abstract

A reversed phase-high performance liquid chromatography method was developed to quantify sinigrin, sinalbin, allyl isothiocyanate and benzyl isothiocyanate present in aqueous and freeze-dried yellow and Oriental (brown) mustard extract samples using two pre-treatment methods (autoclaving, boiling) to prevent degradation by myrosinase. The lowest detection limits for sinigrin and sinalbin were 0.05 mg/L and for allyl- and benzyl isothiocyanate were 2 mg/L. The methods developed make it possible to quantify both the glucosinolates (sinigrin, and sinalbin) and their hydrolysis products (allyl- and benzyl isothiocyanate) with the same mobile phase, and only require adjustment of the wavelength and a change in the ratio of the high performance liquid chromatography mobile phase solvents (tetrabutylammonium hydrogen sulphate and acetonitrile). The use of a single method yielded accurate and rapid results for the four compounds (sinigrin, sinalbin, allyl- and benzyl isothiocyanate). Autoclaving of both yellow and brown mustard powder before glucosinolate extraction did not consistently improve the amount of sinalbin and sinigrin recovered over boiling treatments because the thermal stability of myrosinase proved problematic in glucosinolate recovery. Nonetheless, the highest extract yields found were 4.06 g/100 g for sinigrin and 2.57 g/100 g for sinalbin, respectively, which represented over 94 g/100 g extract yield of sinigrin from the Oriental mustard powder.